[mythtvnz] Trying to troubleshoot DVB-T artifacts
Jean-Francois Pirus
jfp at clearfield.com
Sun Apr 26 01:53:35 BST 2009
I think the SNR is useless if you dont' have an "S" (aka FE_HAS_SIGNAL)
On my Nova-T 500 this is what I get
dvbtune -c 2 - 530000000 -m
Signal=22375, Verror=2097151, SNR=0dB, BlockErrors=0, (C|V|SY|)
Signal=32857, Verror=0, SNR=0dB, BlockErrors=213, (S|L|C|V|SY|)
Signal=32792, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=32817, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=32771, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=32847, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=32838, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=32797, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=32801, Verror=0, SNR=0dB, BlockErrors=0, (S|L|C|V|SY|)
My reading of the values on the Nova-T 500 is
Signal is 0-65535 (Where 65535 is 100%/perfect)
SNR is 0-65535 ( Where 0 is perfect and 65535 is crap)
-------- Original Message --------
> 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
>
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Jean-Francois Pirus <jfp at clearfield.com> Technical Manager
Phone (+64-9) 358 2081 Clearfield Software Ltd
Fax (+64-9) 358 2083 1st Floor 8-10 Whitaker Place
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