[RFI] Plasma TV's

Jim Brown jim at audiosystemsgroup.com
Sat Oct 10 18:52:29 PDT 2009

On Sat, 10 Oct 2009 20:46:01 -0400, Mike Wetzel wrote:

>Can anyone recommend what I might do to try and minimize the RF, other 
>don't beam west, buy him another TV, etc.

Hi Mike, 

If this stuff is radiated common mode on the audio, video, and power 
cables (or even the antenna cables) you can kill it by winding each cable 
several turns around toroids. If 20M is your only problem, you can use 
either #31 or #43 material. Follow the guidelines in my RFI tutorial for 
winding -- that is, wind the chokes to put the broad impedance peak 
(resonance) in the freqency range where you have the problem(s). Use only 
#31 if you have issues on 80 or 160M.  For small diameter cables, use the 
small wire data in Appendix One. For coax, either use the coax data in the 
coax choke section or use the small wire data and 20% fewer turns (to 
compensate for more capacitance between turns). 

If these chokes don't knock it down, it's probably radiated directly from 
the set due to lousy shielding combined with poor EMI design. No cure for 
that short of buying a new one. 


One thing you can do to diagnose it is to take a talkie that receives 20M 
(I use a Kenwood THF6A) and probe around the TV rig to try to figure out 
what's radiating. You may find multiple cables, or only one, or the set 
itself. Also, think of those wires as antennas (they are) and look for the 
ones that look like the best antennas on 20M. 

Here in CA, I had RFI to the audio system on 10M that I traced to short 
cables between the CD player and the amplifier/preamp chassis. And that 
was from an antenna at least 150 ft from the stereo rig. 


Jim Brown K9YC

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