[vdr] Re: Finnish DVB-C problems solved

[Dave Chapman <dave@dchapman.com>]

On Thursday 25 July 2002 19:57, you wrote:
> Hi,
> Antti Lammi got his DVB-C card just recently and he got in touch with me 
> about finnish specific DVB issues. He finally got he's system running and 
> today via trial and error found out that the reason why it was so hard to 
> tune to the bouquets, was that the actual frequencies reported by HTV and 
> the network NIT were infact no precisely correct. According to Antti's 
> tests the the freq. for QAM_64 bouquets should be subtracted by 0.125MHz 
> (i.e. 125000) and the freq. for QAM_128 bouquets by 0.25MHz (250000). 
> After that everything worksl ike a charm. You can even get rid of the 
> 'fix' to the driver (mentioned above).
> 
> I guess this is specific to HTV since no other DVB-C users are complaining 
> about something like this.

This sounds similar to the channel offsets (+/- 167KHz) applied to UK DVB-T 
transmissions.  It is done to help minimise interference with analogue PAL 
broadcasts on adjacent channels.

> A patch to VDR would include subtracting the specified frequency by the 
> appropriate amount stated above before tuning. But since this is Finland 
> specific I guess we'll just have to patch our VDR's our selves. [ 
> channels.conf uses MHz for frequencies, there's no way to specify KHzs in 
> channels.conf ]

I think the correct patch to VDR would be to allow the user to specify the 
frequency in either MHz or KHz.

channels.conf uses KHz for DVB-T frequencies, so it would be logical for VDR 
to accept this format for DVB-C as well - "T" and "C" use similar frequency 
ranges.

This could be made in a way that is compatible with existing cable 
channels.conf files - if the DVB-C frequency is less than 1000, then assume 
it is in MHz, otherwise it is in KHz.

I think that just two lines need to be changed in VDR to implement this:

Replace "* 1000000UL" with "* 1000UL" in dvbapi.c (it only appears once)
Add the line "if (frequency < 1000) frequency*=1000;" after the first sscanf 
in config.c

This would allow (for example) "538MHz" to be written as 538 or 538000.

Regards,

Dave.