[mythtvnz] Trying to troubleshoot DVB-T artifacts

[Steven Ellis]

On Sun, April 26, 2009 8:25 am, Steve V wrote:

> Hmm I get
>
> steve at MythBackEnd:~$ sudo dvbtune -c 0 690000000 -m
> Signal=43211, Verror=2097151, SNR=0dB, BlockErrors=0, (C|V|SY|)
> Signal=49585, Verror=0, SNR=0dB, BlockErrors=19, (S|L|C|V|SY|)
> Signal=49553, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
> Signal=49626, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
> Signal=49580, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
> Signal=49569, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
> Signal=49602, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
> Signal=49576, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
> Signal=49538, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
> Signal=49574, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
> Signal=49612, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
> ^C
> steve at MythBackEnd:~$ dvbtune --version
> dvbtune 0.5
>
> I am running dvbtune over a shh connection from my frontend to my backend,
> but that shouldn't matter should it?

Thats exactly what I'm doing.

> The other thing I am doing is running mythtv-setup just before I run
> dvbtune to stop the backend and free up the DVB card. There is probably a
> more elegant way of doing this. Could this affect my results in dvbtune?

service mythtv-setup stop

> I also notice that not only do I get zero for SNR but I also get all the
> letters at the end of each line which you do not have.
>

I've re-run the test on my Lab box which doesn't have as good reception
due to extra splitters. This is running Ubuntu 8.10 with a standard build
of dvbtune 0.5.

I have a feeling your SNR is too low. You have a high signal but poor
Signal to Noise Ratio.

mythtv at feisty:~/dvb/dtt$ dvbtune -c 1 - 538000000 -m
Signal=34520, Verror=1073, SNR=50115dB, BlockErrors=0, (L|C|V|SY|)
Signal=34136, Verror=1073, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)
Signal=34396, Verror=1073, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)
Signal=34388, Verror=1073, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)
Signal=34216, Verror=1073, SNR=50115dB, BlockErrors=0, (L|C|V|SY|)
Signal=34440, Verror=979, SNR=50115dB, BlockErrors=0, (L|C|V|SY|)

mythtv at feisty:~/dvb/dtt$ dvbtune -c 1 - 570000000 -m
Signal=34176, Verror=610, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)
Signal=34592, Verror=610, SNR=50115dB, BlockErrors=0, (L|C|V|SY|)
Signal=34144, Verror=610, SNR=50115dB, BlockErrors=0, (L|C|V|SY|)
Signal=34264, Verror=692, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)
Signal=34580, Verror=692, SNR=50115dB, BlockErrors=0, (L|C|V|SY|)
Signal=34128, Verror=692, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)
Signal=34384, Verror=692, SNR=50115dB, BlockErrors=0, (L|C|V|SY|)
Signal=34456, Verror=1039, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)
Signal=34116, Verror=1039, SNR=49344dB, BlockErrors=0, (L|C|V|SY|)
Signal=34496, Verror=1039, SNR=49344dB, BlockErrors=0, (L|C|V|SY|)
Signal=34284, Verror=1039, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)

mythtv at feisty:~/dvb/dtt$ dvbtune -c 1 - 666000000 -m
Signal=34128, Verror=1033, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)
Signal=34280, Verror=1033, SNR=49344dB, BlockErrors=0, (L|C|V|SY|)
Signal=34592, Verror=825, SNR=49344dB, BlockErrors=0, (L|C|V|SY|)
Signal=34148, Verror=825, SNR=49601dB, BlockErrors=0, (L|C|V|SY|)
Signal=34420, Verror=825, SNR=49601dB, BlockErrors=0, (L|C|V|SY|)
Signal=34376, Verror=825, SNR=49858dB, BlockErrors=0, (L|C|V|SY|)

Looking at the code for the additional information shows

                if (festatus & FE_HAS_SIGNAL) fprintf(stderr,"S|");
                if (festatus & FE_HAS_LOCK) fprintf(stderr,"L|");
                if (festatus & FE_HAS_CARRIER) fprintf(stderr,"C|");
                if (festatus & FE_HAS_VITERBI) fprintf(stderr,"V|");
                if (festatus & FE_HAS_SYNC) fprintf(stderr,"SY|");

I'm not sure why I don't show FE_HAS_SIGNAL and you do.

Steve

--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email   - steven at openmedia.co.nz
website - http://www.openmedia.co.nz