Some more info below, I checked the amp and its original moulded on on mains plug has a plastic earth pin. It was fine for years, rather than re-type a huge amount i copy paste from a UK low frequency group, so if seems a bit odd that's why, my typing speed is pitiful! Thanks Sean, are you saying use mains earth for the co-ax screens, which are all going to the internal tin RF shielded box, that's well soldered together so it would be hard to see what's within? If a new amp fixes it I am still interested to know what caused this one to go funny... Cleaning (in fact re-making) all the Belling Lee co-ax plug terminations made no diffrence, and as the thing is in a warm, bone dry loft there's no sign whatsoever of dirt or corrosion anywhere. none of co-ax feeds run outside, either.
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Long story, but since stopping LF 136kHz TX for a while in lieu of
some HF working all the digital TV's in the house freeze or totally
blank on all bands above top band, up to 50MHz when I transmit at more
than about 5 or 10W. I have a loft mounted UHF TV aerial feeding an
amplifier cum distribution box. It has an internal mains PSU. Without
it we receive hardly any channels. It's been fine for years, and I
have never had TVI. My HF set up is unchanged from when I had no
issues. I put the TV antenna co-ax direct into my SA and on circa 531
MHZ see a broad digiTV signal that's strong. If I TX on say 20 meters
at high power into my antenna I see zero change in the TV signal. I
have also fed the output of my HF TX (TS-590 Kenwood) into the SA via
an attenuator and the output looks spotless on all bands. However, if
I connect the TV aerial amp / distribution box up and look at the
output from it the TV signal immediately drops into the noise when I
TX. My neighbours have no issues at all.
This seems to have occurred since I have been active on LF, and I had a
stage where full power would trip the main RCD in the consumer unit,
so RF was getting into the mains. Is it conceivable something has
occurred to perhaps a mains filter in the TV amp? I looked inside the
plastic case and it has a small mains transformer that feeds feed
throughs into a screening can with all the RF stuff within it. If
there is any mains input filtering it must be on the low voltage side
of the transformer. The unit has a moulded on three pin mains plug, but
with a plastic earth pin, so the unit is not grounded.
Is it possible to make a mains input filter for a piece of equipment
that would filter 136kHz but not affect normal 50Hz mains operation?
Has anyone experienced anything like this?
I have ordered a new amp / distribution box of known make, and will
just try replacing it, but would also like to know if my LF activity
could have done this?
Thanks.
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