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First (restarted) VLF earth-mode test
2 April 2015 | by  |
| 5W VLF beacon TX |
OK, I was only testing from the shack to the lounge, but this is a start. TX is 5W from my TDA2003 beacon.
TX frequency 8.976kHz initially with 10wpm CW, 300Hz bandwidth, sending my callsign and a dash. Nothing copied at first using a dummy load but over 70dB over noise using the earth-electrode “antenna” with no attempt to optimise match (fed via the same 3C90 step-up transformer used on 472kHz). With no probe at all (i.e.no RX antenna) the S/N was still some 40dB i.e. very good using the TX into the earth-electrodes.
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| QRSS3 signal received on Spectran (0.37Hz BW) |
Later with QRSS3, a 50 ohm TX dummy load, E-field probe at the RX, I got the signal at 10-20dB S/N. At the RX end I was using my simple E-field probe into a USB soundcard into my Windows 8.1 laptop.
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| E-field probe |
The blue photo shows the signal at the RX. The first part shows the TX signal on the earth-electrodes and the second part (weaker) was the signal on the EFP with the TX into a dummy load.
Honestly, this has really exhausted me!
Roger Lapthorn, G3XBM, is a regular contributor to AmateurRadio.com and writes from Cambridge, England.
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