[vdr] Re: femon values explanations and possible fixes, possible

[Rolf Ahrenberg <rahrenbe@cc.hut.fi>]

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