El Tue, Jan 13, 2004 at 03:46:02PM -0500, Jack Smith escribio:
> >If it is a fairly narrowband signal, centered on 50kHz, maybe you could mix
> >it down to a lower frequency, say 1kHz, then do the processing, in the same
> >way that a radio mixes the RF down to an IF where the gain/filtering stages
> >are easier. As long as the "IF" is high enough that any side bands are
> >preserved you should be OK.
>
> This is an area in which I know enough to be dangerous, so no warranty on
> the comments ...
>
> If the signal is band limited, can't you simply subsample at a divisor of
> the IF rate, thereby doing the mixing and A/D conversion in one step.


It's possible, but you'll need [1] a good sample & hold, with enought
input BW (at least HF+IF) and a short and stable window width (stable
to much better than 1/(2*HF) ), and a good analog band-pass filter
centered at HF and with an atenuation better than the S/N that you could
allow at HF+-SF.

    Daniel.


Notes:
[1] BW = Bandwidth, HF = the "Carrier" frequency, in this example 50KHz,
IF = the "intermediate" frequency, can be the same as the side-band's
frequency plus some headroom, SF = sampling frequency.

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