This is a CW carrier
that has been present on 136.645 or thereabouts for as long as I have been
listening on LF from my present QTH. It is of the order of several uV/m, so
quite strong when the band is quiet, and often makes it difficult to copy CW
stations here. It is just a carrier, with no modulation I can detect, and I
have never known it to be QRT.
I D/F’d it a few
years ago to a 400kV overhead power line that runs from a switching yard near
Aldenham, Watford, just beside the M1
motorway, to another switching yard north of Luton, also beside the M1.
The signal strength increases very rapidly under the lines, so I guess the
signal is transmitted differentially between two or more of the conductors,
and the radiated carrier is just “leakage” from the transmission line caused
by imbalance of one kind or another.
I believe the range
9kHz to 148.5kHz is used in Europe for power line signaling - If you want to
find out whether a particular power line is carrying a similar signal, I would
recommend going /P and getting as close up to the power line as possible – the
high signal strength will then make it relatively easy to differentiate
between power line signals and the other noises one hears on LF. It should be
fairly easy to follow the route of the cable, and see if the noise is
associated with it at several places – LF noise seems to propagate for a long
way down most kinds of cable.
Cheers, Jim
Moritz
73 de
M0BMU
