-=> Roy J. Tellason said to Jasen Betts
 -=> about "BAG OF CHIPS" on 01-12-04  20:17.....

 RJT> Yes,  in contrast to one site in oz that's offering all sorts of
 RJT> tutorial material but where he didn't quite spell it right.    I
 RJT> understand it,  but the thing is,  even with double conversion,  you
 RJT> still want some RF gain in front of the first mixer stage,  and some

I would want some RF gain, but a lot of units don't provide any.

If I can remember the Yasue FRG-7, or possibly I'm thinking
of another receiver from that era, the signal went through a
fixed 30MHz low pass filter then to a (diode?) mixer stage where
it was heterodyned up to about 70MHz. Most of the gain was in the
70MHz IF strip, IIRC.

The way they generated the local oscillator signal was quite
ingenious, but quite beyond my powers to remember or work it out
now -- I wish I'd taken a copy of the circuit.

 RJT> selectivity in there,  and that's where I get hung up.  How the heck do
 RJT> they deal with that many frequencies?  I guess you can switch coils in
 RJT> and out with diode switching or whatever,  but that sure hits me as
 RJT> getting awfully complicated.  I guess one of these days I'll have to

It's a lot simpler than mechanical switching.

 RJT> get a hold of a scanner schematic diagram and see how they do it.

Yeah 

From Greg Mayman, in beautiful Adelaide, South Australia
   "Queen City of The South"    34:55 S  138:36 E

... Bionic Air Stewardess Weds Automatic Pilot - headline(?)
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