Hey OM:

I beg to differ there are frequencies below ZERO hertz you are just
not aware of them.

Simply put the frequencies add and subtract, towit below ZERO. When
mixing frequencies they add and subtract there is no doubt about it.
So it must be for all cases.

If I take 2 frequencies and mix them I get the Sum and the Difference
of those frequencies plus the original frequencies. NO?

Tell me this is wrong?

Because that is what you have just told me?

73 OM
de n8zu


There are no frequencies below zero. *When you are using only a single
mixer, both sidebands will produce frequencies above zero. *And there
will be no suppression of the "unwanted" sideband.
(the synchronous AM detector is a dual-sideband detector)

the synchronous AM detector is a dual-sideband detector

Some are, some aren't.

My Sony ICF-SW7600GR lets you select sidebands while in Synchro mode,
as does my homebrew DSP RX.

Selecting sideband in AM mode is most useful.

..................... Zim

raypsi wrote:
Hey OM:

I beg to differ there are frequencies below ZERO hertz you are just
not aware of them.

Because the "frequencies below zero" will come out of a single mixer
as equal frequencies above zero. Only the phase is different. So
when you use two mixers and quadrature signals, it is possible to
select a sideband. But with a single mixer and synchronous detection,
this is not possible.

Graeme Zimmer wrote:
the synchronous AM detector is a dual-sideband detector

Some are, some aren't.

My Sony ICF-SW7600GR lets you select sidebands while in Synchro mode,
as does my homebrew DSP RX.

Selecting sideband in AM mode is most useful.

Ok it can be done but not with the circuit described in this thread
and on the referenced site.

You need two mixers and 90deg phase shifts to do it.

Hey OM:

The ole TV systems that used NTSC type signals, the video is Vestigial
Sideband.
So if what you say is TRUE then I never ever would have seen anything
on an NTSC tv but the low frequencies that are present in NTSC signal
part of the lower sideband.
All the now defunked, latest NTSC tv's used synchro' detection on the
Vistigial Sidband video.

I made a living repairing those old NTSC tv's that had synchro'
detection of the Vestigial Sideband video.

73 OM
de n8zu





On Jul 19, 4:00 am, Rob wrote:
But with a single mixer and synchronous detection,
this is not possible.

raypsi wrote:
Hey OM:

The ole TV systems that used NTSC type signals, the video is Vestigial
Sideband.
So if what you say is TRUE then I never ever would have seen anything
on an NTSC tv but the low frequencies that are present in NTSC signal
part of the lower sideband.
All the now defunked, latest NTSC tv's used synchro' detection on the
Vistigial Sidband video.

In those TVs, the selection of the sideband is not done by the detector
but by an IF filter that passes only the frequencies of interest.

I did not say the synchronous detector cannot demodulate a single sideband,
I said it cannot select the sideband. So if you pass both sidebands
to the detector, it will demodulate both of them. Unless you use a
quadrature approach.

(and it cannot demodulate SSB because there is no carrier. in TV VSB
there is a carrier present that can be used to control the synchronous
detector)