MIKE ROSS wrote in a message to Jasen Betts:

 MR> "Jasen Betts" bravely wrote to "Roy J.
Tellason" (11 Jan 04 
 MR> 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.

 MR> I think with logic circuits that can switch at GHz speeds it is an
 MR> easy matter to directly synthesize the actual carrier frequency for
 MR> direct conversion instead of heterodyning. 

Easy?  Yeah,  maybe if you're both a bleeding-edge digital designer _and_
experienced with and equipped to deal with RF design as well.  I don't see
anybody around here that fits that description...  :-)

I'm talking here about hobby-type stuff,  the sort of thing that it might
be remotely possible to *build*.  Heck,  that kind of gear isn't something
I'd even think about tackling,  if I absolutely had to have one for some
reason then I supposed I'd have to buy one!

 MR> Varactor diodes are unnecessary with this sort of scenario. This 
 MR> type of circuit behaves like a super fast digital filter instead 
 MR> of the usual tuner/oscillator/mixer approach. I saw this idea once 
 MR> in a logic handbook, where they showed how to make digital 
 MR> filters. The only trouble was it would only work for a few 10's of 
 MR> Khz but I can see where using GHz logic it would work even at UHF! 

Yeah,  probably.

But that doesn't do _me_ any good.  

---