Geoffrey S. Mendelson wrote:
Bob Dobbs wrote:
When there is audio (modulation) present, there most certainly is a carrier,
otherwise it's suppressed and therefore problematic for sync-det.
If someone were to modulate their SSB signal with anything close to a steady
tone the sync-det could possibly get a lock.
note* - there isn't a way to engage the sync-det in either of the SSB modes on
the only radio I have that has it.


No. Most ham rigs made since 1980 don't actually produce an AM signal, they
produce a double sideband reduced carrier signal. Ham rigs produce a signal
by taking an AM signal and running it through a filter to remove
the carrier and the other sideband.

Their "AM" mode signal is made by recombining the the upper and lower sideband
signals, with only a tiny residual carrier.

Most AM receivers can receive this signal, but there is no carrier to lock
on to, so I doubt that a sync detector can lock onto them.

Geoff.




Actually, though transceivers vary, most do produce a real AM
signal. (The old Drake C-lines produced DX-60-like "controlled
carrier" screen modulation, which _is_ AM though the average carrier
level goes up and down with modulation. A few older Collins and
other SSB transceivers just insert carrier on an SSB signal,
producing a rather distorted poor excuse for an AM signal called
"AME" or "AM equivalent." But they're rare. Most transceivers today
generate real AM.)

They do this by either bypassing the SSB filter or replacing it with
a wider one, and then unbalancing the balanced modulator by adding
an adjustable DC component to its audio input port. When the audio
and DC levels are balanced correctly, this can produce perfect
amplitude modulation. (Some amateurs, of course, don't adjust things
correctly, which can cause distortion and other problems.)

Before all my equipment was stolen with the complicity of the FBI, I
had a modified Kenwood TS440S which used this scheme. The stock 440
produced pretty good AM, but I wanted better. The modifications
included bypassing the low IF filters entirely in the AM transmit
mode, and reconfiguring the audio chain for better waveform
fidelity. It produced 25 watts of AM with better quality than many
broadcast stations.


With all good wishes,


Kevin, WB4AIO.
--
http://kevinalfredstrom.com/