Since the 73kHz tests on Tuesday I have been monitoring at several times a
day and find a consistent and steady noise-level that is about 20dB below
the signal at 138.8kHz, and about 6dB below the one at 75kHz. Its a mains
type of buzz, beating at times with itself. Like most I have had this in
the past and put it down to RFI from switched-mode PSUs, however, it was
only sporadic in the past so I am wondering if it's something new. It seems
to be all the way up the LF band to just below the LW broadcast band (but
that cut-off could be a function of my aerial's resonance set at 73kHz).
The only thoughts that I have is ADSL or signalling on the HV underground
cable somewhere beneath my garden. Certainly, ADSL will have become much
more used locally since I last did an serious listening on LF, but I would
have thought the radiation would be fairly low from the balanced overhead
telephone lines that are at least 200m from my aerial. I would have thought
that the shielding around underground HV mains cables would be sufficient to
stop low-level signaling causing problems.
I can't see a real reason why TV related interfernce should increase near to
my home. How far away do TV's etc need to be before they cause problems, or
is it more caused by the interference conducting itself along the mains
cabling, etc.
Any thoughts?
73 John, G3WKL
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