[mythtv-users] Interference lines in all recordings

Tim Gray tim at p-a-a-i.com
Fri Feb 9 20:14:25 UTC 2007

Thanks a bunch, I already ran that route...
Cables are hand made RG6quad with firmly crimped connectors, they are 
good.  they go into a single splitter to take the signal into both cards 
whuch works good when you view from a TV on the same.  I also have +10DB 
CATV signal coming in as far as my NTSC/QUAM cable analyzer is telling 
me, although channel 96 is only +3DB so there is a little bit of 
difference from one end to the other.

signal coming into the tuners is verified to be 100% interference free 
by hooking up a replayTV and viewing recordings that are 100% clear. 
which leads me to be sure the interference is coming from inside the PC.

Has anyone found a way to shield the cards better or ground them better 
to get rid of PC generated interference?

Brian Wood wrote:
> On Feb 9, 2007, at 12:35 PM, Tim Gray wrote:
>> I know this is not mythtv specific.  But someone out there has had to
>> deal with this and I cant find anything out there that talks about it.
>> I have a mythtv box with 2 PVR-350 cards  It records great except all
>> recordings have a diagonal set of interference lines recorded in them.
>> each channel has the lines at different angles some have them very
>> faint.  How can I get rid of these?  I am sure it has to be a problem
>> with the PC generating it as nothing else in the house shows those  
>> lines
>> when watching the same channels live.
>> copy the file to a laptop, see the lines, so they are getting  
>> recorded.
>> Is there a way to get rid of the interference from the PC getting into
>> the tuners?
> First do all the obvious stuff:
> Make sure you are using good quality shielded cable with the correct  
> connectors crimped properly (ie: not fishing line crimped with a pair  
> of pliers).
> Make sure you don't have any extensions  with 300-ohm twinlead  
> running under a carpet or the like (don't laugh, I've seen it).
> Make sure that all connectors are tight, either very firmly hand- 
> tight or very gently wrench tight. The connectors on capture cards  
> can be hard to reach and get properly tightened but you have to make  
> sure they are.
> Make sure any unused ports on splitters or couplers are properly  
> terminated with a 75-ohm termination.
> Make sure your computer case is properly closed up with the screws  
> in, not running with the side off or the like.
> In other words make sure all your shielding is tight, both on the  
> cable system and the computer itself. It sounds like radiation from  
> somewhere is getting into your PVR tuners, it may be from your  
> computer or something else but your supposition is likely.
> A tightly shielded system going into the PVR tuner, which is  
> shielded, should not pick up outside sources of signal (much).
> If all this is OK you might make sure the press-on top of the shield  
> can on the PVRs is tight. I once had one where I had to put a dab of  
> solder on each side of the can lid to clear up a similar problem to  
> what you describe. This is probably not your problem since it's  
> happening on 2 cards but I thought I'd mention it
> A monitor cable can sometimes be a source of radiation, using a good  
> quality cable helps, especially if you are using an extension. If you  
> are feeding a TV set separate from your computer monitor try  
> disconnecting the monitor cable from the computer and see if it helps.
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