[NLRS] TV pulsing noise
[email protected]
[email protected]
Mon, 27 Oct 2003 08:39:23 -0600
Hi Brent. In the old (old old) days, when you turned a TV OFF, that
usually meant that the 110 VAC was removed from the power supply. Now
days when you turn your TV set off its simply a command to the
microprocessor to turn the display off; the rest of the TV is still on.
As such my guess is that the pulsing noise is coming from either the
(switching?) power supply (which is always ON) or the TV's internal
electronics (which is always ON).
The noise can leave the TV set in one of two ways. It can be conducted
and/or it can be radiated. Conducted means that the signal is generated
inside the TV set but its leaving the TV by conducting itself along the 110
VAC power cord, and perhaps the antenna lead, to the outside world. Once
the signal leaves the TV set your house's electrical system can act like an
antenna and thus you pick it up everywhere. (Gosh, this sounds like
BPL). One possible fix is to use some ferrite material, I think Radio
Shack sells some, and wrap both the 110 VAC power line and the TV coax with
it (two separate ferrite's). This acts as a choke to help prevent low
frequency RF from flowing out the cable. The ferrite should be located
close to the TV (like right where the cables leave the TV).
Radiated interference is caused by signals radiated into the air ala what
radio signals do. The only fix for this problem is to put the TV in a
better box and to employ better (electronic and RF) design practices ....
its something that is very difficult to fix given a finished design (your
TV set).
Interfering signals can also be conducted onto the 110 VAC power line (or
TV cable feed line) and be radiated from there .... kind of a conducted
then radiated interference problem. In this situation adding ferrite
material should help reduce the problem.
My recommendation is to try adding some ferrite filters on the power cord
and coax cable before you open up the TV. Perhaps those with more
experience in using ferrite to reduce HF interference can comment.
73, Jon
W0ZQ
Brent Casavant
<b.j.casavant@ieee To: Northern Lights Radio Society <[email protected]>
.org> cc:
Sent by: Subject: [NLRS] TV pulsing noise
nlrs-admin@mailman
.qth.net
10/26/03 11:12 PM
Please respond to
Brent Casavant
Hello,
I picked up a shortwave receiver at Hamfest Minnesota this weekend,
and got around to playing with it today. It seems to work well, and
would probalby be much more enjoyable if my French weren't so rusty.
However I ran into an EMI problem. I noticed a strong regular pulsing
noise at about 4 Hz, which I can best describe as sounding a bit like a
rapid "ticking" white noise. It seems to be strongest when I tune
in the vicinity of 9MHz, though I hear it from the 6MHz band up through
about the 13MHz band (I'm not sure if there's more accepted terminology
for shortwave bands).
Intrigued, I moved around the house with the receiver, and finally
ended up with an incredibly strong "signal" near my TV. Sure
enough, unplugging the TV immediately removed the noise. It
does not matter whether the TV is on or off, the noise remains as
long as it is plugged in.
I realize HF questions are rare around here, but I'm hoping someone out
there has run into this type of noise before. In particular I'm hoping
that someone knows what sort of component may be causing this noise, and
a way to eliminate it (which I imagine involves opening up the TV and
firing up the soldering iron). Not so much because I'm an active
shortwave listening, but I figure when I do start working HF (and
maybe when using HF IF frequencies for driving transverters) this will
become a real problem.
Any thoughts are most appreciated.
Thanks,
Brent Casavant
--
Brent Casavant http://www.angeltread.org/
KD5EMB -.- -.. ..... . --
-...
44 54'24"N 93 03'21"W 907FASL EN34lv
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