From: "Holger Waechtler" <[EMAIL PROTECTED]> > Robert Schlabbach wrote: > > AFAIK, there is no such thing as "I/Q wires", only a (typically > > differential) IF signal between the tuner and the demodulator. > > I and Q are the names of the two IF wires between tuner and the demod. > It's the usual notation for complex numbers, the two signals specify > the modulation point in the complex I/Q plane.
I beg to differ ;) You are correct about I and Q specifying the constellation point, with I being the In-phase amplitude and Q being the quadrature amplitude. But you cannot say one of the differential IF lines carries the I signal and the other carries the Q signal. In fact, you could only use one IF line to carry the signal, with both I and Q in it... BTW, I wasn't quite right about the spectral inversion. Here is a good quick explanation of what it is: http://www.rfcafe.com/references/electrical/spectral_inv.htm Basically, it means the signal spectrum is "mirrored" around the center frequency: What was originally above the center frequency ends up below it, and vice versa. And this effect happens when the LO (=PLL) frequency in a downconversion is greater than the target frequency - a scenario you have with typical tuners, where you add the IF center frequency to the target frequency. So to not have a spectral inversion in the tuner, you would have to have a tuner in which you _subtract_ the IF center frequency from the desired target frequency to get the PLL frequency. Do such tuner modules really exist? If not, they *all* spectrally invert the signal... Regards, -- Robert Schlabbach e-mail: [EMAIL PROTECTED] Berlin, Germany -- Info: To unsubscribe send a mail to [EMAIL PROTECTED] with "unsubscribe linux-dvb" as subject.
