[linux-dvb] Finnish DVB-C problems solved

["Lauri Pesonen" <lauri.pesonen@firsthop.com>]

Hi,

I've been mailing a lot of reports on the list in the past about problems 
with tuning in the HTV's (a finnish cable provider) network. The problem, 
pure and simple, was that it was very difficult for the driver to tune to 
QAM_128 modulated bouquets. QAM_64 modulated bouquets worked a lot better, 
but there was only one of those. 

I suspected that the reason was either a bug in the driver (I had no idea
where) or then it was caused by a lousy signal strenght / SNR from the
cable provider.

In the beginning it was not possible to tune to any channel. Kenneth Falck 
submitted a finnish fix for this: increase the delay interval in the DVB 
driver (dvb_frontend.c - fe_zigzag()) to 2*HZ from the original HZ. This 
enabled the driver to tune to channels, but it failed most of the time.

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.

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 ]

br, Lauri


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