[RFI] TVI solved

["John Rader" <k5xtx@hotmail.com>]

My new tower is located against the back wall of our house, and is just a 
few feet form the TV. My TV, a 52" Mitsubishi projection TV in a wooden 
cabinet, was experiencing fundamental overload. The prior install had no 
TVI, but this time I knew the feedline and TV antenna were too close 
together and would require some serious attention to eliminate overloa. But 
how?

After posting this issue to the RFI reflector I recieved a number of 
excellent suggestions. Fortunately the first one I tried stopped the TVI, 
which occured with as little as 20 watts.  After following Tom, N5EGs 
suggestion on TV grounding, I am now able to run 1,000 watts without audio 
or picture interference.

Tom's suggestion:
> From an RFI perspective at the TV receiver, there is a dipole
antenna the two halves of which are:

       the braid of the TV feedline, and
       the AC power wiring (hot+neutral in parallel).

       The TV set sits in the middle of this dipole, and
detects strong RF fields, sometimes causing fundamental overload.
Since you moved your transmission feedline closer to the TV
feedline, you increased the coupling to this dipole.

       You want to short out this dipole so that no RFI voltage
exists between the TV set and it's ground. It would be easy,
except... most TV sets do not have a ground connection in
the power cord (they use a 2-wire cord).

       So here are the steps to take:

       1. Purchase a AC power strip that has F-type connectors
in it. Get one that connects the F-connector shell to AC-power
ground. The TV antenna cable connects to one F-connector on
the power strip. You will need to make a short jumper (a
couple feet) to go from the other AC power strip F-connector
to the TV receiver.

       2. You also want the type of AC power strip that uses
capacitors to bypass the hot and neutral wires to ground. This
puts the RF potential of the hot, neutral, and ground wires all
at the same value. These capacitors usually have about 1.6kv to
2kv rating so that voltage transients on the power line don't
cause them to fail (which could present a hazard). Of course
if the TV receiver had a three wire cord, this would become a
non-problem.


       This setup shorts the braid of the feedline to the AC power
ground, and makes sure the TV set frame is AC grounded to the same
point. In essence you have shorted out the spurious dipole around
the TV set.

       Make sure you shop around - there's some outrageously
priced AC power strips. You should be able to find one that's not
so pricey if you know what you are looking for and shop carefully.

       -- Tom, N5EG

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