[mythtv-users] recommend PCI DVB-T Tuner Card?

Ed W lists at wildgooses.com
Thu May 13 15:28:20 UTC 2010


>>> And be prepared to get a powered USB hub, since
>>> even a single tuner draws pretty close to the 500ma limit while
>>> streaming (thereby hitting the power limit on a single port).
>>>        
>> Same as above. I have 3 USB devices (2 single and one double tuner) running off
>> the ports on my mobo.
>>      
> You've probably got a motherboard that provides 500ma *per* port.
> Again, you're lucky enough to have ended up with hardware that is well
> designed.  You shouldn't assume that everyone will be so lucky.
>    

Hi Devin,  I wonder if you can help.  OK, I've set myself up for failure 
here by hoping to switch to USB DVB-T cards, and last week on my test 
Atom itx board I successfully plugged in 3x PEAK dual dvb-t tuners and 
all was well!  The ATOM was under powered so I just bought a new Asus 
board with a Core2 3Ghz on it and now even a single DVB-T usb card is 
giving me big picture breakup every few seconds...

However, the symptoms are more complex than they seem.  Help on 
diagnosing appreciated:

- Older recordings on the same card, but recorded on older MB are fine
- Newer live tv *starts out* perfect, but breaks up only after a couple 
of minutes of viewing...  If I quit Livetv and go back in I get a few 
mins glitch free! In fact re-tuning to the same channel stops the 
breakup for another few minutes...
- Some recordings are perfect, I can't figure out the correlation though?
- Swapping USB port hasn't obviously affected things
- For long periods of time femon is not showing the slightest error.  I 
just turned on a recording and after 2-3 mins the picture started 
breaking up, during that time BER remained zero, as did uncorrectable 
errors. Retuning stopped the breakup for another few mins and then it 
restarted...
- Antenna has been working well for several years and is amplified with 
good quality coax

I am unsure how to debug this properly.  Can anyone recommend some 
settings I might fiddle with, or tools that could help me monitor this?  
Are there kernel settings such as APIC/ACPI that affect usb timings and 
might improve or worsen things?

Do the above symptoms even fit with an obvious cause?  It's as though 
the problem is within Myth rather than the usb card?  However, the 
change is due to swapping motherboard, so it seems likely to be more a 
function of USB behaviour or something that the computer is doing which 
is affecting interrupts or latency or something causing these glitches?  
(Actually I did change HEAD version of mythtv thinking about it, so it 
could be mythtv code, but I don't see anyone else commenting on 
recording gremlins?)

There used to be some signal strength monitoring code, however, I can't 
see anything obvious on the backend that I can enable to give me some 
stats on what I'm recording.  I obviously haven't turned on the right 
logging on the frontend because I'm not yet seeing logs about the cause 
of these decoding glitches?  Any tips on how ot turn up the logging in 
Mythtv?

I'm really very keen to try and make the USB cards work, baffled as to 
how to debug this further though?  Google gives me surprisingly little 
on toggling kernel / MB params to try and tweak this?

Thanks for any help?

Ed W


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