How to quickly troubleshoot the plasma TV RFI? Disconnect all of the cables
(except the AC power) from the TV. If I needs video to keep the screen active
you can connect a source of NTSC video. Many digital still cameras and all
video cameras have this. Run the device on batteries and connect to the TV
video
input via a short cable.
Now all you have as a point of RF egress is the power cable. If the 1.8 MHz
RFI is still nice and strong then you can focus on the AC power. You can
purchase off-the-shelf AC line filters that provide good common-mode and
normal-mode
attentuation at 1.8 MHz. I would not fool around with constructing my own
when fne filters, that are UL certified, are available.
To construct your own and have it meet UL 60950 you need to use components
rated for AC line use and maintain "creepage" and "clearance" of - I think - 3
mm or more from line-to-line and line-to-earth ground. You must also take care
to properly bond the filter case to earth ground such that the connection
cannot be removed from outside the box and it must be able to take 30 amps or
so
and have a resistance below so many ohms. I don't have a copy of the standard
and am working from memory. Since it's not your TV or house I would sure steer
away from putting homebrew filtering in the neighbor's house.
Let's say the AC line is not the point of egress. Connect the video input
back. Let's say the RFI becomes strong now. You will need a few hundred ohms of
common-mode attentuation at 1.8 MHz. A ferrite core and several turns of the
coax will do it, given the correct core.
Anyway, this method of troubleshooting will get you right to the problem and
you can avoid randomly placing ferrites and filters all over your neighbor's
TV.
Dave WX7G
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