Practical_Antenna_Handbook_0071639586
328 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 Concluding Thoughts At HF it is very difficult to erect any horizontally polarized antenna high enough to be able to forget about the effect of the earth below. In principle, the theoretical 6-dB gain that results from the ground reflection is worthwhile, but in practice the reflection gain from real earth is either far less than 6 dB or the antenna is so low (in terms of wavelengths) that the increased signal goes mostly into the ionosphere at very high angles, where it is often of no use, depending on your operating or listening interests. Similarly, the theoretical 3-dB gain from the second radiating element (the other half of the loop) is seldom achieved in the real world. Part of the reason for this is that in the case of 1l loops and quad elements, the spacing of the opposing sides is only l/4—leading to quadrature phasing and partial, rather than full, cancellation of the signal in unused directions. Equally important, the radiated field from the lower leg of a square loop is subject to the ground reflection pattern of a much lower height, so in general a loop’s maximum gain is at a somewhat higher elevation angle than it is for the top leg alone. In the author’s opinion, unless one has some other reason for choosing the quad— such as the high-power corona discharge problem at HCJB—the mechanical complexity of the quad may outweigh its benefits. Often, more can be realized by analyzing the ground reflection factor for different antenna heights and then applying the same (or less) effort to putting a simple two- or three-element Yagi up at a height that yields the desired elevation pattern.
High-Frequency Antennas for Specialized Uses Part V Chapter 14 Receiving Antennas for High Frequency Chapter 15 Hidden and Limited-Space Antennas Chapter 16 Mobile and Marine Antennas Chapter 17 Emergency and Portable Antennas
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High-Frequency <strong>Antenna</strong>s<br />
for Specialized Uses<br />
Part V<br />
Chapter 14<br />
Receiving <strong>Antenna</strong>s for High Frequency<br />
Chapter 15<br />
Hidden and Limited-Space <strong>Antenna</strong>s<br />
Chapter 16<br />
Mobile and Marine <strong>Antenna</strong>s<br />
Chapter 17<br />
Emergency and Portable <strong>Antenna</strong>s
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