I did a compliance test some years back on several TV's. Included were both
plasma and LCD models. Tests included both standard conducted and radiated
modes. Noise via the conducted path, otherwise via the power cable or any
other cable, wire or connection is relatively easy to correct with a common
mode choke being no more than a ferrite donut with a few turns of the
offending wire wrapped through the core. This must be located as close or
inside the TV for maximum effectiveness. As to radiated emissions, only
shielding the box will correct the situation. An extreme approach is to
find the offending component or components and place a ferrite bead on each
leg of the component or put the module in a shielded box.
In rotating the plasma TV's on a turntable and measuring the radiation for
360 degrees horizontally and then measuring the same in a vertical mode, it
was noted the most of the radiation was from the front of the set. The back
case or cover may have some copper spray coating or some conductive metallic
coating to minimize the radiation in that direction.
It is sad today that although every manufacturer selling or distributing
electronic product in the USA is required to perform these tests and certify
that the device is in compliance. Unfortunately cost-down measures after
certification often eliminate critical components and methods that are in
place to reduce or eliminate the radiation. {Hey what do bean counters know
about EMI cause and effect?} It is up to us, the user, to determine that
the device is out of compliance and then file a written complaint with the
manufacturer. Making this determination is not easy nor inexpensive. Just
hearing the noise is not justification. The general criteria is being
specific as to frequency, bandwidth, and actual level measured in microvolts
per meter. Also data on residual background noise is required along the
same criteria. Once the complaint is filed, it is then their responsibility
to correct the issue. And finally after all the reposts, measurements and
paper work is done and the appropriate waiting time has expired only then
can we file with the FCC to have anything done. This of course is unless
the offending device is causing interference to critical services such as
aircraft communications, national security and emergency services. And with
the scaled down enforcement branch of the FCC in this area, it would likely
be years before anything is actually done.
Bottom line, if one has a problem, find it and fix it. You'll be a lot
better off and with a solution much sooner.
73
Bob, K4TAX
P.S. - That is a very good link that Jim has provided. Do save it for
reference.
----- Original Message -----
From: "Jim Brown K9YC" <k9yc@audiosystemsgroup.com>
To: <tentec@contesting.com>
Sent: Monday, January 19, 2009 11:39 AM
Subject: Re: [TenTec] Ground, noise blankers in the Omni V and plasma TV's
On Sun, 18 Jan 2009 17:54:16 -0500, Scott Sheppard wrote:
Dealing with some very bad RFI from my plasma TV (Panasonic).Have
improved my ground to no avail (I honestly did'nt think it would do
anything anyway--in fact it stays the same with no ground at all).
All products are different -- they have their own ways of radiating
trash depending on how they are built. If the dominant mechanism is
direct radiation from the screen, as K4TAX has described, you're
hosed -- there's nothing you can do but turn it off or dispose of
it.
IF, however, the trash is radiated common mode by cable attached to
the set (that is, that wiring is an antenna), you can make a MAJOR
dent in the noise with a common mode choke. The tutorial below
explains these mechanisms and describes how to kill them.
http://audiosystemsgroup.com/RFI-Ham.pdf
73,
Jim Brown K9YC
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