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Re: LF: Can LF damage a mains input filter?

To: [email protected]
Subject: Re: LF: Can LF damage a mains input filter?
From: Lawrence Galea <[email protected]>
Date: Thu, 19 May 2016 08:01:55 +0200
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Hello Chris.
Apart from the suggestions from others, I would suggest a small 1.5 -
2 turn link right across the input of the amplifier. You could wind it
on say a 2mm twist drill for size. Such a coil would present a
reasonable impedance to the UHF TV signals but would effectively be a
short circuit for HF and lower VHF signals, shorting them to earth at
the amplifier input. and prevent saturation of the amplifier with your
transmitter signals.

On 5/18/16, Mal Hamilton <[email protected]> wrote:
> Chris
> Avoid TV amps
> Change over to Freesat to avoid all the problems you describe
> It is cheap and easy to install yourself
> De Mal/g3kev
> On 18 May 2016, at 17:04, Chris Wilson <[email protected]> wrote:
>> 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:[email protected]
>> My        part        time        LF        grabber       is       at

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