13 Jan 2011

Further 8.76kHz VLF test transmissions today

8.76kHz earth mode tests - best DX 5.1km and 4.75km
Today being mild and dry (for the first time in almost 6 weeks) I decided to do a field test with my improved 8-9kHz tuned preamp and loop antenna. A 5W "earth mode" (through the ground) test signal was emitted on 8.760kHz from the Burwell QTH and I ventured out into the countryside armed with the 80cm loop and preamp to see where the signal could be copied. In addition to my usual test sites at 1.6 and 5.1km I tried other directions and sites today. The map attached shows where signals were received and where no copy was achieved. The signal does seem to travel along the metal water pipes, which must be absent to the east where I assume they must be plastic, at least in places.


Anonymous said...

Hello Roger

you seem to be getting good coverage with the metal water pipes. I womder how far you get with 20 Watts.


Roger G3XBM said...

Not a lot further I suspect Tony. In most directions from the village I have now found the limit of coverage with 5W. Going to 20W (+6dB) should not theoretically increase distance much because of the inverse cubed attenuation rate.