A simple ground stake or single wire counterpoise can be expected to produce antenna efficiencies of over 90% when used with an end fed *half wave* wire.
The ground resistance is in series with the radiation resistance. A half wave shows several thousands of ohms at the end while even a crummy ground rod usually will show a few hundred ohms. So almost all the RF is dissipated in the radiation resistance of the antenna and only a small percentage is dissipated in the ground connection resistance. Where that scenario breaks down is when the antenna is shorter. At 1/4 wavelength it has a radiation resistance of about 35 ohms. Now more than 90% of the RF is lost in a 300+ ohm ground connection and less than 10% is radiated. At lengths less than 1/4 wavelength the situation worsens. It's not uncommon for a short whip and single wire ground counterpoise to have an efficiency of only 1 or 2 percent. The problem with 1/2 wave wires is that most antenna tuners, including the various tuners offered by Elecraft, can't match to them. The high impedance that makes them efficient is too high for the ATU to handle. So when using most ATU's a compromise length is needed that is as close to 1/2 wavelength, or a multiple of 1/2 wavelength, but still within range of the ATU. The efficiency will still be good. Ron AC7AC -----Original Message----- ) In a message dated 8/3/04 8:25:23 PM Eastern Daylight Time, [EMAIL PROTECTED] writes: > Mediocre? I'll match it against any trap dipole. If I didn't have > the > G5RV I would suggest a windom. Had a trap dipole once and long wire beat it G5 > RV beat the long wire. I have read varying reports on the G5RV some call it > compromise others love it. I would say it's the best antenna I have had. My results have been that a *good* trap dipole beats a G5RV - but not by much. Both beat an equivalent long wire *unless* the long wire has a good ground system (as in more than a few radials and a ground stake). YMMV The keys to trap dipoles are the trap construction and overall adjustment. Lossy, low Q traps will give mediocre results. Good high Q traps will do much better - typically less than 1 dB down from a full size dipole. 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
