[linux-dvb] Re: Another issue: frontend timeout value and low symbol rates

[Andrew de Quincey <adq_dvb@lidskialf.net>]

On Saturday 21 February 2004 02:44, Robert Schlabbach wrote:
> From: "Andrew de Quincey" <adq_dvb@lidskialf.net>
>
> > Now, I'm able to lock on to low symbol rate signals...
> > I've just managed it with a 4340000 symbol rate...
> > getting a REALLY good signal from it, but it took about 10 seconds
> > to tune (the current timeout is hardcoded to 2 seconds). The STV0299B
> > docs say it needs a certain number of symbols before being able to
> > get a lock...
>
> That can't explain the long lock time. My card is locking to the 22000 and
> 27500 MBaud ASTRA transponders in less than 5ms. Since 4340 MBaud is about
> 1/5th to 1/6th of that, the demodulator would get the same amount of
> symbols in 5-6 times that, i.e. in 25-30ms. That's nowhere near 10 seconds.
>
> But have you checked the AFC reading after the demodulator was locked on?
> Low symbol rate transponders are using a much narrower frequency band than
> high symbol rate ones, and thus exact tuning may be much more important. A
> 1MHz offset may not be much in a 30MHz band, but it makes much more of a
> difference in a 5MHz band...
>
> If possible, try compensating the offset by adjusting the tuner PLL
> frequency as much as possible and see if/how that affects the lock times...

I think I mustn't be doing something right with the tuner.. I had it locking 
on to low symrates in about 3 seconds for a while... then it just... stopped 
working. I think I'll concentrate on the general tuning problem first.


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