Message-ID: <573C9E42.7090300@posteo.de>
Date: Wed, 18 May 2016 18:54:26 +0200
From: DK7FC <selberdenken@posteo.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <1934937394.20160518170418@chriswilson.tv>
In-Reply-To: <1934937394.20160518170418@chriswilson.tv>
Subject: Re: LF: Can LF damage a mains input filter?
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

Hi Chris,

It is possible the RF currents have destroyed some mains filter components.
Does your LF antenna has a separate RF earth near the antenna feed 
point? I would recommend it. If you have a separate LF earth there can 
still be RF currents in the house electricity, maybe destroying a common 
mode choke in a small EMI filter.
You could try to measure common mode currents on your coax to confirm 
your assumption.

It is one reason why many LF OPs recommend to use an isolating 
transformer for the LF RF near the feed point. A LF antenna with a 
separate ground, then a big ferrite core used as a RF transformer with 
two galvanic decoupled windings, transforming your loss resistance to 50 
Ohm, and then a normal coax to the output of the PA. This prevents 
unwanted common mode RF currents on the coax screen flowing somewhere, 
through the ground of your power supply and then through the mains grid 
back to earth.

73, GL, Stefan

Am 18.05.2016 18:04, schrieb Chris Wilson:
> 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.
>
>
>
>