[linux-dvb] CAM inserted/used reduces signal and SNR ?

Luc Brosens dvb at bsc-bvba.be
Sun Nov 18 12:43:28 CET 2007



Ben Bucksch wrote:
> Luc Brosens schrieb:
>> why does inserting and accessing a CAM reduce the signal and SNR levels ? (even if no descrambling is needed, as for BBC World)
>>   
> 
> My *guess*:
> I guess it's due to power - the cards need a lot of power to go over the
> wire to the dish. The CAM may push it over the limit. The fact that you
> have 2 PCI cards probably doesn't help.
> 
>>>
>>> so I removed the second card, and I'm relieved that this didn't solve the problem
>>> I have succeeded to descramble several of the other channels, but only rarely succeed at it : mostly tuning just fails
>>> most successes seem to occur after a (cold) boot ?
>>> it seems that gnutv either gets a lock immediately (before the CAM messages) or not at all
>>> could it be that tuning and CAM access are interfering ?
>>> is there a way to skip the tuning part of gnutv ? (I could tune with szap -x, take over descrambling with gnutv)
>>>
>>> as for power consumption : neither of the cards are warm, not even slightly
>>> my other mythtv-box contains a Hauppauge MCE500 and a PVR350 : these cards run really hot, surely these KNC1s should be OK ?
>>> the total power consumption of my box (1GB RAM, 300GB SATA HD, AMD 64X2 3600+) is only 61W, including the two KNC1 cards and CI slot
>>>
>> how can this be solved ?
>>   
> 
> - Ensure more power on PCI bus
> - shorter cable to dish
> - different mainboard / cards
> - less cards
> - USB DVB adapters, on powered USB switch
> etc.
> 
>>>
>>> removing the second card didn't help
>>> there are only 2 PCI slots, the other one contained the other KNC1
>>> both PCIe slots (16x and 1x) are empty
>>> don't see how I could get more power to the PCI bus ...
>>>
>>> I admit that my cables are long, but my settop box is happy :
>>> signal strength 70% and up, SNR 90% and up
>>>
>> anyone out there having the same problems ?
>>   
> 
> hm, I hope I don't. I just added the second card and seeing strange
> problems.
>
>>>
>>> hope you get the second card working OK !
>>> remember to check the PCI slots : my first motherboard had a defective slot
>>>

> Ben
> 



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