Date: Wed, 18 May 2016 17:04:18 +0100
From: Chris Wilson <chris@chriswilson.tv>
Organization: Gatesgarth Developments
Message-ID: <1934937394.20160518170418@chriswilson.tv>
To: rsgb_lf_group@blacksheep.org
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Subject: LF: Can LF damage a mains input filter?
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Status: O

18 May 2016


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.


-- 


Best regards,
 Chris  2E0ILY                           mailto:chris@chriswilson.tv

 My        part        time        LF        grabber       is       at
 http://www.chriswilson.tv/grabber.html