[linux-dvb] Re: Siemens DVB-C and QAM_128

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

On Fri, 2002-05-03 at 10:24, Panu Kekäläinen wrote:

> > FYI: I have a TechnoTrend DVB-C full featured card which tunes both to
> > QAM_&¤ and QAM_128 bouquets. I'm using VDR with my DVB-C card and I
> > hacked VDR to parse the used QAM value from the channel definition in
> > channels.conf. 
> 
> Yes, that was the first thing I did also. But since it did not work I started
> to dig a little deeper. For example, I'm using dtv_scan, different version for
> both modulations. The only QAM_64 bouguet available tunes and locks always at
> first try.
> 
> If QAM_64 scanner finds signal and carrier occasionally in QAM_128 frequencies,
> but of course can not lock.
> 
> But if I try to scan QAM_128 modulated channels. Frontend finds occasionally
> signal and carrier around the QAM_64 frequency. But it cannot lock to
> QAM_128-bouquets either. Tuner starts zigzagging around the set frequency. (I
> also tried to disable the fe_zigzag and increase the waiting time - with no
> success)
> 

Ok. This resembles my experiences as well. The QAM_64 bouquet locks
immediately. With QAM_128 bouquets I typically have to retry three four
times before a lock. I've been able to tune to all bouquets with
dtv_scan although after a couple of tries. Channel switches within the
same bouquet work very well.

My waiting time in fe_zigzag is 2*HZ currently. I've tried other values,
but this seems to work most reliably. 

> > Are you sure that the driver is the problem and not the software
> > interfacing to the driver?
> 
> No, not sure at all. :) But it was my best guess after hours of hacking with
> sources. Could you please send me the patch you have made to vdr sources, I
> could try those also. If that does not work, I guess I must install windows and
> test the card in that environment, not that I'd like to. 
> 

The windows driver seems to suffer from the same problems. I.e. it won't
find all bouquets all the time. Channel switching on the other hand
seems to work better than with Linux (i.e. no retries needed). 

I'll email the patch to you privately since the list won't accept
attachments.

I'd be a very happy camper if someone could solve these problems. I
sucks that you don't dare to switch the channel during a commercial
since you might not be able to switch back.


br, Lauri



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