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

[Misty P]

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).

> I think it's system load related but the box doesn't seem heavily
> loaded ever and I'm not sure if I'm fooling myself, difficult to know
> when the box is only a ssh session to me! Unfortunately the HVR 950
> doesn't seem to report BER or any other meaningful measure of signal
> quality, he tells me that if he uses the HVR 950 on the laptop the
> signal is good for the local stations and I can see that the more
> remote stations are unusable, that's fair.

Install the dvb-utils package.  Then, launch femon:


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



~$ 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.


(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!  ;) )


Hope that helps!