TV audio/video noises from the media PC

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vladidan

Hello,
I've connected the Dell 531s desktop to my TV to act as a simple media
PC for on-line video streaming. Same TV has a RCA audio/video input
from the cable TV STB. I see a very strong distortion now on both
audio and video signals coming from the STB. The interesting part is
the distortion persists when I turn off the PC. It does go away if I
unplug PC from the power.
Could it be related to the WiFi interface on the PC? Perhaps I should
go with a wired connection.
The "plan B" scenario is getting high quality double-shielded audio/
video cables, though I really try to keep the cost of the media center
down.

Any suggestions?

Thanks,
Vlad
 
Hello,
I've connected the Dell 531s desktop to my TV to act as a simple media
PC for on-line video streaming. Same TV has a RCA audio/video input
from the cable TV STB. I see a very strong distortion now on both
audio and video signals coming from the STB. The interesting part is
the distortion persists when I turn off the PC. It does go away if I
unplug PC from the power.
Could it be related to the WiFi interface on the PC? Perhaps I should
go with a wired connection.
The "plan B" scenario is getting high quality double-shielded audio/
video cables, though I really try to keep the cost of the media center
down.

Any suggestions?

Thanks,
Vlad
Click to expand...

Based on:

"It does go away if I unplug PC from the power"

that says you have a grounding problem. Gold plated cables won't help with
that :-)

There is an example here of video noise (hum bars). And what I find puzzling,
is they don't seem capable of listing a price for a Balun (transformer) to
isolate the ground.

http://www.foresight-cctv.com/Ground Loop.htm

http://www.teleconnect.com.au/videogli.htm

http://www.gemelec.com/Video Ground Loop Isolator.htm

Finally found a site with prices - not good prices but at least some prices.

http://www.yourcablehookup.com/ground-loop-isolators-c-195.html

They want $51 for an stereo audio isolator, while RadioShack has one listed
here for $17. The RadioShack one has no specs, so you cannot tell what
frequency it rolls off at. But at least the RadioShack one will allow you
to test and see if it helps or not.

http://www.radioshack.com/product/index.jsp?productId=2062214

Basically, the idea is, to isolate the ground between two parts of your
project. If the PC is sending stereo audio and a composite video signal,
then you'd need a stereo audio isolator and a composite video isolator.

You would think the S-video one should be twice as expensive.
The S-video one would have two transformers in it, one for the Y signal
and one for the C signal. And yet the price charged is not double.

Video isolation shouldn't be expensive, as "ordinary" baluns are normally
not that expensive. The video isolator shouldn't be any more complicated
than one of these. The difference is, this one goes from 300 ohms to
75 ohms, and you'd want one which does 75 ohms to 75 ohms (1:1 turns ratio).

http://www.radioshack.com/product/index.jsp?productId=2062054

Perhaps you could visit a local stereo/TV store and talk to someone
there. But when you price their stuff, I'm sure they'll charge a lot
for a solution. I was shocked when they wanted $50 for a S-video DIN to
composite RCA adapter, so they'll likely want a bundle for a simple
isolator solution.

My best guess,
Paul
 
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