LF: 8.76kHz earth mode and a mystery signal to ID

[Roger Lapthorn <rogerlapthorn@gmail.com>]

This morning I slightly changed my VLF low input impedance tuned preamp - tuned circuit Q and gain of the first stage increased by around 
6dB. After lunch I did a test at 6km from home to see what effect this 
had on the S/N of my 5W beacon. In a 45mHz bandwidth (previously 11mHz) I
 was getting a signal around 18dB S/N using Spectrum Lab on my 80cm 
square loop on the ground. With an earth electrode RX antenna the signal 
was marginally weaker and the noise level higher. This is my best S/N yet at this distance. I now need to find a new test site at >10km from home. 

My signal is the steady carrier (with a 2min ID break by my XYL) at 8.7605kHz. The
 large wobbly line is interference, but who or what is the signal at 
8.754kHz? This is rock steady and appears to key on and off every 5 
minutes. It looks like some sort of control signal, or is someone else 
near Cambridge testing with earth mode? I think Chris G3XIZ observed something similar a few weeks ago.

I'm now starting to really question how far might be possible....

With 100W power (+13dB up on 5W), reducing RX bandwidth to 420uHz for long carrier tests (about +30dB compared with 45mHz BW) the range could be increased by a factor of 4 i.e. to 24km for the same S/N. This is still using just a 20m baseline earth electrode system at home and assuming inverse cubed attenuation rate. If these tests are to be done later this autumn I will need more stations looking for me as going out in the car every time is becoming a time consuming task, HI.

73s
Roger G3XBM
 


73s
Roger G3XBM
-- 
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