On Wed, 20 Jan 2016, gareth wrote:

"Michael Black" wrote in message
news:alpine.LNX.2.02.1601201350360.31828@darkstar. example.org...
The one advantage of AM is that it may be easier to build a low power AM
transmitter than an SSB transmitter, though now that everyone wants a VFO,
it may not.

Sorry, don't follow that logic!

In the old days, you'd run a VFO at 80 or 40metres, and multiply up, all
the HF bands being 3.5MHz. But that multiplied the drift of the VFO, and
for each higher band, the segment of the dial that covered that band got
smaller the higher up you got. And with the WARC bands, you need other
frequencies.

If multiplying the VFO is no longer so great, then heterodyning the VFO is
the way to go, and once you have that, adding a balanced modulator and a
filter to get SSB is only incrementally more difficult.



On the other hand, that's when DSB with a suppressed carrier stepped in.

Actually, most of those who TX DSBSC do NOT have the appropriate
means of receiving it, for, unless you cheat by chopping off one of the
sidebands
(not to be confused with sidetone, STC) you need a injection oscillator
tightly phase locked to the original carrier, for a 90 degrees phase error
will result
in a received signal strength of zero!

I dont' see that. Receivers are so much better now, it may be finicky
about tuning but you should be able to knock the unwanted sideband off the
side of the filter.

That was exactly how it was done in the fifties and sixties when DSBsc got
a lot of promition, often by the modification of an AM transmitter so the
output stage became a high level balanced modulator. Most people would
never know you were sending DSBsc unless you told them, since SSB
receivers had become increasingly the norm, so they thought it was just
another SSB signal.

Synchronous detection was described in "CQ" about 1957, I think it wsa
someone from GE who wrote the article, and while some built them through
the years, they were never common. It wasn't until the Sony 2010 came
along in the eighties that synchronous detection became a 'big thing".

Long before phase comes into play, if you don't have the carrier in the
right place between sidebands, you really can't understand what's going
on, since if the BFO is in the wrong place, each sideband is translated to
a different spot in audio. So they clash with each other. That's why one
can live with a mistuned BFO on SSB, it simply sounds low or high pitched.

Michael