"Scott Dorsey" wrote in message
...
Dave J. wrote:

Just out of interest, how long has diversity encoding been
around? I
thought of it as relatively modern, and I've only read
about it from the
POV of digital signals. Is there anywhere anyone'd
recommend for a bit of
research? Something semi chronological would be nice.

Back to the thirties at least. Earlier diversity systems
were comparatively
crude, though, normally just looking at two antenna
systems separated in
space or in polarization and picking the one with the
higher AGC voltage.
This can give a remarkable improvement in dealing with
ionospheric fading,
though. Was standard practice for remote shortwave links
on broadcast
networks.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Space diversity is indeed that old but there were some
fairly sophisticated methods such as the Bell Labs MUSA
Multiple Unit Steerable Antenna which could be varied in
vertical angle electrically. RCA was using triple space
diversity receiving systems at the Riverhead N.Y. receiving
station in the 1930s. I suspect one could find a lot of
literature in the old Jornal of the IRE and probably also
the Bell Labs Technical Journal and RCA Review although I
don't have specific citations.
Around the 1950s Leonard Kahn and others worked out
means of combining the sidbands of a conventional AM or
double sideband suppressed carrier signal using a
synchronous detector. In effect this was a sort of frequency
diversity. It also reduced distortion due to selective
fading since it regenerated the carrier locally.

--
Richard Knoppow
Los Angeles
WB6KBL

On Sat, 7 Nov 2009, Richard Knoppow wrote:

Around the 1950s Leonard Kahn and others worked out
means of combining the sidbands of a conventional AM or
double sideband suppressed carrier signal using a
synchronous detector. In effect this was a sort of frequency
diversity. It also reduced distortion due to selective
fading since it regenerated the carrier locally.

Wasn't it Webb at GE that was doing the work on DSB? That's the name on
the synchronous detector article in "CQ" in the late fifties, and that was
either preceeded or followed by an article about DSBsc in general.

And John Costas of course came up with the Costas Loop for receiving AM,
and I see he was at GE in the fifties when he came up with the Loop.


Michael VE2BVW

"Michael Black" wrote in message
mple.net...
On Sat, 7 Nov 2009, Richard Knoppow wrote:

Around the 1950s Leonard Kahn and others worked out
means of combining the sidbands of a conventional AM or
double sideband suppressed carrier signal using a
synchronous detector. In effect this was a sort of
frequency
diversity. It also reduced distortion due to selective
fading since it regenerated the carrier locally.

Wasn't it Webb at GE that was doing the work on DSB?
That's the name on the synchronous detector article in
"CQ" in the late fifties, and that was either preceeded or
followed by an article about DSBsc in general.

And John Costas of course came up with the Costas Loop for
receiving AM,
and I see he was at GE in the fifties when he came up with
the Loop.


Michael VE2BVW

You may be right. GE did a lot of early work on SSB and
DSB. GE had a very fine research department until John
Welsch killed it.



-- Richard Knoppow
Los Angeles
WB6KBL