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If you have some time, can you comment on this recent post from the Community Radio forum. I am particularly wondering about the statement “buried ground radials need not be longer than the antenna is tall, since a shortened, loaded vertical antenna has a more compact near field”.
Also, our buried ground radials need not be longer than the antenna is tall, since a shortened, loaded vertical antenna has a more compact near field. A 6 meter wide shallow-buried square or circle of copper sheet (or 120 three-meter long buried bare copper wires) work better than fewer longer radials.
Buried ground radials don’t have to be resonant. As this University of Hawaii Ham Radio web page http://www.chem.hawaii.edu/uham/radials.html explains:
“Ground radials need not be resonant…Ground radials do not need to be much longer than the antenna is tall. A shortened antenna with loading coils will have a more compact “near field” where the majority of the antenna field is. The ground needs only reach out as far as the near field extends. Field intensity drops off with the square of the distance from the base of the antenna…The ground around a vertical monopole type antenna can be viewed as strings of series connected resistors fanning out from the base. The purpose of the radials can be viewed as attempting to short circuit as many of these resistors near the base as possible. This is especially critical very close to the base where RF field density is highest, and its importance drops off quickly beyond 1/8th wavelength from the base of any vertical antenna, where the RF field density per unit area goes down sharply.”
“It is important not to confuse this application with elevated ground planes. We are talking about radials that supplement the return of ground currents to the base of the antenna, especially in the near field. They work “in parallel” with the existing earth ground surface to supplement it. Elevated radials are a resonant element and serve a decoupling function and establish a completely artificial ground. They should be resonant, quarter wave wires, but still in fair numbers, probably more than the four usually seen, for best results.”
The web page also describes interesting portable set-ups (which could be used for Part 15 AM remote broadcasts) in which they use large metal gluing clamps to connect ground leads to fire hydrants, irrigation pipes, backflow preventers, and large water mains (“These masses of metal act as giant counterpoises as well as being metalic paths for ground currents to supplement soil conductivity. Plus since they are buried in the ground, they have good ground contact over a very large surface area for many wavelengths.”) — Jason