Re: [LAD] Smallest, simplest, silliest SDR?

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 !
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