"Frank Dresser" ) writes:
"Kachina 78" wrote in message
...
I fired up the SW-4A this morning, and I'm monitoring Radio Australia, at
0915
UTC, on 9590khz. I've got it hooked up to the Antenna Supermarket
Eavesdropper
SWL Sloper. I'm the original owner, and no I'm sorry, but it's not for
sale. I
purchased it in 1975, from Trigger Amateur Electronics, in River Forest,
Illinois, a suburb of Chicago. I've never had to change a tube, or a
filter
capacitor, and the crystal controlled direct frequency dialing is still
dead-on
accurate.I believe this was the first shortwave receiver to offer the
crystal
controlled direct frequency dialing.

The radio's local oscillator is only half crystal controlled. The bands are
determined by which crystal is switched in and the actual local oscillator
frequency is determined by a permeability tuned oscillator. Similiar PTOs
(without crystals) have been used in car radios for decades.

Other Drake radios going back to the late 50s have used pretty much the same
setup.

I was going to comment on that line, but then I suddenly couldn't remember
the mixing scheme of the receiver. I seem to recall that it used premixing,
ie the variable oscillator is mixed with the crystal oscillator to provide
the signal needed for the actual signal mixer. I know that was done in
some of the Drakes, getting away from the scheme used in their earlier
receivers where they had in effect a receiver that tuned a fixed 500KHz
range, and then a crystal controlled converter ahead of it to get the various
bands. The premixing has the advantage that another mixer isn't in the signal
chain to overload, though I think it's up in the air how much else it might
save since one has to filter that output of the premixer well to avoid spurs.

But since I couldn't remember if the SW4 used premixing or not, I wasn't sure
if that was what the poster was talking about, though his term
"crystal controlled direct frequency dialing" is rather ambiguous.

And of course, Drake wasn't the first to use the scheme of a tuneable receiver
with a crystal controlled converter ahead of it. The date from the late
forties or early fifties in some commercial receivers, with Collins likely
being the first to issue such receivers.

Michael