[mythtvnz] Trying to troubleshoot DVB-T artifacts

Steven Ellis steven at openmedia.co.nz
Sun Apr 26 02:16:43 BST 2009 

On Sun, April 26, 2009 12:53 pm, Jean-Francois Pirus wrote:
>
> 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)

I currently have two USB DVB-T tuners, a freecom and a Hauppauge HVR-900.

Just tried the freecom unit under Ubuntu 8.10

dvbtune -c 1 -f 538000000 -m

Using DVB card "WideView USB DVB-T"
tuning DVB-T (in United Kingdom) to 538000000 Hz
polling....
Getting frontend event
FE_STATUS:
polling....
Getting frontend event
FE_STATUS: FE_HAS_SIGNAL FE_HAS_LOCK FE_HAS_CARRIER FE_HAS_VITERBI
FE_HAS_SYNC
Event:  Frequency: 0
        SymbolRate: 0
        FEC_inner:  0
Bit error rate: 0
Signal strength: 21845
SNR: 61423
FE_STATUS: FE_HAS_SIGNAL FE_HAS_LOCK FE_HAS_CARRIER FE_HAS_VITERBI
FE_HAS_SYNC
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61166dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61166dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61166dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=21845, Verror=0, SNR=61166dB, BlockErrors=0, (S|L|C|V|SY|)


I tried tweaking the parameters for the Hauppauge usb tuner, but it
doesn't appear to make a difference, I still don't show a signal lock.

dvbtune -c 1 -f 538000000 -m -tm 8 -cr AUTO -gi 8
Using DVB card "Zarlink ZL10353 DVB-T"
tuning DVB-T (in United Kingdom) to 538000000 Hz
polling....
Getting frontend event
FE_STATUS:
polling....
Getting frontend event
FE_STATUS: FE_HAS_LOCK FE_HAS_CARRIER FE_HAS_VITERBI FE_HAS_SYNC
Event:  Frequency: 0
        SymbolRate: 0
        FEC_inner:  3
Bit error rate: 0
Signal strength: 34548
SNR: 46517
FE_STATUS: FE_HAS_LOCK FE_HAS_CARRIER FE_HAS_VITERBI FE_HAS_SYNC
Signal=34780, Verror=0, SNR=46517dB, BlockErrors=0, (L|C|V|SY|)
Signal=34436, Verror=0, SNR=46517dB, BlockErrors=0, (L|C|V|SY|)
Signal=34768, Verror=0, SNR=46517dB, BlockErrors=0, (L|C|V|SY|)
Signal=34472, Verror=0, SNR=46774dB, BlockErrors=0, (L|C|V|SY|)


> -------- 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
>>
>> _______________________________________________
>> mythtvnz mailing list
>> mythtvnz at lists.linuxnut.co.nz
>> http://lists.ourshack.com/mailman/listinfo/mythtvnz
>> Archives http://www.gossamer-threads.com/lists/mythtv/mythtvnz/
>
>
> --
> ------------------------------------------------------------------------
> 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
> Mob   (+64-21) 640 779                P O Box 3901 Auckland, New Zealand
> ------------------------------------------------------------------------
>
>
> _______________________________________________
> mythtvnz mailing list
> mythtvnz at lists.linuxnut.co.nz
> http://lists.ourshack.com/mailman/listinfo/mythtvnz
> Archives http://www.gossamer-threads.com/lists/mythtv/mythtvnz/
>


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

More information about the mythtvnz mailing list