On Thu, 3 Feb 2011, John Rabson wrote:
Some years ago, we tried using a small loop to couple a Heyphone (4 W
output on 87 kHz) into a running rail in a disused railway tunnel in the
English Midlands (we had permission from the owners of the line). A
similar setup was used for receive and we achieved a range of 1.6 km
along the line.
1.6km is a very good result, since a Heyphone is basically a lf ssb
transceiver so you probably used voice, and the loop was probably
unmatched. you would achieve much larger distances if you tried qrss with
a better matched antenna. you can try this with overhead powerlines in
rural areas too if you can fit your signal between the harmonics. long
phone lines work well too.
btw. i have tried running a few watts at 8.9kHz to a loop abt. 1.5x2.5m in
the middle of the city (who knows what it's coupling to :). the signal can
be received at over 600m distance with a small loop antenna near power
lines, and is generally a nice indicator of underground conductive
structures (this method is also used to find illegal tunels)
jacek
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