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[RFI] Eliminating TVI

To: rfi@contesting.com
Subject: [RFI] Eliminating TVI
From: "N6KJ" <kelly@thejohnsons.ws>
Date: Tue, 23 Dec 2003 09:45:11 -0800 (PST)
List-post: <mailto:rfi@contesting.com>
While I have some spare time during the Christmas Holiday season I am going
to try once again to eliminate my TVI problem.  I have tried everything and
nothing fixes it.  I still think it is probably direct coupling into the
TV circuitry, but before I give up completely I want to try a couple more 
things on the outside of the case.  

BTW, moving the antenna farther away is no longer an option.  I've moved it
as far away as I can on my small city lot.

First, here is my setup:
1) Mitsubishi 35 inch CRT (about 8 or 9 years old).  The only external
   connections are the S-Video input and the A/C power line.  S-Video
   input has about 6 ferrite beads on it.  A/C power line has a
   toroid (mix 43) on it with about 6 turns.
2) Satellite Dish, VCR, and DVD feed a switch box which is connected via
   S-Video connector to my TV
3) All equipment is connected to a surge-suppressor/power junction which
   is then connected to a single wall outlet.  A/C power line has a
   Radio Shack A/C line filter on it.

Here is the symptom:
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.

The problem occurs whether I am watching DSS TV, VHS video, or DVD.  This
would seem to exonerate the DSS feed as the problem.

If I record a DSS signal on my VCR while at the same time watching the
TV and transmitting I see the TVI, but if I then rewind the VCR and play it
back there is no TVI in the recorded signal.  This would seem to suggest
that only the TV is seeing the interfering signal (or at least only seeing
it strong enough to cause a problem).

The problem occurs with 2 different rigs.  The rigs are adequately
grounded and I've even tried transmitting with my rig connected to a
car battery deep in my backyard.  I've tried moving the antenna and it
seemed to help, but not enough.  The antenna has a balun on it and the
coax has been coiled several times to choke off RF running down the
outside of the coax.  When transmitting in the back yard, the coax
never gets close to the house.  I did this to confirm that RF running down
the outside of the coax is not the problem.  The rig has a low-pass
filter on it too.

Personally, I suspect direct coupling into the color burst circuitry but
I could be wrong.

Now for the questions:
1) Earlier this year, I switched my TV input from the standard RF input
jack to the S-Video input because someone said that the S-Video input was
less likely to receive TVI.  It didn't help or hurt.  Is S-Video input
really a better choice?  Are there any TVI filters available for S-Video?
If I were using the RF input I could put a channel 3/4 bandpass filter on
it or a high-pass filter (which I have done), but I don't know what you
can do with S-Video.  What frequencies are carried over the S-Video
connector?  Baseband?

2) Anybody know how I can get schematics for this TV so I can go in and
try to shield parts inside if external filtering still doesn't fix my problem?

3) Any final suggestions before I open the case OR buy a new TV.
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