[mythtv-users] Interference lines in all recordings

Tim Gray tim at p-a-a-i.com
Mon Feb 12 13:44:29 UTC 2007

I was silly and built a nice tiny setup. 2 pci slots only and it's a 
micro itx with everything built on board as it's a backend recorder 
only. I have not tried the move the wores around although at the start I 
tye wraped all wires away from the cards as far as I could go assuming 
that anything inside the case will mess with the cards to begin with.  I 
will try soldering down the can caps, I am sure it will help if it does 
not fix the problem.  I also never thought of the over/underclocking 
thing.  I'll give that a try and see what happens with the recordings.  
I was also thinking of cutting a piece of aluminum and grounding it, and 
wrap it in electrical tape and slide it in-between the two cards just in 
case they are interfering with each other.

the 3 motherboard screws are tight, the rest are those teflon standoffs.

Thanks a ton for your help and ideas, I'll see what happens with all 
these different suggestions and report back.

Brian Wood wrote:
> On Feb 9, 2007, at 1:14 PM, Tim Gray wrote:
>> 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?
> Great, it sounds like you know what you're doing, but I had no way to  
> know that at first :-)
> I assume you've tried moving your PVRs to different slots, if you  
> have them. I'm guessing you're getting interference with the baseband  
> video on the PVRs and not RF into the tuners, but it couldn't hurt to  
> make sure the can tops are tight, or even solder them.
> What sort of PC is this? Could you re-route internal cables to try  
> and get them away from the PVRs?
> Otherwise you are talking about trying to put shielding material  
> around the cards, not any fun but it might be your only solution.
> Also make sure all the motherboard mounting screws are tight, loose  
> connections can act as detectors and cause trouble.
> If there are any cards in the PC that you can get rid of do that as  
> well, but I suspect you've tried that if it's even posible.
> If there's any way you can narrow things down to what portion of the  
> PC is generating the interference it would help. For example if you  
> could boot without a graphics card and SSH into the machine to make a  
> manual recording you could prove or eliminate that card as the source  
> of the problem.
> This one's a little off the wall: If you can change the frequency of  
> the interference you might cause the beats to be moving fast enough  
> to at least be less disturbing. Under/Over clocking the machine by  
> 5%-10% might cause a significant change in the perceived if not the  
> measured interference.
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