[mythtv] what are the right frequency offsets?

[Nick Morrott]

On 5 April 2010 11:23, Janne Grunau <janne-mythtv at grunau.be> wrote:
> On Sun, Apr 04, 2010 at 04:37:09PM +0200, Petr Stehlik wrote:
>>
>> in libs/libmythtv/frequencytables.cpp's init_freq_tables() there's a
>> list of tables for various countries. I have submitted a Czech DVB-T
>> table that works great for some tuners (much better than Germany or
>> France tables that we used to use before) but is worse for certain other
>> tuners (ASUS My Cinema-P7131 Hybrid).
>
> Yeah, I guess some tuners search enough spectrum to find the pilots also
> on the offsetted frequencies. It also depends on the transmitter.
>
>> After some trial&error it turned
>> out that by using the French offsets (the last two parameters, -166000
>> and 167000) the channel scanning works better.
>>
>> Thus I am wondering how I can find out the correct offsets for DVB-T.
>> I've seen it set to 0,0 for most countries but some have 125000 and
>> other have the -166k/167k.
>
> http://forum.team-mediaportal.com/submit-epg-grabbers-tuningdetails-296/dvb-t-updated-tuning-parameters-czech-republic-ostrava-74844/
> uses 12.5k as offsets.
>
>> Thanks for any pointer. I'd  like to get it fixed in time for 0.23 but
>> before submitting a patch with the French offsets for the Czech table
>> I'd like to know if it's possible to compute the parameters somehow
>> instead of guessing them.
>
> This are official transmitter parameters and should be published
> somewhere. I couldn't find anything in english.

Although I haven't found a definitive answer (yet) in official
technical documentation (from ETSI, for example), other research
suggests that for DVB-T transmission, channels having a 7MHz
separation can have a +/- 125kHz offset, and channels having an 8MHz
separation can have a +/- 167kHz offset. This does seem to be borne
out in the UK and Australia (8MHz and 7MHz channel separation
respectively, AFAICT).

Cheers,
Nick

-- 
Nick Morrott

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