matt weber ) writes:

Actually most interesting design in a single conversion receiver I
think I ever was was in the mid 1960's Squires-Saunders built one with
a tuned RF stage with a Q muliplier on it, so they had a Q of a couple
thousand on the front end and made a killing on the gain as a result
of gain-bandwidth product. Suffices to say that with that sort of
front end selectivity, image rejection wasn't a problem. Obviously
impedance matching with the antenna was crucial to performance, but it
was undoubtedly the best single conversion HF receiver every
commercially built (and had a price tag to match).

But the Squires-Saunders had a high IF. According to one quick check,
it was a first IF tuneable from 5 to 5.5MHz, and then 1MHz. That
was part of the wave of receivers with crystal controlled first mixers, in
order to get a nice tuning range and stability. If they'd gone to
a fixed IF, then either the local oscillator would have to be switched
from band to band, or premixed with a crystal oscillator before the signal
went into the signal mixer.

Note it's an example of how down conversion can still work. For so
long, people always thought in terms of the early superhet with the
IF being down in the hundreds of KHz range, but the issue isn't that
it was converted down but that the IF was so low.

That Squires-Saunders arrive as crystal filters were still a new
thing. There's a famous 1963 article in QST by Squires or Saunders (I
forget which), discussing the philosophy and design of the receiver.
Some of the issues were keep rf amplification before the mixer to
a minimun, and use the 7360 beam deflection tube for the mixer for
a well balanced mixer. Few or no receivers used a balanced mixer
before the SS-1R, at least not affordable receivers. So the front
end Q-multiplier was brought in to deal with the simple front end.
For the rest of the decade, the basic concept, a 7360 mixer and a front
end q-multiplier, bounced around in various construction articles. But
in some ways it was just because it had been done, because there
were no front end Q-multipliers after the late sixties or early seventies.
And of course, solid state components came along, making it easier to
build a balanced mixer, be it with schottky diodes or active components,
without a bunch of bulky tubes.

All the receivers I saw that used a front end Q-multiplier used a high
IF, ie at least 2MHz and most often 9MHz.

Michael