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

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

Mike Grant wrote:
> 
> Justin Cormack wrote:
> > ok, have more or less worked out how to do this. The only thing is what
> > frequency these channels are on. I cant work out how to convert from channel
> > number to frequency for the uk...
> 
>  From http://www.linuxstb.org/dvb-t/index.shtml:
> 
> centre frequency = (UHF Channel Number)*8 + 306
> 
> This gives you a frequency in MHz.  VDR uses kHz (MHz * 1000) and
> dvbstream, etc use Hz (MHz * 1000000) so you'll need to pad it out to
> the correct length.
> 
> Also note that most channels have an offset from the centre frequency,
> which must also be added.  You can find these offsets by looking at your
> local transmitter info on:
> 
> http://www.itc.org.uk/uk_television_sector/reception_advice/digital_trans_guide/index.asp?region=show_all
> 
> For example, the Rowridge transmitter has multiplex 1 on channel 23,
> offset -167kHz (listed as '-') and multiplex B on channel 32, offset
> +167kHz (listed as '+').  No offset is listed as '0'.  So,
> 
> multiplex 1 freq in kHz = (23 * 8 + 306) * 1000 - 167 = 489833 kHz
> multiplex B freq in kHz = (32 * 8 + 306) * 1000 + 167 = 562167 kHz
> 
> When converting these to Hz, I tend to assume the ITC meant 166.666..kHz
> rather than 167kHz so I get 489833334Hz and 562166667Hz instead of
> 489833000Hz and 562167000Hz.  I don't think that it matters though..

Are these frequency offsets always +/-167kHz? Will that be the same for
other countries, too?

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?

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
_______________________________________________________________


-- 
Info:
To unsubscribe send a mail to listar@linuxtv.org with "unsubscribe linux-dvb" as subject.