Plasma TV sets generate a complex and broad modulated signal that have
different components which change in frequency and amplitude when the
video on the screen changes. Fast live action like a football game
will produce a lot of noise that can't be nulled out. You can
perhaps null out part of it but you can't get it all.
A lot depends on proximity to the source and frequency. What you
hear on 160 m. close to a TV is very different from what you might
pick up on 20 m. farther away. Making it worse are perhaps poorly
filtered TV power supplies and the fact that the RF in various forms
may be coupled to the TV's power cord, internet, or even telephone
line if these are somehow connected or near the set. This can have
the result of the TV no longer being a point source. They can be
really nasty buggers.
To get an idea of what a plasma TV is like so you can ID one at your
home QTH, I advise getting a small battery powered shortwave portable
receiver like a Grundig Yacht Boy and take that to an appliance store
like Best Buy where there are a lot of TVs on display. Put the
receiver on 160, or 75 meters AM, extend the telescoping antenna a
couple of feet and tune around walking amongst the TVs. You'll hear
the plasmas beginning at around 50 feet or more from the TV
department. No other appliance in the store will put out like that.
They are really RFI hell up there with these square wave grow light
power supplies and a trivial problem like an arcing power line
insulator will seem tame afterwards. That exceedingly broad complex
wave form which jumps frequency and is randomly bursting with whatever
is being shown on the screen is a demon.
73
Rob
K5UJ
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