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Re: [RFI] Eliminating TVI

To: rfi@contesting.com
Subject: Re: [RFI] Eliminating TVI
From: "N6KJ" <kelly@thejohnsons.ws>
Date: Tue, 23 Dec 2003 10:25:55 -0800 (PST)
List-post: <mailto:rfi@contesting.com>
On Tue, 23 Dec 2003 12:03:39 -0600, "Jim Brown" wrote:

> On Tue, 23 Dec 2003 09:45:11 -0800 (PST), N6KJ wrote:
> >The color goes away (screen switches to black/white) whenever I transmit
> >on 80 or 40 meters.  No problems with 20 meters and higher.  TVI present with
> >as little as 10 watts output into a dipole about 30 feet from the TV.
> Sounds like a really severe case!

Yes, I've been trying to fix this for most of this past year (off-and-on).
As I said, the problem is in the color.  I don't see any herringbones or
any other visual distortion.  I also hear no interference in the audio.

> I suspect either power line or antenna line coupling, and I suspect the
> filters you are using are ineffective below 20 meters. The 43 material
> is primarily a VHF material. I would try toroids optimized for HF, and
> wrap as many turns as possible around them on all the wirng entering
> the TV. And I would disconnect any extra wiring so that I was looking
> at only one connection at a time (for example, power and antenna
> connected, VCR disconnected). 

After all of this, you still suspect that it is not direct coupling into
the circuitry?  I hope you are right.

I just realized this week that my toroids ARE 43 material so I will buy some
77's and try them as soon as I can get some.

I've already tried disconnecting everything but the TV and an input source
(DSS set top box or DVD player).  It didn't fix anything.  I did NOT try
rabbit ears as you suggest below, but I figured running my DVD player
into the TV was as good (or better) than the rabbit ear test.  Do you
disagree?  In that test I disconnected everything but the DVD player
input and the TV.  This did not eliminate the problem.

I was thinking of renting a gas powered generator (I wish I owned one)
for a day and running the tv off it to see if that helped.  Does this sound
like a worthwhile test?

> Along the same line: What happens with rabbit ears or equivalent on the
> TV and nothing else connected but power?  If you still have the
> problem, this suggests either a shielding problem or a power line
> coupling. 

See note above about my DVD-only test.

> And is the color going away because RF is getting into the color
> circuitry, or because the RF signal is dropping in level in the
> presence of RF? 

I'm not a TV expert so I don't know the answer.  What I can say is that
if 10 watts of RF on 80/40 meters with a dipole 30 feet away is swamping
the input then somebody did a pretty crappy shielding job on this tv.
I used to run 100 watts into a dipole that was about 1 or 2 feet from our
TV antenna when I lived with my parents with no problems.  Of course, that
was a different TV.
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