[linux-dvb] Re: DVB-C tuning

[rmdvb@bj-ig.de]

On Mon, 28 May 2001, Ralph Metzler wrote:

> rmdvb@bj-ig.de writes:
>  > I'm still "playing" to get my TT-DVB-C Budget running. Still I'm not
>  > really able to get the tuner working. What I found: the frequency scale
>  > used for DVB-C and for DVB-S differs by a factor of 1000 - is this a bug
>
> No, this is intended.
>
>  > or meant to work this way? FE_GET_NEXT_FREQUENCY is using the same scale
>  > for DVB-C as for DVB-S so I tend to see it as a bug. The line
>
> How do you know the scale FE_GET_NEXT_FREQUENCY uses for DVB-C?

Ok - I meant QAM_FE_INFO. Anyway. The values you get back with
FE_GET_NEXT_FREQUENCY are incremented by 1000 - it makes no
difference between DVB-C and DVB-S. I suppose this should mean
increment by 1000kHz - everything else would be crazy.
You have a signal of >5MHz bandwidth - which is "autotuned" (AFC
and some tuning algorithm: "zigzag"-whatever). So trying frequencies
in 1MHz steps would be adequate. QAM_FE_INFO gives kHz
values (40000-870000) so it's a bit strange that QAM_TUNE
expects Hz and if I remember correctly QAM_GET_EVENT delivers Hz.
QPSK_TUNE on the other hand expects kHz. I my eyes this is a little
bit inconsistent.

> > Just libdvb/ptest is still not working. BTW: which program do you
> > use to make basic tests?
>
> ntuxzap, which works nicely with cable.

Ok - I will try this.

Do you have an idea why tuning to 346MHz 10 times one after the
other (ok - incremented by 1Hz between tries to trigger tuning) - what
definitly is the frequency of a valid DVB channel - only works in about
50% of all cases? Tuning is done by a loop of QAM_TUNE, QAM_GET_EVENT
calls which gives much to often FE_FAILURE_EV. Any idea?

Ralf

-- 
Van Roy's Law: -------------------------------------------------------
       An unbreakable toy is useful for breaking other toys.




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