[mythtv-users] Audio interference on cable TV

[Rod Smith]

Hi,

I've been futzing with my configuration in an attempt to get things working 
and I've run into what I suspect is an RF interference problem inside my 
computer case. I've got a pcHDTV 3000 card that, because of its poor QAM 
reception, I'm now trying to use solely as an NTSC frame grabber. The card 
works fine when recording from its S-video or composite inputs, and using the 
audio input jack for audio. The problem comes when I try to use it to record 
from cable TV channels: I get a weak audio signal from the selected program 
with what sounds like a distorted audio signal from another channel, or 
perhaps a radio station, superimposed on it. The result sounds a lot like 
what happens when an analog FM radio is tuned in-between two stations or in a 
fringe area where two stations on similar frequencies are competing for 
reception. I have the same problem no matter what analog station I tune. I 
also hear the same distortion when I plug speakers directly into the pcHDTV 
3000's audio output, so I'm certain the audio corruption is appearing in the 
pcHDTV 3000, not somewhere else in the chain.

This problem disappears when I move the card to another computer in another 
room, fed from the same source cable system. In fact, I've got two pcHDTV 
3000 cards, and both exhibit the same problem in the one system but are OK in 
the other. An ordinary TV, hooked directly to the cable where the problem 
system resides, can tune all channels OK, so the problem doesn't seem to be 
with the cable feed.

For these reasons I suspect something inside the computer's case is creating 
the interference, but I have no idea what it might be. Power supply? Video 
card? Motherboard? If anybody's experienced (and solved) a similar problem, 
I'd appreciate hearing from you before I start ripping things out one by one 
in an attempt to find the cause by trial and error.

Alternatively, I'm considering replacing the headache-inducing pcHDTV 3000 
with an external NTSC tuner, like a Plextor ConvertX, and later adding 
another HD tuner. Any pointers on what might work well for an external NTSC 
tuner? The Plextor gets mentioned a fair amount, but I've run across 
references to other external USB tuners working with MythTV, and if one of 
them would work well I'll consider it. I'm thinking of an AverMedia A180 or 
an HDHomeRun for HD, but I don't think I'll be getting one immediately unless 
I run across a real bargain.

Thanks for any suggestions.

-- 
Rod Smith
http://www.rodsbooks.com