[linux-dvb] How does bad reception influence quality
r.scobie at clear.net.nz
Fri Feb 16 07:54:45 CET 2007
lynx.abraxas at freenet.de wrote:
> This is very valuable to know. Sadly I couldn't find any info on this in the
> What would You recon is ment with "signal strength" and "signal quality" in
> the M$ windows dvb-t programme? Would it be SIG and SNR as reportet by
> dvbsnoop or tzap? What do the other values discribe? SNR is never changing
> although it is reported. Here is some output of usbsnoop and tzap:
> tzap ard
> using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
> reading channels from file '/home/lynx/.tzap/channels.conf'
> tuning to 191500000 Hz
> video pid 0x0201, audio pid 0x0202
> status 03 | signal 8675 | snr 0000 | ber 001fffff | unc 00000000 |
> status 1f | signal 8435 | snr 0000 | ber 00000000 | unc 00000013 | FE_HAS_LOCK
> status 1f | signal 8455 | snr 0000 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
> status 1f | signal 844e | snr 0000 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
The crucial ones here are ber and unc.
Ideally both should be zero. BER is a measure of bit errors in the
stream and up to a certain point, these errors are fully corrected with
the original data able to be recovered by using the error correction
code which is part of the encoding.
Once the number of errors exceeds the error correction capability, the
picture/sound starts to show visible/audible artifacting and this will
show up in the unc - uncorrected errors column.
I am a little puzzled as to why the second entry in your example is
showing uncorrected errors and yet has a ber of 0.
The ber numbers can be quite useful for fine tuning your dish alignment,
particularly LNB skew.
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