Avery Fineman wrote:
Can one get separated sidebands on AM DSB with a DC receiver?
Absolutely!

That's good to know. At present I'm going to quit performing these
"intellectual experiments" and start building something, and while I'm after
C-QUAM AM stereo (rather than upper/lower sideband stereo), it's good to
know what else _could_ be received.

BTW, if anyone wants to see the block diagram of what I'm planning to do,
see he http://oregonstate.edu/~kolstadj/RadioProj.gif . Keep in mind
it's designed primarily for simplicity, not for phoenomenally good noise
performance, sensitivity, selectivity, etc.

(I'd be particularly interested in comments on how to implement the low pass
filters -- it seems one would want phase preserving filters such as Bessels
or a cascade of a Chebyshev followed by an all-pass phase restoration
filter.)

Nooo...AM "came about" with absurdly SIMPLE components first,
not even using any vacuum tubes!

Wow... I realize now there's a large gap in my knowledge of the history of
the progression of radio inbetween "spark gap transmitter" and "diode-based
envelope detector!" I have read of coherers before in Lee's book, "Design
of CMOS Radio-Frequency Integrated Circuits" where he claims that nobody
ever really did figure out _how_ they worked -- interest wanted as better
detectors were available before they were around long enough for someone to
do so.

You have a phoenomenal memory, Len... I wish I could recall the details as
well as you have!

Long-distance telephony was the birthplace of SSB. Frequency
multiplexing was the only practical way to cram four telephone
circuits on a single pair of wires running many miles way back when.

If you tell me people were already using IQ modulation back then as well
I'll be quite impressed...

If you want synchronous detection of AM DSB, then you concentrate
on getting a carrier reinsertion oscillator locked to the received
carrier. Primary object is to get that lock.

I'm planning to write a (software) quadrature detector, and once that works,
start worrying about obtaining phase lock so that stereo can be decoded.

Can you get a synchronous detection of AM SSB? Difficult unless
the transmitter at the other end has sloppy carrier suppression.

Without a carrier of some pilot tone (as a reference) it seems as though
it's difficult to even claim there could be such a thing as 'synchronous
detection.'

DC receivers (also called "Zero-IF") came into popularity in Europe
THREE decades ago. RSGB's Radio Communication magazines of
1973 were showing stuff in Pat Hawker's monthly column. I got
interested in the Mike Gingell polyphase R-C network by seeing it
first in there.

I took a quick look at the Gingell networks and they seem quite novel --
even made their way into a Real Commerical Product (a Maxim IC).
(Interestingly enough, Dr. Gabor Temes -- who spent a long time designing
telephone network filters before going into academia, where he is now, all
of about 500' away from me here -- says there is still some black magic
involved in making them work. :-) )

Thanks for all the advice Len... I'd be offering to take you to dinner by
now if you were halfway local!

---Joel