[linux-dvb] Re: tuning problem

[rolf.siebrecht@t-online.de (Rolf Siebrecht)]

Hi!

On Thu, 28 Feb 2002, Arpi wrote:
> > > Or it just drives LNB to some disallowd freq range ?
> > There is no frequency control data sent to the LNB.
> ah. so LNB works like an antenna, and the dvb card filters out the requested
> freqency band out of the lnb signal?
> i always thought that oscillator freq is 'sent' to lnb and it 'sends back'
> only the requested band...

Okay, a *band* information is sent. It is the well-known 22-kHz resp.
DiSEqC control. It's just a "digital" info: either Low-band or High-band.
The LNB-internal oscillator freq is switched as part of this info. But no
command is sent that may "tune" an LNB to a (single) out-of-band
frequency.
 
> > > What's the relation between FrontendParameters.Frequency, and the LNB limi
> > ts
> > > (9750, 10600 and switch freq 11700) ?
> > The frontend device relates to tuner hardware module and its properties.
> > LNB settings must be dealt via the SEC device.
> How can i transform between real absolute freq and these lnb parameters +
> oscillator freq values?

   // transponder_freq given as [MHz]
   if (transponder_freq > 11700) {
       tuner_freq = transponder_freq - 10600;
       send_via_SEC_device (HI_BAND);
   } else {
       tuner_freq = transponder_freq - 9750;
       send_via_SEC_device (LO_BAND);
   }
   if (tuner_freq >= 950 && tuner_freq <= 2150) {	// see below
       FeParam.Frequency = tuner_freq * 1000;		// MHz -> kHz
       set_via_FE_device (FeParam);
   }
   else
       ...

dvbtune, dvbstream, libdvb,... show equivalent code.

> > >         printf("get_info=%d\n",ioctl(fd,FE_GET_INFO,&info));
> > Returned values are not reliable. An allowed frequency range of
> > 500..2700000 kHz for DVB-S is nonsense IMHO. Unfortunately out-of-range
> > or "silly" input values are not rejected, neither by dvb.o nor tuner.o.
> I see. What are the real allowed values?

I would rely on the parameters from the tuner datasheet. The BSRV2-301A of
the DVB-S 1.3 card has the usual input frequency range of 950..2150 MHz.
 

Bye,
     Rolf




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