Today I ended my brief foray into 137 kHz. The battery was
going flat on the rx so I took it down.
Reception at LF seems quite easy compared to VLF: much lower
noise levels and much less interference. Strong Opera and
WSPR transmissions can be a problem and Loran provides a rich
spectrum of sidebands, but apart from that it seems fairly
clean.
Coherent BPSK tests with DF6NM and IZ7SLZ were successful
down to symbol periods of 0.1 seconds. Channel capacity exceeded
9000 bits/hour on a 1Mm daytime path with 0.3W ERP using just
E-field reception.
Phase remains stable on 2Mm paths for at least a couple of
hours during daytime.
Unfortunately there were no other transmissions available
with which to measure longer paths. Some distant carrier
transmissions would have been very useful.
If there is any interest in doing more tests I can put the rx
back out after some modifications to improve performance.
Thanks to Domenico and Markus for providing some interesting
signals to play with.
--
Paul Nicholson
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