The type of ground locally probably enters into the propagation equation without influence on the ERP figure, and may be enhancing my signals a dB or so.   For example, I am on quite good conductive heavy clay, and there is a lot of it in the area.    I've sunk something like 15 x 1 to 2m long copper tubes and rods into it all round the small gargen, and cros slinked them in a completely random way  in lieu of being able to put out any worthwhile radials.  This may have (quite inadvertently) been a good thing.

 

Back in the 73kHz days, several stations were surprised just how good a signal was getting out from my antenna,  quite significantly smaller than those of just about every other operator on that band.   Down on 73k, measuring efficiency in the same way as the ratio of Rrad to Rload, I estimated -48 to -50dB gain giving 1mW ERP from 100 W.   This seemed to stack-up with received signal stregths and the more predictable propagation loss estimates down on those frequencies.

 

Mind you, the local vegetation and trees by the antenna have grown since then, but I strongly suspect the resulting near-field lossey capacitance is absorbed into the loss resistance, so more-or-less correctly appears in the efficiency calculation without having to be added in as a frig-factor.  Anyway, won't this component have less contribution at 7 times the frequency?

The most surprising finding back then was how much the loss resistance increased when it rained - when one would have expected a decrease in wet conditions.   Once the lossy near-field termination effect was realised, it all made sense.

Andy
www.g4jnt.com

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