[linux-dvb] Re: Question about inversion and DVB-S

["Robert Schlabbach" <robert_s@gmx.net>]

From: "Andrew de Quincey" <adq_dvb@lidskialf.net>
> With the new code I'm not able to lock on 11747 at all. But.. as I
> was despairing of things to try, I tried turning inversion ON.
> Now I can lock on  to that signal perfectly (but none of the others,
> 'cos they require inversion OFF).
>
> Can someone please explain what would cause this?

DVB-S inversion is one thing I haven't quite figured out yet. A signal will
be spectrally inverted if you downmix it with a LOF > target frequency. But
DVB-S uses zero-IF, i.e. LOF = target frequency (where LOF is actually
two-stage; first LOF is in the LNB, second in the tuner). So what happens
when the LOF is slightly off so that it is above the target frequency...?

According to the Hotbird 2 Frequency Plan:

http://www.eutelsat.com/satellites/pdf/Frequency_plans/fp_hb_2.pdf

The exact frequency of this transponder is 11746.66MHz. I wonder if that
makes any difference? With 250kHz step size, you should be able to tune to
11746.75 or 11746.50MHz. Could you try these and see if it makes any
difference wrt spectral inversion...?

It could also be that this broadcaster is delivering an inverted signal...

Regards,
--
Robert Schlabbach
e-mail: robert_s@gmx.net
Berlin, Germany



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