On Fri, 28 Oct 2005 13:45:17 -0700, Richard Clark
wrote:

On Fri, 28 Oct 2005 20:12:48 GMT, Owen Duffy wrote:

Didn't Don Stoner describe a synchronous detector way back. I think I
remember reading an article in the mid sixties in "The Sideband
Handbook" or similar.

I was about 15 then, so a detector that had something like 17 bottles
in it seemed overkill when I was copying CW and SSB on an AM receiver
(ie diode detector) with BFO.

The appeal being an all-mode detector (including DSBSC), but
synchrounous detectors didn't seem to catch on in comms receivers,
well not until DSP detection... well I don't recall coming across them
anyway.

Hi Owen,

17 bottles indeed. That seems to strike a resonant chord in the
ganglia because my construction was on a utility box of about 3" x 9"
x 15" (not counting power supply requirements). We were working from
a printed article certainly; and to confirm your recollection, there
was a list of modes that could be detected that was long.

My perception of the resurgence of interest in synchronous detection
(it seems to have many names) is that a considerable body of knowledge
evaporated in the 70s and 80s to leave only fragments of what this
detector was useful at.

I think the appeal of it in the early days of suppressed carrier
exploitation by amateurs lay in its application to DSBSC demodulation.

It probably fell by the wayside when filter method SSB transceivers
became lower in cost.

Here is an interesting hypothetical. Australian amateurs at the
unrestricted licence grade are subject to the following power
restrictions:

16 Transmitter output power
(1) Subject to section 15, the licensee must not operate an amateur
unrestricted station, using a transmitter output power of more than
400 watts pX, if the emission mode of the station includes:
(a) C3F; or
(b) J3E; or
(c) R3E.
(2) The licensee must not operate an amateur unrestricted station,
with an emission mode not mentioned in subsection (1), using a
transmitter output power of more than 120 watts pY.

Since the emission mode for DSBSC is not one of those mentioned in
16(1), then the power limit is 120W pY. If the pX/pY (PEP/Average)
power ratio for radiotelephony is somewhere around 12dB to 15dB, that
suggests that (using a worst case of 15dB) that the 120W pY DSBSC
telephony transmitter is around 3800W pX (PEP), whereas you will note
that if we use SSBSC (J3E) we are limited to 400W pX.

Doesn't make sense, does it. Did I get the maths wrong?

Owen
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