[linux-dvb] Re: DVB-T UK Frequencies

[Gavin Hamill <gdh@acentral.co.uk>]

> Actually I'm not sure I have - I verified it was actually writing the
> stream, but upon playback the mpeg is VERY jerky (imagine trying to
> playback a dvd on an old pentium, it plays it but very slowly as if it
> can't decode fast enough). 

It's only playing maybe one frame in 5?

This is almost certainly poor reception quality - I only have access to a 
small set-top aerial and have spent many happy hours making minute 
adjustments to its positioning, and then sitting in 'just the right place' to 
get a smooth playback.

dvbtune is your friend here... 

$ dvbtune -f 537833 -qam 16 -cr 3_4 

to lock onto the signal 

then

$ dvbtune -f 537833 -qam 16 -cr 3_4 -m

to view a monitor of signal quality:

Signal=9766, Verror=24462, SNR=41120dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=9766, Verror=24100, SNR=40349dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=9766, Verror=23684, SNR=41120dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=10023, Verror=23201, SNR=40606dB, BlockErrors=0, (S|L|C|V|SY|)

That's the current output from my main BBC mux. Even though it Report 
BlockErrors = 0, my picture is still jerky and shows artefacts...

You really need a Verror value of about 10,000 or lower before you will get 
reliably smooth reception.

If you have a VCR or a Sky Digibox or something, try feeding the roof-top 
aerial through that, and connecting the output directly to your Nova-t . The 
VCR/Digibox will act as a pre-amplifier and you should get better pictures :)

Be aware that if you are joining two pieces of RF cable, you will lose huge 
amounts of signal strength! =)

Cheers,
Gavin.


 I used the following command line:

> ./dvbstream -o -ps -qam 16 -cr 3_4 -f 537833 201 202 > tmf.mpg
>
> Output:
> Streaming 2 streams
> Videostream: ASPECT: 4:3  Size = 720x576  FRate: 25 fps  BRate: 8.00
> Mbit/s
> Audiostream: Layer: 2  BRate: 192 kb/s  Freq: 48.0 kHz
>
>
> Now since I don't know about these extra fields (qam and cr), could it
> be this frequency has different settings to say BBC's?
>
> > , sorry to jump back in the thread,
> > but I notice
> > your channels.conf is showing the same as mine in that there are no
> > entries for the Sky and UKHistory channels.
> >
> > FYI these are:-
> > Sky News (TV):578166:V:0:27500:101:102,104:0:0:22080
> > Sky Spts News (TV):578166:V:0:27500:201:202,204:0:0:22144
> > Sky Travel (TV):578166:V:0:27500:301:302,304:0:0:22208
> > UKHistory (TV):578166:V:0:27500:401:402,404:0:0:22272
> >
> > I have been assuming this is due to a bad signal, although
> > usually manage
> > to get a lock, but are others also seeing this?
>
> I can't get a lock on those either.  Not too bothered about those
> channels, but the more the merrier :)
>
> Andy.


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