"Tim Wescott" wrote in message
...
Does Mouser still sell them?

Somewhat surprisingly, yes, they do. (Although of the many hundreds they have
listed in their system, it's only something like a couple dozen they actually
have stock of.)

The point of the IF transformer was twofold: to provide selectivity, and
to give a good impedance match between stages. I think there must have
been a standard receiver design, as there just seemed to be one choice
for each coil -- this in spite of the fact that as soon as you start
juggling feedback and/or standing currents, you change the impedances,
and therefor the required transformer.

Agreed -- and I additionally suspect that many people who made those receivers
didn't necessarily understand the design itself that well. I.e., if it
basically worked and wasn't clearly deaf, it became a product -- few if any
AM/FM receivers found on the shelves of, e.g., Sears listed things like their
sensitivity, adjacent channel rejection, etc. (From the flip side, though, I
suppose that's one of the things the FCC did: Coordinated frequencies and
power levels such that just about any radio would work "reasonably" well; it's
a very different market from, say, amateur radio where there's little or no
coordination of these parameters and the customer may very well want to try
to listen to some QRP station on 14.15MHz while there's some big gun blasting
away on 14.14MHz...)

I think if I were going to design a broadcast-band receiver, I wouldn't
just re-do the old schematic from 1960 -- I'd start from a clean sheet of
paper, and see where I could go from there.

I agree insofar as the actual design goes, but I like to study these older
technologies because I think it's all too easy to not realize just how good
the performance of some of the old designs were (for your new design you'd
like to start with specs that are hopefully some improvement or at least as
good as the old ones...), and also because a lot of the same *techniques* can
be applied to modern designs just as well as they could to old ones (e.g.,
varactor tuning is just an evolution of mechanical tuning, neutralization
applies just as much to BJTs as it does to tubes, etc.).

(Actually, I think the first
thing that'd go onto that clean sheet of paper would be an ADC -- I'm a
luddite in a lot of ways, but not in how I'd like to see a receiver laid
out).

That works, but consider that if you digitize the entire broadcast FM band at
once (all 20MHz of it), compared to a $20 superhet receiver:

-- Your weak signal sensitivity may be worse, since your dynamic range is
spread across the entire band rather than just what'll fit through an IF
filter.
-- You'll likely suck rather more power from a battery.
-- It'll probably cost more.
-- For the channels you can receive well, you'll have infinitely more options
on being able to reduce noise, change your audio bandwidth, recovery stereo,
decode RDS, an so on. :-)

---Joel