[linux-dvb] Re: Spectral Inversion (was Re: Re: patch for scan (-t bitfield select))

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

From: "Ralph Metzler" <rjkm@metzlerbros.de>
> Anyway, the inversion of the signal inside the tuner and how it
> reaches the demodulator is irrelevant. The user space parameter
> "inversion" should reflect the property of the signal as it is sent
> (or maybe better how it reaches the tuner in case of satellite bands
> where the usual LNB LO is above the signal frequency? Are there any?).
> The driver should compensate for any internal inversions.

I agree with that last point. "INVERSION_OFF" should mean that the
front-end is "inversion neutral", i.e. has no or an even number of
inversions within it. For a typical cable/terrestrial frontend, this means
that "INVERSION_OFF" translates to inversion being _enabled_ in the
demodulator, and "INVERSION_ON" translates to inversion being _disabled_ in
the demodulator, since the tuner already spectrally inverts the signal
once.

For satellite systems, this should exclude the LNB, though, which may or
may not invert the signal (I think typical ones do not).

Thanks for helping me get a clear idea of this parameter, which had always
been a mystery to me :)

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



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