It is encouraging to see interest in amateur tx experiments
in the VLF band. Calculations suggest that ranges of 100km
or more would be possible with QRSS given about 1mW ERP
which is not an unreasonable target for a determined amateur.
The limiting factor is the VLF background noise, which at 9kHz
is typically 5uV/m/sqrt(Hz) or 30fT/sqrt(Hz), give or take a
few dB of diurnal and seasonal variation.
Here is a live spectrum display of the band 8790Hz, +/- 0.5Hz
with 0.005Hz resolution,
http://abelian.org/vlf/live/nb.png
as received at Todmorden, UK, 53.703N 2.072W, on an east-west
loop antenna. System sensitivity is about 0.03fT in the
bin bandwidth but the VLF background noise floor is at about 2fT.
The above spectrum is implemented with a bank of Goertzel
filters and sferics are removed before the filters. The spike
is a test signal at 1V RMS from a laptop soundcard line output
into a 700uH 25 turn loop enclosing 0.2 sq metres, located
about 180m from the rx loop. The test signal should be about
5fT at the rx site but appears a little stronger for some reason.
Here is the full VLF spectrum rxed at Todmorden on orthogonal
loops,
http://abelian.org/vlf/spectrum.shtml
and there is a live audio/video display at
http://abelian.org/vlf/test.html
Looking forward with great interest to further news of
transmitting experiments from Stefan DK7FC, Markus DF6NM,
Jacek SQ5BPF, et al.
--
Paul Nicholson
http://abelian.org/vlf
Todmorden, UK.
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