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

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

Dave Chapman wrote:
> 
> On Tuesday 08 October 2002 22:19, Klaus Schmidinger wrote:
> > Are these frequency offsets always +/-167kHz? Will that be the same for
> > other countries, too?
> 
> In the UK the offsets (if present) are always +/- 167KHz.  I haven't heard
> about offsets being used in other countries.
> 
> > I'm asking because I would like to make the frequency for DVB-T channels
> > in VDR's channels.conf also be in MHz, and if that offset thing is in any
> > way standardized we could just add another DVB-T specific parameter to
> > cover the offset (like O0 = 0 kHz, O1 = +167 kHz, O2 = -167kHz).
> >
> > I wonder, though, why that offset is necessary, and whether the driver
> > shouldn't be able to tune to a channel at, say, 490 MHz - 167 kHz
> > automatically if it is given an inital frequency of 490 MHz. I mean
> > 167 kHz isn't _that_ far off for a transponder with several MHz bandwith.
> > Or am I missing something important here?
> 
> No, trying to tune to a frequency of 488.833MHz by approximating to 489MHz
> doesn't work - I've just tried it.

That's odd... IIRC with DVB-S you can be off by even 1 or 2 MHz and the driver will
tune to the transponder correctly, so I really wonder why this isn't possible with
DVB-T. I mean it's just a mere 166 kHz! Is there no AFC in the DVB-T part of
the driver?

Can one of the driver developers comment on this?

> I think the "O" option would just make the channels.conf more confusing - it
> is much simpler just to keep the frequency the way it is, in KHz.

The problem is that I would like to be able to use the transponder frequency
as a parameter in a "unique channel ID" (I know, there are people who would
like that to be the NID, TID whatsoever - there will be a switch to configure that!).
Anyway, since the "official" frequencies are apparently given as integer MHz values
(for instance 23 * 8 + 306) and the "offset" is mentioned as an additional parameter,
see http://www.itc.org.uk/uk_television_sector/reception_advice/digital_trans_guide/show_transmitter.asp?siteID=81.
So I would prefer _all_ frequencies in channels.conf to be in MHz, so that the numbers 
can be expressed in 16 bit values. And regarding channels.conf being "confusing": well,
that's mainly because DVB-T needs so many parameters! I don't know why they have to
have _that_ many of them, but that's just the way it is. And apparently the "offset"
is just another of these parameters.

Can somebody with DVB-T please run a program that parses the NITs and reports
the transponder frequencies given there? I'd say if these are given as the "real"
values (like 488.833MHz), then VDR should store them as such in channels.conf.
But if they are given as integer MHz values (like 489MHz) then there's no point in
having them in kHz in channels.conf.

Slightly OT, but in the same area of interest: can somebody with DVB-C do the same thing?
There have been reports from DVB-C users in Finnland that they need to add an offset to
the DVB-C frequencies as well, so I'd like to know whether the "official" frequencies
given in the NITs include these offsets or not.

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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