As a follow-up to my recent tests at 8.97kHz, today I repeated the QRSS3 earth-mode (through the ground) tests with my latest receiving equipment but this time at around 18kHz and 1.1kHz. TXing at 18kHz is legal as there is no appreciable radiation. As before, the TX was 5W into earth electrodes 20m apart back at home. I wanted to see how signal levels varied compared with 8.97kHz at my 3 usual test sites out to 6km distance from home.
Results were interesting: although signals were copied at 1.6km and 3.6km on both test frequencies,
nothing at all was copied at 6km, where very good signals were copied on 8.97kHz a few weeks ago. Ground conductivity and weather conditions were identical on both test days: dry for the last several days, so conductivity likely to be lower than when the fen soil is saturated.
I have no real idea why 8.97kHz should appear to be a "sweet spot" in frequency. It is possible that other frequencies lower than 8.97kHz and higher than 1.1kHz may be even better. In all cases the RX loop was resonated and positioned on the ground varied for best signal.
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| 1.12kHz earth-mode signal at 1.6km | |
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| 17.952kHz earth-mode signal at 1.6km |
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| 1.12kHz earth-mode signal at 3.6km |
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| 17.952kHz earth-mode signal at 3.6km (note MSK signals close by) |
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