Mailing List archive
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[vdr] Re: femon values explanations and possible fixes, possible
On Fri, 6 Aug 2004, Nicolas Huillard wrote:
Some transponders have no lock (ie. no channel on this transponder seems to
lock), with a STR (Signal strength) that varies a lot : from 30% to 50%
within a few seconds. For those, SNR (Signal-to-noise ratio) is quite stable
(47-53%).
--> is there any nominal STR/SNR values below which a channel have no change
to lock and be decoded ?
The signal strength and signal-to-noise ratio values are comparable only
between the same brand/model frontends, so I cannot tell you which values
are good enough. For example my terrestial card gives signal strength 19%
no matter is the antenna connected or not :) However your varying STR
implicates that there's something wrong with your dvb card & signal...
The BER (Bit error rate) max value seems to be 0000fff0 (with extremely low
STR but still a carrier) (Skystar2, if that matters).
--> is there a level between 0 and that max above which the image begins to
degrade (MPEG squares, glitches, etc.) ?
Well, I'm having BER rate ~0x500 and haven't noticed any MPEG2 artefacts.
There might be a more educated guesses for the BER error free mpeg2 upper
limit in the DVB mailinglist.
The UNC (Uncorrected blocks) is always 0, even though there are sound and
video errors, and the BER is high. I would induce that the higher BER (Bit
error rate) is, the higher is the risk to have UNC (Uncorrected blocks).
--> is the UNC value a rate (uncorrected block for refresh interval) or a
counter (number of uncorrected blocks in that stream since lock acquisition)
I was hoping that DVB drivers clear that variable after a lock in enabled,
but I haven't checked that. BER seems to be a good enoung indicator for
signal quality. And yes, it's a rate.
In my case, BER hardly goes below 0000fff0 (but UNC is always 0), even though
STR stays at 67% and SNR at 58% on some transponders.
--> can this explain jerky video and audio (I also use softdevice, that seems
to be jerky on it's own).
Yes.
Finally : do I need to better point my dish (dual head 80cm dish) to get
better than STR 6% / SNR 58% or are these values OK ? Is it normal that some
transponder can't ever lock but others from the same satellite do well.
Or do I need to search on the softdevice side ?
Personally I'd try the tweak the dish position first...
--
rofa
Home |
Main Index |
Thread Index