From: =?iso-8859-1?Q?VIGILANT_Luis_Fern=E1ndez?= <luis@vigilant.es>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Thread-Topic: Can LF damage a mains input filter?
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Date: Wed, 18 May 2016 16:39:37 +0000
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Subject: LF: RE: Can LF damage a mains input filter?
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Hi Chris

What about the input of the TV Amp and the problem being not related to RF into the mains ?

May be the strong LF field damaged the first amplifier stage and now is generating harmonics with strong HF signals
That happens also with bad (rushed) TV coax connections performing as semiconductors (diodes) and generating
harmonics in TV bands when a strong HF signal gets in

Just an idea

73 de Luis
EA5DOM


-----Mensaje original-----
De: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] En nombre de Chris Wilson
Enviado el: miércoles, 18 de mayo de 2016 18:04
Para: rsgb_lf_group@blacksheep.org
Asunto: LF: Can LF damage a mains input filter?

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