[vdr] femon values explanations and possible fixes, possible

[Nicolas Huillard <nhuillard@ghs.fr>]

Hello,

I compiled and tested femon tonight : what a great tool. I wonder why I 
waited so long before I installed it !

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%).
Your screenshots on http://www.saunalahti.fi/~rahrenbe/vdr/femon/ show 
STR at 19%, with SNR at 77%, and still the channel have lock and your 
have a good image on screen...
--> is there any nominal STR/SNR values below which a channel have no 
change to lock and be decoded ?

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.) ?

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) ?

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).

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 ?

TIA

--
NH