"Michael Black" wrote in message
...
"Tom Holden" ) writes:
I've been tinkering with an add-on project for a RS DX-394 receiver
based on
Stirling Olberg's (W1SNN) "Reciprocating Detector" design(s) published
in
Ham Radio in 1972 to 1978. Has anybody had any experience with this
design.
Is it fundamentally any different from a synchronous detector such as
the
NE602 design by OH2GF in the current ARRL Handbook?

Tom


I've read those articles, and specifically reread them last year, and
for the life of me I really not sure how it's supposed to work. The way
he explains it, it sure seems like there is some specific little bit that
is happening in there. If I'm remembering, he claims it works for FM
too, and I don't see how it could demodulate FM if it was just a
synchronous
detector.

I got started on this from a schematic sent to me by a Czech ham/swl who
also has a DX-394. He derived his schematic from a translation of one or
more of the articles. I'm not sure he understands it because he can't
explain well in English and my is Czech non-existent.

The design uses discrete transistors, not many parts and is cheap. I have a
breadboard version working, after a fashion. It does lock when within 200 Hz
or so and sounds pretty good. I was initially puzzled by an apparent null or
minimum audio in the centre of lock on DSB signals. It is fundamentally a
product detector with a synchronised BFO, so the difference products of the
two sidebands are anti-phase. I would assume that all synchronous demods use
product detectors and would behave similarly in that regard. It definitely
does better than the DX-394's envelope detector on DSB with selective fading
and fades out very gracefully and cleanly on weak signals, although lock may
be lost before signal is completely unreadable. At the moment my LO is very
unstable with temperature.

He references some professional article or paper as the source of
scheme, and one would hope if someone could get ahold of that, what
is going on might be clearer.

I found most of Olberg's HR articles at the Metro Toronto Reference Library
but did not look for the IEEE Comm paper by Badessa, who I think was a
colleague. I don't know if synchronous detectors were in vogue in 1971 and
were known as such. Did Badessa and Olberg coin the name "Reciprocating
Detector" because it was truly pioneeering work uninfluenced by the name
that eventually dominated or were they trying to get a patent by tinkering
with the fundamentals and giving it a different name. The only obvious thing
I can see that may be different is the 500 hz filter between the local
oscillator and the product detector (that's the part I haven't got working
yet - a straight wire is the minimum requirement).

When I did some searches on the internet last year, I sure didn't find
anything more about it. A handful of Usenet posts, none of which added
to the scheme or even an understanding of it.

Hence my posting. HR accepted 4 or 5 articles on the RD or receivers using
the RD by Olberg and there appears to have been considerable response. I
daresay that, if this Usenet group had been around then, there would have
been some hot and heavy debates about the Reciprocating Detector!


Michael VE2BVW