Bob Dobbs wrote:
joe wrote:
Bob Dobbs wrote:
SC Dxing wrote:
Operator Bob,

I guess the questions I am asking. Does having separate USB/LSB switch
make a difference when listening to sideband signals?
Sure does!

Will having
separate USB/LSB along with synch detection make that much of a
difference trying to listen to weak AM signals both on AM and
shortwave?
If your experience matches mine you might have some difficulty getting the
sync-det to lock on the variable intensity SSB signals but on AM it will make a
difference depending on which side of the signal is being encroached.
I guess you mean AMBCB and SW in which case the operation is the same.

A sync detector is not designed to be used on an SSB signal. It is no
wonder that you have some difficulty.

Was just answering the question from the person I responded to,
I know full well how it works but I can see where my answer might be
misconstrued and confusing.

A sync detector works by locking onto the carrier of the signal. In SSB
there is no carrier.

When there is audio (modulation) present, there most certainly is a carrier,
otherwise it's suppressed and therefore problematic for sync-det.

In SSB there is no carrier at all, you seem to be saying that there is.

The common AM mode (DSB modulation with carrier) has a carrier,
modulated or not. SSB is nothing with no modulation and one sideband
only when there is modulation.


If someone were to modulate their SSB signal with anything close to a steady
tone the sync-det could possibly get a lock.

True as a steady tone is just like a carrier. Because it may look like
one does not mean it is.

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.

Of course not, it would make no sense.

However, if your radio has USB/LSB selectable sync modes, then the only
difference between that and SSB is the injected carrier to the product
detector is either phase locked, or not.

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.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or
understanding, as in he has a sub-wikipedia understanding of the situation.
i.e possessing less facts or information than can be found in the Wikipedia.