On 28 Apr 2010 at 17:27, Rik Strobbe wrote:

> Hi Alan,
> 
> indeed, "low voltage" loops suffer far less from these losses.
> But the radiation resistance of a loop falls with the 4th power of the
> wavelength, whereas for a vertical it is only with the 2nd power. At
> 9kHz a loop of 15m high and 40m long will have a radiation resistance of
> merely 10 nanoOhm (on 137kHz it is 0.5 milliOhm). So get out 1mW on 9kHz
> one would need to pump 330A into the antenna. Using 1cm diameter solid
> copper wire for the loop (anything less will probably act as a fuse) the
> loss resistance is at least 0.025 Ohm (just copper loss, no stray
> currents etc) and 2.5kW will be needed.
> 
> 73, Rik  ON7YD

Indeed. With all the problems I had with a small loop on 136kHz and the 
high circulating currents (20A ish at a few watts) I would imagine on 
at a 1/18th of the frequency would have an efficiency not far above 
zero....

73 Dave G3YMC

http://www.davesergeant.com