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

Mike Perkins mikep at randomtraveller.org.uk
Thu May 13 17:37:09 UTC 2010

Ed W wrote:
>>>> 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?
This does sound to me like some kind of power problem. The USB device starts, 
works for a while and then quits. Just like something that gets too warm once it 
starts processing, or like something that sucks all the available power from the 
supply and drags the rail down.

As suggested above, try using a powered USB hub for elimination purposes. And, 
from personal experience, make sure it's one with some grunt in the PSU.


Mike Perkins

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