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314 P a r t I V : D i r e c t i o n a l H i g h - F r e q u e n c y A n t e n n a A r r a y s ences. However, there are many excellent resources already in print, as summarized here. Perhaps more to the point, however, the easy availability of inexpensive or free antenna modeling software makes it possible for any reader interested in designing and building a custom Yagi from scratch to “play with the numbers” and develop his/her own intuitions as to how key parameters (forward gain, F/B ratio, bandwidth, etc.) vary as dimensions are changed. Further Reading The designs and construction techniques of this chapter do not take into account the special demands of severe environments. The unusually high winds of mountaintops and coastal areas, the icing that must always be expected between midlatitudes and the poles, and saltwater mist for coastal and island installations all impose extra burdens on antennas and their supports. Further, the interplay between mechanical and electrical considerations becomes far more critical the longer the boom and elements are. The definitive resource for understanding why and how to strengthen a Yagi is Physical Design of Yagi Antennas, by David B. Leeson, W6NL (ex-W6QHS), available from ARRL. In addition to explaining why and to what extent booms, elements, brackets, and masts should be reinforced and balanced, it is chock-full of valuable practical information—extending beyond purely mechanical considerations—for anyone interested in modifying commercial antennas or designing and building his/her own. Another seminal work is Yagi Antenna Design, by James L. Lawson (deceased), ex- W2PV, ARRL, 1986. Here the principal focus is on the electrical design and performance of HF Yagis, and many practical families of designs with complete dimensions are provided for beams having between two and eight elements. Unfortunately, this book predates amateur access (in the United States, at least) to the so-called WARC bands at 30, 17, and 12 m. Low-Band DXing, by John Devoldere, ON4UN, ARRL, fifth edition, 2011, is not primarily about Yagi antennas but does treat their design and performance on 80 and 40 m at some length. There is also an extended section on hairpin matching, including some explanatory calculations coupled with experimental techniques for obtaining the best match.
CHAPTER 13 Cubical Quads and Delta Loops Two popular multielement types of antennas employ elements formed from wire loops having a total length of approximately one wavelength. The cubical quad employs square loops and the delta loop is built with triangular loops. Both antenna types are found in single-element and multielement varieties, and both are easily analyzed in terms of equivalent half-wave dipoles that make them up. The single-Â element version of each is a form of 1l loop that was evaluated in Chap. 7. Cubical Quad The cubical quad was desgned in the mid-1940s at radio station HCJB in Quito, Ecuador. HCJB is a Protestant missionary shortwave radio station that delivers a booming signal worldwide from its high-altitude location. According to the story, HCJB originally used Yagi antennas to provide consistent signal strength in selected directions. In the thin air of Quito, the high voltages at the ends of the elements caused coronal arcing that resulted in instantaneous voltage standing wave ratio (VSWR) changes capable of shutting down or damaging the high-power transmitters and, over time, destroying the element tips themselves. Station engineer Clarence Moore designed the cubical quad antenna to solve this problem. Figure 13.1 shows the dimensions and construction techniques for a typical quad loop. Figure 13.1 Quad loop antenna. 315
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CHAPTER 13<br />
Cubical Quads and<br />
Delta Loops<br />
Two popular multielement types of antennas employ elements formed from wire<br />
loops having a total length of approximately one wavelength. The cubical quad<br />
employs square loops and the delta loop is built with triangular loops. Both antenna<br />
types are found in single-element and multielement varieties, and both are easily<br />
analyzed in terms of equivalent half-wave dipoles that make them up. The single-Â<br />
element version of each is a form of 1l loop that was evaluated in Chap. 7.<br />
Cubical Quad<br />
The cubical quad was desgned in the mid-1940s at radio station HCJB in Quito, Ecuador.<br />
HCJB is a Protestant missionary shortwave radio station that delivers a booming signal<br />
worldwide from its high-altitude location. According to the story, HCJB originally used<br />
Yagi antennas to provide consistent<br />
signal strength in selected<br />
directions. In the thin<br />
air of Quito, the high voltages<br />
at the ends of the elements<br />
caused coronal arcing that resulted<br />
in instantaneous voltage<br />
standing wave ratio<br />
(VSWR) changes capable of<br />
shutting down or damaging<br />
the high-power transmitters<br />
and, over time, destroying the<br />
element tips themselves. Station<br />
engineer Clarence Moore<br />
designed the cubical quad antenna<br />
to solve this problem.<br />
Figure 13.1 shows the dimensions<br />
and construction techniques<br />
for a typical quad loop.<br />
Figure 13.1 Quad loop antenna.<br />
315