In message , gareth
writes
"Ian Jackson" wrote in message
...

Ian, with your greater experience than mine, it is the concept of
single-signal reception in which I am interested.

Have you any clues about that, please?

The only clue I can offer is that 'single-signal reception' is vague - but
presumably self-explanatory, ie the filtering is very narrow, enabling you
to receive only one signal (unless you have more than one on or very close
to the same frequency). It's a term that I recall being around when I were
a lad, but I can't say I've heard it much since. I guess it's been
replaced by more scientific descriptions of how good the filtering is.

Thank you, Ian. I have a vague memory of something in BadCon from about 40
years ago which
related to setting up for single signal reception, which involved no further
adjustments to phasing or BFO once it had been set. I am fairly sure, hence
my
enquiry that it involved phasing out the audio image as well as involving
the peaking
that comes from a single series resonant crystal.

Hence my assumption that the BFO frequency must lie half way between the
peak and the notch.

I've no experience of such things. The HRO I had in my possession 20 years
ago did not posses
the crystal filter, but in an effort to speed up development of my RX
project, it seemed to me
that a single crystal filter would be an easier starting point than a ladder
filter.

You're not confusing SSB generation (and reception) by the 'phasing
method', are you? That requires something quite different from the
action of the elementary single crystal filter we're talking about.

While a single crystal filter can provide a fair amount of selectivity
(combined, if you choose to use it, useful suck-blow or blow-suck
frequency response), it is not really suitable for 'serious' SSB
filtering. Its frequency selectivity characteristics don't really use
clever phasing out of the audio image. The passband peak is really too
sharp for either the generation or reception of good quality SSB, and
you usually need a 'proper' flat-topped filter, a 'proper' SSB phasing
TX or RX (which also does exist in a direct-conversion form) - or if
you're really clever, a 'third method' phasing TX (or, I suppose, RX).
That said, I'm sure that 'KISS' transmitters and receivers have been
made using a single-crystal filter - albeit having a somewhat limited
performance.
--
Ian