Following the great success on 160m with the 20m spaced earth electrodes yesterday, I fired up the WSPR transverter into the same "antenna" today on 137.5kHz. Although I managed to decode G8IMR at 188km several times, no reports of my signal were received. This ties up with tests last year which suggested the earth electrode system was around 8dB down on my 80sq m vertical wire loop. With results on 137.5kHz hard to get with 500uW ERP it was perhaps not surprising that no-one managed to decode me on the earth electrodes.
I now have a choice on 137kHz: either re-erect the wire loop, but double the wire thickness when I do so, or change to a Marconi vertical with a large loading coil. The thicker loop will increase ERP by up to 6dB but I suspect more is to be had with the vertical. It would be daft of me not to give the Marconi a try both on 137.5kHz and on 500kHz. Even with my limited space I can still manage around 8m of vertical with around 20m of top section.
Hello Roger,
ReplyDeleteFor small loops (relative to the wave length) the efficiency is very low and increases proportional with the diameter of the wire.
But the efficiency increases proportional with the length of the wire to the power 3.
So increasing the length is more much effective than increasing the diameter.
Increasing the length with 26% (x 1.26), is just as effective as doubling the diameter of the wire.
(1.26 to the power 3 = 2)
Doubling the length of the wire, will give an efficiency that is 8 times as high. hi
Good luck with the intersting experiments, 73, Bert