Dear John, LF Group,
Saw very good signals from CT1DRP last night between 2100 - 2300, which
could easily have been copied at QRSS3, and which were often weakly
audible - I think this is the first time I have actually heard Brian's
signals.
I find almost any mains electrical appliance with any electronics in it is
a potential source of severe interference at LF. Things in "standby" mode
can often generate more noise than when they are operating, so the only way
to be sure if something is a noise source is to pull the mains plug out.
Even if I switch off the mains supply to the house completely, the noise
level is not greatly reduced, presumably due to common-mode signals from
some distance away propagating along the mains earth wire. Strangely, my
previous QTH in North London was almost totally free of mains noise. Any
antenna close to the house will pick up noise from the house wiring; quite
severely at 5m distance, and still annoying at 10m. Since my TX antenna has
to come right up to the house to use the available space effectively, it is
always noisy on receive. This means I have to resort to separate receive
antennas to get reasonable reception, which tend to cluster at the bottom
of the garden. Even then, there seem to be relatively distant noise
sources which can prove sporadically troublesome.
Apart from a few trials, I think the wide-area PLT schemes are not yet
"legal" due to their requirement to push high levels of signal into the
mains cabling in order to overcome the high intrinsic noise levels. For
this reason, If they do become generally used, they are bound to make the
mains noise situation worse.
Cheers, Jim Moritz
73 de M0BMU
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