Hi Roger,
> Thank you for publishing your results. Most interesting. What sort of power
> does your antenna analyser put out?
I checked the manual and it seems the antenna analyser produces +13
dBm (20 mW) on a 50 ohm load.
> Can you remind us what sort of soil/rock geology you have there? It sounds
> like it may have similar properties to mine here where the 2 earth rods
> separated by 20m look close to 60 ohms resistive.
The dominant type of geological formation under the soil is shale. The
soil is not very deep, in some places there is no soil, in others it
can be over a metre. We have had some really hot days here, so the
ground is quite dry, which probably affects its resistivity.
> Here, I have not tried wires on the ground unterminated although I can only
> manage 15-20m max in my small garden.
This feels like the ideal portable antenna, doesn't it! My next test
will be a full dipole on the ground which, if it works as well, is
more convenient as there is no requirement for earth stakes.
> This week I hope to measure my 137kHz field strength from my earth-electrode
> antenna and 8W beacon at about 10km (to get ERP) by comparing the level
> against the strong Greek commercial signal near the band which I am told is
> about 1mV/m in the UK.
That's a good way to derive an absolute field strength for your signal!
> We have lots to learn still about earth antennas!
We sure do!
73, Dimitris VK1SV
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