[mythtv-users] What does ATSC poor signal look like? or is the PCnot up to it?
Misty P
mistyp at thekorn.net
Thu Apr 16 16:42:51 UTC 2009
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!
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