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I have a noise problem on 40, 20, and 15 meters originating from the plasma TV I own. Turning on the TV raises the noise level by 2–4 S units, depending on the frequency. The TV is located below the antenna in the attic. The RFI also affects my outdoor antenna, to a lesser extent. My troubleshooting so far:

Things that don’t help

  • Plug either the TV or the transceiver into a battery power station, while the other is on grid power.
  • Wrap the TV’s power cable through a toroid core close to the TV (3–4 turns through an FT240-43).
  • Same type toroid core at antenna feed point, 8 turns.

Things that eliminate the noise

  • Power off the TV.
  • Unplug the coax feed line from the transceiver.

Things that reduce the noise strength

  • Unplug the antenna from the coax feed line. Noise is still present but quieter. Touching the center prong of the PL-259 coax feeds noise into it, as if I'm also an antenna.

My conclusion is that the TV is radiating RFI, without even the cables acting as antenna wires. Perhaps the metal mounting frame is acting as an antenna?

What might I do to eliminate the noise? Do I have options for this indoor attic antenna other than an expensive noise cancellation device?

FYI, the TV is an LG 60PB5600 60” Class Full HD 1080p Plasma TV

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    $\begingroup$ References suggest you may have to apply the ferrite to all wires going into and out of both the TV and your rig at the same time; i.e., a "one at a time" or "process of elimination" approach might not work. If the interference changes as the program scenes change, then the screen itself is the likely culprit and would have to be shielded to eliminate the noise, but it's tough to see the TV through tin foil! $\endgroup$
    – Brian K1LI
    Feb 13 at 13:30
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    $\begingroup$ Yes, the noise does change in shape significantly depending on what’s shown on the screen. During testing, the power cable was the only attached wire. $\endgroup$ Feb 14 at 16:29
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    $\begingroup$ If you could edit your question to add the make and model of your plasma TV, that would be helpful to future readers. $\endgroup$
    – Mike Waters
    Feb 14 at 18:40
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    $\begingroup$ Great idea! Done. $\endgroup$ Feb 15 at 19:33
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The RFI is generated by —and is radiated from— the screen itself.

You would have to put the plasma TV inside a Faraday cage to eliminate your RFI. This is why plasma TVs are no longer being made. (Having said that, there was at least one brand of plasma TV (Panasonic?) that was not a prolific RFI generator.)

A plasma set, unlike a LCD, requires relatively high voltage to turn the pixels on and off (rather like a neon bulb) and this is occurring at the refresh rate of the TV. This generates significant wideband interference due to the harmonics from this high voltage switching.

Reference

Sorry to be the bringer of bad news here, but about the only solution is to sell the plasma TV and buy a newer type that doesn't spew RFI.

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    $\begingroup$ My solution is going to be to replace this TV set. Thanks! $\endgroup$ Feb 15 at 19:35

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