[linux-dvb] Re: New UK DVB-T channels testing

[Klaus Schmidinger <Klaus.Schmidinger@cadsoft.de>]

Lauri Pesonen wrote:
> 
> On Wed, Oct 09, 2002 at 11:51:18AM +0200, Holger Waechtler wrote:
> > Klaus Schmidinger wrote:
> >
> > >  The NIT reports frequencies like 283000000Hz when I'm using 282750000Hz
> > >  with VDR. So The NIT reports the 'official' freqs without the offset.
> > >  Offsets are -250kHz for QAM_128 freqs and -125kHz for QAM_64 freqs.
> > >
> > >Therefore it should be sufficient to store the "center frequency" and
> > >allow for
> > >an offset handling, which in case of DVB-T could be done by an 'O'
> > >parameter
> > >(note that it's the character between 'N' and 'P', not the number 'zero'),
> > >and in case of DVB-C a table of offsets for the various QAM modes should
> > >do the trick.
> >
> > Are you sure that these offsets are related to the used modulation? What
> > makes you sure of that?
> >
> > Holger
> 
> I emailed about theo ffset in DVB-C in Finland (the text segment Klaus
> quoted above).
> 
> Some guy in Finland (sorry, I can't remember your name) came up with the
> offsets after trial and error. There is no guarantee that they are correct
> or that the offset is related to the modulation. Actually the only QAM_64
> bouquet in my providers network is on 162MHz and all QAM_128 bouquets
> (that I'm whatching) are above that, e.g. in the range of 283MHz. So the
> offset might also be related to the freq rather than the modulation (which
> would make more sense to me).
> 
> All I can say for sure is that I have offset the QAM_64 bouquet by -125kHz
> and all the QAM_128 bouquets by -250kHz and all channels work perfectly.
> Before I applied the offset 80% of my channels switches across bouquets
> failed.

Well, after all these postings I guess the bottom line is that it will be best
to store both DVB-T _and_ DVB-C frequencies generally in kHz (I believe
going all the way down to Hz would be really unnecessary, because the user would
then have to enter a NINE digit number when defining a channel in VDR's OSD - pretty
sure six of which would be zeroes).

VDR would then in no way bother with any offsets, these would have to be added to
the frequency in whatever way the person or program that generates the data sees fit.
The only question left is whether the data broadcast in the data stream really defines
the frequency *precisely*.

Klaus
-- 
_______________________________________________________________

Klaus Schmidinger                       Phone: +49-8635-6989-10
CadSoft Computer GmbH                   Fax:   +49-8635-6989-40
Hofmark 2                               Email:   kls@cadsoft.de
D-84568 Pleiskirchen, Germany           URL:     www.cadsoft.de
_______________________________________________________________


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