On Sun, Feb 28, 2010 at 11:46:21PM +0000, Gordon JC Pearce wrote: > The incoming RF is downconverted to the audio range, but not > demodulated. Effectively you've mixed a chunk of RF (7MHz band, in the > case of my sample file) down to an audio range but not yet demodulated. > > At this point you may have a signal at 7066kHz which has been downmixed > to 10kHz, but that's outside the receiver passband - you can't hear it. > By mixing a further 10kHz signal into the audio you bring that down to > 0kHz, and if it's an LSB speech signal it now occupies a range of > frequencies up to about 3kHz with an "image" at 20kHz. Now we've got it > in the speech range and we can demodulate it by summing the imaginary > and real components so that the image cancels out. > > Think of the SDR hardware as being a pair of direct-conversion receivers > with the local oscillators 90 degrees out of phase so the output is a > vector rather than a scalar.
It's similar to Steve Harris' Bode Shifter plugin, except that this takes a single (real) signal and converts it to complex internally using a Hilbert transform. Ciao, -- FA O tu, che porte, correndo si ? E guerra e morte ! _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
