whit@milton.u.washington.edu (John Whitmore) (11/19/90)
In article <39884@ut-emx.uucp> tkelman@emx.utexas.edu (Todd Kelman) writes: >Problem: I have a signal with frequency components from 20Hz - 3000Hz, that >I need to shift to fit in a range from 300-3400Hz. While you could shift the whole signal (as you described) in one go, it might be just as easy to shift it in pieces; filter out the 20 Hz-300 Hz and upshift it with a 3400 Hz local oscillator; the lower sideband (3100 Hz to 3380 Hz) can simply be added to the original signal. A perhaps more straightforward approach (to make the filters less tricky) might be to mix up with a 450 kHz LO, filter the unwanted sideband with a standard IF crystal filter (cheap mass produced ones for AM radio are available from various places), then mix the whole thing back down with a 446 kHz LO. Mixers can be very simple for this sort of thing (because the spurious double-LO frequency is pretty darned far from the range of interest). You'd be using the simplest of mixers (maybe even just a diode), so the fact that there's two wouldn't be much of a problem. John Whitmore