On 11 May 2007 at 11:52, Rik Strobbe wrote:

> Dear all,
> 
> did anyone try a loop antenna (for transmitting) on 500 kHz ?
> As the radiation resistance of a small loop increases with the 4th
> power of the frequency a loop should be about 22 dB more efficient on
> 500 kHz compared to 136 kHz. A rather modest 100 m^2 loop should have
> a radiation resistance of about 0.0024 Ohm and thus require only 6.5 A
> antennacurrent to get 0.1 W ERP. For a vertical the gain is "only"
> about 11 dB (plus whatever is gained from lower losses).
> 
> 73, Rik  ON7YD

Interesting thought Rik. When I finally get my 10m vertical resonated 
I will see how that performs and if it fails I have two choices - my 
110ft low long wire (terrible on 160m) or put my 136kHz loop back up. 
But remember that 'only 6.5A' is rather a lot more antenna current 
than most of us use on the band and a lot more than my single 
transistor PA will do.

The TX is now finished, apart from sorting out a netting method. 
First time I connected it to the antenna I found the SWR was 
infinite! Yesterday I lashed up a simple impedance meter (effectively 
a noise bridge with the 'noise' from my sig genny. That showed me 
that it had a beautiful resonance on 160m, where it worked before I 
added the extra loading coil. I have just reconfigured the 
connections to the loading so about to check it again and hopefully 
resonate it on the right frequency. All part of our experimentation!

You used to be able to see my 136kHz loop on Google Earth but they 
have just updated their mapping and it is no longer there (which is 
right!!)

73 Dave G3YMC

http://www.davesergeant.com