Chapter 18

VHF and UHF

Antenna Systems

A good antenna system is one of the most valuable the least attractive part of the job. Even with high-gain assets available to the VHF/UHF enthusiast. Com-antennas, experimentation is greatly simplified at VHF

pared to an antenna of lesser quality, an antenna that is and UHF because the antennas are a physically manage-well designed, is built of good quality materials, and is able size. Setting up a home antenna range is within the well maintained, will increase transmitting range, enhance means of most amateurs, and much can be learned about reception of weak signals and reduce interference prob-the nature and adjustment of antennas. No large invest-lems. The work itself building antennas is by no means ment in test equipment is necessary.

The Basics

Selecting the best VHF or UHF antenna for a given tional antennas, and omnidirectional antennas having installation involves much more than scanning gain fig-some gain are especially bad in these respects. Maximum ures and prices in a manufacturer’s catalog. There is no gain and low radiation angle are usually prime interests one “best” VHF or UHF antenna design for all purposes.

of the weak-signal DX aspirant. A clean pattern, with low-The first step in choosing an antenna is figuring out what est possible pickup and radiation off the sides and back, you want it to do.

may be important in high-activity areas, or where the noise level is high.

Gain

At VHF and UHF, it is possible to build Yagi anten-Frequency Response

nas with very high gain⎯15 to 20 dBi⎯on a physically The ability to work over an entire VHF band may be manageable boom. Such antennas can be combined in important in some types of work. Modern Yagis can achieve arrays of two, four, six, eight or more antennas. These performance over a remarkably wide frequency range, pro-arrays are attractive for EME, tropospheric scatter or other viding that the boom length is long enough and enough weak-signal communications modes.

elements are used to populate the boom. Modern Yagi designs in fact are competitive with directly driven col-Radiation Patterns

linear arrays of similar size and complexity. The primary Antenna radiation can be made omnidirectional,

performance parameters of gain, front-to-rear ratio and bidirectional, practically unidirectional, or anything SWR can be optimized over all the VHF or UHF amateur between these conditions. A VHF net operator may find bands readily, with the exception of the full 6meter band an omnidirectional system almost a necessity, but it may from 50.0 to 54.0 MHz, which is an 8% wide bandwidth.

be a poor choice otherwise. Noise pickup and other A Yagi can be easily designed to cover any 2.0 MHz por-interference problems are greater with such omnidirection of the 6-meter band with superb performance.

VHF and UHF Antenna Systems

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Height Gain

TRANSMISSION LINES

In general, higher is better in VHF and UHF antenna Transmission line principles are covered in detail in installations. Raising the antenna over nearby obstruc-Chapter 24, Transmission Lines. Techniques that apply tions may make dramatic improvements in coverage.

to VHF and UHF operation are dealt with in greater Within reason, greater height is almost always worth its detail here. The principles of carrying RF from one loca-cost, but height gain (see Chapter 23, Radio Wave Propa-tion to another via a feed line are the same for all radio gation) must be balanced against increased transmission-frequencies. As at HF, RF is carried principally via open line loss. This loss can be considerable, and it increases wire lines and coaxial cables at VHF/UHF. Certain with frequency. The best available line may not be very aspects of these lines characterize them as good or bad good if the run is long in terms of wavelengths. Line loss for use above 50 MHz.

considerations (see Chapter 24, Transmission Lines) are Properly built open-wire line can operate with very important in antenna planning.

low loss in VHF and UHF installations. A total line loss under 2 dB per 100 feet at 432 MHz can easily be ob-Physical Size

tained. A line made of #12 wire, spaced 3/4 inch or more A given antenna design for 432 MHz has the same

with Teflon spreaders and run essentially straight from gain as the same design for 144 MHz, but being only one-antenna to station, can be better than anything but the most third as large intercepts only one-ninth as much energy expensive coax. Such line can be home made or purchased in receiving. In other words, the antenna has less pickup at a fraction of the cost of coaxial cables, with compa-efficiency at 432 MHz. To be equal in communication rable loss characteristics. Careful attention must be paid effectiveness, the 432-MHz array should be at least equal to efficient impedance matching if the benefits of this sys-in size to the 144-MHz antenna, which requires roughly tem are to be realized. A similar system for 144 MHz can three times as many elements. With all the extra difficul-easily provide a line loss under 1 dB.

ties involved in using the higher frequencies effectively, Small coax such as RG-58 or RG-59 should never

it is best to keep antennas as large as possible for these be used in VHF work if the run is more than a few feet.

bands.

Lines of 1/2-inch diameter (RG-8 or RG-11) work fairly well at 50 MHz, and are acceptable for 144-MHz runs of DESIGN FACTORS

50 feet or less. These lines are somewhat better if they With the objectives sorted out in a general way, employ foam instead of ordinary PE dielectric material.

decisions on specifics, such as polarization, type of trans-Aluminum-jacket hardline coaxial cables with large mission line, matching methods and mechanical design inner conductors and foam insulation are well worth their must be made.

cost, and can sometimes be obtained for free from local Cable TV operators as “end runs”⎯pieces at the end of a Polarization

roll. The most common CATV cable is 1/2-inch OD 75-Ω

Whether to position antenna elements vertically or hardline. Matched-line loss for this cable is about 1.0 dB/

horizontally has been widely debated since early VHF

100 feet at 146 MHz and 2.0 dB/100 feet at 432 MHz.

pioneering days. Tests have shown little evidence about Less commonly available from CATV companies is the which polarization sense is most desirable. On long propa-3/4-inch 75Ω hardline, sometimes with a black self-heal-gation paths there is no consistent advantage either way.

ing hard plastic covering. This line has 0.8 dB of loss per Shorter paths tend to yield higher signal levels with hori-100 feet at 146 MHz, and 1.6 dB loss per 100 feet at zontally polarized antennas over some kinds of terrain.

432 MHz. There will be small additional losses for either Man-made noise, especially ignition interference, also line if 75-to-50Ω transformers are used at each end.

tends to be lower with horizontal antennas. These factors Commercial connectors for hardline are expensive but make horizontal polarization somewhat more desirable provide reliable connections with full waterproofing.

for weak-signal communications. On the other hand, ver-Enterprising amateurs have homebrewed low-cost connec-tically polarized antennas are much simpler to use in tors. If they are properly water proofed, connectors and omnidirectional systems and in mobile work.

hardline can last almost indefinitely. Hardline must not Vertical polarization was widely used in early VHF

be bent too sharply, because it will kink. See Chapter 24, work, but horizontal polarization gained favor when Transmission Lines, for details on hardline connectors.

directional arrays started to become widely used. The Beware of any “bargains” in coax for VHF or UHF

major use of FM and repeaters, particularly in the VHF/

use. Feed-line loss can be compensated to some extent UHF bands, has tipped the balance in favor of vertical by increasing transmitter power, but once lost, a weak antennas in mobile and repeater use. Horizontal polar-signal can never be recovered in the receiver. Effects of ization predominates in other communication on 50 MHz weather on transmission lines should not be ignored. Well-and higher frequencies. An additional loss of 20 dB or constructed open-wire line works optimally in nearly any more can be expected when cross-polarized antennas are weather, and it stands up well. Twin-lead is almost use-used.

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coax are completely impervious to weather—they can be with frequency for a given size of guide, and there is only run underground, fastened to metal towers without insu-one possible mode (called the dominant mode) for the lation and bent into any convenient position with no lowest frequency that can be transmitted. The dominant adverse effects on performance.

mode is the one generally used in amateur work.

WAVEGUIDES

Waveguide Dimensions

Above 2 GHz, coaxial cable is a losing proposition In rectangular guide the critical dimension is X in for communications work. Fortunately, at this frequency Fig 1. This dimension must be more than 1/2 λ at the low-the wavelength is short enough to allow practical, effi-est frequency to be transmitted. In practice, the Y dimen-cient energy transfer by an entirely different means. A sion usually is made about equal to 1/2 X to avoid the waveguide is a conducting tube through which energy is possibility of operation in other than the dominant mode.

transmitted in the form of electromagnetic waves. The Cross-sectional shapes other than a rectangle can be tube is not considered as carrying a current in the same used, the most important being the circular pipe. Much sense that the wires of a two-conductor line do, but rather the same considerations apply as in the rectangular case.

as a boundary that confines the waves in the enclosed Wavelength dimensions for rectangular and circular space. Skin effect prevents any electromagnetic effects guides are given in Table 1, where X is the width of a from being evident outside the guide. The energy is rectangular guide and r is the radius of a circular guide.

injected at one end, either through capacitive or induc-All figures apply to the dominant mode.

tive coupling or by radiation, and is removed from the other end in a like manner. Waveguide merely confines the energy of the fields, which are propagated through it to the receiving end by means of reflections against its inner walls.

Analysis of waveguide operation is based on the

assumption that the guide material is a perfect conductor of electricity. Typical distributions of electric and magnetic fields in a rectangular guide are shown in Fig 1.

The intensity of the electric field is greatest (as indicated by closer spacing of the lines of force) at the center along the X dimension (Fig 1C), diminishing to zero at the end walls. The fields must diminish in this manner, because the existence of any electric field parallel to the walls at the surface would cause an infinite current to flow in a perfect conductor. Waveguides, of course, cannot carry RF in this fashion.

Modes of Propagation

Fig 1 represents the most basic distribution of the electric and magnetic fields in a waveguide. There are an infinite number of ways in which the fields can arrange themselves in a waveguide (for frequencies above the low cutoff frequency of the guide in use). Each of these field configurations is called a mode.

The modes may be separated into two general

groups. One group, designated TM (transverse magnetic), has the magnetic field entirely transverse to the direction of propagation, but has a component of the electric field in that direction. The other type, designated TE (transverse electric) has the electric field entirely transverse, but has a component of magnetic field in the direction of propagation. TM waves are sometimes called E waves, and TE waves are sometimes called H waves, but the TM

and TE designations are preferred.

The mode of propagation is identified by the group letters followed by two subscript numerals. For example, Fig 1—Field distribution in a rectangular waveguide.

TE10, TM11, etc. The number of possible modes increases The TE10 mode of propagation is depicted.

VHF and UHF Antenna Systems

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Coupling to Waveguides

Table 1

Energy may be introduced into or extracted from a Waveguide Dimensions

waveguide or resonator by means of either the electric or Rectangular

Circular

magnetic field. The energy transfer frequently is through Cutoff wavelength

2X

3.41r

a coaxial line. Two methods for coupling to coaxial line Longest wavelength transmitted

1.6X

3.2r

are shown in Fig 2. The probe shown at A is simply a with little attenuation

short extension of the inner conductor of the coaxial line, Shortest wavelength before next 1.1X

2.8r

oriented so that it is parallel to the electric lines of force.

mode becomes possible

The loop shown at B is arranged so that it encloses some of the magnetic lines of force. The point at which maximum coupling is obtained depends upon the mode of propagation in the guide or cavity. Coupling is maximum when the coupling device is in the most intense field.

Coupling can be varied by turning the probe or loop through a 90° angle. When the probe is perpendicular to the electric lines the coupling is minimum. Similarly, when the plane of the loop is parallel to the magnetic lines the coupling is minimum.

If a waveguide is left open at one end it will radiate energy. This radiation can be greatly enhanced by flaring the waveguide to form a pyramidal horn antenna. The horn acts as a transition between the confines of the waveguide and free space. To effect the proper impedance transformation the horn must be at least 1/2 λ on a Fig 2—Coupling coaxial line to waveguide and

side. A horn of this dimension (cutoff) has a unidirec-resonators.

tional radiation pattern with a null toward the waveguide transition. The gain at the cutoff frequency is 3 dB, increasing 6 dB with each doubling of frequency. Horns how a rectangular waveguide evolves from a two-wire are used extensively in microwave work, both as primary parallel transmission line as described. This simplified radiators and as feed elements for more elaborate focus-analysis also shows why the cutoff dimension is 1/2 λ.

ing systems. Details for constructing 10-GHz horn While the operation of waveguides is usually

antennas are given later in this chapter.

described in terms of fields, current does flow on the inside walls, just as on the conductors of a two-wire trans-Evolution of a Waveguide

mission line. At the waveguide cutoff frequency, the cur-Suppose an open-wire line is used to carry RF

rent is concentrated in the center of the walls, and disperses energy from a generator to a load. If the line has any toward the floor and ceiling as the frequency increases.

appreciable length it must be mechanically supported. The line must be well insulated from the supports if high losses IMPEDANCE MATCHING

are to be avoided. Because high-quality insulators are Impedance matching is covered in detail in Chapter difficult to construct at microwave frequencies, the logi-25, Coupling the Transmitter to the Line, and Chapter cal alternative is to support the transmission line with 26, Coupling the Line to the Antenna. The theory is the 1/4 λ stubs, shorted at the end opposite the feed line. The same for frequencies above 50 MHz. Practical aspects open end of such a stub presents an infinite impedance to are similar, but physical size can be a major factor in the the transmission line, provided the shorted stub is choice of methods. Only the matching devices used in nonreactive. However, the shorting link has a finite length, practical construction examples later in this chapter are and therefore some inductance. The effect of this induc-discussed in detail here. This should not rule out consid-tance can be removed by making the RF current flow on eration of other methods, however, and you should read the surface of a plate rather than a thin wire. If the plate the relevant portions of both Chapters 25 and 26.

is large enough, it will prevent the magnetic lines of force from encircling the RF current.

Universal Stub

An infinite number of these 1/4 λ stubs may be con-As its name universal stub implies, the double-ad-nected in parallel without affecting the standing waves justment stub of Fig 4A is useful for many matching pur-of voltage and current. The transmission line may be sup-poses. The stub length is varied to resonate the system ported from the top as well as the bottom, and when an and the transmission-line attachment point is varied until infinite number of supports are added, they form the walls the transmission line and stub impedances are equal. In of a waveguide at its cutoff frequency. Fig 3 illustrates practice this involves moving both the sliding short and 18-4

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/ 2

Waveguide

Open Wire

Inductance—

Line

Cancelling Plate

/ 4 Stub

Fig 3—At its cutoff frequency a rectangular waveguide can be thought of as a parallel two-conductor transmission line supported from top and bottom by an infinite number of 1/4-λ stubs.

the point of line connection for zero reflected power, as indicated on an SWR bridge connected in the line.

The universal stub allows for tuning out any small reactance present in the driven part of the system. It permits matching the antenna to the line without knowledge of the actual impedances involved. The position of the short yielding the best match gives some indication of the amount of reactance present. With little or no reactive component to be tuned out, the stub must be approximately 1/2 λ from load toward the short.

The stub should be made of stiff bare wire or rod, spaced no more than 1/20 λ apart. Preferably it should be Fig 4—Matching methods commonly used at VHF. The mounted rigidly, on insulators. Once the position of the universal stub, A, combines tuning and matching. The short is determined, the center of the short can be adjustable short on the stub and the points of connection of the transmission line are adjusted for grounded, if desired, and the portion of the stub no longer minimum reflected power on the line. In the delta needed can be removed.

match, B and C, the line is fanned out and connected It is not necessary that the stub be connected directly to the dipole at the point of optimum impedance match.

to the driven element. It can be made part of an open-Impedances need not be known in A, B or C. The wire line as a device to match coaxial cable to the line.

gamma match, D, is for direct connection of coax. C1

tunes out inductance in the arm. A folded dipole of The stub can be connected to the lower end of a delta uniform conductor size, E, steps up antenna

match or placed at the feed point of a phased array.

impedance by a factor of four. Using a larger conductor Examples of these uses are given later.

in the unbroken portion of the folded dipole, F, gives higher orders of impedance transformation.

Delta Match

Probably the most basic impedance matching device is the delta match, fanned ends of an open-wire line tapped onto a 1/2 λ antenna at the point of the most-efficient power transfer. This is shown in Fig 4B. Both the side length dimensions in this use are not particularly critical. It and the points of connection either side of the center of should be checked out carefully in applications like that the element must be adjusted for minimum reflected of Fig 4C, where no tuning device is used.

power on the line, but as with the universal stub, you needn’t know the impedances. The delta match makes no Gamma and T Matches

provision for tuning out reactance, so the universal stub An application of the same principle allowing di-is often used as a termination for it.

rect connection of coax is the gamma match, Fig 4D.

At one time, the delta match was thought to be infe-Because the RF voltage at the center of a 1/2 λ dipole is rior for VHF applications because of its tendency to zero, the outer conductor of the coax is connected to the radiate if improperly adjusted. The delta has come back element at this point. This may also be the junction with into favor now that accurate methods are available for a metallic or wooden boom. The inner conductor, carry-measuring the effects of matching. It is very handy for ing the RF current, is tapped out on the element at the phasing multiple-bay arrays with open-wire lines, and its matching point. Inductance of the arm is tuned out by VHF and UHF Antenna Systems

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means of C1, resulting in electrical balance. Both the point mismatch. If a 4:1 balun is used, the antenna can be fed of contact with the element and the setting of the capaci-with 75Ω coaxial cable. (See balun information presented tor are adjusted for zero reflected power, with a bridge below.) Higher step-up impedance transformation can be connected in the coaxial line.

obtained if the unbroken portion is made larger in cross-The capacitance can be varied until the required section than the fed portion, as shown in Fig 4F.

value is found, and the variable capacitor replaced with a fixed unit of that value. C1 can be mounted in a water-Hairpin Match

proof box. The maximum required value should be about The feed-point resistance of most multielement Yagi 100 pF for 50 MHz and 35 to 50 pF for 144 MHz.

arrays is less than 50 Ω. If the driven element is split and fed The capacitor and arm can be combined in one

at the center, it may be shortened from its resonant length to coaxial assembly, with the arm connected to the driven add capacitive reactance at the feed point. Then, shunting element by means of a sliding clamp and the inner end of the feed point with a wire loop resembling a hairpin causes the arm sliding inside a sleeve connected to the center a step-up of the feed-point resistance. The hairpin match is conductor of the coax. An assembly of this type can be used together with a 4:1 coaxial balun in the 50 MHz arrays constructed from concentric pieces of tubing, insulated described later in this chapter. See Chapter 26, Coupling by plastic or heat-shrink sleeving. RF voltage across the the Line to the Antenna, for details on the hairpin match.

capacitor is low when the match is adjusted properly, so with a good dielectric, insulation presents no great prob-BALUNS AND ANTENNA TUNERS

lem. The initial adjustment should be made with low Conversion from balanced loads to unbalanced lines power. A clean, permanent high-conductivity bond (or vice versa) can be performed with electrical circuits, between arm and element is important, since the RF cur-or their equivalents made of coaxial cable. A balun made rent is high at this point.

from flexible coax is shown in Fig 5A. The looped por-Because it is inherently somewhat unbalanced, the tion is an electrical 1/2 λ. The physical length depends on gamma match can sometimes introduce pattern distortion, the velocity factor of the line used, so it is important to particularly on long-boom, highly directive Yagi arrays.

check its resonant frequency as shown in Fig 5B. The two The T-match, essentially two gamma matches in series ends are shorted, and the loop at one end is coupled to a creating a balanced feed system, has become popular for dip meter coil. This type of balun gives an impedance step-this reason. A coaxial balun like that shown in Fig 5 is up of 4:1 (typically 50 to 200 Ω, or 75 to 300 Ω).

used from the 200 Ω balanced T-match to the unbalanced Coaxial baluns that yield 1:1 impedance transfor-50 Ω coaxial line going to the transmitter. See the K1FO

mations are shown in Fig 6. The coaxial sleeve, open at Yagi designs later in this chapter for details on practical the top and connected to the outer conductor of the line use of a T-match.

at the lower end (A) is the preferred type. At B, a conductor of approximately the same size as the line is used Folded Dipole

with the outer conductor to form a 1/4 λ stub. Another The impedance of a 1/2 λ dipole broken at its center piece of coax, using only the outer conductor, will serve is about 70 Ω. If a single conductor of uniform size is this purpose. Both baluns are intended to present an infi-folded to make a 1/2 λ dipole as shown in Fig 4E, the impedance is stepped up four times. Such a folded dipole can be fed directly with 300Ω line with no appreciable Fig 5—Conversion from unbalanced coax to a balanced Fig 6—The balun conversion function, with no

load can be done with a ½-λ, coaxial balun at A.

impedance transformation, can be accomplished with Electrical length of the looped section should be ¼-λ lines, open at the top and connected to the coax checked with a dip meter, with the ends shorted, as at outer conductor at the bottom. The coaxial sleeve at A B. The 1/2-λ balun gives a 4:1 impedance step-up.

is preferred.

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nite impedance to any RF current that might otherwise Optimum vertical spacing for Yagis with boom longer flow on the outer conductor of the coax.

than 1 λ or more is about 1 λ (984/50.1 =

The functions of the balun and the impedance trans-19.64 feet), but this may be too much for many builders of former can be handled by various tuned circuits. Such a 50-MHz antennas to handle. Worthwhile results can be device, commonly called an antenna tuner or a obtained with as little as 1/2 λ (10 feet), but 5/8 λ (12 feet) is Transmatch, can provide a wide range of impedance trans-markedly better. The difference between 12 and 20 feet, formations. Additional selectivity inherent in the antenna however, may not be worth the added structural problems tuner can reduce RFI problems.

involved in the wider spacing, at least at 50 MHz. The closer spacings give lower measured gain, but the antenna patterns THE YAGI AT VHF AND UHF

are cleaner in both azimuth and elevation than with 1 λ spac-Without doubt, the Yagi is king of home-station

ing. Extra gain with wider spacings is usually the objective antennas these days. Today’s best designs are computer on 144 MHz and higher-frequency bands, where the struc-optimized. For years amateurs as well as professionals tural problems are not as severe.

designed Yagi arrays experimentally. Now we have pow-Yagis can also be stacked in the same plane (col-erful (and inexpensive) personal computers and sophisti-linear elements) for sharper azimuthal directivity. A spac-cated software for antenna modeling. These have brought ing of 5/8 λ between the ends of the inner elements yields us antennas with improved performance, with little or no the maximum gain within the main lobe of the array.

element pruning required. Chapter 11, HF Yagi Arrays, If individual antennas of a stacked array are properly describes the parameters associated with Yagi-Uda arrays.

designed, they look like noninductive resistors to the phas-Except for somewhat tighter dimensional tolerances ing system that connects them. The impedances involved needed at VHF and UHF, the properties that make a good can thus be treated the same as resistances in parallel.

Yagi at HF also are needed on the higher frequencies.

Three sets of stacked dipoles are shown in Fig 7.

See the end of this chapter for practical Yagi designs.

Whether these are merely dipoles or the driven elements of Yagi arrays makes no difference for the purpose of STACKING YAGIS

these examples. Two 300 Ω antennas at A are 1 λ apart, Where suitable provision can be made for support-resulting in a paralleled feed-point impedance of 150 Ω

ing them, two Yagis mounted one above the other and at the center. (Actually it is slightly less than 150 Ω

fed in phase can provide better performance than one long because of coupling between bays, but this can be Yagi with the same theoretical or measured gain. The pair neglected for illustrative purposes.) This value remains occupies a much smaller turning space for the same gain, the same regardless of the impedance of the phasing line.

and their wider elevation coverage can provide excellent Thus, any convenient line can be used for phasing, as results. The wide azimuthal coverage for a vertical stack long as the electrical length of each line is the same.

often results in QSOs that might be missed with a single The velocity factor of the line must be taken into narrow-beam long-boom Yagi pointed in a different account as well. As with coax, this is subject to so much direction. On long ionospheric paths, a stacked pair variation that it is important to make a resonance check occasionally may show an apparent gain much greater on the actual line used. The method for doing this is shown than the measured 2 to 3 dB of stacking gain. (See also in Fig 5B. A 1/2 λ line is resonant both open and shorted, the extensive section on stacking Yagis in Chapter 11, but the shorted condition (both ends) is usually the more HF Yagi Arrays.)

convenient test condition.

Fig 7—Three methods of feeding

stacked VHF arrays. A and B are

for bays having balanced driven

elements, where a balanced

phasing line is desired. Array C

has an all-coaxial matching and

phasing system. If the lower

section is also 3/4 λ no trans-

position of line connections

is needed.

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The impedance transforming property of a 1/4 λ line taped or grounded to it, or arranged in any way that is section can be used in combination matching and phas-mechanically convenient. The spacing between bays can ing lines, as shown in Fig 7B and C. At B, two bays spaced be set at the most desirable value, and the phasing lines 1/2 λ apart are phased and matched by a 400-Ω line, act-placed anywhere necessary.

ing as a double-Q section, so that a 300-Ω main transmission line is matched to two 300-Ω bays. The two Stacking Yagis for Different Frequencies

halves of this phasing line could also be 3/4-λ or 5/4-λ long, In stacking horizontal Yagis one above the other on if such lengths serve a useful mechanical purpose. (An a single rotating support, certain considerations apply example is the stacking of two Yagis where the desirable when the bays are for different bands. As a very general spacing is more than 1/2 λ.)

rule of thumb, the minimum desirable spacing is half the A double-Q section of coaxial line is illustrated in boom length of the higher frequency Yagi.

Fig 7C. This is useful for feeding stacked bays that were For example, assume the stacked two-band array of designed for 50-Ω feed. A spacing of 5/8 λ is useful for Fig 8A is for 50 and 144 MHz. This vertical arrangement small Yagis, and this is the equivalent of a full electrical is commonly referred to as a Christmas tree, because it wavelength of solid-dielectric coax such as RG-11.

resembles one. The 50MHz Yagi has 5elements on a If one phasing line is electrically 1/4 λ and 3/4 λ on 12-foot boom. It tends to look like “ground” to the the other, the connection to one driven element should be 8-element 144 MHz Yagi on a 12-foot boom directly reversed with respect to the other to keep the RF currents above it. [The exact Yagi designs for the examples used in the elements in phase⎯the gamma match is located in this section are located on the CD-ROM accompany-on opposite sides of the driven elements in Fig 7C. If the ing this book. They may be evaluated as monoband Yagis number of 1/4 λ lengths is the same on either side of the using the YW (Yagi for Windows) program also supplied feed point, the two connections should be in the same on the CD-ROM. In each case the bottom Yagi in the stack position, and not reversed. Practically speaking however, (at the top of the tower) is assumed to be 20 feet high.]

you can ensure proper phasing by using exactly equal lengths of line from the same roll of coax. This ensures SWR Change in a Multi-Frequency Stack

that the velocity factor for each line is identical.

Earlier editions of The ARRL Antenna Book stated One marked advantage of coaxial phasing lines is that the feed-point impedance of the higher-frequency that they can be wrapped around the vertical support, antenna would likely be affected the most by the proxim-Fig 8—In stacking Yagi arrays one above the other, the minimum spacing between bays (S) should be about half the boom length of the smaller array. Wider spacing is desirable, in which case it should be ½ λ or some multiple thereof, at the frequency of the smaller array. At A, stack of 8-element 2-meter Yagi on a 12foot boom over a 5element 6-meter Yagi, also on a 12foot boom. At B, 5element 2-meter beam on a 6-foot boom over a 3element 6-meter beam on a 4-foot boom.

At C, a 14-element 70-cm beam on a 9-foot boom, mounted over a 8-element 2-meter beam on a 12-foot boom and a 7-element 6-meter beam on a 22-foot boom.

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ity of the lower-frequency Yagi. Modern computer mod-complicated (and sometimes is non-intuitive as well).

eling programs reveal that while the feed-point SWR can What happens when a different kind of 6-meter Yagi indeed be affected, by far the greatest degradation is in is mounted below the 8-element 2-meter Yagi? Fig 11

the forward gain and rearward pattern of the higher-fre-compares the change in forward gain and the worst-case quency Yagi when the booms are closely spaced. In fact, F/R performance as a function of spacing between the the SWR curve is usually not affected enough to make it booms for two varieties of 6-meter Yagis: the 5element a good diagnostic indicator of interaction between the design on a 12-foot boom and a 7-element Yagi on a two Yagis.

Fig 9 shows an overlay of the SWR curves across the 2-meter band for four configurations: an 8-element 2-meter Yagi by itself, and then over a 5element 6-meter Yagi with spacings between the booms of 1, 2, 4 and 6 feet. The SWR curves are similar—it would be difficult to see any difference between these configurations using typical amateur SWR indicators for anything but the very closest (1-foot) spacing. For example, the SWR

curve for the 2-foot spacing case is virtually indistinguish-able from that of the Yagi by itself, while the forward gain has dropped more than 0.6 dB because of interactions with the 6-meter Yagi below it.

Gain and Pattern Degradation Due to Stacking

Fig 10 shows four overlaid rectangular plots of the azimuth response from 0° to 180° for the 8-element 2-meter Yagi described above, spaced 1, 2, 4 and 6 feet over a 5element 6-meter beam. The rectangular presentation gives more detail than a polar plot. The most closely spaced configuration (with 1-foot spacing between the Fig 10—Plots of the 8-element 2-meter Yagi’s azimuth booms) shows the largest degradation in the forward gain, response from 0° to 180° for spacing distances from 1

a drop of 1.7 dB. The worst-case front-to-rear ratio for to 6 feet. The sidelobe at about 60° varies about 6 dB

the 6-foot spacing is 29.0 dB, while it is 36.4 dB for the over the range of boom spacings, while the shape of worst-case F/R curve varies considerably due to 1-foot spacing—actually better than the F/R for the interactions with the lower 6-meter beam. The gain for 8-element 2-meter Yagi by itself. Performance change due the 1-foot spacing is degraded by more than 3 dB

to the nearby presence of other Yagis can be enormously compared to the 2-meter antenna by itself.

Fig 9—SWR curves for different boom spacing between Fig 11—Plot of 8-element 2-meter Yagi’s gain and 8-element 2-meter Yagi on 12-foot boom, over a worst-case F/R as a function of distance over two 5element 6-meter Yagi on a 12-foot boom. For spacings types of 6-meter beams, one on a 12-foot boom and the greater than 1 foot between the booms, differences other on a 22-foot boom. Beyond a spacing of about 5

between the SWR curves are difficult to discern.

feet the performance is degraded a minimal amount.

VHF and UHF Antenna Systems

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22-foot boom. The spacing of “0 feet” represents the if the rule of thumb for spacing the booms still holds.

8-element 2-meter Yagi when it is used alone, with no Fig 12 shows the performance curves versus boom spac-other antenna nearby. This sets the reference expectations ing for a 5element 2-meter Yagi on a 4-foot boom stacked for gain and F/R.

over a 3element 6-meter Yagi on a 6-foot boom. Again, The most severe degradation occurs for the 1-foot the 1-foot spacing produces a substantial gain reduction spacing, as you might imagine, for both the 12 and of about 1.3 dB compared to the reference gain when the 22-foot boom lengths. Over the 5element 6-meter Yagi, 2-meter Yagi is used by itself. Beyond a boom spacing of the 2-meter gain doesn’t recover to the reference level of 3 feet the 2-meter gain drops less than 0.25 dB from the the 8-element 2-meter beam by itself until the spacing is reference level of the 2-meter Yagi by itself and the F/R

greater than 9 feet. However, the gain is within 0.25 dB

remains above about 20 dB. In this example, the simple of the reference level for spacings of 3 feet or more.

rule of thumb that the minimum spacing between booms Interestingly, the F/R is higher than that of the 2-meter be greater than half the boom length (half of 4 feet) of antenna by itself for the 1, 2 and 5-foot spacings and for the higher-frequency Yagi does not hold up. However, spacings greater than 11 feet. The 2-meter F/R in the pres-the same minimum spacing of 3 feet we found for the ence of the 12-foot 5element 6-meter Yagi remains above larger 2-meter Yagi remains true. Three feet spacing is 20 dB for spacings beyond 1 feet.

almost 0.5 λ between the booms at the higher frequency.

Overall, the 2-meter beam performs reasonably well for spacings of 3 feet or more over the 5element 6-meter Adding a 70-cm Yagi to the Christmas Tree

Yagi. Put another way, the 2-meter beam’s performance Let’s get more ambitious and set up a larger VHF/

is degraded only slightly for boom spacings greater than UHF Christmas tree, with a 14-element 70-cm Yagi on a 3 feet. A spacing of 3 feet is less than the old rule of 9-foot boom at the top, mounted 5 feet over an 8-element thumb that the minimum spacing between booms be

2-meter Yagi on a 12-foot boom. At the bottom of the greater than one-half the boomlength of the higher-fre-stack (at the top of the tower) is either the 5element quency Yagi, which in this case is 6 feet long.

6-meter beam on a 12-foot boom, or a 7-element 6-meter For the 7-element 6-meter Yagi, the 2-meter gain re-beam on a 22-foot boom. See Fig 8C. As before, we will covers to the reference level for spacings beyond 7 feet, but vary the spacing between the 70-cm Yagi and the 2-meter the F/R is degraded below the reference level for all spac-Yagi below it to assess the interactions that degrade the ings shown in Fig 11. If we use a gain reduction criterion of 70-cm performance.

less than 0.25 dB and a 20-dB F/R level as the minimum Fig 13 compares the change in gain and F/R curves acceptable level, then the spacing must be 5 feet or more as a function of boom spacings between the 70-cm and over the larger 6-meter Yagi. Again, this is less than the rule 2-meter Yagis for the two different 6-meter Yagis (with a of thumb that the minimum spacing between booms be greater fixed distance of 5 feet between the 2-meter and 6-meter than one-half the boomlength of the higher-frequency Yagi.

Yagis). In this example, the 70-cm Yagi was designed to Now, let’s try a smaller setup of 2-and 6-meter Yagis be an intrinsic 50-Ω feed, where the F/R has been com-stacked vertically in a Christmas-tree configuration to see promised to some extent. Still, the F/R is greater than 20 dB when the 70-cm Yagi is used by itself.

For spacings greater than 4 feet between the 70-cm and 2-meter booms, the 70-cm gain is equal to or even slightly greater than that of the 70-cm antenna by itself.

The increase of gain indicates that the elevation pattern of the 70-cm antenna is slightly compressed by the presence of the other Yagis below it. The F/R stays above at 19.5 dB for spacings greater than or equal to 4 feet. This falls just below our desired lower limit of 20 dB, but it is highly doubtful that anyone would notice this 0.5-dB drop in actual operation. A spacing of 4 feet between booms falls under the rule of thumb that the minimum spacing be at least half the boomlength of the higher-frequency Yagi, which in this case is 9 feet.

What should be obvious in this discussion is that you should model the exact configuration you plan to build to avoid unnecessary performance degradation.

Fig 12— Plot of gain and worst-case F/R of a 5element 2-meter Yagi on a 4-foot boom as a function of distance Stacking Same-Frequency Yagis

over a 3element 6-meter beam on a 6-foot boom.

This subject has been examined in some detail in Beyond a spacing of about 3 feet the performance is degraded a minimal amount.

Chapter 11, HF Yagi Arrays. The same basic principles 18-10

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Fig 14—HFTA comparison plots of the elevation responses for two 5element 6-meter Yagis mounted at Fig 13—Performance of a 14-element 70-cm Yagi on a 42 and 30 feet above flat ground, when they are fed in-9-foot boom, mounted a variable distance over an 8-phase and out-of-phase. By switching the phasing element 2-meter Yagi on a 12-foot boom, which is (adding a half-wavelength of coax to one of the mounted 5 feet above either a 5element 6-meter Yagi antennas), the elevation angle can be controlled to on a 12-foot boom or a 7-element 6-meter Yagi on a enhance performance when a Sporadic-E cloud is 22-foot boom. Beyond a spacing of about 4 feet, the nearly overhead.

performance of the 70-cm beam is degraded a minimal amount.

hold at VHF and UHF as they do on HF. That is, the gain mounted on a 2-foot boom (occupying 0.28 λ of that increases gradually with increasing spacing between the boom). The 5element Yagi is on a 4-foot boom (0.51 λ

booms, and then falls off gradually past a certain spacing of the boom), while the 8-element Yagi is on a 12-foot distance.

boom (1.72 λ of boom). The biggest antenna in the group At HF, Chapter 11 emphasizes that you should avoid has 16 elements, on a 27-foot boom (4.0 λ of boom). This nulls in the antenna’s elevation response—so that you can range of boom lengths pretty much covers the practical cover all the angles needed for geographic areas of inter-range of antennas used by hams.

est. At VHF/UHF, propagation is usually at low elevation The stack of two 3element Yagis peaks at 3.2 dB of angles for most propagation modes, and signals are often additional gain over a single Yagi for 0.75 λ spacing extremely weak. Thus, achieving maximum gain is the most between the booms. Further increases in spacing see the common design objective for a VHF/UHF stack. Of sec-gain change gradually drop off. Fig 15B shows the worst-ondary importance is the cleanliness of the beam pattern, case F/R of the four stacks, again as a function of boom to discriminate against interference and noise sources.

length. The F/R of a single 3element Yagi is just over 24

Six-meter Sporadic-E can sometimes occur at high dB, but in the presence of the second 3element Yagi in the elevation angles, especially if the Es cloud is overhead, stack, the F/R of the pair oscillates between 15 to 26 dB, or nearly overhead. Since Sporadic-E is exactly that, spo-finally remaining consistently over the desired 20-dB level radic, it’s not a good design practice to try to cover a for spacings greater than about 1.7 λ, where the gain has wide range of elevation angles, as you must often do at fallen about 0.6 dB from the peak possible gain. A boom HF to cover large geographic areas. On 6 meters, you spacing of 1.7 λ at 146 MHz is 11.5 feet. Thus you must can change to high-angle coverage when necessary. For compromise in choosing the boom spacing between achiev-example, you might switch to a separate Yagi mounted at ing maximum gain and the best pattern.

a low height, or you might provide means to feed stacked The increase in gain of the stack of two 5element antennas out-of-phase. Fig 14 shows an HFTA (HF Ter-Yagis peaks at a spacing of about 1 λ (6.7 feet), where rain Assessment) plot of two 5element 6-meter Yagis, the F/R is an excellent 25 dB. Having more elements on fed either in-phase or out-of-phase to cover a much wider a particular length of boom aids in holding a more con-range of elevation angles than the in-phase stack alone.

sistent F/R in the presence of the second antenna.

Fig 15A shows the change in gain for four 2-meter The gain increase for the bigger stack of 8-element stacked designs, as a function of the spacing in wave-Yagis peaks at a spacing of about 1.5 λ (10.1 feet), where lengths between the booms. The 3element Yagi is the F/R is more than 27 dB. The 16-element Yagi’s gain VHF and UHF Antenna Systems

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Fig 15—Performance of two different 2-meter Yagis (5elements on 4-foot boom and 8-elements on 12-foot boom) fed in-phase, as a function of spacing between the booms. Note that the distance is measured in wavelengths.

increase is 2.6 dB for a spacing of about 2.25 λ

spheric propagation conditions. See Chapter 11, HF Yagi (15.2 feet), where the F/R remains close to 25 dB. The Arrays. The designer of a flexible HF stack thus usually stacking distance of 15.2 feet for an antenna with a doesn’t try to redo the element lengths and spacings of 27-foot long boom may be a real challenge physically, the Yagis to optimize a particular stack.

requiring a very sturdy rotating mast to withstand wind pressures without bending.

Stacking Stacks of Different-Frequency Yagis

These examples show that the exact spacing between The investment in a tower is usually substantial, and booms is not overly critical, since the gain varies rela-most hams want to put as many antennas as possible on a tively slowly around the peak. Fig 15A shows that the tower, provided that interaction between the antennas can boom spacing needed to achieve peak gain from a stack be held to a reasonable level. Really ambitious weak-increases when higher-gain (longer-boom) individual signal VHF/UHF enthusiasts may want “stacked

antennas are used in that stack. It also shows that the stacks”—sets of stacked Yagis that cover different bands.

increase in maximum gain from stacking decreases for For example, a VHF contester might want a stack of two long-boom antennas. Fig 15B shows that beyond boom 8-element 2-meter Yagis mounted on the same rotating spacings of about 1 λ, the F/R pattern holds well for Yagi mast as a stack of two 5element 6-meter Yagis. Let’s designs with booms longer than about 0.5 λ, which is assume that the boom length of the 8-element 2-meter about 4 feet at 146 MHz.

Yagis is 12 feet (1.78 λ). We’ll assume a boom length of The plots in Fig 15 are representative of typical mod-12 feet (0.61 λ) for the 5element 6-meter Yagis.

ern Yagis. You could simply implement these designs as From Fig 15, we find the stacking distance between is, and you’ll achieve good results. However, we recom-the 8-element 2-meter beams for peak gain and good pat-mend that you model any specific stack you design, just tern is 1.5 λ, or 10 feet, but adequate performance can be to make sure. Since the boom spacings are displayed in had for a boom spacing of 0.75 λ, which is 5 feet on 2 meters.

terms of wavelength, you can extend the results for The boom spacing for two 5element 6-meter

2 meters to other bands, provided that you use properly beams is 1 λ for peak stacking gain, but a compromise of scaled Yagi designs to the other bands too.

0.625 λ (12 feet) still yields an acceptable gain increase You can even tweak the element dimensions and

of 2 dB over a single Yagi. The overall height of the spacings of each Yagi used in a stack to optimize the rotating mast sticking out of the top of the tower is thus rearward pattern for a particular stacking distance. This set by the 0.625 λ stacking distance on 6 meters, at strategy can work out well at VHF/UHF, where stacks 12 feet. In-between the 6-meter Yagis at the bottom and are often configured for best gain (and pattern) and are top of the rotating mast we will mount the 2-meter Yagi

“hard-wired” with fixed lengths of feed lines permanently stack. With only 12 feet available on the mast, the spacing junctioned together.

for symmetric placement of the two 2-meter Yagis in-be-This is in contrast to the situation at HF (and even tween the 6-meter Yagis dictates a distance of only 4 feet on 6 meters). The HF operator usually wants flexibility between the 2-meter beams. This is less than optimal.

to select individual Yagis (or combinations of Yagis) from The performance of the 2-meter stack in this “stack the stack, to match the array’s takeoff angle with iono-within a stack” is affected by the close spacing, but the 18-12

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interactions are not disastrous. The stacking gain is was spaced 0.25 λ and the director 0.15 λ. A square 1.62 dB more than the gain for a single 8-element 2-meter array using four 3element bays worked extremely well.

Yagi and the F/R remains above 20 dB across the 2-meter band.

VHF AND UHF QUAGIS

On 6 meters, the stacking gain for two 5element At higher frequencies, especially 420 MHz and

6-meter Yagis spaced 12 feet apart is 2.2 dB more than the above, Yagi arrays using dipole-driven elements can be gain of a single Yagi, while the F/R pattern remains about difficult to feed and match, unless special care is taken to 20 dB over the weak-signal portion of the 6-meter band. As keep the feed-point impedance relatively high by proper described in Chapter 11, HF Yagi Arrays, stacking gives more element spacing and tuning. The cubical quad described advantages than merely a gain increase, and 6-meter propa-earlier overcomes the feed problems to some extent. When gation does require coverage of a range of elevation angles many parasitic elements are used, however, the loops are because much of the time ionospheric modes are involved.

not nearly as convenient to assemble and tune as are Increasing the length of the rotating mast to 18 feet straight cylindrical ones used in conventional Yagis. The sticking out of the top of the tower will increase perfor-Quagi, designed and popularized by Wayne Overbeck, mance, particularly on 2 meters. The stacking gain on N6NB, is an antenna having a full-wave loop driven ele-6 meters will increase to 2.3 dB while the F/R decreases ment and reflector, and Yagi type straight rod directors.

to 18.5 dB, modest changes both. The 18-foot mast Construction details and examples are given in the allows the 2-meter Yagis to be spaced 6 feet from each projects later in this chapter.

other and 6 feet away from both top and bottom 6-meter antennas. The stacking gain goes to 2.14 dB and the F/R

COLLINEAR ANTENNAS

approaches 27 dB in the weak-signal portion of the The information given earlier in this chapter per-2-meter band.

tains mainly to parasitic arrays, but the collinear array is Whether the modest increase in stacking gain is

worthy of consideration in VHF/UHF operations. This worth the cost and mechanical complexity of stacking array tends to be tolerant of construction tolerances, mak-two 2-meter Yagis in-between a stack of 6-meter Yagis is ing it easy to build and adjust for VHF applications. The a choice left to the operator. Certainly the cost and weight of a rotating mast that is 20 feet long (18 feet out of the use of many collinear driven elements was once popular top of the tower and 2 feet down inside the tower), a mast in very large phased arrays, such as those required in that must be sturdy enough to support the antennas in moonbounce (EME) communications, but the advent of high winds without bending, should give pause to even computer-optimized Yagis has changed this.

the most enthusiastic 6-meter weak-signal operator.

Large Collinear Arrays

QUADS FOR VHF

Bidirectional curtain arrays of four, six, and eight half waves in phase are shown in Fig 16. Usually reflec-The quad antenna can be built with inexpensive

materials, yet its performance is comparable to other tor elements are added, normally at about 0.2 λ behind arrays of its size. Adjustment for resonance and imped-each driven element, for more gain and a unidirectional ance matching can be accomplished readily. Quads can pattern. Such parasitic elements are omitted from the be stacked horizontally and vertically to provide high sketch in the interest of clarity.

gain, without sharply limiting frequency response. Con-The feed-point impedance of two half waves in phase struction of quad antennas for VHF use is covered later is high, typically 1000 Ω or more. When they are com-in this chapter.

bined in parallel and parasitic elements are added, the feed impedance is low enough for direct connection to Stacking Quads

open wire line or twin-lead, connected at the points indi-Quads can be mounted side by side or one above the cated by black dots. With coaxial line and a balun, it is other, or both, in the same general way as other beam suggested that the universal stub match, Fig 4A, be used antennas. Sets of driven elements can also be mounted in at the feed point. All elements should be mounted at their front of a screen reflector. The recommended spacing electrical centers, as indicated by open circles in Fig 16.

between adjacent element sides is 1/

The framework can be metal or insulating material. The 2 λ. Phasing and feed

methods are similar to those employed with other anten-metal supporting structure is entirely behind the plane of nas described in this chapter.

the reflector elements. Sheet-metal clamps can be cut from scraps of aluminum for this kind of assembly. Collinear Adding Quad Directors

elements of this type should be mounted at their centers Parasitic elements ahead of the driven element work (where the RF voltage is zero), rather than at their ends, in a manner similar to those in a Yagi array. Closed loops where the voltage is high and insulation losses and can be used for directors by making them 5% shorter than detuning can be harmful.

the driven element. Spacings are similar to those for con-Collinear arrays of 32, 48, 64 and even 128 elements ventional Yagis. In an experimental model the reflector can give outstanding performance. Any collinear array VHF and UHF Antenna Systems

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should be fed at the center of the system, to ensure balA reflecting plane, which may be sheet metal, wire anced current distribution. This is very important in large mesh, or even closely spaced elements of tubing or wire, arrays, where sets of six or eight driven elements are can be used in place of parasitic reflectors. To be effec-treated as “sub arrays,” and are fed through a balanced tive, the plane reflector must extend on all sides to at least harness. The sections of the harness are resonant lengths, 1/4 λ beyond the area occupied by the driven elements. The usually of open wire line. The 48-element collinear array plane reflector provides high F/B ratio, a clean pattern, for 432 MHz in Fig 17 illustrates this principle.

and somewhat more gain than parasitic elements, but large physical size limits it to use above 420 MHz. An interesting space-saving possibility lies in using a single plane reflector with elements for two different bands mounted on opposite sides. Reflector spacing from the driven element is not critical. About 0.2 λ is common.

THE CORNER REFLECTOR

When a single driven element is used, the reflector screen may be bent to form an angle, giving an improvement in the radiation pattern and gain. At 222 and 420 MHz its size assumes practical proportions, and at 902 MHz and higher, practical reflectors can approach ideal dimensions (very large in terms of wavelengths), resulting in more gain and sharper patterns. The corner reflector can be used at 144 MHz, though usually at much less than optimum size. For a given aperture, the corner Fig 16—Element arrangements for 8-, 12-and 16-element collinear arrays. Elements are ½ λ long and reflector does not equal a parabola in gain, but it is simple spaced ½ λ. Parasitic reflectors, omitted here for to construct, broadbanded, and offers gains from about 9

clarity, are 5% longer and 0.2 λ behind the driven to 14 dBi, depending on the angle and size. This section elements. Feed points are indicated by black dots.

was written by Paul M. Wilson, W4HHK.

Open circles show recommended support points. The The corner angle can be 90, 60 or 45°, but the side elements can run through wood or metal booms, without insulation, if supported at their centers in this length must be increased as the angle is narrowed. For a way. Insulators at the element ends (points of high RF

90° corner, the driven element spacing can be anything voltage) detune and unbalance the system.

from 0.25 to 0.7 λ, 0.35 to 0.75 λ for 60°, and 0.5 to Fig 17—Large collinear arrays should be fed as sets of no more than eight driven elements each, interconnected by phasing lines. This 48-element array for 432 MHz (A) is treated as if it were four 12-element collinear antennas.

Reflector elements are omitted for clarity. The phasing harness is shown at B. Squares represent insulators.

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0.8 λ for 45°. In each case the gain variation over the range of spacings given is about 1.5 dB. Because the spacing is not very critical to gain, it may be varied for impedance-matching purposes. Closer spacings yield lower feed-point impedances, but a folded dipole radiator could be used to raise this to a more convenient level.

Radiation resistance is shown as a function of spacing in Fig 18. The maximum gain obtained with minimum spacing is the primary mode (the one generally used at 144, 222 and 432 MHz to maintain reasonable side lengths). A 90° corner, for example, should have a minimum side length (S, Fig 19) equal to twice the dipole spacing, or 1 λ long for 0.5-λ spacing. A side length greater than 2 λ is ideal. Gain with a 60° or 90° corner reflector with 1-λ sides is about 10 dB. A 60° corner with 2-λ sides has about 13 dBi gain, and a 45° corner with 3-λ sides has about 14 dBi gain.

Reflector length (L, Fig 19) should be a minimum of 0.6 λ. Less than that spacing causes radiation to increase to the sides and rear, and decreases gain.

Fig 18—Radiation resistance of the driven element in a Spacing between reflector rods (G, Fig 19) should corner reflector array for corner angles of 180° (flat sheet), 90°, 60° and 45° as a function of spacing D, as not exceed 0.06 λ for best results. A spacing of 0.06 λ

shown in Fig 19.

results in a rear lobe that is about 6% of the forward lobe Fig 19—Construction of a corner reflector array. The frame can be wood or metal. Reflector elements are stiff wire or tubing. Dimensions for several bands are given in Table 2. Reflector element spacing, G, is the maximum that should be used for the frequency; closer spacings are optional. The hinge permits folding for portable use.

VHF and UHF Antenna Systems

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(down 12 dB). A small mesh screen or solid sheet is pref-use side lengths of four times the spacing, and 2304 MHz erable at the higher frequencies to obtain maximum effi-corners employ side lengths of six times the spacing.

ciency and highest F/B ratio, and to simplify construction.

Reflector lengths of 2, 3, and 4 wavelengths are used on A spacing of 0.06 λ at 1296 MHz, for example, requires the 915, 1296 and 2304 MHz reflectors, respectively. A mounting reflector rods about every 1/2 inch along the 4 × 6 λ reflector closely approximates a sheet of infinite sides. Rods or spines may be used to reduce wind load-dimensions.

ing. The support used for mounting the reflector rods may A corner reflector may be used for several bands, or be of insulating or conductive material. Rods or mesh for UHF television reception, as well as amateur UHF

weave should be parallel to the radiator.

work. For operation on more than one frequency, side A suggested arrangement for a corner reflector is length and reflector length should be selected for the low-shown in Fig 19. The frame may be made of wood or est frequency, and reflector spacing for the highest fre-metal, with a hinge at the corner to facilitate portable work quency. The type of driven element plays a part in or assembly atop a tower. A hinged corner is also useful determining bandwidth, as does the spacing to the cor-in experimenting with different angles. Table 2 gives the ner. A fat cylindrical element (small λ/dia ratio) or trian-principal dimensions for corner reflector arrays for 144

gular dipole (bow tie) gives more bandwidth than a thin to 2300 MHz. The arrays for 144, 222 and 420 MHz have driven element. Wider spacings between driven element side lengths of twice to four times the driven element and corner give greater bandwidths. A small increase in spacing. The 915 MHz corner reflectors use side lengths gain can be obtained for any corner reflector by mount-of three times the element spacing, 1296 MHz corners ing collinear elements in a reflector of sufficient size, but Table 2

Dimensions of Corner Reflector Arrays for VHF and UHF

Side

Dipole

Reflector

Reflector

Corner

Radiation

Freq,

Length to Vertex

Length

Spacing

Angle,

Resistance,

MHz

S, in.

D, in.

L, in.

G, in.

Vo

Ω

144*

65

27½

48

7¾

90

70

144

80

40

48

4

90

150

222*

42

18

30

5

90

70

222

52

25

30

3

90

150

222

100

25

30

Screen

60

70

420

27

8¾

16¼

25/8

90

70

420

54

13½

16¼

Screen

60

70

915

20

6½

25¾

0.65

90

70

915

51

16¾

25¾

Screen

60

65

915

78

25¾

25¾

Screen

45

70

1296

18

4½

27½

½

90

70

1296

48

11¾

27½

Screen

60

65

1296

72

18¼

27½

Screen

45

70

2304

15½

2½

20½

¼

90

70

2304

40

6¾

20½

Screen

60

65

2304

61

10¼

20½

Screen

45

70

*Side length and number of reflector elements somewhat below optimum—slight reduction in gain.

Notes:

915 MHz

Wavelength is 12.9 in.

Side length S is 3 × D, dipole to vertex distance Reflector length L is 2.0 λ

Reflector spacing G is 0.05 λ

1296 MHz

Wavelength is 9.11 in.

Side length S is 4 × D, dipole to vertex distance Reflector length L is 3.0 λ

Reflector spacing G is 0.05 λ

2304 MHz

Wavelength is 5.12 in.

Side length S is 6 × D, dipole to vertex distance Reflector length L is 4.0 λ

Reflector spacing G is 0.05 λ

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the simple feed of a dipole is lost if more than two ele-provides performance very similar to the corner reflec-ments are used.

tor, and presents fewer mechanical problems because the A dipole radiator is usually employed with a corner plane center portion is relatively easy to mount on the reflector. This requires a balun between the coaxial line mast. The sides are considerably shorter, as well.

and the balanced feed-point impedance of the antenna.

The gain of both corner reflectors and trough reflec-Baluns are easily constructed of coaxial line on the lower tors may be increased by stacking two or more and VHF bands, but become more difficult at the higher fre-arranging them to radiate in phase, or alternatively by quencies. This problem may be overcome by using a ground-plane corner reflector, which can be used for vertical polarization. A ground-plane corner with monopole driven element is shown in Fig 20. The corner reflector and a 1/4 λ radiator are mounted on the ground plane, per-mitting direct connection to a coaxial line if the proper spacing is used. The effective aperture is reduced, but at the higher frequencies, second-or third-mode radiator spacing and larger reflectors can be employed to obtain more gain and offset the loss in effective aperture. A J antenna could be used to maintain the aperture area and provide a match to a coaxial line.

For vertical polarization work, four 90° corner

reflectors built back-to-back (with common reflectors) could be used for scanning 360° of horizon with modest gain. Feed-line switching could be used to select the desired sector.

Angle

Value of S for

Gain

Value of T

α

maximum gain

TROUGH REFLECTORS

90°

1.5 λ

13.5 dB 1λ - 1.25 λ

60°

1.75 λ

15 dB

1.0 λ

To reduce the overall dimensions of a large corner 45°

2.0 λ

16 dB

1.9 λ

reflector the vertex can be cut off and replaced with a plane reflector. Such an arrangement is known as a trough Fig 21—The trough reflector. This is a useful reflector. See Fig 21. Performance similar to that of the modification of the corner reflector. The vertex has been cut off and replaced by a simple plane section.

large corner reflector can thereby be had, provided that The tabulated data shows the gain obtainable for the dimensions of S and T as shown in Fig 21 do not greater values of S than those covered in Table 2, exceed the limits indicated in the figure. This antenna assuming that the reflector is of adequate size.

Fig 20—A ground-plane corner reflector antenna for vertical polarization, such as FM communications or packet radio. The dimension ½ λ in the front view refers to data in Table 2.

VHF and UHF Antenna Systems

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adding further collinear dipoles (fed in phase) within a PARABOLIC ANTENNAS

wider reflector. Not more than two or three radiating units When an antenna is located at the focus of a para-should be used, because the great virtue of the simple bolic reflector (dish), it is possible to obtain consider-feeder arrangement would then be lost.

able gain. Furthermore, the beamwidth of the radiated HORN ANTENNAS FOR THE

energy will be very narrow, provided all the energy from the driven element is directed toward the reflector. This MICROWAVE BANDS

section was written by Paul M. Wilson, W4HHK.

Horn antennas were briefly introduced in the sec-Gain is a function of parabolic reflector diameter, tion on coupling energy into and out of waveguides. For surface accuracy and proper illumination of the reflector amateur purposes, horns begin to show usable gain with by the feed. Gain may be found from

practical dimensions in the 902 MHz band.

2

It isn’t necessary to feed a horn with waveguide. If

⎛ πD ⎞

G =

k

log

10

⎜

⎟

only two sides of a pyramidal horn are constructed, the (Eq 1)

⎝ λ ⎠

antenna may be fed at the apex with a two-conductor where

transmission line. The impedance of this arrangement is G = gain over an isotropic antenna, dBi (subtract on the order of 300 to 400 Ω. A 60° two-sided pyramidal 2.15 dB for gain over a dipole)

horn with 18 inch sides is shown in Fig 22. This antenna k = efficiency factor, usually about 55%

has a theoretical gain of 15 dBi at 1296 MHz, although D = dish diameter in feet

the feed system detailed in Fig 23 probably degrades this λ = wavelength in feet

value somewhat. A 1/4 λ, 150-Ω matching section made from two parallel lengths of twin-lead connects to a See Table 3 for parabolic antenna gain for the bands bazooka balun made from RG-58 cable and a brass tube.

420 MHz through 10 GHz and diameters of 2 to 30 feet.

This matching system was assembled strictly for the pur-A close approximation of beamwidth may be found

pose of demonstrating the two-sided horn in a 50-Ω

from

system. In a practical installation the horn would be fed 70λ

with open-wire line and matched to 50 Ω at the station ψ =

(Eq 2)

D

equipment.

where

ψ = beamwidth in degrees at half-power points

(3 dB down)

D = dish diameter in feet

λ = wavelength in feet

At 420 MHz and higher, the parabolic dish becomes a practical antenna. A simple, single feed point eliminates phasing harnesses and balun requirements. Gain is dependent on good surface accuracy, which is more difficult to achieve with increasing frequency. Surface Fig 23—Matching

system used to

test the horn.

Better performance

Fig 22—An experimental two-sided pyramidal horn would be realized

constructed in the ARRL laboratory. A pair of muffler with open wire line.

clamps allows mounting the antenna on a mast. This See text.

model has sheet-aluminum sides, although window screen would work as well. Temporary elements could be made from cardboard covered with aluminum foil.

The horizontal spreaders are Plexiglas rod. Oriented as shown here, the antenna radiates horizontally polarized waves.

18-18

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Table 3

Gain, Parabolic Antennas*

Dish Diameter (Feet)

Frequency

2

4

6

10

15

20

30

420 MHz

6.0

12.0

15.5

20.0

23.5

26.0

29.5

902

12.5

18.5

22.0

26.5

30.0

32.5

36.0

1215

15.0

21.0

24.5

29.0

32.5

35.0

38.5

2300

20.5

26.5

30.0

34.5

38.0

40.5

44.0

3300

24.0

30.0

33.5

37.5

41.5

43.5

47.5

5650

28.5

34.5

38.0

42.5

46.0

48.5

52.0

10 GHz

33.5

39.5

43.0

47.5

51.0

53.5

57.0

*Gain over an isotropic antenna (subtract 2.1 dB for gain over a dipole antenna). Reflector efficiency of 55% assumed.

length to diameter (f/D) ratio provides optimum illumination at 902 MHz and higher. This, however, is imprac-tical at 432 MHz, where a dipole and plane reflector are often used. An f/D ratio between 0.4 and 0.6 is considered ideal for maximum gain and simple feeds.

The focal length of a dish may be found from

D2

f =

(Eq 3)

16d

where

f = focal length

D = diameter

d = depth distance from plane at mouth of dish to vertex (see Fig 17)

The units of focal length f are the same as those used to measure the depth and diameter. Table 4 gives the sub-tended angle at focus for dish f/D ratios from 0.2 to 1.0.

A dish, for example, with a typical f/D of 0.4 requires a Fig 24—Details of the parabolic curve, Y2 = 4SX. This 10-dB beamwidth of 130°. A circular waveguide feed with curve is the locus of points that are equidistant from a a diameter of approximately 0.7

fixed point, the focus (F), and a fixed line (AB) that is λ provides nearly opti-called the directrix. Hence, FP = PC. The focus (F) is mum illumination, but does not uniformly illuminate the located at coordinates S,0.

reflector in both the magnetic (TM) and electric (TE) planes. Fig 25 shows data for plotting radiation patterns from circular guides. The waveguide feed aperture can errors should not exceed 1/

be modified to change the beamwidth.

8 λ in amateur work. At

430 MHz 1/

One approach used successfully by some experiment-8 λ is 3.4 inches, but at 10 GHz it is

0.1476 inch! Mesh can be used for the reflector surface to ers is the use of a disc at a short distance behind the aper-reduce weight and wind loading, but hole size should be ture as shown in Fig 26. As the distance between the less than 1/

aperture and disc is changed, the TM plane patterns 12 λ. At 430 MHz the use of 2-inch hole diameter poultry netting (chicken wire) is acceptable. Fine mesh become alternately broader and narrower than with an aluminum screening works well as high as 10 GHz.

unmodified aperture. A disc about 2 λ in diameter appears to be as effective as a much larger one. Some experimentA support form may be fashioned to provide the

ers have noted a 1 to 2 dB increase in dish gain with this proper parabolic shape by plotting a curve (Fig 24) from modified feed. Rectangular waveguide feeds can also be Y2 = 4SX

used, but dish illumination is not as uniform as with round guide feeds.

as shown in the figure.

The circular feed can be made of copper, brass,

Optimum illumination occurs when power at the

aluminum or even tin in the form of a coffee or juice can, reflector edge is 10 dB less than that at the center. A cir-but the latter must be painted on the outside to prevent cular waveguide feed of correct diameter and length for rust or corrosion. The circular feed must be within a the frequency and correct beamwidth for the dish focal proper size (diameter) range for the frequency being used.

VHF and UHF Antenna Systems

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This feed operates in the dominant circular waveguide 9034.85

mode known as the

F (TM

) =

11

TE mode. The guide must be large

C

01

(Eq 5)

(inches)

d

enough to pass the

11

TE mode with no attenuation, but

smaller than the diameter that permits the next higher The wavelength in a waveguide always exceeds the free-space wavelength and is called guide wavelength, λ

TM

mode to propagate. To support the desirable

g.

01

11

TE

It is related to the cutoff frequency and operating frequency mode in circular waveguide, the cutoff frequency, C

F , is

by the equation

given by

11802.85

6917.26

λ =

F (TE

) =

g

(Eq 6)

C

11

(Eq 4)

2

2

(inches)

d

f

−

0

fC

where

where

λg = guide wavelength, inches

C

F = cutoff frequency in MHz for

11

TE mode

d = waveguide inner diameter

f = operating frequency, MHz

0

f =

Circular waveguide will support the TM mode

C

11

TE waveguide cutoff frequency, MHz

01

having a cutoff frequency

An inside diameter range of about 0.66 to 0.76 l is Fig 25—This graph can be used in conjunction with Table 4 for selecting the proper diameter waveguide to illuminate a parabolic reflector.

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Table 4

Table 5

f/D Versus Subtended Angle at Focus of a

Circular Waveguide Dish Feeds

Parabolic Reflector Antenna

Inside Diameter

Subtended

Subtended

Freq.

Circular Waveguide

f/D

Angle (Deg.)

f/D

Angle (Deg.)

(MHz)

Range (in.)

0.20

203

0.65

80

915

8.52-9.84

0.25

181

0.70

75

1296

6.02-6.94

0.30

161

0.75

69

2304

3.39-3.91

0.35

145

0.80

64

3400

2.29-2.65

0.40

130

0.85

60

5800

1.34-1.55

0.45

117

0.90

57

10,250

0.76-0.88

0.50

106

0.95

55

0.55

97

1.00

52

0.60

88

Taken from graph “f/D vs Subtended Angle at Focus,” page mounts should permit adjustment of the aperture either 170 of the 1966 Microwave Engineers’ Handbook and side of the focal point and should present a minimum of Buyers Guide. Graph courtesy of K. S. Kelleher, Aero Geo blockage to the reflector. Correct distance to the dish Astro Corp, Alexandria, Virginia

center places the focal point about 1 inch inside the feed aperture. The use of a nonmetallic support minimizes blockage. PVC pipe, fiberglass and Plexiglas are commonly used materials. A simple test by placing a material in a microwave oven reveals if it is satisfactory up to 2450 MHz. PVC pipe has tested satisfactorily and appears to work well at 2300 MHz. A simple, clean looking mount for a 4-foot dish with 18 inches focal length, for example, can be made by mounting a length of 4-inch PVC pipe using a PVC flange at the center of the dish. At 2304 MHz the circular feed is approximately 4 inches ID, making a snug fit with the PVC pipe. Precautions should be taken to keep rain and small birds from enter-ing the feed.

Never look into the open end of a waveguide when Fig 26—Details of a circular waveguide feed.

power is applied, or stand directly in front of a dish while transmitting. Tests and adjustments in these areas should be done while receiving or at extremely low levels of transmitter power (less than 0.1 watt). The US Government has suggested. The lower frequency limit (longer dimension) set a limit of 10 mW/cm2 averaged over a 6-minute period is dictated by proximity to the cutoff frequency. The as the safe maximum. Other authorities believe even lower higher frequency limit (shorter dimension) is dictated by levels should be used. Destructive thermal heating of body higher order waves. See Table 5 for recommended in-tissue results from excessive exposure. This heating effect side diameter dimensions for the 902-to 10,000-MHz is especially dangerous to the eyes. The accepted safe level amateur bands.

of 10 mW/cm2 is reached in the near field of a parabolic The probe that excites the waveguide and makes the antenna if the level at 2D2/λ is 0.242 mW/cm2. The equa-transition from coaxial cable to waveguide is 1/4 λ long tion for power density at the far-field boundary is and spaced from the closed end of the guide by 1/4 guide wavelength. The length of the feed should be two to three 137.8 P

2

Power density =

mW/cm

guide wavelengths. The latter is preferred if a second 2

(Eq 7)

D

probe is to be mounted for polarization change or for where

polaplexer work where duplex communication (simulta-P = average power in kilowatts

neous transmission and reception) is possible because of D = antenna diameter in feet

the isolation between two properly located and oriented λ = wavelength in feet

probes. The second probe for polarization switching or polaplexer work should be spaced 3/4 guide wavelength New commercial dishes are expensive, but surplus from the closed end and mounted at right angles to the ones can often be purchased at low cost. Some amateurs first probe.

build theirs, while others modify UHF TV dishes or cir-The feed aperture is located at the focal point of the cular metal snow sleds for the amateur bands. Fig 27

dish and aimed at the center of the reflector. The feed shows a dish using the homemade feed just described.

VHF and UHF Antenna Systems

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Fig 29—Detailed look at the hub assembly for the ZL1BJQ dish. Most of the structural members are made from ¾-inch T section.

Fig 27—Coffee-can 2304 MHz feed described

in text and Fig 26 mounted on a 4-ft dish.

Photos showing a highly ambitious dish project under construction by ZL1BJQ appear in Figs 28 and 29. Practical details for constructing this type of antenna are given in Chapter 19. Dick Knadle, K2RIW, described modern UHF antenna test procedures in February 1976 QST (see Bibliography). Also see Chapter 19.

OMNIDIRECTIONAL ANTENNAS FOR

VHF AND UHF

Local work with mobile stations requires an antenna with wide coverage capabilities. Most mobile work is on FM, and the polarization used with this mode is generally vertical. Some simple vertical systems are described below. Additional material on antennas of Fig 28—Aluminum framework for a 23-foot dish under this type is presented in Chapter 16, Mobile and Mari-construction by ZL1BJQ.

time Antennas.

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Ground-plane Antennas for 144, 222 and 440 MHz

For the FM operator living in the primary coverage The 144-MHz model shown in Fig 30 uses a flat area of a repeater, the ease of construction and low cost piece of sheet aluminum, to which radials are connected of a 1/4 λ ground-plane antenna make it an ideal choice.

with machine screws. A 45° bend is made in each of the Three different types of construction are detailed in Figs radials. This bend can be made with an ordinary bench 30 through 43; the choice of construction method depends vise. An SO239 chassis connector is mounted at the cen-upon the materials at hand and the desired style of ter of the aluminum plate with the threaded part of the antenna mounting.

connector facing down. The vertical portion of the Fig 30—These drawings illustrate the dimensions for the 144-MHz ground-plane antenna. The radials are bent down at a 45° angle.

Fig 31—Dimensional information for the 222-MHz ground-plane antenna. Lengths for A, B, C and D are the total distances measured from the center of the SO-239 connector. The corners of the aluminum plate are bent down at a 45° angle rather than bending the aluminum rod as in the 144-MHz model. Either method is suitable for these antennas.

VHF and UHF Antenna Systems

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Fig 33—A 440-MHz ground-plane constructed using only an SO-239 connector, no. 4-40 hardware and 1/16-in. brass welding rod.

Fig 32—Simple ground-plane antenna for the 144-, 222-and 440-MHz bands. The vertical element and radials are 3/32-or 1/16-in. brass welding rod. Although 3/32-in. rod is preferred for the 144-MHz antenna, #10 or #12

connector and some no. 4-40 hardware. A small loop copper wire can also be used.

formed at the inside end of each radial is used to attach the radial directly to the mounting holes of the coaxial connector. After the radial is fastened to the SO-239 with antenna is made of #12 copper wire soldered directly to no. 4-40 hardware, a large soldering iron or propane torch the center pin of the SO-239 connector.

is used to solder the radial and the mounting hardware to The 222-MHz version, Fig 31, uses a slightly dif-the coaxial connector. The radials are bent to a 45° angle ferent technique for mounting and sloping the radials. In and the vertical portion is soldered to the center pin to this case the corners of the aluminum plate are bent down complete the antenna. The antenna can be mounted by at a 45° angle with respect to the remainder of the plate.

passing the feed line through a mast of ¾-inch ID plastic The four radials are held to the plate with machine screws, or aluminum tubing. A compression hose clamp can be lock washers and nuts. A mounting tab is included in the used to secure the PL-259 connector, attached to the feed design of this antenna as part of the aluminum base. A line, in the end of the mast. Dimensions for the 144-, compression type of hose clamp could be used to secure 222-and 440-MHz bands are given in Fig 32.

the antenna to a mast. As with the 144-MHz version, the If these antennas are to be mounted outside it is wise vertical portion of the antenna is soldered directly to the to apply a small amount of RTV sealant or similar mate-SO-239 connector.

rial around the areas of the center pin of the connector to A very simple method of construction, shown in

prevent the entry of water into the connector and coax Figs 32 and 33, requires nothing more than an SO-239

line.

18-24

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The J-Pole Antenna

The J-Pole is a half-wave antenna that is end-fed at the bottom, making the antenna look like the letter “J,”

at its bottom. Since the radiator is longer than that of a and giving the antenna its name.

1/4-wave ground-plane antenna, the vertical lobe is com-Rigid copper tubing, fittings and assorted hardware pressed down toward the horizon and it has about 1.5 dB

can be used to make a really rugged J-pole antenna for of gain compared to the ground-plane configuration. The 2 meters. When copper tubing is used, the entire assem-stub-matching section used to transform the high imped-bly can be soldered together, ensuring electrical integ-ance seen looking into a half-wave to 50 Ω coax is shorted rity, and making the whole antenna weatherproof. This Fig 34—At A, exploded assembly diagram of all-copper J-Pole antenna. At B, detail of clamp assemblies. Both clamp assemblies are the same.

Item Qty Part or Material Name

1

1

¾-inch × 10 foot length of rigid copper

tubing (enough for 2 antennas, 60 inches

per antenna)

2

1

½-inch × 10 ft length of rigid copper tubing

(enough for 6 antennas, 20 inches per

antenna)

3

2

¾-inch copper pipe clamps

4

2

½-inch copper pipe clamps

5

1

½-inch copper elbow

6

1

¾ × ½-inch copper tee

7

1

¾-inch copper end cap

8

1

½-inch copper end cap

9

1

½ × 1¼-inch copper nipple (Make from item

2. See text)

10

1

¾ × 3 ¼-inch copper nipple (Make from

item 1. See text)

11

1

Your choice of coupling to mast fitting

(¾ × 1 inch NPT used at KD8JB)

12

6

# 8-32 × ½-inch brass machine screws

(round, pan, or binder head)

13

6

# 8 brass flat washers

14

6

# 8-32 brass hex nuts

VHF and UHF Antenna Systems

18-25

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material came from an article by Michael Hood, KD8JB, through a choke balun (3 turns of the feed coax rolled in The ARRL Antenna Compendium,Vol. 4.

into a coil about 8 inches in diameter and held together No special hardware or machined parts are used in this with electrical tape). Before tuning, mount the antenna antenna, nor are insulating materials needed, since the an-vertically, about 5 to 10 feet from the ground. A short tenna is always at dc ground. Best of all, even if the parts TV mast on a tripod works well for this purpose. When aren’t on sale, the antenna can be built for less than $15. If tuning VHF antennas, keep in mind that they are sensi-you only build one antenna, you’ll have enough tubing left tive to nearby objects—such as your body. Attach the feed over to make most of a second antenna.

line to the clamps on the antenna, and make sure all the nuts and screws are at least finger tight. It really doesn’t Construction

matter to which element (¾-wave element or stub) you Copper and brass is used exclusively in this antenna.

attach the coaxial center lead. The author has done it both These metals get along together, so dissimilar metal cor-ways with no variation in performance. Tune the antenna rosion is eliminated. Both metals solder well, too. See by moving the two feed-point clamps equal distances a Fig 34. Cut the copper tubing to the lengths indicated.

small amount each time until the SWR is minimum at the Item 9 is a 11/4-inch nipple cut from the 20-inch length of desired frequency. The SWR will be close to 1:1.

1/2-inch tubing. This leaves 183/4 inches for the 1/4-matching stub. Item 10 is a 31/

Final Assembly

4-inch long nipple cut from the

60-inch length of 3/4-inch tubing. The 3/4-wave element The final assembly of the antenna will determine its should measure 563/4-inches long. Remove burrs from the long-term survivability. Perform the following steps with ends of the tubing after cutting, and clean the mating care. After adjusting the clamps for minimum SWR, mark surfaces with sandpaper, steel wool, or emery cloth.

the clamp positions with a pencil and then remove the After cleaning, apply a very thin coat of flux to the feed line and clamps. Apply a very thin coating of flux to mating elements and assemble the tubing, elbow, tee, end the inside of the clamp and the corresponding surface of caps and stubs. Solder the assembled parts with a pro-the antenna element where the clamp attaches. Install the pane torch and rosin-core solder. Wipe off excess solder clamps and tighten the clamp screws.

with a damp cloth, being careful not to burn yourself.

Solder the feed line clamps where they are attached The copper tubing will hold heat for a long time after to the antenna elements. Now, apply a small amount of you’ve finished soldering. After soldering, set the assem-solder around the screw heads and nuts where they con-bly aside to cool.

tact the clamps. Don’t get solder on the screw threads!

Flatten one each of the 1/2-inch and 3/4-inch pipe Clean away excess flux with a non-corrosive solvent.

clamps. Drill a hole in the flattened clamp as shown in After final assembly and erecting/mounting the antenna Fig 34A. Assemble the clamps and cut off the excess metal in the desired location, attach the feed line and secure from the flattened clamp using the unmodified clamp as with the remaining washer and nut. Weather-seal this joint a template. Disassemble the clamps.

with RTV. Otherwise, you may find yourself repairing Assemble the 1/2-inch clamp around the 1/4-wave

the feed line after a couple years.

element and secure with two of the screws, washers, and nuts as shown in Fig 34B. Do the same with the 3/

On-the-Air Performance

4-inch

clamp around the 3/4-wave element. Set the clamps ini-Years ago, prior to building the first J-Pole antenna tially to a spot about 4 inches above the bottom of the “J”

for this station, the author used a standard 1/4-wave ground on their respective elements. Tighten the clamps only fin-plane vertical antenna. While he had no problem work-ger tight, since you’ll need to move them when tuning.

ing various repeaters around town with a 1/4-wave antenna, simplex operation left a lot to be desired. The J-Pole per-Tuning

forms just as well as a Ringo Ranger, and significantly The J-Pole can be fed directly from 50-Ω coax

better than the 1/4-wave ground-plane vertical.

18-26

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Practical 6-Meter Yagis

Boom length often proves to be the deciding factor which is 0.25 inches thick and 4 × 4 inches square. Stain-when one selects a Yagi design. Table 6 shows three less steel is the best choice for hardware, however, gal-6-meter Yagis designed for convenient boom lengths (6, vanized hardware can be substituted. Automotive muffler 12 and 22 feet). The 3element, 6-foot boom design has clamps do not work well in this application, because they 8.0 dBi gain in free space; the 12 foot boom, 5element are not galvanized and quickly rust once exposed to the version has 10.1 dBi gain, and the 22-foot, 7 element Yagi weather. Please note that the element lengths shown in has a gain of 11.3 dBi. All antennas exhibit better than Table 6 are half the overall element lengths. See page 22 dB front-to-rear ratio and cover 50 to 51 MHz with 20-7 to 20-11 in Chapter 20 for practical details of tele-better than 1.7:1 SWR.

scoping aluminum elements.

Half-element lengths and spacings are given in the The driven element is mounted to the boom on a

table. Elements can be mounted to the boom as shown in Bakelite or G-10 fiberglass plate of similar dimension to Fig 35. Two muffler clamps hold each aluminum plate to the other mounting plates. A 12-inch piece of Plexiglas the boom, and two U bolts fasten each element to the plate, rod is inserted into the driven element halves. The Plexiglas allows the use of a single clamp on each side of the element and also seals the center of the elements Fig 35—The element

against moisture. Self-tapping screws are used for elec-to boom clamp. U

trical connection to the driven element.

bolts are used to

Refer to Fig 36 for driven-element and hairpin match hold the element to

details. A bracket made from a piece of aluminum is used the plate, and 2-in.

to mount the three SO239 connectors to the driven ele-galvanized muffler

clamps hold the

ment plate. A 4:1 transmission-line balun connects the plates to the boom.

two element halves, transforming the 200 Ω resistance at the hairpin match to 50 Ω at the center connector. Note Fig 36—This shows how the driven element and feed system are attached to the boom. The phasing line is coiled and taped to the boom. The center of the hairpin loop may be connected to the boom electrically and mechanically if desired.

Phasing-line lengths:

For cable with 0.80 velocity factor – 7 ft, 103/8 in.

For cable with 0.66 velocity factor – 6 ft, 53/4 in.

VHF and UHF Antenna Systems

18-27

chap18.pmd

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Table 6

Optimized 6-Meter Yagi Designs

Spacing

Seg 1

Seg2

Midband

Spacing

Seg 1

Seg2

Midband

Between

OD*

OD*

Gain

Between

OD*

OD*

Gain

Elements

Length

Length

F/R

Elements

Length

Length

F/R

inches

inches

inches

inches

inches

inches

306-06

706-22

OD

0.750

0.625

OD

0.750

0.625

Refl.

0

36

23.500

7.9 dBi

Refl.

0

36

25.000

11.3 dBi

D.E.

24

36

16.000

27.2 dB

D.E.

27

36

17.250

29.9 dB

Dir. 1

66

36

15.500

Dir. 1

16

36

18.500

Dir. 2

51

36

15.375

506-12

Dir. 3

54

36

15.875

OD

0.750

0.625

Dir. 4

53

36

16.500

Refl.

0

36

24.000

10.1 dBi

Dir. 5

58

36

12.500

D.E.

24

36

17.125

24.7 dB

*See pages 20-7 to 20-11 for telescoping aluminum Dir. 1

12

36

19.375

tubing details.

Dir. 2

44

36

18.250

Dir. 3

58

36

15.375

that the electrical length of the balun is λ/2, but the physi-However, you may have to change the length of the driven cal length will be shorter due to the velocity factor of the element slightly to obtain the best match in your preferred particular coaxial cable used. The hairpin is connected portion of the band. Changing the driven-element length directly across the element halves. The exact center of will not adversely affect antenna performance. Do not the hairpin is electrically neutral and should be fastened adjust the lengths or spacings of the other elements—

to the boom. This has the advantage of placing the driven they are optimized already. If you decide to use a gamma element at dc ground potential.

match, add 3 inches to each side of the driven element The hairpin match requires no adjustment as such.

lengths given in the table for all antennas.

High-Performance Yagis for 144, 222 and

432 MHz

This construction information is presented as an both varying element spacings and varying element introduction to the three high-performance VHF/UHF

lengths.

Yagis that follow. All were designed and built by Steve This design approach starts with closely spaced

Powlishen, K1FO. For years the design of long Yagi directors. The director spacings gradually increase until antennas seemed to be a mystical black art. The problem a constant spacing of about 0.4 λ is reached. Conversely, of simultaneously optimizing 20 or more element spac-the director lengths start out longest with the first direc-ings and element lengths presented an almost unsolvable tor and decrease in length in a decreasing rate of change set of simultaneous equations. With the unprecedented until they are virtually constant in length. This method increase in computer power and widespread availability of construction results in a wide gain bandwidth. A band-of antenna analysis software, we are now able to quickly width of 7% of the center frequency at the –1 dB for-examine many Yagi designs and determine which

ward-gain points is typical for these Yagis even when they approaches work and which designs to avoid.

are longer than 10 λ. The log-taper design also

At 144 MHz and above, most operators desire Yagi reduces the rate of change in driven-element impedance antennas two or more wavelengths in length. This length vs frequency. This allows the use of simple dipole driven (2λ) is where most classical designs start to fall apart in elements while still obtaining acceptable driven-element terms of gain per boom length, bandwidth and pattern SWR over a wide frequency range. Another benefit is quality. Extensive computer and antenna range analysis that the resonant frequency of the Yagi changes very little has proven that the best possible design is a Yagi that has as the boom length is increased.

18-28

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The driven-element impedance also changes mod-While short antennas (< 1.5 λ) may show increased erately with boom length. The tapered approach creates gain with the use of quad or loop elements, long Yagis a Yagi with a very clean radiation pattern. Typically, first (> 2 λ) will not exhibit measurably greater forward gain side lobe levels of ∼17 dB in the E plane, ∼15 dB in the or pattern integrity with loop-type elements. Similarly, H plane, and all other lobes at ∼20 dB or more are pos-loops used as driven elements and reflectors will not sig-sible on designs from 2 λ to more than 14 λ.

nificantly change the properties of a long log-taper Yagi.

The actual rate of change in element lengths is

Multiple-dipole driven-element assemblies will also not determined by the diameter of the elements (in wave-result in any significant gain increase per given boom lengths). The spacings can be optimized for an individual length when compared to single-dipole feeds.

boom length or chosen as a best compromise for most Once a long-Yagi director string is properly tuned, boom lengths.

the reflector becomes relatively non critical. Reflector The gain of long Yagis has been the subject of much spacings between 0.15 λ and 0.2 λ are preferred. The debate. Recent measurements and computer analysis by spacing can be chosen for best pattern and driven ele-both amateurs and professionals indicates that given an ment impedance. Multiple-reflector arrangements will not optimum design, doubling a Yagi’s boom length will significantly increase the forward gain of a Yagi which result in a maximum theoretical gain increase of about has its directors properly optimized for forward gain.

2.6 dB. In practice, the real gain increase may be less Many multiple-reflector schemes such as tri-reflectors because of escalating resistive losses and the greater pos-and corner reflectors have the disadvantage of lowering sibility of construction error. Fig 37 shows the maximum the driven element impedance compared to a single opti-possible gain per boom length expressed in decibels, ref-mum-length reflector. The plane or grid reflector, shown erenced to an isotropic radiator. The actual number of in Fig 38, may however reduce the intensity of unwanted directors does not play an important part in determining rear lobes. This can be used to reduce noise pickup on the gain vs boom length as long as a reasonable number EME or satellite arrays. This type of reflector will usu-of directors are used. The use of more directors per boom ally increase the driven-element impedance compared to length will normally give a wider gain bandwidth, how-a single reflector. This sometimes makes driven-element ever, a point exists where too many directors will matching easier. Keep in mind that even for EME, a plane adversely affect all performance aspects.

reflector will add considerable wind load and weight for Fig 37—This chart shows maximum gain per boom length for optimally Fig 38—Front and side views of a

designed long Yagi antennas.

plane-reflector antenna.

VHF and UHF Antenna Systems

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only a few tenths of a decibel of receive signal-to-noise Elements may be mounted insulated or uninsulated, improvement.

above or through the boom. Mounting uninsulated elements through a metal boom is the least desirable method Yagi Construction

unless the elements are welded in place. The Yagi ele-Normally, aluminum tubing or rod is used for Yagi ments will oscillate, even in moderate winds. Over sev-elements. Hard-drawn enamel-covered copper wire can eral years this element oscillation will work open the also be used on Yagis above 420 MHz. Resistive losses boom holes. This will allow the elements to move in the are inversely proportional to the square of the element boom. This will create noise (in your receiver) when the diameter and the square root of its conductivity.

wind blows, as the element contact changes. Eventually Element diameters of less than 3/16 inch or 4 mm the element-to-boom junction will corrode (aluminum should not be used on any band. The size should be cho-oxide is a good insulator). This loss of electrical contact sen for reasonable strength. Half-inch diameter is suit-between the boom and element will reduce the boom’s able for 50 MHz, 3/16 to 3/8 inch for 144 MHz and 3/16 inch effect and change the resonant frequency of the Yagi.

is recommended for the higher bands. Steel, including Noninsulated elements mounted above the boom

stainless steel and unprotected brass or copper wire, will perform fine as long as a good mechanical connec-should not be used for elements.

tion is made. Insulating blocks mounted above the boom Boom material may be aluminum tubing, either

will also work, but they require additional fabrication.

square or round. High-strength aluminum alloys such as One of the most popular construction methods is to mount 6061-T6 or 6063-T651 offer the best strength-to-weight the elements through the boom using insulating shoul-advantages. Fiberglass poles have been used (where avail-der washers. This method is lightweight and durable. Its able as surplus). Wood is a popular low-cost boom mate-main disadvantage is difficult disassembly, making this rial. The wood should be well seasoned and free from method of limited use for portable arrays.

knots. Clear pine, spruce and Douglas fir are often used.

If a conductive boom is used, element lengths must The wood should be well treated to avoid water absorp-be corrected for the mounting method used. The amount tion and warping.

of correction is dependent upon the boom diameter in Fig 40—Measured E-plane pattern

for the 22-element Yagi. Note: This

antenna pattern is drawn on a

linear dB grid, rather than on the

standard ARRL log-periodic grid,

to emphasize low sidelobes.

Fig 39—Yagi element correction vs boom diameter. Curve A is for elements mounted through a round or square conductive boom, with the elements in mechanical contact with the boom. Curve B is for insulated elements mounted through a conductive boom, and for elements mounted on top of a conductive boom (elements make electrical contact with the boom). The patterns were corrected to computer simulations to determine Yagi tuning.

The amount of element correction is not affected by element diameter.

18-30

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wavelengths. See Fig 39. Elements mounted through the shown in Fig 40. Note that a 1-dB-per-division axis is boom and not insulated require the greatest correction.

used to show pattern detail. A complete description of Mounting on top of the boom or through the boom on the design process and construction methods appears in insulated shoulder washers requires about half of the December 1987 and January 1988 QST.

through-the-boom correction. Insulated elements

Like other log-taper Yagi designs, this one can eas-mounted at least one element diameter above the boom ily be adapted to other boom lengths. Versions of this require no correction over the free-space length.

Yagi have been built by many amateurs. Boom lengths The three following antennas have been optimized ranged between 5.3 λ (20 elements) and 12.2 λ (37 ele-for typical boom lengths on each band.

ments).

The size of the original Yagi (169 inches long,

A HIGH-PERFORMANCE 432-MHz YAGI

6.1 λ) was chosen so the antenna could be built from This 22-element, 6.1-λ, 432-MHz Yagi was origi-small-diameter boom material (7/8-inch and 1 inch round nally designed for use in a 12-Yagi EME array built by 6061-T6 aluminum) and still survive high winds and ice K1FO. A lengthy evaluation and development process loading. The 22-element Yagi weighs about 3.5 pounds preceded its construction. Many designs were considered and has a wind load of approximately 0.8 square feet.

and then analyzed on the computer. Next, test models This allows a high-gain EME array to be built with man-were constructed and evaluated on a homemade antenna ageable wind load and weight. This same low wind load range. The resulting design is based on WlEJ’s computer-and weight lets the tropo operator add a high-performance optimized spacings.

432-MHz array to an existing tower without sacrificing The attention paid to the design process has been antennas on other bands.

worth the effort. The 22-element Yagi not only has ex-Table 7 lists the gain and stacking specifications for ceptional forward gain (17.9 dBi), but has an unusually the various length Yagis. The basic Yagi dimensions are clean radiation pattern. The measured E-plane pattern is shown in Table 8. These are free-space element lengths for 3/16-inch-diameter elements. Boom corrections for the element mounting method must be added in. The element-length correction column gives the length that must be Table 7

added to keep the Yagi’s center frequency optimized for Specifications for 432-MHz Yagi Family

use at 432 MHz. This correction is required to use the F/B

DE

Beamwidth Stacking

same spacing pattern over a wide range of boom lengths.

No.

Boom

Gain

ratio imped E/H

E/H

Although any length Yagi will work well, this design is of Ele. length(λ) (dBi)* (dB) (Ω)

(°)

(inches)

at its best when made with 18 elements or more (4.6 λ).

15

3.4

15.67

21

23

30/32

53/49

Element material of less than 3/16-inch diameter is not 16

3.8

16.05

19

23

29/31

55/51

recommended because resistive losses will reduce the gain 17

4.2

16.45

20

27

28/30

56/53

by about 0.1 dB, and wet-weather performance will be 18

4.6

16.8

25

32

27/29

58/55

19

4.9

17.1

25

30

26/28

61/57

worse.

20

5.3

17.4

21

24

25.5/27

62/59

Quarter-inch-diameter elements could be used if all 21

5.7

17.65

20

22

25/26.5

63/60

elements are shortened by 3 mm. The element lengths 22

6.1

17.9

22

25

24/26

65/62

are intended for use with a slight chamfer (0.5 mm) cut 23

6.5

18.15

27

30

23.5/25

67/64

into the element ends. The gain peak of the array is cen-24

6.9

18.35

29

29

23/24

69/66

tered at 437 MHz. This allows acceptable wet-weather 25

7.3

18.55

23

25

22.5/23.5

71/68

performance, while reducing the gain at 432 MHz by only 26

7.7

18.8

22

22

22/23

73/70

27

8.1

19.0

22

21

21.5/22.5

75/72

0.05 dB.

28

8.5

19.20

25

25

21/22

77/75

The gain bandwidth of the 22-element Yagi is

29

8.9

19.4

25

25

20.5/21.5

79/77

31 MHz (at the –1 dB points). The SWR of the Yagi is less 30

9.3

19.55

26

27

20/21

80/78

than l.4: l between 420 and 440 MHz. Fig 41 is a network 31

9.7

19.7

24

25

19.6/20.5

81/79

analyzer plot of the driven-element SWR vs frequency.

32

10.2

19.8

23

22

19.3/20

2/80

These numbers indicate just how wide the frequency re-33

10.6

9.9

23

23

19/19.5

83/81

sponse of a log-taper Yagi can be, even with a simple di-34

11.0

20.05

25

22

18.8/19.2

84/82

35

11.4

20.2

27

25

18.5/19.0

85/83

pole driven element. In fact, at one antenna gain contest, 36

11.8

20.3

27

26

18.3/18.8

86/84

some ATV operators conducted gain vs frequency measure-37

12.2

20.4

26

26

18.1/18.6

87/85

ments from 420 to 440 MHz. The 22-element Yagi beat all 38

12.7

20.5

25

25

18.9/18.4

88/86

entrants including those with so-called broadband feeds.

39

13.1

20.6

25

23

18.7/18.2

89/87

To peak the Yagi for use on 435 MHz (for satellite 40

13.5

20.8

26

21

17.5/18

90/88

use), you may want to shorten all the elements by 2 mm.

*Gain is approximate real gain based on gain measurements To peak it for use on 438 MHz (for ATV applications), made on six different-length Yagis.

shorten all elements by 4 mm. If you want to use the Yagi VHF and UHF Antenna Systems

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Table 8

Free-Space Dimensions for 432-MHz Yagi Family

*Element correction is the amount to shorten or lengthen all elements when building a Yagi of that length.

Element lengths are for 3/16-inch diameter material.

Ele.

Element

Element

Element

No.

Position

Length

Correction*

(mm from

(mm)

reflector)

Refl

0

340

DE

104

334

D1

146

315

D2

224

306

D3

332

299

D4

466

295

D5

622

291

D6

798

289

D7

990

287

D8

1196

285

D9

1414

283

Fig 41—SWR performance of the 22-element Yagi in dry D10

1642

281

–2

weather.

D11

1879

279

–2

D12

2122

278

–2

D13

2373

277

–2

D14

2629

276

–2

D15

2890

275

–1

D16

3154

274

–1

D17

3422

273

–1

D18

3693

272

0

D19

3967

271

0

D20

4242

270

0

D21

4520

269

0

D22

4798

269

0

D23

5079

268

0

D24

5360

268

+1

D25

5642

267

+1

D26

5925

267

+1

D27

6209

266

+1

D28

6494

266

+1

D29

6779

265

+2

D30

7064

265

+2

D31

7350

264

+2

D32

7636

264

+2

Fig 42—Element-mounting detail. Elements are

D33

7922

263

+2

mounted through the boom using plastic insulators.

D34

8209

263

+2

Stainless steel push-nut retaining rings hold the D35

8496

262

+2

element in place.

D36

8783

262

+2

D37

9070

261

+3

D38

9359

261

+3

Element holes should be drilled within ±2 mm. Element lengths should be kept within ±0.5 mm. Elements can be accurately constructed if they are first rough cut with a hack saw and then held in a vise and filed to the exact on FM between 440 MHz and 450 MHz, shorten all the length.

elements by 10 mm. This will provide 17.6 dBi gain at The larger the array, the more attention you should pay 440 MHz, and 18.0 dBi gain at 450 MHz. The driven to making all Yagis identical. Elements are mounted on element may have to be adjusted if the element lengths shoulder insulators and run through the boom (see are shortened.

Fig 42). The element retainers are stainless-steel push nuts.

Although this Yagi design is relatively broadband, These are made by several companies, including Industrial it is suggested that close attention be paid to copying the Retaining Ring Co in Irvington, New Jersey, and AuVeco in design exactly as built. Metric dimensions are used Ft Mitchell, Kentucky. Local industrial hardware distribu-because they are convenient for a Yagi sized for 432 MHz.

tors can usually order them for you. The element insulators 18-32

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Fig 43—Several views of the driven

element and T match.

Fig 44—Details of the driven element and T match for the 22-element Yagi.

Lengths are given in millimeters to allow precise duplication of the antenna. See text.

Fig 45—Boom-construction information for the 22-element Yagi Lengths are given in millimeters to allow precise duplication of the antenna. See text.

VHF and UHF Antenna Systems

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Fig 46—Boom-construction

information for the 33-element Yagi.

Lengths are given in millimeters to

allow precise duplication of the

antenna.

are not critical. Teflon or black polyethylene are prob-gain per boom length, an extremely clean pattern and wide ably the best materials. The Yagi in the photographs is bandwidth. The design is based upon the spacings used made with black Delryn insulators, available from C3i in in a 4.5-λ 432-MHz computerdeveloped design by W1EJ.

Washington, DC.

It is quite similar to the 432MHz Yagi described else-The driven element uses a UG-58A/U connector

where in this chapter. Refer to that project for additional mounted on a small bracket. The UG58A/U should be construction diagrams and photographs.

the type with the press-in center pin. UG-58s with center Mathematical models do not always directly trans-pins held in by “C” clips will usually leak water. Some late into real working examples. Although the computer connectors use steel retaining clips, which will rust and design provided a good starting point, the author, Steve leave a conductive stripe across the insulator. The T-match Powlishen, K1FO, built several test models before the wires are supported by the UT-141 balun. RG-303/U or final working Yagi was obtained. This hands-on tuning RG-142/U Tefloninsulated cable could be used if UT-141

included changing the element-taper rate in order to cannot be obtained. Fig 43A and Fig 42B show details of obtain the flexibility that allows the Yagi to be built with the driven-element construction. Driven element dimen-different boom lengths.

sions are given in Fig 44.

The design is suitable for use from 1.8 λ (10 elements) Dimensions for the 22-element Yagi are listed in to 5.1 λ (19 elements). When elements are added to a Yagi, Table 9. Fig 45 details the Yagi’s boom layout. Element the center frequency, feed impedance and front-to-back material can be either 3/16 inch 6061-T6 aluminum rod or ratio will range up and down. A modern tapered design hard aluminum welding rod.

will minimize this effect and allow the builder to select A 24-foot-long, 10.6-λ, 33-element Yagi was also any desired boom length. This Yagi’s design capabilities built. The construction methods used were the same as per boom length are listed in Table 11.

the 22-element Yagi. Telescoping round boom sections The gain of any Yagi built around this design will be of 1, 11/8, and 11/4 inches in diameter were used. A boom within 0.1 to 0.2 dB of the maximum theoretical gain at support is required to keep boom sag acceptable. At the design frequency of 144.2 MHz. The design is 432 MHz, if boom sag is much more than two or three intentionally peaked high in frequency (calculated gain inches, H-plane pattern distortion will occur. Greater peak is about 144.7 MHz). It has been found that by amounts of boom sag will reduce the gain of a Yagi.

doing this, the SWR bandwidth and pattern at 144.0 to Table 10 lists the proper dimensions for the antenna when 144.3 MHz will be better, the Yagi will be less affected built with the previously given boom diameters. The by weather and its performance in arrays will be more boom layout is shown in Fig 46, and the driven element predictable. This design starts to drop off in performance is described in Fig 47. The 33-element Yagi exhibits if built with fewer than 10 elements. At less than 2 λ, the same clean pattern traits as the 22-element Yagi (see more traditional designs perform well.

Fig 48). Measured gain of the 33-element Yagi is Table 12 gives free-space element lengths for 1/4 inch-19.9 dBi at 432 MHz. A measured gain sweep of the diameter elements. The use of metric notation allows for 33-element Yagi gave a –1 dB gain bandwidth of 14 MHz much easier dimensional changes during the design stage.

with the –1 dB points at 424.5 MHz and 438.5 MHz.

Once you become familiar with the metric system, you’ll probably find that construction is easier without the burden A HIGH-PERFORMANCE 144MHZ YAGI

of cumbersome English fractional units. For 3/16 inch-This 144MHz Yagi design uses the latest log-tapered diameter elements, lengthen all parasitic elements by 3 mm.

element spacings and lengths. It offers near theoretical If 3/8 inch diameter elements are used, shorten all of the 18-34

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Table 9

Table 10

Dimensions for the 22-Element 432-MHz Yagi

Dimensions for the 33-Element 432-MHz Yagi

Element

Element

Element

Boom

Element

Element

Element

Boom

Number

Position

Length

Diam

Number

Position

Length

Diam

(mm from

(mm)

(in)

(mm from

(mm)

(in)

reflector)

reflector)

Refl

30

346

REF

30

348

DE

134

340

DE

134

342

D1

176

321

D1

176

323

D2

254

311

7/8

D2

254

313

D3

362

305

D3

362

307

D4

496

301

D4

496

303

1

D5

652

297

D5

652

299

D6

828

295

D6

828

297

D7

1020

293

D7

1020

295

D8

1226

291

D8

1226

293

D9

1444

289

D9

1444

291

D10

1672

288

D10

1672

290

D11

1909

286

D11

1909

288

D12

2152

285

1

D12

2152

287

11/8

D13

2403

284

D13

2403

286

D14

2659

283

D14

2659

285

D15

2920

281

D15

2920

284

D16

3184

280

D16

3184

284

D17

3452

279

7/8

D17

3452

283

D18

3723

278

D18

3723

282

1¼

D19

3997

277

D19

3997

281

D20

4272

276

D20

4272

280

D21

4550

278

D22

4828

278

D23

5109

277

11/8

directors and the reflector by 6 mm. The driven element D24

5390

277

will have to be adjusted for the individual Yagi if the D25

5672

276

12-element design is not adhered to.

D26

5956

275

For the 12-element Yagi, 1/4-inch diameter elements D27

6239

274

were selected because smaller-diameter elements become D28

6524

274

1

rather flimsy at 2 meters. Other diameter elements can D29

6809

273

be used as described previously. The 2.5—

D30

7094

273

λ boom was cho—

D31

7380

272

sen because it has an excellent size and wind load vs gain and pattern trade-off. The size is also convenient; three 6-foot-long pieces of aluminum tubing can be used without any waste. The relatively large-diameter boom sizes (11/4 and 13/8 inches) were chosen, as they provide an Longer versions could be made by telescoping

extremely rugged Yagi that does not require a boom sup-smaller-size boom sections into the last section. Some sort port. The 12-element 17-foot-long design has a calcu-of boom support will be required on versions longer than lated wind survival of close to 120 mph! The absence of 22 feet. The elements are mounted on shoulder insulators a boom support also makes vertical polarization possible.

and mounted through the boom. However, elements may Fig 47—Details of the driven

element and T match for the 33-

element Yagi. Lengths are given in

millimeters to allow precise

duplication of the antenna.

VHF and UHF Antenna Systems

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Table 11

Table 12

Specifications for the 144-MHz Yagi Family

Free-Space Dimensions for the

Beamwidth Stacking

144-MHz Yagi Family

No. of Boom

Gain

DE Imped FB Ratio

E/H

E/H

Element diameter is ¼ inch

Ele.

Length(λ) (dBd) (Ω)

(dB)

(°)

(°)

Element

Element

Element

10

1.8

11.4

27

17

39/42

10.2/9.5

No.

Position (mm

Length

11

2.2

12.0

38

19

36/40

11.0/10.0

from reflector)

12

2.5

12.5

28

23

34/37

11.7/10.8

Refl.

0

1038

13

2.9

13.0

23

20

32/35

12.5/11.4

DE

312

955

14

3.2

13.4

27

18

31/33

12.8/12.0

D1

447

956

15

3.6

13.8

35

20

30/32

13.2/12.4

D2

699

932

16

4.0

14.2

32

24

29/30

13.7/13.2

D3

1050

916

17

4.4

14.5

25

23

28/29

14.1/13.6

D4

1482

906

18

4.8

14.8

25

21

27/28.5

14.6/13.9

D5

1986

897

19

5.2

15.0

30

22

26/27.5

15.2/14.4

D6

2553

891

D7

3168

887

D8

3831

883

be mounted, insulated or uninsulated, above or through D9

4527

879

D10

5259

875

the boom, as long as appropriate element length correc-D11

6015

870

tions are made. Proper tuning can be verified by checking D12

6786

865

the depth of the nulls between the main lobe and first side D13

7566

861

lobes. The nulls should be 5 to 10 dB below the first side-D14

8352

857

lobe level at the primary operating frequency. The boom D15

9144

853

layout for the 12-element model is shown in Fig 49. The D16

9942

849

actual corrected element dimensions for the 12-element D17

10744

845

2.5-λ Yagi are shown in Table 13.

The design may also be cut for use at 147 MHz.

There is no need to change element spacings. The element lengths should be shortened by 17 mm for best driven-element dimensions are required if you change the operation between 146 and 148 MHz. Again, the driven boom length. The calculated natural driven-element element will have to be adjusted as required.

impedance is given as a guideline. A balanced T-match The driven-element size (1/2-inch diameter) was cho-was chosen because it’s easy to adjust for best SWR and sen to allow easy impedance matching. Any reasonably provides a balanced radiation pattern. A 4:1 half-wave sized driven element could be used, as long as appropri-coaxial balun is used, although impedance-transforming ate length and T-match adjustments are made. Different quarter-wave sleeve baluns could also be used. The cal-Fig 48—E-plane pattern for the 33-

Fig 49—Boom layout for the 12-element 144-MHz Yagi. Lengths are given in element Yagi. This pattern is drawn on

millimeters to allow precise duplication.

a linear dB grid scale, rather than the

standard ARRL log-periodic grid, to

emphasize low sidelobes.

18-36

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Fig 50—Driven-element detail for the 12-element 144-MHz Yagi. Lengths are given in millimeters to allow precise duplication.

VHF and UHF Antenna Systems

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Table 13

Table 14

Dimensions for the 12-Element 2.5-λ Yagi Free-Space Dimensions for the 222-MHz Yagi

Element

Element

Element

Boom

Family

Number

Position

Length

Diam

Element diameter is 3/16-inch.

(mm from

(mm)

(in)

Element

Element

Element

reflector)

No.

Position

Length

Refl.

0

1044

(mm from

(mm)

DE

312

955

reflector)

D1

447

962

11/4

Refl.

0

676

D2

699

938

DE

204

647

D3

1050

922

D1

292

623

D4

1482

912

D2

450

608

D5

1986

904

D3

668

594

D6

2553

898

13/8

D4

938

597

D7

3168

894

D5

1251

581

D8

3831

889

D6

1602

576

D9

4527

885

11/4

D7

1985

573

D10

5259

882

D8

2395

569

D9

2829

565

D10

3283

562

D11

3755

558

D12

4243

556

D13

4745

554

D14

5259

553

D15

5783

552

D16

6315

551

D17

6853

550

D18

7395

549

D19

7939

548

D20

8483

547

Fig 51 shows computer-predicted E-and H-plane radiation patterns for the 12-element Yagi. The patterns are plotted on a l-dB-per-division linear scale instead of the usual ARRL polar-plot graph. This expanded scale Fig 51—H-and E-plane pattern for the 12-element plot is used to show greater pattern detail. The pattern 144-MHz Yagi.

for the 12-element Yagi is so clean that a plot done in the standard ARRL format would be almost featureless, except for the main lobe and first sidelobes.

culated natural impedance will be useful in determining The excellent performance of the 12-element Yagi what impedance transformation will be required at the is demonstrated by the reception of Moon echoes from 200-Ω balanced feed point. Chapter 26, Coupling the Line several of the larger 144MHz EME stations with only to the Antenna, contains information on calculating one 12-element Yagi. Four of the 12-element Yagis will folded-dipole and T-match driven-element parameters. A make an excellent starter EME array, capable of working balanced feed is important for best operation on this many EME QSOs while being relatively small in size.

antenna. Gamma matches can severely distort the pattern The advanced antenna builder can use the information in balance. Other useful driven-element arrangements are Table 11 to design a dream array of virtually any size.

the Delta match and the folded dipole, if you’re willing to sacrifice some flexibility. Fig 50 details the driven-A HIGH-PERFORMANCE 222-MHz YAGI

element dimensions.

Modern tapered Yagi designs are easily applied to A noninsulated driven element was chosen for

222 MHz. This design uses a spacing progression that is mounting convenience. An insulated driven element may in between the 12-element 144-MHz design, and the also be used. A grounded driven element may be less 22-element 432-MHz design presented elsewhere in this affected by static build-up. On the other hand, an insu-chapter. The result is a design with maximum gain per lated driven element allows the operator to easily check boom length, a clean, symmetrical radiation pattern, and his feed lines for water or other contamination by the use wide bandwidth. Although it was designed for weak-sig-of an ohmmeter from the shack.

nal work (tropospheric scatter and EME), the design is 18-38

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are shortened by 3 mm. Three-eighths-inch-diameter Table 15

elements would require 10-mm shorter lengths. Elements Specifications for the 222-MHz Yagi Family

smaller than 3/16 inch-diameter are not recommended. The FB

DE

Beamwidth Stacking

elements are insulated and run through the boom. Plastic No of Boom

Gain

Ratio Imped E/H

E/H

Ele.

Length(λ) (dBd) (dB) (Ω)

(°)

(feet)

shoulder washers and stainless steel retainers are used to hold the elements in place. The various pieces needed to 12

2.4

12.3

22

23

37/39

7.1/6.7

13

2.8

12.8

19

28

33/36

7.8/7.2

build the Yagi may be obtained from C3i in Washington, 14

3.1

13.2

20

34

32/34

8.1/7.6

DC. Fig 52 details the boom layout for the 16-element 15

3.5

13.6

24

30

30/33

8.6/7.8

Yagi. Table 16 gives the dimensions for the 16-element 16

3.9

14.0

23

23

29/31

8.9/8.3

Yagi as built. The driven element is fed with a T match 17

4.3

14.35 20

24

28/30.5

9.3/8.5

and a 4:1 balun. See Fig 53 for construction details. See 18

4.6

14.7

20

29

27/29

9.6/8.9

the 432-MHz Yagi project elsewhere in this chapter for 19

5.0

15.0

22

33

26/28

9.9/9.3

additional photographs and construction diagrams.

20

5.4

15.3

24

29

25/27

10.3/9.6

21

5.8

15.55 23

24

24.5/26.5

10.5/9.8

The Yagi has a relatively broad gain and SWR curve, 22

6.2

15.8

21

23

24/26

10.7/10.2

as is typical of a tapered design, making it usable over a wide frequency range. The example dimensions are intended for use at 222.0 to 222.5 MHz. The 16-element suited to all modes of 222-MHz operation, such as packet Yagi is quite usable to more than 223 MHz. The best com-radio, FM repeater operation and control links.

promise for covering the entire band is to shorten all para-The spacings were chosen as the best compromise

sitic elements by 4 mm. The driven element will have to for a 3.9-λ 16-element Yagi. The 3.9-λ design was cho-be adjusted in length for best match. The position of the sen, like the 12-element 144-MHz design, because it fits T-wire shorting straps may also have to be moved.

perfectly on a boom made from three 6-foot-long alumi-The aluminum boom provides superior strength, is num tubing sections. The design is quite extensible, and lightweight, and has a low wind-load cross section. Alumi-models from 12 elements (2.4 λ) to 22 elements (6.2 λ) num is doubly attractive, as it will long outlast wood and can be built from the dimensions given in Table 14. Note fiberglass. Using state-of-the-art designs, it is unlikely that that free-space lengths are given. They must be corrected significant performance increases will be achieved in the for the element-mounting method. Specifications for vari-next few years. Therefore, it’s in your best interest to build ous boom lengths are shown in Table 15.

an antenna that will last many years. If suitable wood or fiberglass poles are readily available, they may be used with-Construction

out any performance degradation, at least when the wood is Large-diameter (11/4-and 13/8-inch diameter) boom new and dry. Use the free-space element lengths given in construction is used, eliminating the need for boom sup-Table 16 for insulated-boom construction.

ports. The Yagi can also be used vertically polarized.

The pattern of the 16-element Yagi is shown in

Three-sixteenths-inch-diameter aluminum elements are Fig 54. Like the 144-MHz Yagi, a l-dB-per-division plot used. The exact alloy is not critical; 6061-T6 was used, is used to detail the pattern accurately. This 16-element but hard aluminum welding rod is also suitable. Quarter-design makes a good building block for EME or tropo inch-diameter elements could also be used if all elements DX arrays. Old-style narrow-band Yagis often perform Fig 52—Boom layout for the 16-element 222-MHz Yagi. Lengths

are given in millimeters to allow

precise duplication.

VHF and UHF Antenna Systems

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Table 16

Dimensions for 16-Element 3.9-λ 222-MHz Yagi Element

Element

Element

Boom

Number

Position

Length

Diam

(mm from

(mm)

(in)

reflector)

Refl.

0

683

DE

204

664

D1

292

630

D2

450

615

D3

668

601

11/4

D4

938

594

D5

1251

588

D6

1602

583

D7

1985

580

D8

2395

576

D9

2829

572

13/8

D10

3283

569

D11

3755

565

D12

4243

563

D13

4745

561

11/4

D14

5259

560

unpredictably when used in arrays. The theoretical 3.0-dB stacking gain is rarely observed. The 16-element Yagi (and other versions of the design) reliably provides stacking gains of nearly 3 dB. (The spacing dimensions listed in Table 15 show just over 2.9 dB stacking gain.) This has been found to be the best compromise between Fig 54—H-and E-plane patterns for the 16-element gain, pattern integrity and array size. Any phasing line 222-MHz Yagi at A. The driven-element T-match dimensions were chosen for the best SWR compromise losses will subtract from the possible stacking gain.

between wet and dry weather conditions. The SWR vs Mechanical misalignment will also degrade the perfor-frequency curve shown at B demonstrates the broad mance of an array.

frequency response of the Yagi design.

Fig 53—Driven-element detail for the 16-element 222-MHz Yagi. Lengths are given in millimeters to allow precise duplication.

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A 144 MHz 2-Element Quad

The basic 2-element quad array for 144 MHz is shown in Fig 55. The supporting frame is 1 × 1-inch wood, of any kind suitable for outdoor use. Elements are #8 aluminum wire. The driven element is 1 λ (83 inches) long, and the reflector five percent longer (87 inches). Dimensions are not critical, as the quad is relatively broad in frequency response.

The driven element is open at the bottom, its ends fastened to a plastic block. The block is mounted at the bottom of the forward vertical support. The top portion of the element runs through the support and is held firmly by a screw running into the wood and then bearing on the aluminum wire. Feed is by means of 50-Ω coax, connected to the driven-element loop.

The reflector is a closed loop, its top and bottom portions running through the rear vertical support. It is held in position with screws at the top and bottom. The loop can be closed by fitting a length of tubing over the element ends, or by hammering them flat and bolting them together as shown in the sketch.

The elements in this model are not adjustable, though this can easily be done by the use of stubs. It would then Fig 55—Mechanical details of a 2-element quad for 144 MHz. The driven element, L1, is one wavelength be desirable to make the loops slightly smaller to com-long; reflector L2 is 5% longer. With the transmission pensate for the wire in the adjusting stubs. The driven line connected as shown here, the resulting radiation element stub would be trimmed for length and the point is horizontally polarized. Sets of elements of this type of connection for the coax would be adjustable for best can be stacked horizontally and vertically for high gain match. The reflector stub can be adjusted for maximum with broad frequency response. Recommended bay spacing is 1/2 λ between adjacent element sides. The gain or maximum F/B ratio, depending on the builder’s example shown may be fed directly with 50-Ω coax.

requirements.

In the model shown only the spacing is adjusted, and this is not particularly critical. If the wooden sup-has little effect on the gain (from 0.15 to 0.25 λ), so the ports are made as shown, the spacing between the ele-variation in impedance with spacing can be used for ments can be adjusted for best match, as indicated by an matching. This also permits use of either 50-or 75-Ω

SWR meter connected in the coaxial line. The spacing coax for the transmission line.

A Portable 144 MHz 4-Element Quad

Element spacing for quad antennas found in the lit-erature ranges from 0.14 λ to 0.25 λ. Factors such as the 1046.8

Reflector length (ft)

=

(Eq 8)

number of elements in the array and the parameters to be fMHz

optimized (F/B ratio, forward gain, bandwidth, etc), determine the optimum element spacing within this range.

985.5

=

The 4-element quad antenna described here was designed Driven

(ft)

element

(Eq 9)

fMHz

for portable use, so a compromise between these factors was chosen. This antenna, pictured in Fig 56, was 937.3

designed and built by Philip D’Agostino, W1KSC.

Directors (ft)

=

(Eq 10)

Based on several experimentally determined correction fMHz

factors related to the frequency of operation and the wire size, Cutting the loops for 146 MHz provides satisfac-optimum design dimensions were found to be as follows.

tory performance across the entire 144MHz band.

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Fig 57—The complete portable quad, broken down for travel. Visible in the foreground is the driven element.

The pine box in the background is a carrying case for equipment and accessories. A hole in the lid accepts the mast, so the box doubles as a base for a short mast during portable operation. (W1MPO photo) Table 17

Parts List for the 144 MHz 4-element Quad

Boom: ¾ × ¾ ×48-in. pine

Driven element support (spreader):

½ × ¾ × 21¼ in. pine

Driven element feed point strut: ½ × ¾ × 7½ in. pine Reflector support (spreader): ½ × ¾ × 22½ in. pine Director supports (spreaders):

½ × ¾ × 20¼ in. pine, 2 req’d

Fig 56—The 4-element 144-MHz portable quad,

Mast brackets: ¾ × 1½ × 12 in. heavy pine trim, 4 req’d assembled and ready for operation. Sections of Boom to mast bracket: ½ × 15/8 × 5 in. pine

clothes closet poles joined with pine strips make Element wire: Aluminum ground wire

up the mast. (Photo by Adwin Rusczek, W1MPO)

(Radio Shack no. 15-035)

Wire clamps: ¼in. electrician’s copper or zinc plated steel clamps, 3 req’d

Materials

Boom hardware:

6 no. 8-32 × 1½ in. stainless steel machine screws The quad was designed for quick and easy assembly 6 no. 8-32 stainless steel wing nuts

and disassembly, as illustrated in Fig 57. Wood (clear trim 12 no. 8 stainless steel washers

pine) was chosen as the principal building material because Mast hardware:

of its light weight, low cost, and ready availability. Pine is 8 hex bolts, ¼-20 × 3½ in.

used for the boom and element supporting arms. Round 8 hex nuts, ¼-20

wood clothes closet poles comprise the mast material. Strips 16 flat washers

connecting the mast sections are made of heavier pine trim.

Mast material: 15/16 in. × 6 ft wood clothes closet poles, Elements are made of no. 8 aluminum wire. Plexiglas is 3 req’d

used to support the feed point. Table 17 lists the hardware Feed point support plate: 3½ × 2½ in. Plexiglas sheet and other parts needed to duplicate the quad.

Wood preparation materials:

Sandpaper, clear polyurethane, wax

Construction

Feed line: 52-W RG-8 or RG-58 cable

The elements of the quad are assembled first. The Feed line terminals: Solder lugs for no. 8 or larger mounting holes in the boom should be drilled to accom-hardware, 2 req’d

modate 11/

Miscellaneous hardware:

2 inch no. 8 hardware. Measure and mark the

4 small machine screws, nuts, washers; 2 flat-head locations where the holes are to be drilled in the element wood screws

spreaders, Fig 58. Drill the holes in the spreaders just 18-42

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large enough to accept the #8 wire elements. It is impor-and directors, but do not leave any overlap at the feed tant to drill all the holes straight so the elements line up point. The ends of the wires should be 3/4 inch apart where when the antenna is assembled.

they mount on the Plexiglas plate. Leave enough excess Construction of the wire elements is easiest if the that small loops can be bent in the wire for attachment to directors are made first. A handy jig for bending the ele-the coaxial feed line with stainless steel hardware.

ments can be made from a piece of 2 × 3-inch wood cut to Drill the boom as shown in Fig 61. It is a good idea the side length of the directors. It is best to start with about to use hardware with wing nuts to secure the element 82 inches of wire for each director. The excess can be cut spreaders to the boom. After the boom is drilled, clean off when the elements are completed. (The total length of all the wood parts with denatured alcohol, sand them, and each director is 77 inches.) Two bends should initially be give them two coats of glossy polyurethane. After the made so the directors can be slipped into the spreaders polyurethane dries, wax all the wooden parts.

before the remaining corners are bent. See Fig 59.

The boom to mast attachment is made next. Square the Electrician’s copper-wire clamps can be used to join the ends of a 6-foot section of clothes closet pole (a miter box is wires after the final bends are made, and they facilitate useful for this). Drill the center holes in both the boom adjustment of element length. The reflector is made the same way as the directors, but the total length is 86 inches.

The driven element, total length 81 inches, requires special attention, as the feed attachment point needs to be adequately supported. An extra hole is drilled in the driven element spreader to support the feed-point strut, as shown in Fig 60. A Plexiglas plate is used at the feed point to support the feed-point hardware and the feed line. The feed-point support strut should be epoxied to the spreader, and a wood screw used for extra mechanical strength.

For vertical polarization, locate the feed point in the center of one side of the driven element, as shown in Fig 60. Although this arrangement places the spreader supports at voltage maxima points on the four loop conductors, D’Agostino reports no adverse effects during operation. However, if the antenna is to be left exposed to the weather, the builder may wish to modify the design to provide support for the loops at current maxima points, such as shown in Fig 60. (The element of Fig 60

should be rotated 90° for horizontal polarization.) Fig 59—Illustration showing how the aluminum

Orient the driven element spreader so that it mounts element wires are bent. The adjustment clamp and its properly on the boom when the antenna is assembled.

location are also shown.

Bend the driven element the same way as the reflector Fig 60—Layout of the driven element of the 144-MHz quad. The leads of the coaxial cable should be stripped to ½ in. and solder lugs attached for easy connection Fig 58—Dimensions for the pine element spreaders for and disconnection. See text regarding impedance at the 144-MHz 4-element quad.

loop support points.

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Fig 61—Detail of the boom showing hole center Fig 62—Boom to mast plate for the 144-MHz quad.

locations and boom to mast connection points.

The screw hole in the center of the plate should be countersunk so the wood screw attaching it to the mast does not interfere with the fit of the boom.

Fig 63—Mast coupling connector details for the Fig 64—Typical SWR curve for the 144MHz portable portable quad. The plates should be drilled two at a quad. The large wire diameter and the quad design time to ensure the holes line up.

provide excellent bandwidth.

attachment piece and one end of the mast section (Fig 62).

ment of the holes. A drill press is ideal for this job, but Make certain that the mast hole is smaller than the flat-head with care a hand drill can be used if necessary.

screw to be used to ensure a snug fit. Accurately drill the Line up two mast sections end to end, being careful holes for attachment to the boom as shown in Fig 62.

that they are perfectly straight. Use the predrilled con-Countersink the hole for the flat-head screw to pro-nectors to maintain pole straightness, and drill through vide a smooth surface for attachment to the boom. Apply the poles, one at a time. If good alignment is maintained, epoxy cement to the surfaces and screw the boom attach-a straight 18-foot mast section can be made. Label the ment piece securely to the mast section. One 6 foot mast connectors and poles immediately so they are always is used for attachment to the other mast sections.

assembled in the same order.

Two additional 6-foot mast sections are prepared When assembling the antenna, install all the elements next. This brings the total mast height to 18 feet. It is on the boom before attaching the feed line. Connect the coax important to square the ends of each pole so the mast to the screw connections on the driven element support plate stands straight when assembled. Mast-section connectors and run the cable along the strut to the boom. From there, are made of pine as shown in Fig 63. Using 31/2 × 1/4-inch the cable should be routed directly to the mast and down.

hex bolts, washers, and nuts, sections may be attached as Assemble the mast sections to the desired height. The needed, for a total height of 6, 12 or 18 feet. Drill the antenna provides good performance, and has a reasonable holes in two connectors at a time. This ensures good align-SWR curve over the entire 144 MHz band (Fig 64).

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Building Quagi Antennas

The Quagi antenna was designed by Wayne

this changes the resonant frequency slightly. Solder a type Overbeck, N6NB. He first published information on this N connector (an SO-239 is often used at 144 MHz) at the antenna in 1977 (see Bibliography). There are a few tricks midpoint of the driven element bottom side, and close to Quagi building, but nothing very difficult or compli-the reflector loop.

cated is involved. In fact, Overbeck mass produced as many as 16 in one day. Tables 18 and 19 give the dimensions for Quagis for various frequencies up to 446 MHz.

For the designs of Tables 18 and 19, the boom is wood Table 19

or any other nonconductor (such as, fiberglass or Plexiglas).

432MHz, 15-Element, Long Boom Quagi

If a metal boom is used, a new design and new element Construction Data

lengths will be required. Many VHF antenna builders go Element Lengths,

Interelement Spacing,

wrong by failing to follow this rule: If the original uses a Inches

Inches

metal boom, use the same size and shape metal boom when R—28

R-DE7

you duplicate it. If it calls for a wood boom, use a noncon-DE—265/8

DE-D1—51/4

ductor. Many amateurs dislike wood booms, but in a salt air D1—113/4

D1-D2—11

environment they outlast aluminum (and surely cost less).

D21—11/16

D2-D3—57/8

D3—115/

Varnish the boom for added protection.

8

D3-D4—83/4

D4—119/16

D4-D5—83/4

The 144-MHz version is usually built on a 14 foot, D5—111/2

D5-D6—83/4

1 × 3 inch boom, with the boom tapered to 1 inch at both D6—117/16

D6-D7—12

ends. Clear pine is best because of its light weight, but D7—113/8

D7-D8—12

construction grade Douglas fir works well. At 222 MHz D8—115/16

D8-D9—111/4

the boom is under 10 feet long, and most builders use 1 ×

D9—115/16

D9-D10—111/2

2 or (preferably) 3/

D10—111/4

D10-D11—93/16

4 × 11/4 inch pine molding stock. At

D11—113/

432 MHz, except for long-boom versions, the boom 16

D11-D12—123/8

D12—111/8

D12-D13—1-3/4

should be 1/2 inch thick or less. Most builders use strips D13—111/16

of 1/2-inch exterior plywood for 432 MHz.

Boom: 1 × 2in. × 12-ft Douglas fir, tapered to 5/8 in. at The quad elements are supported at the current

both ends.

maxima (the top and bottom, the latter beside the feed Driven element: #12 TW copper wire loop in square point) with Plexiglas or small strips of wood. See Fig 65.

configuration, fed at bottom center with type N connector The quad elements are made of #12 copper wire, com-and 52-Ω coax.

Reflector: #12 TW copper wire loop, closed at bottom.

monly used in house wiring. Some builders may elect to Directors: 1/8 in. rod passing through boom.

use #10 wire on 144 MHz and #14 on 432 MHz, although Table 18

Dimensions, Eight-Element Quagi

Element

Frequency

Lengths

144.5 MHz

147 MHz

222 MHz

432 MHz

446 MHz

Reflector1

865/8"

85"

563/8"

28"

271/8"

Driven2

82"

80"

53½”

265/8"

257/8"

Directors

3515/16"

355/16" to

233/8" to

11¾” to

113/8" to

to 35" in

343/8" in

23¾” in

117/16" in

111/16" in

3/16" steps

3/16" steps

1/8" steps

1/16" steps

1/16" steps

Spacing

R-DE

21"

20½”

135/8"

7"

6.8"

DE-D1

15¾”

153/8"

10¼”

5¼”

5.1"

D1-D2

33"

32½”

21½”

11"

10.7"

D2-D3

17½”

171/8"

113/8"

5.85"

5.68"

D3-D4

26.1"

255/8"

17"

8.73"

8.46"

D4-D5

26.1"

255/8"

17"

8.73"

8.46"

D5-D6

26.1"

255/8"

17"

8.73"

8.46"

Stacking Distance Between Bays

11'

10' 10"

7' 1½”

3’7"

3' 55/8"

1 All #12 TW (electrical) wire, closed loops.

2 All #12 TW wire loops, fed at bottom.

VHF and UHF Antenna Systems

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The directors are mounted through the boom. They essary. Also make sure to get the elements in the right or-can be made of almost any metal rod or wire of about der. The longest director goes closest to the driven element.

1/8-inch diameter. Welding rod or aluminum clothesline Finally, remember that a balanced antenna is being wire works well if straight. (The designer uses 1/8-inch fed with an unbalanced line. Every balun the designer stainless-steel rod obtained from an aircraft surplus store.) tried introduced more trouble in terms of losses than the A TV type U bolt mounts the antenna on a mast. A feed imbalance caused. Some builders have tightly coiled single machine screw, washers and a nut are used to several turns of the feed line near the feed point to limit secure the spreaders to the boom so the antenna can be line radiation. In any case, the feed line should be kept at quickly “flattened” for travel. In permanent installations right angles to the antenna. Run it from the driven ele-two screws are recommended.

ment directly to the supporting mast and then up or down perpendicularly for best results.

Construction Reminders

Based on the experiences of Quagi builders, the fol-QUAGIS FOR 1296 MHz

lowing hints are offered. First, remember that at 432 MHz The Quagi principle has recently been extended to even a 1/8-inch measurement error results in performance the 1296-MHz band, where good performance is

deterioration. Cut the loops and elements as carefully as extremely difficult to obtain from homemade conventional possible. No precision tools are needed, but accuracy is nec-Yagis. Fig 66 shows the construction and Table 20 gives the design information for antennas with 10, 15 and 25

elements.

At 1296 MHz, even slight variations in design or building materials can cause substantial changes in performance. The 1296 MHz antennas described here work every time⎯but only if the same materials are used and the antennas are built exactly as described. This is not to discourage experimentation, but if modifications to these 1296-MHz antenna designs are contemplated, consider building one antenna as described here, so a reference is available against which variations can be compared.

The Quagis (and the cubical quad) are built on

1/4-inch thick Plexiglas booms. The driven element and reflector (and also the directors in the case of the cubical quad) are made of insulated #18 AWG solid copper bell wire, available at hardware and electrical supply stores.

Other types and sizes of wire work equally well, but the dimensions vary with the wire diameter. Even removing Fig 65—A close-up view of the feed method used on a the insulation usually necessitates changing the loop 432-MHz Quagi. This arrangement produces a low SWR

lengths.

and gain in excess of 13 dBi with a 4-ft 10-in. boom!

The same basic arrangement is used on lower

Quad loops are approximately square (Fig 67), frequencies, but wood may be substituted for the although the shape is relatively uncritical. The element Plexiglas spreaders. The boom is ½-in. exterior lengths, however, are critical. At 1296 MHz, variations plywood.

Fig 66—A view of the

10-element version of

the 1296-MHz Quagi. It

is mounted on a 30-in.

Plexiglas boom with a

3 × 3-in. square of

Plexiglas to support

the driven element and

reflector. Note how the

driven element is

attached to a standard

UG-290 BNC

connector. The

elements are held in

place with silicone

sealing compound.

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of 1/16 inch alter the performance measurably, and a mity in construction. Any substitution may alter the driven 1/8 inch departure can cost several decibels of gain. The element electrical length. One end of the 91/4 inch driven loop lengths given are gross lengths. Cut the wire to these loop is pushed as far as it can go into the center pin, and lengths and then solder the two ends together. There is a is soldered in that position. The loop is then shaped and 1/8-inch overlap where the two ends of the reflector (and threaded through small holes drilled in the Plexiglas sup-director) loops are joined, as shown in Fig 67.

port. Finally, the other end is fed into one of the four The driven element is the most important of all. The mounting holes on the BNC connector and soldered. In

#18 wire loop is soldered to a standard UG-290 chassis-most cases, the best SWR is obtained if the end of the mount BNC connector as shown in the photographs. This wire just passes through the hole so it is flush with the exact type of connector must be used to ensure unifor-opposite side of the connector flange.

Table 20

Dimensions, 1296-MHz Quagi Antennas

Note: All lengths are gross lengths. See text and photos for construction technique and recommended overlap at loop junctions. All loops are made of #18 AWG solid-covered copper bell wire. The Yagi type directors are 1/16-in. brass brazing rod. See text for a discussion of director taper.

Feed: Direct with 52-Ω coaxial cable to UG-290 connector at driven element; run coax symmetrically to mast at rear of antenna.

Boom: 11/4-in. thick Plexiglas, 30 in. long for 10-element quad or Quagi and 48 in. long for 15-element Quagi; 84

in. for 25-element Quagi.

10-Element Quagi for 1296 MHz

Length,

Interelement

Element

Inches Construction

Element Spacing, In.

Reflector

9.5625 Loop

R-DE

2.375

Driven

9.25

Loop

DE-D1

2.0

Director 1 3.91

Brass rod

D1-D2

3.67

Director 2 3.88

Brass rod

D2-D3

1.96

Director 3 3.86

Brass rod

D3-D4

2.92

Director 4 3.83

Brass rod

D4-D5

2.92

Director 5 3.80

Brass rod

D5-D6

2.92

Director 6 3.78

Brass rod

D6-D7

4.75

Director 7 3.75

Brass rod

D7-D8

3.94

Director 8 3.72

Brass rod

15-Element Quagi for 1296 MHz

The first 10 elements are the same lengths as above, but the spacing from D6 to D7 is 4.0 in.; 07 to D8 is also 4.0 in.

Director 9

3.70

D8-D9

3.75

Director 10

3.67

D9-D10

3.83

Director 11

3.64

D10-D11 3.06

Director 12

3.62

D11-D12 4.125

Director 13

3.59

D12-D13 4.58

25-Element Quagi for 1296 MHz

The first 15 elements use the same element lengths and spacings as the 15-element model. The additional directors are evenly spaced at 3.0-in. intervals and taper Fig 67—These photos show the construction method in length successively by 0.02 in. per element. Thus, D23

used for the 1296-MHz quad type parasitic elements.

is 3.39 in.

The two ends of the #18 bell wire are brought together with an overlap of 1/8 in. and soldered.

VHF and UHF Antenna Systems

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Loop Yagis for 1296 MHz

Described here are loop Yagis for the 1296-MHz

antenna provides acceptable performance from 1280 to band. The loop Yagi fits into the quad family of anten-1300 MHz.

nas, as each element is a closed loop with a length of These antennas have been built on 6-and 12-foot approximately 1 λ. Several versions are described, so the booms. Results of gain tests at VHF conferences and by builder can choose the boom length and frequency cov-individuals around the country show the gain of the erage desired for the task at hand. Mike Walters, G3JVL, 6-foot model to be about 18 dBi, while the 12-foot ver-brought the original loop-Yagi design to the amateur com-sion provides about 20.5 dBi. Swept measurements indi-munity in the 1970s. Since then, many versions have been cate that gain is about 2 dB down from maximum gain at developed with different loop and boom dimensions. Chip

±30 MHz from the design frequency. The SWR, how—

Angle, N6CA, developed the antennas shown here.

ever, deteriorates within a few megahertz on the low side Three sets of dimensions are given. Good perfor-of the design center frequency.

mance can be expected if the dimensions are carefully followed. Check all dimensions before cutting or drilling The Boom

anything. The 1296-MHz version is intended for weak-The dimensions given here apply only to a ¾-inch signal operation, while the 1270-MHz version is opti-OD boom. If a different boom size is used, the dimen-mized for FM and mode L satellite work. The 1283-MHz sions must be scaled accordingly. Many hardware stores Fig 68—Loop Yagi boom-to-mast plate details are given at A. At B, the mounting of the antenna to the mast is detailed. A boom support for long antennas is shown at C. The arrangement shown in D and E may be used to rear-mount antennas up to 6 or 7 ft long.

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Fig 69—Boom drilling dimensions. These dimensions must be carefully followed and the same materials used if performance is to be optimum. Element spacings are the same for all directors after D6—use as many as necessary to fill the boom.

Fig 71—Element-to-boom mounting details.

machine screws, so a series of no. 33 (0.113inch) holes must be drilled along the center of the boom to accom-Fig 70—Parasitic elements for the loop Yagi are made modate this hardware. Fig 69 shows the element spac-from aluminum sheet, the driven element from copper ings for different parts of the band. Dimensions should sheet. The dimensions given are for ¼-in. wide by be followed as closely as possible.

0.0325-in. thick elements only. Lengths specified are hole to hole distances; the holes are located 1/8 in. from Parasitic Elements

each element end.

The reflectors and directors are cut from 0.032-inch thick aluminum sheet and are 1/4 inch wide. Fig 70 indicates the lengths for the various elements. These lengths carry aluminum tubing in 6-and 8-foot lengths, and that apply only to elements cut from the specified material.

tubing is suitable for a short Yagi. If a 12-foot antenna is For best results, the element strips should be cut with a planned, find a piece of more rugged boom material, such shear. If the edges are left sharp, birds won’t sit on the as 6061-T6 grade aluminum. Do not use anodized tub-elements.

ing. The 12foot antenna must have additional boom sup-Drill the mounting holes as shown in Fig 70 after port to minimize boom sag. The 6 foot version can be carefully marking their locations. After the holes are rear mounted. For rear mounting, allow 41/2 inches of drilled, form each strap into a circle. This is easily done boom behind the last reflector to eliminate SWR effects by wrapping the element around a round form. (A small from the support.

juice can works well.)

The antenna is attached to the mast with a gusset Mount the loops to the boom with no. 4-40 × 1-inch plate. This plate mounts at the boom center. See Fig 68.

machine screws, lock washers and nuts. See Fig 71. It is Drill the plate mounting holes perpendicular to the ele-best to use only stainless steel or plated-brass hardware.

ment mounting holes (assuming the antenna polarization Although the initial cost is higher than for ordinary plated-is to be horizontal).

steel hardware, stainless or brass hardware will not rust Elements are mounted to the boom with no. 4-40

and need replacement after a few years. Unless the antenna VHF and UHF Antenna Systems

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is painted, the hardware will definitely deteriorate.

Driven Element

The driven element is cut from 0.032-inch copper sheet and is 1/4 inch wide. Drill three holes in the strap as detailed in Fig 69. Trim the ends as shown and form the strap into a loop similar to the other elements. This antenna is like a quad; if the loop is fed at the top or bottom, it is horizontally polarized.

Driven element mounting details are shown in Fig 72. A mounting fixture is made from a 1/4-20 × 11/4 inch brass bolt. File the bolt head to a thickness of 1/8 inch.

Bore a 0.144-inch (no. 27 drill) hole lengthwise through the center of the bolt. A piece of 0.141 inch semi-rigid Hardline (UT-141 or equivalent) mounts through this hole and is soldered to the driven loop feed point. The point at which the UT-141 passes through the copper loop and brass mounting fixture should be left unsoldered at this time to allow for matching adjustments when the antenna is completed, although the range of adjustment is not very large.

The UT-141 can be any convenient length. Attach

the connector of your choice (preferably type N). Use a Fig 72—Driven-element details. See Fig 70 and the text short piece of low-loss RG-8 size cable (or 1/2-inch for additional information.

Hardline) for the run down the boom and mast to the main feed line. For best results, the main feed line should be the lowest loss 50-Ω cable obtainable. Good 7/8-inch Hardline has 1.5 dB of loss per 100 feet and virtually quencies cannot be used on 1296 MHz. This is the most eliminates the need for remote mounting of the transmit important reason why all who venture to these frequen-converter or amplifier.

cies are not equally successful. First, when a proven design is used, copy it exactly¾don’t change anything.

Tuning the Driven Element

This is especially true for antennas.

If the antenna is built carefully to the dimensions Use the best feed line you can get. Here are some given, the SWR should be close to 1:1. Just to be sure, realistic measurements of common coaxial cables at check the SWR if you have access to test equipment. Be 1296 MHz (loss per 100 feet).

sure the signal source is clean, however; wattmeters RG-8, 213, 214: 11 dB

respond to “dirty” signals and can give erroneous read-1/2 in. foam/copper Hardline: 4 dB

ings. If problems are encountered, recheck all dimensions.

7/8 in. foam/copper Hardline: 1.5 dB

If they look good, a minor improvement may be realized by changing the shape of the driven element. Slight bend-Mount the antennas to keep feed line losses to an ing of reflector 2 may also improve the SWR. When the absolute minimum. Antenna height is less important than desired match has been obtained, solder the point where keeping the line losses low. Do not allow the mast to pass the UT-141 jacket passes through the loop and brass bolt.

through the elements, as is common on antennas for lower frequencies. Cut all U-bolts to the minimum length Tips for 1296-MHz Antenna Installations

needed; 1/4 λ at 1296 MHz is only a little over 2 inches.

Construction practices that are common on lower fre-Avoid any unnecessary metal around the antenna.

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Trough Reflectors for 432 and 1296 MHz Dimensions are given in Fig 73 for 432-and 1296-ing device adjusted to give optimum match. In the case MHz trough reflectors. The gain to be expected is 16 dBi of the 1296-MHz antenna, the dipole length can be and 15 dBi, respectively. A very convenient arrangement, adjusted by means of the brass screws at the ends of the especially for portable work, is to use a metal hinge at elements. Locking nuts are essential.

each angle of the reflector. This permits the reflector to The reflector should be made of sheet aluminum

be folded flat for transit. It also permits experiments to for 1296 MHz, but can be constructed of wire mesh (with be carried out with different apex angles.

twists parallel to the dipole) for 432 MHz. To increase A housing is required at the dipole center to prevent the gain by 3 dB, a pair of these arrays can be stacked the entry of moisture and, in the case of the 432-MHz so the reflectors are barely separated (to prevent the for-antenna, to support the dipole elements. The dipole may mation of a slot radiator by the edges). The radiating be moved in and out of the reflector to get either mini-dipoles must then be fed in phase, and suitable feeding mum SWR or, if this cannot be measured, maximum gain.

and matching must be arranged. A two-stub tuner can If a two-stub tuner or other matching device is used, the be used for matching either a single-or double-reflector dipole may be placed to give optimum gain and the match-system.

Fig 73—Practical construction information for trough reflector antennas for 432 and 1296 MHz.

VHF and UHF Antenna Systems

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A Horn Antenna for 10 GHz

The horn antenna is the easiest antenna for the

the allowable phase difference is 144° (0.4 λ). If the beginner on 10 GHz to construct. It can be made out of aperture of a pyramidal horn exceeds one wavelength in readily available flat sheet brass. Because it is inherently both planes, the Eplane and Hplane patterns are essen-a broadband structure, minor constructional errors can tially independent and can be analyzed separately.

be tolerated. The one drawback is that horn antennas The usual direction for orienting the waveguide feed become physically cumbersome at gains over about is with the broad face horizontal, giving vertical polar-25 dBi, but for most line-of-sight work this much gain is ization. If this is the case, the H-plane sectoral horn has rarely necessary. This antenna was designed by Bob a narrow horizontal beamwidth and a very wide vertical Atkins, KA1GT, and appeared in QST for April and May, beamwidth. This is not a very useful beam pattern for 1987.

most amateur applications. The E-plane sectoral horn has Horn antennas are usually fed by waveguide. When a narrow vertical beamwidth and a wide horizontal operating in its normal frequency range, waveguide beamwidth. Such a radiation pattern could be useful in a propagation is in the TE

beacon system where wide coverage is desired.

10 mode. This means that the electric (E) field is across the short dimension of the guide The most useful form of the horn for general appli-and the magnetic (H) field is across the wide dimension.

cations is the optimum pyramidal horn. In this configura-This is the reason for the E-plane and H-plane terminol-tion the two beamwidths are almost the same. The E-plane ogy shown in Fig 74.

(vertical) beamwidth is slightly less than the H-plane (hori-There are many varieties of horn antennas. If the zontal), and also has greater side lobe intensity.

waveguide is flared out only in the H-plane, the horn is called an H-plane sectoral horn. Similarly, if the flare is only in the E-plane, an Eplane sectoral horn results. If the flare is in both planes, the antenna is called a pyramidal horn.

For a horn of any given aperture, directivity (gain along the axis) is maximum when the field distribution across the aperture is uniform in magnitude and phase.

When the fields are not uniform, side lobes that reduce the directivity of the antenna are formed. To obtain a uniform distribution, the horn should be as long as possible with minimum flare angle. From a practical point of view, however, the horn should be as short as possible, so there is an obvious conflict between performance and convenience.

Fig 75 illustrates this problem. For a given flare Fig 74—10-GHz antennas are usually fed with

angle and a given side length, there is a path-length dif-waveguide. See text for a discussion of waveguide ference from the apex of the horn to the center of the propagation characteristics.

aperture (L), and from the apex of the horn to the edge of the aperture (L’). This causes a phase difference in the field across the aperture, which in turn causes formation of side lobes, degrading directivity (gain along the axis) of the antenna. If L is large this difference is small, and the field is almost uniform. As L decreases however, the phase difference increases and directivity suffers. An optimum (shortest possible) horn is constructed so that this phase difference is the maximum allowable before side lobes become excessive and axial gain markedly decreases.

The magnitude of this permissible phase difference is different for E-plane and H-plane horns. For the E-plane horn, the field intensity is quite constant across the aperture. For the H-plane horn, the field tapers to zero at the edge. Consequently, the phase difference at the edge of the aperture in the E-plane horn is more critical and Fig 75—The path-length (phase) difference between should be held to less than 90° (1/4 λ). In an H-plane horn, the center and edge of a horn antenna is δ.

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Building the Antenna

A 10-GHz pyramidal horn with 18.5 dBi gain is

shown in Fig 76. The first design parameter is usually the required gain, or the maximum antenna size. These are of course related, and the relationships can be approximated by the following:

L = H-plane length (λ) = 0.0654 × gain (Eq 1) A = H-plane aperture (λ) = 0.0443 × gain (Eq 2) B = E-plane aperture (λ) = 0.81 A (Eq 3) where

gain is expressed as a ratio; 20 dBi gain = 100

L, A and B are dimensions shown in Fig 77.

From these equations, the dimensions for a 20-dBi gain horn for 10.368 GHz can be determined. One wavelength at 10.368 GHz is 1.138 inches. The length (L) of Fig 76—This pyramidal horn has 18.5 dBi gain at such a horn is 0.0654 × 100 = 6.54 λ. At 10.368 GHz, 10 GHz. Construction details are given in the text.

this is 7.44 inches. The corresponding H-plane aperture (A) is 4.43 λ (5.04 inches), and the E-plane aperture (B), 4.08 inches.

The easiest way to make such a horn is to cut pieces from brass sheet stock and solder them together. Fig 77

shows the dimensions of the triangular pieces for the sides and a square piece for the waveguide flange. (A standard commercial waveguide flange could also be used.) Because the E-plane and H-plane apertures are different, the horn opening is not square. Sheet thickness is unim-portant; 0.02 to 0.03 inch works well. Brass sheet is often available from hardware or hobby shops.

Note that the triangular pieces are trimmed at the apex to fit the waveguide aperture (0.9 × 0.4 inch). This necessitates that the length, from base to apex, of the smaller triangle (side B) is shorter than that of the larger (side A). Note that the length, S, of the two different sides of the horn must be the same if the horn is to fit together!

For such a simple looking object, getting the parts to fit together properly requires careful fabrication.

The dimensions of the sides can be calculated with simple geometry, but it is easier to draw out templates on a sheet of cardboard first. The templates can be used to build a mock antenna to make sure everything fits together properly before cutting the sheet brass.

First, mark out the larger triangle (side A) on cardboard. Determine at what point its width is 0.9 inch and draw a line parallel to the base as shown in Fig 77. Measure the length of the side S; this is also the length of the sides of the smaller (side B) pieces.

Mark out the shape of the smaller pieces by first drawing a line of length B and then constructing a second line of length S. One end of line S is an end of line B, and the other is 0.2 inch above a line perpendicular to the center of line B as shown in Fig 76. (This procedure is much more easily followed than described.) These smaller pieces are made slightly oversize (shaded area in Fig 77—Dimensions of the brass pieces used to make Fig 77) so you can construct the horn with solder seams the 10-GHz horn antenna. Construction requires two of on the outside of the horn during assembly.

each of the triangular pieces (side A and side B).

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Cut out two cardboard pieces for side A and two for side B and tape them together in the shape of the horn.

The aperture at the waveguide end should measure 0.9 ×

0.4 inch and the aperture at the other end should measure 5.04 × 4.08 inches.

If these dimensions are correct, use the cardboard templates to mark out pieces of brass sheet. The brass sheet should be cut with a bench shear if one is available, because scissors type shears tend to bend the metal. Jig the pieces together and solder them on the outside of the seams. It is important to keep both solder and rosin from contaminating the inside of the horn; they can absorb RF

and reduce gain at these frequencies.

Assembly is shown in Fig 78. When the horn is completed, it can be soldered to a standard waveguide flange, or one cut out of sheet metal as shown in Fig 77. The transition between the flange and the horn must be smooth. This antenna provides an excellent performance-to-cost ratio (about 20 dBi gain for about five dollars in parts).

Fig 78—Assembly of the

10-GHz horn antenna.

Periscope Antenna Systems

One problem common to all who use microwaves is

ily. Additionally, with a correct choice of reflector size, that of mounting an antenna at the maximum possible dish size, and dish to reflector spacing, feed losses can height while trying to minimize feed-line losses. The be made small, increasing the effective system gain. In higher the frequency, the more severe this problem be-fact, for some particular system configurations, the gain comes, as feeder losses increase with frequency. Because of the overall system can be greater than that of the feed parabolic dish reflectors are most often used on the higher antenna alone.

bands, there is also the difficulty of waterproofing feeds (particularly waveguide feeds). Inaccessibility of the dish Gain of a Periscope System

is also a problem when changing bands. Unless the tower Fig 80 shows the relationship between the effective is climbed every time and the feed changed, there must be gain of the antenna system and the distance between the a feed for each band mounted on the dish. One way around reflector and feed antenna for an elliptical reflector. At these problems is to use a periscope antenna system (some-first sight, it is not at all obvious how the antenna system times called a “flyswatter antenna”).

can have a higher gain than the feed alone. The reason The material in this section was prepared by Bob lies in the fact that, depending on the feed to reflector Atkins, KA1GT, and appeared in QST for January and spacing, the reflector may be in the near field (Fresnel) February 1984. Fig 79 shows a schematic representation region of the antenna, the far field (Fraunhöffer) region, of a periscope antenna system. A plane reflector is or the transition region between the two.

mounted at the top of a rotating tower at an angle of 45°.

In the far field region, the gain is proportional to the This reflector can be elliptical with a major to minor axis reflector area and inversely proportional to the distance ratio of 1.41, or rectangular. At the base of the tower is between the feed and reflector. In the near field region, mounted a dish or other type of antenna such as a Yagi, seemingly strange things can happen, such as decreasing pointing straight up. The advantage of such a system is gain with decreasing feed to reflector separation. The that the feed antenna can be changed and worked on eas-reason for this gain decrease is that, although the reflec-18-54

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tor is intercepting more of the energy radiated by the feed, it does not all contribute in phase at a distant point, and so the gain decreases.

In practice, rectangular reflectors are more common than elliptical. A rectangular reflector with sides equal in length to the major and minor axes of the ellipse will, in fact, normally give a slight gain increase. In the far field region, the gain will be proportional to the area of the reflector. To use Fig 80 with a rectangular reflector, R2 may be replaced by A / π, where A is the projected area of the reflector. The antenna pattern depends in a complicated way on the system parameters (spacing and size of the elements), but Table 21 gives an approximation of what to expect. R is the radius of the projected circular area of the elliptical reflector (equal to the minor axis radius), and b is the length of the side of the projected square area of the rectangular reflector (equal to the length of the short side of the rectangle).

For those wishing a rigorous mathematical analysis of this type of antenna system, several references are given in the Bibliography at the end of this chapter.

Mechanical Considerations

There are some problems with the physical construction of a periscope antenna system. Since the antenna gain of a microwave system is high and, hence, its beamwidth Fig 79—The basic periscope antenna. This design narrow, the reflector must be accurately aligned. If the makes it easy to adjust the feed antenna.

reflector does not produce a beam that is horizontal, the Fig 80—Gain of a periscope antenna using a plane elliptical reflector (after Jasik—see Bibliography).

VHF and UHF Antenna Systems

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the horizontal as the system is rotated, and the effective Table 21

gain at the horizon will fluctuate. Despite these prob-Radiation Patterns of Periscope Antenna Systems lems, amateurs have used periscope antennas success-Elliptical

Rectangular

fully on the bands through 10 GHz. Periscope antennas Reflector

Reflector

are used frequently in commercial service, though usu-3-dB beamwidth,

60 λ/2R

52 λ/b

ally for point-to-point transmission. Such a commercial degrees

system is shown in Fig 81.

6-dB beamwidth,

82 λ/2R

68 λ/b

Circular polarization is not often used for terrestrial degrees

First minimum,

73 λ/2R

58 λ/b

work, but if it is used with a periscope system there is an degrees from axis

important point to remember. The circularity sense First maximum,

95 λ/2R

84 λ/b

changes when the signal is reflected. Thus, for right hand degrees from axis

circularity with a periscope antenna system, the feed Second minimum,

130 λ/2R

116 λ/b

arrangement on the ground should produce left hand cir-degrees from axis

cularity. It should also be mentioned that it is possible Second maximum,

156 λ/2R

142 λ/b

(though more difficult for amateurs) to construct a peri-degrees from axis

Third minimum,

185 λ/2R

174 λ/b

scope antenna system using a parabolically curved degrees from axis

reflector. The antenna system can then be regarded as an offset fed parabola. More gain is available from such a system at the added complexity of constructing a parabolically curved reflector, accurate to 1/10 λ.

BIBLIOGRAPHY

Source material and more extended discussion of

topics covered in this chapter can be found in the references given below and in the textbooks listed at the end of Chapter 2, Antenna Fundamentals.

B. Atkins, “Periscope Antenna Systems,” The New Frontier, QST, Jan and Feb 1984.

B. Atkins, “Horn Antennas for 10 GHz,” The New Frontier, QST, Apr and May 1987.

J. Drexler, “An Experimental Study of a Microwave Periscope,” Proc. IRE, Correspondence, Vol 42, Jun 1954, p 1022.

D. Evans and G. Jessop, VHF-UHF Manual, 3rd ed.

(London: RSGB), 1976.

N. Foot, “WA9HUV 12foot Dish for 432 and 1296 MHz,”

The World Above 50 Mc., QST, Jun 1971, pp 98-101, 107.

Fig 81—Commercial periscope antennas, such as this N. Foot, “Cylindrical Feed Horn for Parabolic Reflec-one, are often used for point-to-point communication.

tors,” Ham Radio, May 1976.

G. Gobau, “Single-Conductor Surface-Wave Transmission Lines,” Proc. IRE, Vol 39, Jun 1951, pp 619-useful gain of the system will be reduced. From the 624; also see Journal of Applied Physics, Vol 21

geometry of the system, an angular misalignment of the (1950), pp 1119-1128.

reflector of X degrees in the vertical plane will result in an R. E. Greenquist and A. J. Orlando, “An Analysis of Pas-angular misalignment of 2X degrees in the vertical align-sive Reflector Antenna Systems,” Proc. IRE, Vol 42, ment of the antenna system pattern. Thus, for a dish point-Jul 1954, pp 1173-1178.

ing straight up (the usual case), the reflector must be at an G. A. Hatherell, “Putting the G Line to Work,” QST, Jun angle of 45° to the vertical and should not fluctuate from 1974, pp 11-15, 152, 154, 156.

factors such as wind loading.

D. L. Hilliard, “A 902MHz Loop Yagi Antenna,” QST, The reflector itself should be flat to better than 1/10

Nov 1985, pp 30-32.

λ for the frequency in use. It may be made of mesh, pro-W. C. Jakes, Jr., “A Theoretical Study of an Antenna-vided that the holes in the mesh are also less than 1/10 λ in Reflector Problem,” Proc. IRE, Vol 41, Feb 1953, pp diameter. A second problem is getting the support mast 272-274.

to rotate about a truly vertical axis. If the mast is not H. Jasik, Antenna Engineering Handbook, 1st ed. (New vertical, the resulting beam will swing up and down from York: McGraw-Hill, 1961).

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R. T. Knadle, “UHF Antenna Ratiometry,” QST, Feb 1976, Transmission (New York: D. Van Nostrand Co, 1950).

pp 22-25.

P. P. Viezbicke, “Yagi Antenna Design,” NBS Technical T. Moreno, Microwave Transmission Design Data (New Note 688 (U. S. Dept. of Commerce/National Bureau York: McGraw-Hill, 1948).

of Standards, Boulder, CO), Dec 1976.

W. Overbeck, “The VHF Quagi,” QST, Apr 1977, pp 11-14.

D. Vilardi, “Easily Constructed Antennas for 1296 MHz,”

W. Overbeck, “The Long-Boom Quagi,” QST, Feb 1978, QST, Jun 1969.

pp 20-21.

D. Vilardi, “Simple and Efficient Feed for Parabolic W. Overbeck, “Reproducible Quagi Antennas for

Antennas,” QST, Mar 1973.

1296 MHz,” QST, Aug 1981, pp 11-15.

Radio Communication Handbook, 5th ed. (London: G. Southworth, Principles and Applications of Waveguide RSGB, 1976).

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Document Outline

Introduction to the CD-ROM Edition

Using this CD

Installing Adobe Acrobat Reader

The ARRL Antenna Book, 20th Edition

Covers

Contributors

Copyright

Foreword

Contents

Schematic Symbols Used in Circuit Diagrams

About the ARRL

Feedback

Chapter 1 - Safety First

Tower Safety

CLOTHING

SAFETY BELT & CLIMBING ACCESSORIES

THE GIN POLE

INSTALLING ANTENNAS ON THE TOWER

SOME TOWER CLIMBING TIPS

THE TOWER SHIELD

Electrical Safety

AC & DC SAFETY

Lightning and EMP Protection

ELECTROMAGNETIC PULSE & THE RADIO AMATEUR

RF Radiation and Electromagnetic Field Safety

THERMAL EFFECTS OF RF ENERGY

ATHERMAL EFFECTS OF EMR

Chapter 2 - Antenna Fundamentals

Essential Characteristics of Antennas

FEED-POINT IMPEDANCE

ANTENNA DIRECTIVITY & GAIN

POLARIZATION

Other Antenna Characteristics

RECIPROCITY IN RECEIVING & TRANSMITTING

FREQUENCY SCALING

The Vertical Monopole

BIBLIOGRAPHY

TEXTBOOKS ON ANTENNAS

Chapter 3 - The Effects of Ground

The Effects of Ground in the Reactive Near Field

FEED-POINT IMPEDANCE VS HEIGHT ABOVE GROUND

GROUND SYSTEMS FOR VERTICAL MONOPOLES

The Effect of Ground in the Far Field

FAR-FIELD GROUND REFLECTIONS & THE VERTICAL ANTENNA

THE PSEUDO-BREWSTER ANGLE & THE VERTICAL ANTENNA

FLAT-GROUND REFLECTIONS & HORIZONTALLY POLARIZED WAVES

DEPTH OF RF CURRENT PENETRATION

DIRECTIVE PATTERNS OVER REAL GROUND

The Effects of Irregular Local Terrain in the Far Field

WHAT IS THE RANGE OF ELEVATION ANGLES NEEDED?

DRAWBACKS OF COMPUTER MODELS FOR ANTENNAS OVER REAL TERRAIN

RAY-TRACING OVER UNEVEN LOCAL TERRAIN

SIMULATION OF REALITY--SOME SIMPLE EXAMPLES FIRST

USING HFTA

BIBLIOGRAPHY

Chapter 4 - Antenna Modeling & System Planning

OVERVIEW: ANTENNA ANALYSIS BY COMPUTER

THE BASICS OF ANTENNA MODELING

PROGRAM OUTPUTS

PROGRAM INPUTS: WIRE GEOMETRY

Coordinates in an X, Y and Z World

Segmentation and Specifying a Source Segment

Some Caveats and Limitations Concerning Geometry

Some Other Practical Antenna Geometries

THE MODELING ENVIRONMENT

The Ground

Modeling Environment: Frequency

Frequency Scaling

REVISITING SOURCE SPECIFICATION

Sensitivity to Source Placement

Voltage and Current Sources

LOADS

ACCURACY TESTS

Convergence Test

Average Gain Test

OTHER POSSIBLE MODEL LIMITATIONS

Closely Spaced Wires

Fat Wires Connected to Skinny Wires

NEAR-FIELD OUTPUTS

ANTENNA MODELING SUMMARY

Practical Aspects, Designing Your Antenna System

WHAT DO YOU REALLY WANT?

SITE PLANNING

ANALYSIS

BUILDING THE SYSTEM

COMPROMISES

EXAMPLES

ANOTHER EXAMPLE

Apartment Possibilities

Antennas for Limited Space

INVISIBLE ANTENNAS

IINDOOR ANTENNAS

THE RESONANT BREAKER

Construction Details and Practical Considerations

END EFFECT

INSULATORS

INSTALLING TRANSMISSION LINES

RUNNING THE FEED LINE FROM THE ANTENNA TO THE STATION

LIGHTNING PROTECTION

Chapter 5 - Loop Antennas

Half-Wave Loops

One-Wavelength Loops

Small Loop Antennas

The Basic Loop

TUNED LOOPS

LOOP Q

FERRITE-CORE LOOP ANTENNAS

PROPAGATION EFFECTS ON NULL DEPTH

SITING EFFECTS ON THE LOOP

LOOP ANTENNA ARRAYS

SMALL TRANSMITTING LOOP ANTENNAS

PRACTICAL COMPACT TRANSMITTING LOOPS

TYPICAL LOOP CONSTRUCTION

The Loop Skywire

THE DESIGN

CONSTRUCTION

7-MHz Loop

A Receiving Loop for 1.8 MHz

An Indoor Stealth Loop

BIBLIOGRAPHY

Chapter 6 - Low-Frequency Antennas

The Importance of Low Angles on the Low Bands

Short/Medium-Range Communications

HAM RADIO RESPONSE IN NATURAL DISASTERS

GEOGRAPHIC COVERAGE FOR NVIS

CHOOSING THE RIGHT NVIS FREQUENCY

SOME OTHER OBSERVATIONS ABOUT NVIS--STRATEGY

SOME OTHER OBSERVATIONS ABOUT NVIS--ANTENNA HEIGHT

LOW NVIS ANTENNAS AND LOCAL POWERLINE NOISE

ELEVATION ANGLES FOR MODERATE DISTANCES ON 75/80 METERS

ELEVATION ANGLES FOR MODERATE DISTANCES ON 40 METERS

NVIS SUMMARY

Horizontal Antennas for the Low Bands

DIPOLE ANTENNAS

PHASED HORIZONTAL ARRAYS

A MODIFIED EXTENDED DOUBLE ZEPP

Vertical Antennas

THE HALF-WAVE VERTICAL DIPOLE (HVD)

MONOPOLE VERTICALS WITH GROUND PLANE RADIALS

ELEVATED RADIALS & COUNTERPOISES

GROUND-PLANE ANTENNAS

EXAMPLES OF VERTICALS

1.8 TO 3.5-MHz VERTICAL USING AN EXISTING TOWER

SIMPLE, EFFECTIVE, ELEVATED GROUND-PLANE ANTENNAS

PHASED VERTICALS

The Half-Square Antenna

Short Vertical Antennas

BASE LOADING A SHORT VERTICAL ANTENAN

OTHER WAYS OF LOADING A SHORT ANTENNA FOR RESONANCE

THE COMPACT VERTICAL DIPOLE

LINEAR LOADING

COMBINED LOADING

SHORTENING THE RADIALS

EXAMPLES OF SHORT VERTICALS

SHORTENED DIPOLES

Inverted-L Antennas

A DIFFERENT APPROACH

Sloper Antennas

THE HALF-WAVE SLOPING DIPOLE

THE QUARTER-WAVELENGTH "HALF SLOPER"

1.8-MHz ANTENNA SYSTEMS USING TOWERS

THE K1WA 7-MHz "SLOPER SYSTEM"

BIBLIOGRAPHY

Chapter 7 - Multiband Antennas

Simple Wire Antennas

END-FED ANTENNAS

CENTER-FED ANTENNAS

THE 135-FOOT, 80 TO 100-METER DIPOLE

THE G5RV MULTIBAND ANTENNA

THE WINDOM ANTENNA

MULTIPLE-DIPOLE ANTENNAS

OFF-CENTER-FED DIPOLES

Trap Antennas

Trap Losses

FIVE-BAND W3DZZ TRAP ANTENNA

TWO W8NX MULTIBAND, COAX-TRAP DIPOLES

Multiband Vertical Antennas

A TRAP VERTICAL FOR 21 & 28 MHz

The Open-Sleeve Antenna

Practical Construction and Evaluation

The Coupled-Resonator Dipole

The Coupled-Resonator Principle

Some History

A Little Math

Characteristics of C-R Antennas

A 30/17/12-Meter Dipole

Summary

HF Discone Antennas

History of the Discone

W8NWF's First Discone: the A-Frame Discone

A Really Big Discone

Radiation Patterns for the Discones

Harmonic Radiation from Multiband Antennas

BIBLIOGRAPHY

Chapter 8 - Multielement Arrays

DEFINITIONS

Phase

Ground Effects

MUTUAL IMPEDANCE

Amplitude of Induced Current

Phase Relationships

Tuning Conditions

MUTUAL IMPEDANCE & GAIN

GAIN & ARRAY DIMENSIONS

PARASITIC ARRAYS

Driven Arrays

Current Distribution in Phased Arrays

Phased Array Techniques

OVERVIEW

FUNDAMENTALS OF PHASED ARRAYS

Radiation Efficiency

Field Reinforcement and Cancellation

Gain

Nulls

Mutual Coupling

Loss Resistance, Mutual Coupling & Antenna Gain

FEEDING PHASED ARRAYS

The Role of Element Currents

Feed-point vs Element Current

COMMON PHASED-ARRAY FEED SYSTEMS

The "Phasing-Line" Approach

The Wilkinson Divider

The Hybrid Coupler

Large Array Feed Systems

The Broadcast Approach

The "Magic Bullet"

RECOMMENDED FEED METHODS FOR AMATEUR ARRAYS

Current Forcing with Quarter-Wave Lines--Elements In-Phase or 180° Out-of-Phase

"The Simplest Phased Array Feed System--That Works"

An Adjustable L-Network Feed System

Additional Considerations

Feeding 4-Element and Larger Arrays

What if the Elements Aren't Identical

Shunt and Gamma Fed Towers & Elements

Loading, Matching & Other Networks

Baluns in Phased Arrays

Receiving Arrays

Phased Array Design Examples

General Array Design Considerations

Choosing Arrayfeed1 Solutions

90° Fed, 90° Spaced Array

"Simplest" (Transmission Line Only) Feed System

L Network Feed System

Pattern Verification & Effect of Loss Resistance--"Simplest" System

A Three-Element Binomial Broadside Array

A "Four-Square" Array

"Simplest" (Transmission Line Only) Feed System

L-Network Feed System

A Four-Element Rectangular Array

"Simplest" (Transmission-Line Only) Feed System

L-Network Feed System

120° Fed, 60° Spaced Dipole Array

"Simplest (Transmission Line Only) Feed System

L-Network Feed System

PRACTICAL ASPECTS OF PHASED ARRAY DESIGN

Adjusting Phased Array Feed Systems

Measuring Element Currents

Directional Switching of Arrays

Basic Switching Methods

Powering Relays Through Feed Lines

Improving Array-Switching Systems

Measuring the Electrical Length of Feed Lines

Measuring Mutual Impedance

Broadside Arrays

COLLINEAR ARRAYS

POWER GAIN

DIRECTIVITY

TWO-ELEMENT ARRAYS

THREE- & FOUR-ELEMENT ARRAYS

ADJUSTMENT

THE EXTENDED DOUBLE ZEPP

THE STERBA ARRAY

Parallel Broadside Arrays

POWER GAIN

DIRECTIVITY

Other Forms Of Broadside Arrays

NON-UNIFORM ELEMENT CURRENTS

HALF-SQUARE ANTENNA

BOBTAIL CURTAIN

THE BRUCE ARRAY

FOUR-ELEMENT BROADSIDE ARRAY

THE BI-SQUARE ANTENNA

End-Fire Arrays

TWO-ELEMENT END-FIRE ARRAY

THE W8JK ARRAY

FOUR-ELEMENT END-FIRE & COLLINEAR ARRAYS

FOUR-ELEMENT DRIVEN ARRAYS

EIGHT-ELEMENT DRIVEN ARRAYS

PHASING ARROWS IN ARRAY ELEMENTS

BIBLIOGRAPHY

Appendix A--EZNEC-ARRL Examples

Chapter 9 - Broadband Antenna Matching

GENERAL CONCEPTS

The Objective

Resonant Antennas

Loss

Simple Broadband Matching Techniques

The Cage Dipole

Stagger-Tuned Dipoles

Stagger Tuned Radials

FEED-LINE IMPEDANCE MATCHING

PARALLEL-TUNED CIRCUITS AT THE ANTENNA TERMINALS

The Double Bazooka

The Crossed Double Bazooka

MATCHING NETWORK DESIGN

Optimum Matching

Chevyshev Matching

LC-MATCHING NETWORKS

80-Meter DXer's Delight

PROPERTIES OF TRANSMISSION-LINE RESONATORS

The TLR Transformer

TRANSMISSION-LINE RESONATORS AS PART OF THE ANTENNA

The Coaxial-Resonator Match

The Snyder Dipole

The Improved Crossed-Double Bazooka

TRANSMISSION-LINE RESONATORS AS PART OF THE FEED LINE

A Simple Broadband Dipole for 80 Meters

80-Meter Dipole with the TLR Transformer

BIBLIOGRAPHY

Chapter 10 - Log Periodic Arrays

BASIC DESIGN CONSIDERATIONS

LPDA Design and Computers

LPDA Behavior

Feeding and Constructing the LPDA

Special Design Corrections

A DESIGN PROCEDURE FOR AN LPDA

Log-Cell Yagis

Wire Log-Periodic Dipole Arrays for 3.5 or 7 MHz

DESIGN OF THE LOG-PERIODIC DIPOLE ARRAYS

5-Band Log Periodic Dipole Array

The Telerana

Improving the Telerana

The Pounder: A Single-Band 144-MHz LPDA

Construction

The Feed Arrangement

Log Periodic-Yagi Arrays

THE LOG-YAG ARRAY

BIBLIOGRAPHY

Chapter 11 - HF Yagi Arrays

Yagi Performance Parameters

YAGI GAIN

RESPONSE PATTERNS--FRONT-TO-REAR RATIO

DRIVE IMPEDANCE & SWR

Monoband Yagi Performance Optimization

DESIGN GOALS

DESIGN VARIABLES

GAIN & BOOM LENGTH

OPTIMUM DESIGNS & ELEMENT SPACING

Two-Element Yagis

Element Spacing in Larger Yagis

ELEMENT TUNING

Specific Monoband Yagi Designs

Half Elements

Matching System

10-METER YAGIS

12-METER YAGIS

15-METER YAGIS

17-METER YAGIS

20-METER YAGIS

30-METER YAGIS

40-METER YAGIS

Modifying Monoband Hy-Gain Yagis

Multiband Yagis

INTERLACING ELEMENTS

TRAPPED MULTIBANDERS

Christmas Tree Stacks

Forward Staggering

Stacked Yagis

STACKS & GAIN

STACKS & WIDE ELEVATION FOOTPRINTS

A 10-Meter Example

A 15-Meter Example

A 20-Meter Example

SPARE ME THE NULLS!

STACKING DISTANCES BETWEEN YAGIS

Switching Out Yagis in the Stack

Stacking Distance & Lobes at HF

Changing the Stack Spacing

Longer Boom Length & Stack Spacing

Are Higher-Angle Lobes Important?

Stacking Distances for Multiband Yagis

Summary, Stacking Distances

STACKS & FADING

STACKS & PRECIPITATION STATIC

STACKS & AZIMUTHAL DIVERSITY

THE N6BV/1 ANTENNA SYSTEM--BRUTE FORCE FEEDING

WHY TRIBANDERS?

THE K1VR ARRAY: A MORE ELEGANT APPROACH TO MATCHING

SOME SUGGESTIONS FOR STACKING TRIBANDERS

THE WX0B APPROACH TO STACK MATCHING & FEEDING

"BIP/BOP" OPERATION

STACKING DISIMILAR YAGIS

Real-World Terrain and Stacks

OPTIMIZING OVER LOCAL TERRAIN

SO NEAR, YET SO FAR

Moxon Rectangle Beams

Chapter 12 - Quad Arrays

Is a Quad Better at Low Heights than a Yagi?

Multiband Quads

CONSTRUCTING A QUAD

Making It Sturdy

Diamond or Square?

Two Multiband Quads

A FIVE-ELEMENT, 26-FOOT BOOM TRIBAND QUAD

A TWO-ELEMENT, 8-FOOT BOOM PENTABAND QUAD

BIBLIOGRAPHY

Chapter 13 - Long-Wire and Traveling-Wave Antennas

Long Wires Versus Multielement Arrays

General Characteristics of Long-Wire Antennas

Directivity

Calculating Length

Tilted Wires

Feeding Long Wires

COMBINATIONS OF LONG WIRES

Parallel Wires

The V-Beam Antenna

Other V Combinations

Feeding the V Beam

THE RESONANT RHOMBIC ANTENNA

TERMINATED LONG-WIRE ANTENNAS

Directional Characteristics

THE TERMINATED RHOMBIC ANTENNA

Tilt Angle

Multiband Design

Termination

Multiwire Rhombics

Front-to-Back Ratio

Methods of Feed

Receiving Wave Antennas

THE BEVERAGE ANTENNA

Beverage Theory

Performance in Other Directions

Feed-Point Transformers for Single-Wire Beverages

The Two-Wire Beverage

Beverages in Echelon

Practical Considerations

BIBLIOGRAPHY

Chapter 14 - Direction Finding Antennas

RDF by Triangulation

DIRECTION FINDING SYSTEMS

Loop Antennas

Loop Circuits and Criteria

Ferrite Rod Antennas

Sensing Antennas

PHASED ARRAYS

The Adcock Antenna

LOOPS VS PHASED ARRAYS

THE GONIOMETER

Electronic Antenna Rotation

RDF SYSTEM CALIBRATION & USE

FRAME LOOPS

SHIELDED FRAME LOOPS

FERRITE-CORE LOOPS

Obtaining a Cardioid Pattern

A SHIELDED LOOP WITH SENSING ANTENNA FOR 28 MHz

Sensing Antenna

THE SNOOP LOOP--FOR CLOSE-RANGE HF RDF

A LOOPSTICK FOR 3.5 MHz

Adjustment

A 144-MHz CARDIOID-PATTERN RDF ANTENNA

The Phasing Harness

Tuning

THE DOUBLE-DUCKY DIRECTION FINDER

Specific Design

DDDF Operation

A FOX-HUNTING DF TWIN 'TENNA

The Yagi

An Interferometer

Circuit Construction

Antenna Construction

Using the Antenna

Antenna Alternative

THE FOUR-WAY MOBILE DF SYSTEM

Circuit Description

Antenna Switching

Detector Circuit

Construction

Switch Board

Feed Lines

Mechanical Assembly

Final Adjustments

Audio Level Adjustments

Fox Hunting

A TAPE-MEASURE BEAM FOR RDFING

BIBLIOGRAPHY

Chapter 15 - Portable Antennas

A SIMPLE TWIN-LEAD ANTENNA FOR HF PORTABLE OPERATION

ZIP-CORD ANTENNAS

Zip Cord as a Transmission Line

Zip Cord Wire as the Radiator

A TREE-MOUNTED HF GROUND-PLANE ANTENNA

A PORTABLE DIPOLE FOR 80 TO 2 METERS

Construction

Aluminum Element

Loading Coil

Wire and Spool

Operation

80 Meters

2 Meters

Continuous Coverage

THE HF CABOVER ANTENNA

TWO PORTABLE 6-METER ANTENNAS

A Portable Two-Element 6-Meter Quad

A Three-Element Portable 6-Meter Yagi

VE7CA 2-Element Portable HF Triband Yagis

A 20/15/10-Meter Triband 2-Element Yagi

The Balun

Flattop or Tilted?

A 30/17/12-Meter Triband 2-Element Yagi

Assembly

V Slings

SWR Adjustment

40-Meter Wire Yagis

Summary

BIBLIOGRAPHY

Chapter 16 - Mobile and Maritime Antennas

HF MOBILE FUNDAMENTALS

The Equivalent Circuit of a Typical Mobile Antenna

Antenna Capacitance

LOADING COIL DESIGN

Base Loading and Center Loading

OPTIMUM DESIGN OF SHORT COIL-LOADED MOBILE ANTENNAS

Radiation Resistance

Required Loading Inductance

Loading Coil Resistance

Radiation Efficiency

Ground Loss

Efficiency Curves

Impedance Matching

Shortened Dipoles

CONTINUOUSLY LOADED ANTENNAS

MATCHING TO THE TRANSMITTER

Tune-Up

TOP-LOADING CAPACITANCE

TAPPED COIL MATCHING NETWORK

THE "SCREWDRIVER" MOBILE ANTENNA

CONSTRUCTING YOUR SCREWDRIVER ANTENNA

MOUNTING THE ANTENNA

A COIL COVER

A MOBILE J ANTENNA FOR 144 MHz

The Length Factor

THE SUPER-J MARITIME ANTENNA

Antenna Operation

Construction and Adjustment

Performance

A TOP-LOADED 144-MHz ANTENNA

Construction

Tune-Up

VHF QUARTER-WAVELENGTH VERTICAL

144-MHz 5/8 WAVELENGTH VERTICAL

Construction

Tune-Up

A 5/8-WAVELENGTH 220-MHz MOBILE ANTENNA

Construction

HF Antennas for Sailboats

ANTENNA MODELING

A SAFET Y NOTE

TRANSOM & MASTHEAD MOUNTED VERTICALS

THE BACKSTAY VERTICAL

A 40-METER BACKSTAY HALF SLOPER

TEMPORARY ANTENNAS

GROUNDING SYSTEMS

Antennas for Power Boats

BIBLIOGRAPHY

Chapter 17 - Repeater Antenna Systems

Basic Concepts

Matching

Repeater Antenna System Design

COMPUTING THE COVERAGE AREA FOR A REPEATER

The Repeater Antenna

Top Mounting and Side Mounting

Effects of Other Conductors

ISOLATION REQUIREMENTS IN REPEATER ANTENNA SYSTEMS

ADVANCED TECHNIQUES

EFFECTIVE ISOTROPIC RADIATED POWER (EIRP)

Assembling a Repeater Antenna System

A 144 MHz Duplexer

THE CIRCUIT

ADJUSTMENT

BIBLIOGRAPHY

Chapter 18 - VHF and UHF Antenna Systems

The Basics

DESIGN FACTORS

TRANSMISSION LINES

WAVEGUIDES

IMPEDANCE MATCHING

BALUNS & ANTENNA TUNERS

THE YAGI AT VHF & UHF

STACKING YAGIS

QUADS FOR VHF

VHF & UHG QUAGIS

COLLINEAR ANTENNAS

THE CORNER REFLECTOR

TROUGH REFLECTORS

HORN ANTENNAS FOR THE MICROWAVE BANDS

PARABOLIC ANTENNAS

OMNIDIRECTION AL ANTENNAS FOR VHF & UHF

Ground-plane Antennas for 144, 222 and 440 MHz

The J-Pole Antenna

Construction

Tuning

Final Assembly

On-the-Air Performance

Practical 6-Meter Yagis

High-Performance Yagis for 144, 222 and 432 MHz

Yagi Construction

A HIGH-PERFORMANCE 432-MHz YAGI

A HIGH-PERFORMANCE 144 MHz YAGI

A HIGH-PERFORMANCE 222-MHz YAGI

A 144 MHz 2-Element Quad

A Portable 144 MHz 4-Element Quad

Materials

Construction

Building Quagi Antennas

QUAGIS FOR 1296 MHz

Loop Yagis for 1296 MHz

The Boom

Parasitic Elements

Driven Element

Tuning the Driven Element

Tips for 1296-MHz Antenna Installations

Trough Reflectors for 432 and 1296 MHz

A Horn Antenna for 10 GHz

Building the Antenna

Periscope Antenna Systems

Gain of a Periscope System

Mechanical Considerations

BIBLIOGRAPHY

Chapter 19 - Antenna Systems for Space Communications

Common Ground

Antennas for Satellite Work

Antennas for LEO Satellites

Antennas for High-Altitude Satellites

CIRCULAR POLARIZATION

ANTENNAS FOR AO-40 OPERATIONS

PORTABLE HELIX FOR 435 MHz

CONVERTED C-BAND TVRO DISHES

NOTES & REFERENCES, SATELLITE ANTENNAS

Antenna Systems for EME Communications

VHF/UHF EME ANTENNAS

DISH ANTENNAS FOR EME

A 12-FOOT STRESSED HOMEBREW PARABOLIC DISH

EME USING SURPLUS TVRO DISH ANTENNAS

SHF EME CHALLENGES

NOTES & REFERENCES, EME ANTENNAS

Chapter 20 - Antenna Materials and Accessories

Wire Antennas

WIRE TYPES

ANTENNA INSULATION

PULLEYS & HALYARDS

Antennas of Aluminum Tubing

SELECTING ALUMINUM TUBING

SOURCES FOR ALUMINUM

CONSTRUCTION WITH ALUMINUM TUBING

Other Materials for Antenna Construction

Plastics

Fiberglass

CONCLUSION

BIBLIOGRAPHY

Chapter 21 - Antenna Products Suppliers

Antenna Manufacturers Products

VHF/UHF/Microwave Antenna Suppliers

HF Antenna Suppliers

Antenna Parts

Suppliers of Quad Antenna Parts

Towers, Masts and Accessories

Transmission Lines

Transmission Line Instruments and Accessories

Suppliers Addresses

Chapter 22 - Antenna Supports

TREES AS ANTENNA SUPPORTS

Wind Compensation

TREES AS SUPPORTS FOR VERTICAL WIRE ANTENNAS

MAST MATERIALS

A Ladder Mast

The A-Frame Mast

TV Mast Material

MAST GUYING

Guy Material

Guy Anchors

Guy Tension

ERECTING A MAST OR OTHER SUPPORT

Tower And Antenna Selection and Installation

THE TOWER

TOWER BASES

TOWER INSTALLATION

GUY WIRES

THE RIGHT TOWER FOR YOUR ANTENNA

ANTENNA INSTALLATION

THE PVRC MOUNT

THE TOWER ALTERNATIVE

ROTATOR SYSTEMS

BIBLIOGRAPHY

Chapter 23 - Radio Wave Propagation

The Nature of Radio Waves

Phase and Wavelength

Polarization

Field Intensity

Wave Attenuation

Bending of Radio Waves

GROUND WAVES

THE SURFACE WAVE

THE SPACE WAVE

VHF/UHF PROPAGATION BEYOND LINE OF SIGHT

ANTENNA POLARIZATION

Polarization Factors Above 50 MHz

PROPAGATION OF VHF WAVES

Weather Effects on VHF/UHF Tropospheric Propagation

Tropospheric Ducting

RELIABLE VHF COVERAGE

VHF/UHF Station Gain

What It All Means

Terrain at VHF/UHF

AURORAL PROPAGATION

HF Sky-Wave Propagation

THE ROLE OF THE SUN

THE IONOSPHERE

SOUNDING THE IONOSPHERE

SKIP DISTANCE

MULTI-HOP PROPAGATION

MAXIMUM USABLE FREQUENCY

LOWEST USABLE FREQUENCY

DISTURBED IONOSPHERIC CONDITIONS

IONOSPHERIC STORMS

ELEVATION ANGLES FOR HF COMMUNICATION

The IONCAP Computer Propagation Model

IONCAP/VOACAP Parameters

Looking at the Elevation-Angle Statistical Data

The Ionosphere Controls Propagation

Looking at the Data--Further Cautions

Antenna Elevation Patterns

ONE-WAY PROPAGATION

SHORT OR LONG PATH?

FADING

OTHER PROPAGATION MODES

GRAY-LINE PROPAGATION

What HF Bands Are Open--Where and When?

THE PROPAGATION BIG PICTURE

Do-It-Yourself Propagation Prediction

Obtaining Sunspot Number/Solar Flux Data

WWV PROPAGATION DATA

BIBLIOGRAPHY

Chapter 24 - Transmission Lines

Basic Theory of Transmission Lines

CURRENT FLOW IN LONG LINES

VELOCITY OF PROPAGATION

CHARACTERISTIC IMPEDANCE

TERMINATED LINES

Practical Transmission Lines

ATTENUATION

REFLECTION COEFFICIENT

STANDING WAVES

ADDITIONAL POWER LOSS DUE TO SWR

LINE VOLTAGES & CURRENTS

Input Impedance

SPECIAL CASES

Voltage/Current Along a Line

Line Construction and Operating Characteristics

AIR-INSULATED LINES

FLEXIBLE LINES

COAXIAL CABLES

SINGLE-WIRE LINE

Line Installation

INSTALLING COAX LINE

TESTING TRANSMISSION LINES

BIBLIOGRAPHY

Chapter 25 - Coupling the Transmitter to the Line

MATCHING THE LINE TO THE TRANSMITTER

The Matching System

Harmonic Attenuation in an Antenna Tuner

MATCHING WITH INDUCTIVE COUPLING

THE L-NETWORK

THE PI-NETWORK

THE T-NETWORK

THE AAT (ANALYZE ANTENNA TUNER) PROGRAM

A Low-Power Link-Coupled Antenna Tuner

The Circuit

Construction

Tune-Up

High-Power ARRL Antenna Tuner for Balanced or Unbalanced Lines

REASONS FOR USING AN ANTENNA TUNER

DESIGN PHILOSOPHY BEHIND THE ARRL HIGH-POWER TUNER

CONSTRUCTION

OPERATION

FURTHER COMMENTS ABOUT THE ARRL ANTENNA TUNER

BIBLIOGRAPHY

Chapter 26 - Coupling the Line to the Antenna

Choosing a Transmission Line

FEEDING A SINGLE-BAND ANTENNA

FEEDING A MULTIBAND RESONANT ANTENNA

FEEDING A MULTIBAND NON-RESONANT ANTENNA

Matched Lines

Operating Considerations

Antenna Resonance

DIRECT MATCHING TO THE ANTENNA

MATCHING DEVICES AT THE ANTENNA

Common-Mode Transmission-Line Currents

UNBALANCED COAX FEEDING A BALANCED DIPOLE

ASYMMETRICAL ROUTING OF THE FEED LINE FOR A DIPOLE

COMMON-MODE EFFECTS WITH DIRECTIONAL ANTENNAS

ELIMINATING COMMON-MODE CURRENTS--THE BALUN

ONE FINAL WORD

BIBLIOGRAPHY

Chapter 27 - Antennas and Transmission-Line Measurements

LINE CURRENT & VOLTAGE

RF VOLTMETER

RF AMMETERS

SWR Measurements

BRIDGE CIRCUITS

Resistance Bridge

AVOIDING ERRORS IN SWR MEASUREMENTS

MEASURING LINE LENGTH

REFLECTOMETERS

The Tandem Match—An Accurate Directional Wattmeter

DESIGN PRINCIPLES

CIRCUIT DESCRIPTION

CONSTRUCTION

ACCURACY

OPERATION

DESIGN VARIATIONS

HIGH-POWER OPERATION

An Inexpensive VHF Directional Coupler

A Calorimeter For VHF And UHF Power Measurements

A Noise Bridge For 1.8 Through 30 MHz

CONSTRUCTION

MEASURING COAXIAL-CABLE PARAMETERS WITH A NOISE BRIDGE

USING A BRIDGE TO MEASURE THE IMPEDANCE OF AN ANTENNA

A Practical Time-Domain Reflectometer

Ground Parameters for Antenna Analysis

A Switchable RF Attenuator

A Portable Field Strength Meter

An RF Current Probe

Antenna Measurements

SOME BASIC IDEAS

ANTENNA TEST SITE SET-UP & EVALUATION

ABSOLUTE GAIN MEASUREMENT

RADIATION-PATTERN MEASUREMENTS

Vector Network Analyzers

S-PARAMETERS

ARRAY MEASUREMENT EXAMPLE

BIBLIOGRAPHY

Chapter 28 - Smith Chart Calculations

IMPEDANCE PLOTTING

Short and Open Circuits

Standing-Wave-Ratio Circles

SOLVING PROBLEMS WITH THE SMITH CHART

ADMITTANCE COORDINATES

DETERMINING ANTENNA IMPEDANCES

DETERMINATION OF LINE LENGTH

LINE-LOSS CONSIDERATIONS WITH THE SMITH CHART

Using a Second SWR Circle

Smith Chart Procedure Summary

ATTENUATION AND Z0 FROM IMPEDANCE MEASUREMENTS

Determining Line Attenuation

Determining Velocity Factor

LINES AS CIRCUIT ELEMENTS

Designing Stub Matches with the Smith Chart

MATCHING WITH LUMPED CONSTANTS

The Series-Section Transformer

An Example

Procedure Summary

BIBLIOGRAPHY

Appendix

Glossary of Terms

Abbreviations

Length Conversions

Metric Equivalents

Gain Reference

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Index

Software

INSTALLING THE PROGRAMS/DATA

PLACING ICONS ON YOUR DESKTOP

SUBDIRECTORIES

PROPAGATION-PREDICTION FILES

Choices, Summary and Detailed Propagation Tables

Sample Summary Propagation-Prediction Table, January from Boston to the World

Sample Detailed Propagation Table for 20 Meters, January, Boston to World for Very High SSN

Propagation Prediction Data

Instructions

Summary Tables Index

Detailed Tables Index