Ron, I have been preaching similar points in ham circles for years now - and I find that many hams cannot visualize the difference between a "ground" (meaning a return path for current) and Mother Earth. Actually any point where the RF current crosses the zero voltage point is a point of RF Ground (it is a potential, not a physical place), and on a balanced antenna it should occur midway between the two sides of the feedpoint - and a vertical with radials *is* a balanced antenna, that is why a balun is needed even on a vertical.
The English do distinguish between "earthing" and "grounding", and I do wish that sort of distinction were also in common use in the US, it certainly would help. BTW - elevated radials *do* radiate in the very near field, but when arranged properly (pairs in opposing directions), the radiation is out of phase and will cancel at a distance from the antenna. Your term "current sink" is not a description I would use. 73, Don W3FPR Ron D'Eau Claire wrote: > Jim, IMX it's a mistake to equate "RF ground" with an Earth connection. > > An RF "ground" is just a low-impedance, low-reactance current sink for RF. > Of course it is an integral part of the antenna circuit. > > An RF "ground" would not be expected to radiate, and most "counterpoise" or > "radial" setups don't radiate a significant amount of energy*: > > 1) Counterpoises near the Earth and on-ground "radials" tend to couple all > their energy into the lossy dielectric of the Earth, never to be seen again. > This is how BCB stations achieve a good RF ground generally using 120 0.2 > wavelength radials around their towers to couple the RF into the Earth. > > 2) Elevated radials will radiate a lot unless they are carefully balanced > and symmetrical so "legs" produce RF fields that cancel each other outside > of the immediate area of the antenna. Such radials, like any RF ground, > *are* part of the antenna circuit but, when properly designed, they are a > non-radiating "current sink". In the common "ground plane" designs, they > also decouple the radiating element from the feed line, providing an RF > "ground" not only for the radiator but also grounding the feed line at the > antenna so RF currents don't flow down the outside of the coax shield. > > Ron AC7AC > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
