First (restarted) VLF earth-mode test

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 ( RX antenna) the S/N was still some 40dB i.e. very good using the TX into the earth-electrodes.

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. 

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 and writes from Cambridge, England.

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