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  #11   Report Post  
Old January 21st 04, 01:30 AM
Pete KE9OA
 
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I did try to e-mail him a copy of the schematic Dale, and it bounced back to
me as undeliverable, so I am not sure what is up with his address. Oh, I did
get the brackets. Thanks!

Pete

"Dale Parfitt" wrote in message
...

"Pete Beals" wrote in message
...
Yes most used AM stereo demodulators but those IC's might not be sold
anymore.

There must be reasonable implementations as many shortwave receivers

have
sync detectors.

I just need one to demodulate AM.


Pete
I think that "as few parts as possible" and "works good" are probably
somewhat mutually exclusive. Have you done the usual google and
altavista searches on "synchronous detector"?


Do a search under KE9OA. Pete is developing a sync detector for use with a
MW RX they are going to market. May possibly sell the sync board

separately.
In talking with Pete, and having built my own sync detector- few parts and
sync detectors that stay locked and retrieve hi fi audio do not go

together.

Dale W4OP




  #12   Report Post  
Old January 21st 04, 01:37 AM
Pete KE9OA
 
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I did do a version of that quasi-sync detector, using a Philips SA637
digital FM receiver chip. I took one of the limiter outputs and fed it back
into the LO input of the on-board mixer. The 455kHz I.F. signal was applied
to the RF input of the on-board mixer, and the audio was taken from the I.F.
output of this mixer. Not bad, although the demodulated audio level was
fairly low (about 50mV p-p). I was actually considering using that detector,
until I discovered the appnote for the Analog Devices AD607.

Pete

"Avery Fineman" wrote in message
...
In article , "Steve Nosko"
writes:

What's the essence of an AM sync detector? Extract the carrier
(filter/clip/amplify the bajeebers out of it) then product detect the
sidebands ?
--
Steve N, K,9;d, c. i My email has no u's.


Essentially, yes. There's a further step, though, and that is
locking a local mixing oscillator to the carrier frequency and
mixing that with the whole thing.

If the local mixing oscillator is in phase with the received
carrier, the mixing results in just a DC component which can
be removed easily. A carrier in-phase lock allows separate
detection of the sidebands...which could be used to
advantage such as having binaural audio modulation with AM.

That also works out well for a quasi-stereo listening with any
signal that is NOT binaurally modulated. The effect of hearing
through such a detector's audio cannot accurately be described
in words. Nearby-signal splatter can be "heard" as left or right
of the desired signal. Strange sound but does allow the mind's
own spatial filtering to sort-of blot out nearby interference.

That quasi-stereo circuit is a lot more complicated (it's usually
a typical Costas Loop with local mixing oscillator having shifts
for quadrature phasing) than the direct amplify-limit-clip-the-
bejeebers out of the carrier and mix that with whole works...as
was done in the Motorola MC1330P 8-pin DIP IC (now obsolete
but Kits&Parts as a few left).

Len Anderson
retired (from regular hours) electronic engineer person



  #13   Report Post  
Old January 21st 04, 04:59 AM
Michael Black
 
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"Pete KE9OA" ) writes:
I did do a version of that quasi-sync detector, using a Philips SA637
digital FM receiver chip. I took one of the limiter outputs and fed it back
into the LO input of the on-board mixer. The 455kHz I.F. signal was applied
to the RF input of the on-board mixer, and the audio was taken from the I.F.
output of this mixer. Not bad, although the demodulated audio level was
fairly low (about 50mV p-p). I was actually considering using that detector,
until I discovered the appnote for the Analog Devices AD607.

Pete

Of course, what we've tended to see is an all or nothing thing when it
comes to AM (with carrier) detection. A simple diode detector, or
a PLL based synchronous detector (with or without phasing for sideband
selection). In some ways, it's been driven by market not by curiosity.
In the early seventies, those Signetic 56X series of analog PLLs came along,
and simple synchronous detectors (or outright receivers) were all over
the place. Most of the people applying them in hobby circles hadn't
woke up one day and said "we need a better AM detector", it was because
all of a sudden one could get the function on a single IC. So there was
a novelty, if nothing else. Various communication type ICs came along
at that point, and people were interested in "all mode" detectors from
them. Since a double balanced mixer was common to most of such ICs
(the MC1496, various FM detectors, the LM373, various Plessey ICs
and let's not forget Ralph Burhan making a Loran C receiver out of
an IC made for simple AM/FM broadcast reception), it certainly caused
an interest in simple quasi-synchronous or outright synchronous
detectors. But again, it often seemed to be "how can we get the most
out of this IC" rather than "let's try to improve the lowly AM
detector".

So there have been very little instances of biased diode detectors
(I think one of the Drake receivers used one, and Rohde showed a
few in his Ham Radio articles a quarter century ago, and I've seen some
in Wireless World in years gone by). Whether or not that is a useful
path, there never was the level of interest in trying such things that
there was for synchronous detectors, even before the latter became
easy with ICs.

And while at one point the limiter feeding the product detector
was described as a "synchronous detector" and worthy of experimentation,
as fancier detectors became more common, they are dismissed as merely
quasi-synchronous and maybe not even worth the effort. Yet, they
are a middle ground, maybe offering some increase in performance
without the extra circuitry of a PLL based detector. I can point
to a 1955 (I think) article in QST where someone built a fancy
receiver, with two parallel IF strips. One was AM bandwidth,
the other CW bandwidth. But, there was switching at the outputs
of the IF strips, so the CW strip could feed the product detector
at the output of the voice IF, and get some level of increased performance.

Let's not forget (to the original poster) that the whole point
of going beyond a diode detector is to improve operation with weak
carriers compared to the sidebands, or for that matter with adjacent
channel interference. The synchronous comes about because one needs
the reinserted carrier right where the incoming carrier is, but
except for that need, it's all about mixing the incoming signal down
to audio, just as in sideband reception. With a strong signal, the diode
mixer works fine for that, mixing the sidebands with the carrier. But as
the carrier weakens, or an adjacent signal becomes stronger to "capture"
the detector, the simple diode detector suffers.

Long before before CQ ran the article about the synchronous detector
in 1958 or so, most or all hams who tried for better AM reception tried
other things. Like boosting the carrier of an incoming signal in
reference to the sidebands, "exalted carrier". The common, or maybe
only means, of doing this was by using a Q-Multiplier, which could
provide a narrow peak for the carrier, but a relatively sloppy
skit so it didn't attenuate the sidebands too much. Nobody talks
about this anymore, even though we've seen in this thread the comment
"simple and good" don't apply to synchronous detectors. But how
much improvement is needed, versus how much circuitry one is willing
to accept?

Michael VE2BVW

  #14   Report Post  
Old January 22nd 04, 07:09 AM
Tim Wescott
 
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I was just looking at my 2002 handbook, and there was a circuit for a
synchronous detector, in the receiver chapter. It wasn't "simple", but it
was there. It also uses NE604s (the companion chip to the '602), which
might not be available any more.

"Pete Beals" wrote in message
...
Has anyone implemented a simple sync detector that uses as few parts as
possible?

Thanks

Pete



  #15   Report Post  
Old January 23rd 04, 10:10 PM
Jake Brodsky
 
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On Wed, 21 Jan 2004 22:09:37 -0800, "Tim Wescott"
wrote:

I was just looking at my 2002 handbook, and there was a circuit for a
synchronous detector, in the receiver chapter. It wasn't "simple", but it
was there. It also uses NE604s (the companion chip to the '602), which
might not be available any more.


I constructed and tested that circuit with a Yaesu FRG-100. It works
reasonably well for ground wave signals. However, it has problems
staying locked during carrier fades. I tinkered extensively with the
phase lock gain and time constants, but to little avail.

The audio quality for local MW stations was amazingly good, however...


Jake Brodsky, AB3A
"Beware of the massive impossible!"


  #16   Report Post  
Old January 24th 04, 10:03 PM
Pete Beals
 
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I like to try the quasi sync circuit with a limiter and product detector on
AM band. Will this work with a TRF receiver?
This probably won't work with weak signals but has anyone tried this?

I'm also looking into a SDR. Basically the computer and soundcard can do
the sync using DSP.
This work be interesting for a HAM or SW receiver.

Pete

  #17   Report Post  
Old January 25th 04, 01:31 AM
J M Noeding
 
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On Sat, 24 Jan 2004 21:03:03 -0000, Pete Beals
wrote:

I like to try the quasi sync circuit with a limiter and product detector on
AM band. Will this work with a TRF receiver?
This probably won't work with weak signals but has anyone tried this?

I'm also looking into a SDR. Basically the computer and soundcard can do
the sync using DSP.
This work be interesting for a HAM or SW receiver.

Pete

It was an article in Wireless World describing AM receiver with
MC1330P8 - suppose it was sort of TRF, but I never had any success
with it, while MC1351P worked far better

-jm
http://home.online.no/~la8ak/c11.htm
--
Amount of SPAM is so large that MailWasher must delete 99% of the incoming mails
Cannot check every email manually.
Please use intelligent title for email.
Mails without titles or using just "hi" are deleted
  #18   Report Post  
Old January 25th 04, 04:28 AM
Pete Beals
 
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So all I need is a limiter and a double balanced mixer.
Well I do have a SA602. How does one make the limiter from discrete
transistors?

I wish to avoid very old/obsolete ICs.

Pete
  #19   Report Post  
Old January 25th 04, 05:59 AM
Michael Black
 
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Pete Beals ) writes:
I like to try the quasi sync circuit with a limiter and product detector on
AM band. Will this work with a TRF receiver?
This probably won't work with weak signals but has anyone tried this?

An obvious point about using it as a TRF is how much selectivity will
you be putting at the front end?

Any time you are using a mixer to convert down to audio (as with SSB
or synchronous detection of some kind for AM), you can get selectivity
at audio, since it's a frequency translation.

But, if you've just got a limiter open to the world, at the very least
it's going to limit on the strongest local signal. If you don't have
enough front end selectivity, I would think you would get relatively
little tuning ability. The strongest signal will "capture" the limiter,
and that will be the "carrier" that beats against the incoming signal
in the mixer.

When people made synchronous receivers out of the old Signetics analog
PLL ICs, at least the PLL had a lock range that provided "selectivity".
so they could run with little or no front end selectivity. Except for
mixer overload, what you got out of the mixer was limited by the audio
circuitry and your hearing, since only one frequency (plus the image)
could convert down to say 0 to 3KHz from the oscilaltor frequency. The same
applies to direct conversion CW/SSB receivers.

A quasi-synchronous receiver will work the same way, in that the output
of the mixer will be within the audio range from the "carrier" out of
the limiter. But if you have no selectivity on the input to the mixer,
enough to separate out signals, then the strongest signal into the
limiter will prevail.

Much of what I've seen about "quasi-synchronous" detectors have placed
them in the IF of a superheterodyne receiver, where the IF bandwidth
ensures that it only reacts to the wanted signal. The only TRF that
I can think of seeing was in an old Technical Topics book from the RSGB,
where there was an MC1330 (which is a quasi-synchronous detector, for
TV use, though I believe the datasheet simply calls it synchronous)
as the detector, but there was an stage of amplification (I think
an MC1350P) ahead of it, with a couple of stages of tuned circuits.
With a quasi, you do indeed need some TRF before the detector.

Michael VE2BVW

  #20   Report Post  
Old February 1st 04, 04:34 AM
Y
 
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A regenerative synchronous detector can be built using a MC1330. A secondary coil
is wound over the limiter coil and connected between the limiter output pin and
ground through an emitter resistor. A .1 mfd capacitor is connected across the
resistor. The secondary coil must be coupled and phased so that oscillation is
possible. The MC1330 will lock to the incoming carrier. Coupling the secondary
coil to the limiter coil is critical and requires experimentation. Jos! VE2 AUC

Michael Black wrote:

Pete Beals ) writes:
I like to try the quasi sync circuit with a limiter and product detector on
AM band. Will this work with a TRF receiver?
This probably won't work with weak signals but has anyone tried this?

An obvious point about using it as a TRF is how much selectivity will
you be putting at the front end?

Any time you are using a mixer to convert down to audio (as with SSB
or synchronous detection of some kind for AM), you can get selectivity
at audio, since it's a frequency translation.

But, if you've just got a limiter open to the world, at the very least
it's going to limit on the strongest local signal. If you don't have
enough front end selectivity, I would think you would get relatively
little tuning ability. The strongest signal will "capture" the limiter,
and that will be the "carrier" that beats against the incoming signal
in the mixer.

When people made synchronous receivers out of the old Signetics analog
PLL ICs, at least the PLL had a lock range that provided "selectivity".
so they could run with little or no front end selectivity. Except for
mixer overload, what you got out of the mixer was limited by the audio
circuitry and your hearing, since only one frequency (plus the image)
could convert down to say 0 to 3KHz from the oscilaltor frequency. The same
applies to direct conversion CW/SSB receivers.

A quasi-synchronous receiver will work the same way, in that the output
of the mixer will be within the audio range from the "carrier" out of
the limiter. But if you have no selectivity on the input to the mixer,
enough to separate out signals, then the strongest signal into the
limiter will prevail.

Much of what I've seen about "quasi-synchronous" detectors have placed
them in the IF of a superheterodyne receiver, where the IF bandwidth
ensures that it only reacts to the wanted signal. The only TRF that
I can think of seeing was in an old Technical Topics book from the RSGB,
where there was an MC1330 (which is a quasi-synchronous detector, for
TV use, though I believe the datasheet simply calls it synchronous)
as the detector, but there was an stage of amplification (I think
an MC1350P) ahead of it, with a couple of stages of tuned circuits.
With a quasi, you do indeed need some TRF before the detector.

Michael VE2BVW


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