[mythtv-users] What does ATSC poor signal look like? or is the PCnot up to it?

Andre Newman mythtv-list at dinkum.org.uk
Thu Apr 16 18:12:13 UTC 2009


On 16 Apr 2009, at 17:42, Misty P wrote:

> Andre Newman wrote:
>> Ok the problem is recordings have sections missing, everything seems
>> fine for a minute or two to maybe even 10 minutes, then the picture
>> freezes with lots of blocks then carries on with what seems like a
>> second or so of programme missed.
>
> That *sounds* like ATSC signal degredation (I'd guess multipath, but  
> that's just a guess).

Probably is but seems to work ok on the laptop.
>
> Install the dvb-utils package.  Then, launch femon:

Got dvb-utils but didn't know about femon.
>
> Have your friend watch TV with myth, and then when he notices  
> picture wonkyness, kill the femon process.  Look at the results.   
> (Word to the wise: pump femon's output to a file!)  You'll see  
> something along the lines of this:
>
> ~$ femon -a 0
> FE: Samsung S5H1409 QAM/8VSB Frontend (ATSC)
> status SCVYL | signal 0127 | snr 0127 | ber 00000000 | unc 00000000  
> | FE_HAS_LOCK
> status SCVYL | signal 0127 | snr 012c | ber 00000000 | unc 00000000  
> | FE_HAS_LOCK
> status SCVYL | signal 0127 | snr 0127 | ber 00000000 | unc 00000000  
> | FE_HAS_LOCK

I read somewhere that the HVR950 doesn't report ber but unc should be  
useful (maybe the ber thing was a older driver) I'm guessing that unc  
is uncorrected, ie packets that the FEC couldn't correct?
>
> ~$ femon -a 1    (I have more than one tuner, this runs femon  
> against my second tuner.)
> FE: Samsung S5H1409 QAM/8VSB Frontend (ATSC)
> status SCVYL | signal 00fa | snr 00fa | ber 00000000 | unc 00000000  
> | FE_HAS_LOCK
> status SCVYL | signal 00fa | snr 00fa | ber 00000000 | unc 00000000  
> | FE_HAS_LOCK
> status SCVYL | signal 00fa | snr 00fa | ber 00000000 | unc 00000000  
> | FE_HAS_LOCK
>
>
> Now those are both examples of stations tuned that have NO errors on  
> them (ber and unc = 0) and have a continuous lock (FE_HAS_LOCK).   
> That's what you *want* to see.
>
> The upshot is to scan the log file and see if you have sections  
> where either the lock drops out or you have ber and/or unc errors.   
> If you do, then everything is working fine and you have signal  
> degredation.  If not, then the signal is fine and you have a problem  
> elsewhere.

Great stuff, just what I have been trying with analysing the transport  
streams but real time is much more meaningful.
>
> (Note:  If your friend changes channels, it's entirely normal for  
> you to lose lock and/or have errors for a second.  Gotta re-attach  
> to the signal at some point!  ;) )

Got that, thanks.

Andre


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