Bill Meara wrote:
This gets to the question of whether DC receivers can be used to copy
DSB and SSB:
By Goodman, W1DX, explained the problem in the 1965 edition of
"Single Sideband for the Radio
Amateur" (page 11): "Unfortunately, if both sidebands are received at
the detector where the carrier is
introduced, the carrier has to have exactly the correct phase
relationship with the sidebands if distortion is
to be avoided. Since exact phase relationship precludes even the
slightest frequency error, such a system
is workable only with very complicated receiving techniques.

In 1965 I can imagine that a Costas loop, two mixers, etc. was considered
'very complicated.' It doesn't seem all that horribly fancy by today's
standards, however. But of course it's not like I've actually _built_ such
a thing yet! :-)

However,
if only one sideband is present at
the detector, there is no need for an exact phase relationship and
there can be some frequency error
without destroying intelligibility. " Modern SSB transcievers send
only one of the sidebands to the
detector, so this distortion problem only occurs when receiving a DSB
signal on a receiver that sends both
sidebands to the detector.

It's ironic that DSB, which came about due to the ease of detection with
diode (envelope detectors) turns out to be somewhat challenging to recover
with a more sophisticated synchronous detection scheme.

Experimental Methods in RF Design points out that direct conversion
receivers have become highly popular in the past couple of decades... this
seems somewhat surprising; I would have guessed people back in the, e.g.,
'60s, would have gone to great lengths to avoid image reject filters and
long IF chains.

---Joel Kolstad