[linux-dvb] How to gather "Signal Quality" information from DVB drivers

Morgan Tørvolt morgan.torvolt at gmail.com
Mon Jul 30 14:48:21 CEST 2007


Hi Wolfgang,

> the SNR value is only dependent on the demodulator you use, so even with
> a different frontend, the values can be directly compared as long as you
> use the same demodulator IC (and firmware, maybe...).
> For most demodulators, you can give a (more or less) simple equation to
> calculate the S/N (or C/N, whatever you want to call it) from the register
> values, but unfortunately there are some exceptions: STV0297 DVB-C for
> example.
You are right. What I said was very wrong. I did think correctly
though, I was just thinking without writing it down =)
What I meant to say was, that even with the same frontend, two cards
synced on the same signal from the same antenna could have different
snr as a result of the sensitivity of the tuner and possibly also the
shielding and the noise coming from the tuner and the signal amplifier
itself.
That said, the snr is probably the best data you have on the quality.
Unfortunately devices like avemerdia volar A808 (I have one of those)
does not give you snr at all. That is very unfortunate. In such a case
the best thing for the driver to do is to calculate the snr from the
ber. It will not be accurate though.


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