Plasma TV radiation ?

w5hro said:

But certainly Plasma TV's generate massive amounts of interference, I don't see how they ever got approval?.

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They don't have to generate RF interference if designed correctly, we had several early Plasma displays that were 'TEMPEST' rated in the 80's but if you reduce costs and push for max brightness cutting, corners by eliminating shielding and EMI protection RFI is what happens. (FCC part 15 is a joke)
**broken link removed**

Plasma TVs are known as the Mother of RFI (Radio Frequency Interference) and for some reason the Panasonic systems seem to be at the top of the big offender list. Apparently Ham Radio operators have come to hate the things. A Google of " plasma tv radio interference" will bring up plenty of hits on the subject and some interesting reading. There is also plenty of reference to FCC Part 15 with a consensus that runs with that of nsaspook.

So yes, large screen plasma display TVs are giant noise generators. YouTube also has some good videos on the subject. There are a number of reasons but yes, they are the mother of RFI noise.

Ron

I'm not sure why everyone wants to keep placing the blame on Plasma EMF on the switching supplies. Yes, switching supplies are noisy and a source of RFI, but that’s not what’s causing the EMF radiation coming from plasma TV’s. It’s not quite the same thing as with LED or LCD TV's.

A good way to try and describe plasma RFI would be to compare it to the old spark gap transmitters hams used starting back before WWI during the very early days of radio. They transmitted by creating an electrical arc between two terminals. Back then there wasn’t really anything for them to interfere with, but if they hadn’t been outlawed after the war they would have been a real nightmare to deal with as the technology advanced and the influx of consumer electronics started to materialize. Old spark gap transmitters produced very wideband RFI and much wider than any plasma TV made today will. Actually, plasma TV RFI is somewhat of a more controlled interference and its limited within certain frequency spectrums. You will just see spikes here and there that move around a little as the picture changes.

Anyway, the point being is that EMF coming from plasma discharge (aka Townsend Discharge) is similar to spark gap transmitter discharge and it produces the interference in much the same way. The main difference is that with plasma TV radiation it’s confined to the surface area of the display itself and then whatever common mode is riding along all of the cable grounds as a result. It will only interfere with stuff in close proximity. Spark gap transmitters on the other hand were connected to actual antennas and would have wiped out everything for miles.

Nigel Goodwin said:

No, it's at a considerably higher frequency - plasma displays can only be ON or OFF (it's a binary display) - in order to give variable brightness the display is fired multiple times per field, normally 256 times.

This is the main source of the RF emissions, but it also comes from the high power 'switch mode' X-SUS and Y-SUS boards, plus of course a much smaller amount from the SMPSU (although even this is a lot higher than an LCD set due to the greater power consumption.

But certainly Plasma TV's generate massive amounts of interference, I don't see how they ever got approval?.

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Mainly because FCC part 15 only tests down to 30MHz at the bottom end???

Mike odom said:

Mainly because FCC part 15 only tests down to 30MHz at the bottom end???

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FCC only applies the USA, not to the rest of the world.