"Jasen Betts" bravely wrote to "Roy J. Tellason" (11
Jan 04  13:54:10)
 --- on the heady topic of "bag of chips"

 RJT> I suspect that this is where things start getting less into
 RJT> ordinary "tech" stuff and more into that "black
art" portion of
 RJT> design that I've been avoiding all these years.  :-

 JB> it'd be real hard to design an RF circuit that'd work from 100Khz all
 JB> the way up to 1Ghz... ISTM most devices get at most factor of 3
 JB> betweens ends of each tunable band, that may be a limitation of tuning
 JB> devices or it may also involve limitations in the filters employed in
 JB> the receiver.

I think with logic circuits that can switch at GHz speeds it is an easy
matter to directly synthesize the actual carrier frequency for direct
conversion instead of heterodyning. Varactor diodes are unnecessary with
this sort of scenario. This type of circuit behaves like a super fast
digital filter instead of the usual tuner/oscillator/mixer approach. I
saw this idea once in a logic handbook, where they showed how to make
digital filters. The only trouble was it would only work for a few 10's
of Khz but I can see where using GHz logic it would work even at UHF!

 Mike
 ****

... Which sparks some mnemonic circuitry.
--- Blue Wave/DOS v2.30