Don I'm running a special on RF grounds today. I've carefully measured out some 1/2 wave wires, cut out 6" from the midpoint and offering these for $25. This will totally eliminate the need for multiple radials. Happy April 1.
Steve Ellington [email protected] ----- Original Message ----- From: "Don Wilhelm" <[email protected]> To: "Ron D'Eau Claire" <[email protected]> Cc: <[email protected]> Sent: Wednesday, April 01, 2009 6:12 PM Subject: Re: [Elecraft] BL-2 Connection To An Unbalanced Wire Antenna > 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 ______________________________________________________________ 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
