From:  https://groups.google.com/forum/#!msg/rec.radio.amateur.misc/sL-wKB5kayc/a2tOMlERx6IJ

Andreas Zilker 	
2/26/92
Hi Netters,

this is a summary to my question "AM sync. demodulators --- How ?"
posted one month ago to <rec.radio.amateur.misc> and <rec.radio.shortwave>.

Many thanks for the input.    --- Andreas
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           +-------------------------------------------+
           |                                           |
           |    SUMMARY: AM-Synchronous Demodulation   |
           |     Principles, References, Circuits...   |
           |           92-02-23 19:38  AZi             |
           +-------------------------------------------+


From: "Glenn E. Thobe" <th...@getunx.info.com>

Simplistically speaking, a synchronous detector consists of a PLL to
track the carrier and a coherent demodulator.  The latter mixes a
synthetic carrier with the IF signal and passes the result through
a low pass filter to get AM.  

My Grundig Sattelit 500 uses a CX857 IC chip.
[...]

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From: hay...@cats.UCSC.EDU (Jim Haynes)

Well, you could go to the library... In particular, there's an interesting
article in Proceedings of the I.R.E. circa 1960 by John Costas titled
"Poisson, Shannon, and the Radio Amateur" (approximately).
[...]

AZi> Well, to make things a bit more precise:
AZi>    J.P. Costas
AZi>    Synchronous Communication
AZi>    Proc. I.R.E. 12 (1956)
AZi>
AZi>    J.P. Costas
AZi>    Poisson, Shannon, and the Radio Amateur
AZi>    Proc. I.R.E. 12 (1959)

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From: "Thomas L. Carney" <tlc2...@uxa.cso.uiuc.edu>

[...]
  Dave Hershberger, W9GR
  Build a Synchronous Detector for AM Radio
  Popular Electronics April, 1982
  pp 61,66-71
[...]

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From: OR...@ciit85.ciit.nrc.ca <Peter Orban>

[...]
The Signetics NE 561 chip contains all the necessary components, the
VCO, the phase comparator, and an extra double balanced mixer to do
the AM demodulation. The '78 Signetics linear catalog has
applications for the circuit. This chip is out of production though,
so you have to make up the circuit from different components, e.g.
from an NE 564 PLL circuit and an MC 1496 mixer. An exellent book on
PLLs is by R.E. Best: PLLs, Theory, Design and Applications. It has
a sample coherent AM receiver with Exar integrated circuits (XR
2206, XR 2208).

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From: Mike Gruber <arrlhq!mgr...@uhasun.hartford.edu>

I have done quite a bit of research on Sync Detectors in the last
few months. I hope to have an article published in QEX on this subject
sometime this year. Hopefully, this will answer all or most of your
questions in greater detail than I can now, but:

1) A simple sync detector can be made from a phase locked loop chip.
   AM stereo chips can be used as sync detectors if properly configured.

2) This type of detector can be of a single chip design. However, much
   of sync detector's advantage over an envelope detector is not utilized
   in this case.

3) A sync detector can, in many cases, be put to better use by employing
   phasing techniques to reject either one of the two AM sidebands at will.
   Interference can be rejected and selective fading can be further reduced.
   The Sony ICF-2010 has this feature. The Drake R8 does not - I am not
   sure about any of the others.

4) The QEX article will hopefully include a schematic to homebrew a sync
   detector using a Sony AM Stereo IC Chip. It will also have a fairly
   extensive bibliography of other articles and construction articles.

  Well, hope I have answered most of your questions for now. The sync
detector is great for short wave broadcast listening and really worth
the effort to build one. I have had an ICF-2010 for almost two years
and still marvel at the improvement a sync detector can make.

                                                    73,
                                              Mike Gruber, WA1SVF
                                              ARRL Lab

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From: dmt...@ptsfa.PacBell.COM (Dave Turner)

[...]
I have been told that Electronics and Wireless World
had a paper on:

  AM Synchronous Demodulator
  Trevor Brook
  E&WW
  September 1989, Vol 95, Number 1643

[...]
Plessey makes (or at least made) a Multimode Detector chip
that can be used as a synchronous detector. Their part no. is SL624C,
but I've only read about them in their application handbooks.
[...]

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A few comments on articles I've been able to look at
(thanks to Mike Gruber, Tom Carney & Dave Turner...)

> Trevor Brook
> AM Synchronous Demodulator
> Electronics & Wireless World
> September 1989, Vol 95, Number 1643
This seems to be the most versatile and up-to-date article for a
homebrew project (till Mike Gruber's article arrives :-)). It
consists of an add-on board with analog filters and a discrete PLL
connectable to the 455kHz output of a SW receiver.

> Dave Hershberger, W9GR
> Build a Synchronous Detector for AM Radio
> Popular Electronics April, 1982
> pp 61,66-71
Add-on to SW receiver, comparable to article above but more exotic
components (gain control with LED-LDR pair).

> J.L. Lindsley Hood
> Synchrodyne AM Receiver
> Electronics & Wireless World  Jan - March 86
Complete design of a AM direct conversion (synchrodyne) receiver for
LW & MW, discrete PLL and MC 1496 dual balanced mixer

> Pat Hawker, G3VA
> Synchronous Detection in Radio Reception
> Wireless World  Sept 72, Nov 72
Historical development of sync. detection (many references), some simple
experiments with TTL chips

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Finally a few, more or less subjective impressions from comparing
- a HAM transceiver (ICOM IC 735, Antenna: 5 m (= 15 feet :-)) of
  wire dangling out of the window, unmatched)
 - a portable SW radio with sync. demodulator (SONY ICF 2010 (=2001),
  using the built-in telescopic antenna)

Station:   "Deutsche Welle"
Frequency: 6075, 9545, 11965, 15410, 17860
Time (UTC): 1:00, 4:00, 7:00, 22:00, 20:00

In plain AM mode both radios show severe distortions from
selective carrier fading. IM-distortions and/or blocking are no
problem because of primitive antenna & resulting low signal levels.

Switching the SONY to SYNC makes the audio sound much smoother and
reduces interference from stations nearby (no change in IF bandwitdth !).

The ICOM can be pushed significantly for speech reception by
switching to SSB (2.4 kHz Filter) and using passband tuning.
Sometimes de-tuning from the carrier and "notching" out the beat also
improves the reception quality for speech to even better results than
the SONY (*not* music !).

Possible conclusion: If you only want to listen to news and speech
broadcast, the HAM transceiver with some *fine* tuning might
deliver better results. The SW receiver with sync. demodulator is by
far more handy and easier to use (one push-button :-)).


