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Hi-Fi AM Radio.



 
 
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  #1  
Old June 17th 04, 04:15 AM
Steven Swift
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Default Hi-Fi AM Radio.

rar+p and rats:

Okay, here's the answer directly from the Radiotron Designer's
Handbook, fourth edition, pages 1226 and 1227:

"Section 3: The Synchrodyne"
[...]
"and hence the synchrodyne is likely to be most popular for
high-quality local-station reception."

There you have it. Are we done. This is a 3-tube design for
local stations. One RF amp, 2 12au7s. Use an IC or two in the
oscillator loop and its perfect, almost a Costas Loop.

Build it; they will come.

Steve.

--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA
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  #2  
Old June 17th 04, 09:08 AM
Patrick Turner
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Steven Swift wrote:

> rar+p and rats:
>
> Okay, here's the answer directly from the Radiotron Designer's
> Handbook, fourth edition, pages 1226 and 1227:
>
> "Section 3: The Synchrodyne"
> [...]
> "and hence the synchrodyne is likely to be most popular for
> high-quality local-station reception."
>
> There you have it. Are we done.


No we are not.
Mr Noring will be submitting test results on the prototype receiver he
is nutting out.

> This is a 3-tube design for
> local stations. One RF amp, 2 12au7s. Use an IC or two in the
> oscillator loop and its perfect, almost a Costas Loop.


The synchrodyne never became commercially viable for home radios
in the old tube era, just twice as expensive to make and adjust.

But when PLLs became easy with chips there were a few synchrodynes made
but I have never seen a synchrodyne AM radio yet.

I tried to make one with RF amp and 6BE6 but it was a poor performer.

The selectivity depends on the audio filter, and when two stations are
9 or 10kHz apart, and both are strong,
you get some weird monkey chatter.
But they should be good for locals which are at least 45 kHz apart;
If they were only 27 kHz apart, the unwanted station modulation appears
at the detector
as a 27 kHz carrier modulated by its audio signal, and if the audio
filter has a pole at 12 kHz, and a steep roll off, the other station is
thus filtered out
by the audio filter, not the RF or IF filter.
This may sound strange, but the wanted station's carrier is locks a
local oscillator's
F to its own F, and so you get the modulation imposed on an "exalted
carrier".
A station 27 kHz away beats with the oscillator F.

RDH4 says very very little about synchrodynes.

But Wireless World ran some very big articles on them
and some very complex (and mostly incomprehensible) circuit designs were
published.

Its all there in the right libraries.


>
> Build it; they will come.


Maybe not many :-/

Patrick Turner.

>
>
> Steve.
>
> --
> Steven D. Swift, , http://www.novatech-instr.com
> NOVATECH INSTRUMENTS, INC. P.O. Box 55997
> 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA


  #3  
Old June 17th 04, 03:00 PM
Frank Dresser
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"Steven Swift" > wrote in message
...
> rar+p and rats:
>
> Okay, here's the answer directly from the Radiotron Designer's
> Handbook, fourth edition, pages 1226 and 1227:
>
> "Section 3: The Synchrodyne"
> [...]
> "and hence the synchrodyne is likely to be most popular for
> high-quality local-station reception."



I think the fact that the synchrodyne never became at all popular as an AM
radio detector in the tube era means something. If I recall correctly, I
read that synchrodyne detectors would howl until they sync'd. Also, the
phasing would have to be perfect to get good demodulation from normal double
sideband AM.


>
> There you have it. Are we done. This is a 3-tube design for
> local stations. One RF amp, 2 12au7s. Use an IC or two in the
> oscillator loop and its perfect, almost a Costas Loop.
>
> Build it; they will come.
>
> Steve.
>


I suppose it's something worth experimenting with, but diode detectors
aren't bad. Even in the solid state era, sync detectors aren't particularly
popular. The add on sync detectors are expensive. It still doesn't seem to
be easy.

Frank Dresser


  #4  
Old June 17th 04, 03:15 PM
Steven Swift
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"Frank Dresser" > writes:

>I think the fact that the synchrodyne never became at all popular as an AM
>radio detector in the tube era means something. If I recall correctly, I
>read that synchrodyne detectors would howl until they sync'd. Also, the
>phasing would have to be perfect to get good demodulation from normal double
>sideband AM.


>Frank Dresser


Yes, they howl. But his channel concept eliminates that problem. In a private
email, I asked Jon if his design can use ICs. If you use a couple of ICs to
generate the "synchronized" signal, I think you can get around the complexity.

Jon has a lot of work. Block diagrams are pretty simple. Details are hard.

Steve.
--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA
  #5  
Old June 17th 04, 03:39 PM
Michael Black
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"Frank Dresser" ) writes:
> "Steven Swift" > wrote in message
> ...
>> rar+p and rats:
>>
>> Okay, here's the answer directly from the Radiotron Designer's
>> Handbook, fourth edition, pages 1226 and 1227:
>>
>> "Section 3: The Synchrodyne"
>> [...]
>> "and hence the synchrodyne is likely to be most popular for
>> high-quality local-station reception."

>
>
> I think the fact that the synchrodyne never became at all popular as an AM
> radio detector in the tube era means something. If I recall correctly, I
> read that synchrodyne detectors would howl until they sync'd. Also, the
> phasing would have to be perfect to get good demodulation from normal double
> sideband AM.
>
>

The quote is about the synchrodyne detector, not synchronous.

While Radiotron mentions "sync'ing" I'd not treat that as a basic of
the synchrodyne. At its basic, it's what we'd now call a direct conversion
receiver, ie beat the incoming signal down to audio. The "high fidelity"
derives from the fact that selectivity comes at audio, and one can build
good audio filters. Because one is translated the RF signal to audio,
any front end selectivity is there to prevent mixer overload. And the
translated signal goes from DC to daylight (a slight exageration), so
putting the filter there is not just a "tone control" but acts the same way
as a good filter further up.

The immediate problem is that such a receiver can do nothing of the audio
image (which is the same thing as the image in a superheterodyne receiver).
This is not a problem with AM, since the audio image (ie the signal on the
other side of the carrier) is the other sideband.

And of course, the lack of anything to sync the local oscillator
to the incomining carrier means that off-tuned receivers will provide
a beat note, and worse, a caucophony of sound as the two sidebands translate
to different audio frequencies and beat against each other.

While obviously there were schemes along these lines, to get better
AM reception, I don't think the synchronous detector was described until
1958 or so. At least, that's when it first hit CQ magazine, and if it wasn't
by Costas himself, it was by a guy named Webb who worked for GE (who were
the commercial proponent of DSBsc).

Michael

>>
>> There you have it. Are we done. This is a 3-tube design for
>> local stations. One RF amp, 2 12au7s. Use an IC or two in the
>> oscillator loop and its perfect, almost a Costas Loop.
>>
>> Build it; they will come.
>>
>> Steve.
>>

>
> I suppose it's something worth experimenting with, but diode detectors
> aren't bad. Even in the solid state era, sync detectors aren't particularly
> popular. The add on sync detectors are expensive. It still doesn't seem to
> be easy.
>
> Frank Dresser
>
>



  #6  
Old June 17th 04, 04:46 PM
Patrick Turner
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Default



Frank Dresser wrote:

> "Steven Swift" > wrote in message
> ...
> > rar+p and rats:
> >
> > Okay, here's the answer directly from the Radiotron Designer's
> > Handbook, fourth edition, pages 1226 and 1227:
> >
> > "Section 3: The Synchrodyne"
> > [...]
> > "and hence the synchrodyne is likely to be most popular for
> > high-quality local-station reception."

>
> I think the fact that the synchrodyne never became at all popular as an AM
> radio detector in the tube era means something. If I recall correctly, I
> read that synchrodyne detectors would howl until they sync'd. Also, the
> phasing would have to be perfect to get good demodulation from normal double
> sideband AM.


Most synchrodynes do howl and whistle while a station is tuned
because the oscillator beats with the wanted station carrier until
the the station carrier is the same F as the oscillator.
PLL wasn't used in many early synchronous applications.
Locked osillators were. These used a sample of the station's carrier to
trigger the oscillator's F to be the same when the two frequencies became close
enough.
To get over the howling, muting circuits were devised to block reception
until the station was tuned, so it was there, or it wasn't, it was either tuned,
or not tuned.
By the time you built all the necessary things to make the old style
synchrodyne livable withable, you have used twice the tube count, and that's a
lot more that
could go wrong as tyhe set aged.

Chip technology changed all that, and I have a couple of simple synchronous,
or otherwise known as direct conversion circuits.

Mr D.G.Tucker's synchrodyne circuit of 1947 is a tantalising circuit, but it
needs extremely
careful layout and preparation to get the darn thing to work as suggested.
I couldn't get the balanced demodulator with a 3 winding tranny to work properly

with its 4 diodes, and the oscilations wouldn't lock properly, or became
unlocked when the modulation % became so high there
wasn't enough carrier left to trigger the locking.
If it wasn't one thing, it was another, so I built a superhet.

> >
> > There you have it. Are we done. This is a 3-tube design for
> > local stations. One RF amp, 2 12au7s. Use an IC or two in the
> > oscillator loop and its perfect, almost a Costas Loop.
> >
> > Build it; they will come.
> >
> > Steve.
> >

>
> I suppose it's something worth experimenting with, but diode detectors
> aren't bad. Even in the solid state era, sync detectors aren't particularly
> popular. The add on sync detectors are expensive. It still doesn't seem to
> be easy.


It isn't easy with discrete components.
Probably far easier with a chip like the NE602,
or LM2111. The application notes might give info about their radio use;
I have two circuits with each of the above within, but its OT
for a tube group.

It should be possible to apply an locked oscillator signal at 455 kHz to
the IF signal, and recover the audio from a mixer circuit where the product is
the audio.

The synchrodyne is similar to a superhet in that the difference between the
a stations F and the ocsillator F is not 455 kHz, its simply the audio
signal, so its audio that comes out of the frequency converter instead of a
455 kHz IF signal. One tube design uses a the same tube type as one would use
for a normal
F converter, the 6BE6.

A PLL isn't all that easy to do with tubes, since changing an oscillator's F
with a varying DC level isn't easy, since rigging a reactance tube up results in
little F change.
This function is much easier with chips, and varicaps, which were not around in
1947.
I even made a 6AU6 RF amp to synchronize the oscillator on a very low threshold
of station carrier,
by means of using a limiter amp like in an FM set where the last IF amp
is run in seriously over loaded conditions to stop any AM of the IF signal
getting into the discriminator, but it never really worked properly
at 100% modulation; one needed a phase locked set up with a slow time constant
driving the voltage control of oscillator F, so that momentary absenses of
station carrier signal didn't let the oscillator F drift off the station F.

Does anyone have a good phase locked loop schematic using tubes
for between 500kHz and 1,700kHz?
I vaguely remember one in Electronics Australia in the 1960s,
but I became uninterested in electronics about then.



Patrick Turner.


>
>
> Frank Dresser


  #7  
Old June 17th 04, 05:16 PM
Henry Kolesnik
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HiFi AM is stretching the definition of HiFi! Designing and building a good
receiver is not a trivial task. When I was a kid in Jr High and didn't know
any better I used whatever was at hand or I could scrounge and most projects
usually worked, and even worked better when certain parts were substituted
by trial and error. But in reality none compared to the war surplus
receivers I converted.
Later in when I was in the RCAF radar school and had more knowledge and
parts I did much better. But still not as good as commercial units.
After college I made a few attempts getting into the details of
characteristic curves for tubes and transistors, load lines and calculating
component values. It's a very big task to select the best tube or
transistor for each stage and decide on stage gain, distortion, etc. But
once that's done, physical layout is very important. After design and
layout the unit is built and it's generally not a proto-type, it's the
final prize. After changing part values to optimize performance one finds
that many things should have been done differently. And I know guys who
have built several re-designs till they were satisfied but again I never saw
one that outperformed a commercial unit.
It's a lot of fun to take an idea from concept to a working unit but anyone
who thinks they're going to build something better than what's available
should learn how to engineer by going to school or get a job around a lot
real smart designers.
These days I know the challenge but I still pick up project parts at
hamfests knowing full well that I may never get around to using them. Mind
games are entertaining but not as much as plugging a project in to listen
for the crackle of static and hoping like hell the smoke stays in. It's
long road from concept to enjoyment with lots of disappointment and
surprises in between.
I've resisted the temptation to post this to the shortwave group so Telamon
could gripe.

--
73
Hank WD5JFR
..
"Steven Swift" > wrote in message
...
> rar+p and rats:
>
> Okay, here's the answer directly from the Radiotron Designer's
> Handbook, fourth edition, pages 1226 and 1227:
>
> "Section 3: The Synchrodyne"
> [...]
> "and hence the synchrodyne is likely to be most popular for
> high-quality local-station reception."
>
> There you have it. Are we done. This is a 3-tube design for
> local stations. One RF amp, 2 12au7s. Use an IC or two in the
> oscillator loop and its perfect, almost a Costas Loop.
>
> Build it; they will come.
>
> Steve.
>
> --
> Steven D. Swift, , http://www.novatech-instr.com
> NOVATECH INSTRUMENTS, INC. P.O. Box 55997
> 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA



  #8  
Old June 17th 04, 05:44 PM
Patrick Turner
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Default

>
> It's a lot of fun to take an idea from concept to a working unit but anyone
> who thinks they're going to build something better than what's available
> should learn how to engineer by going to school or get a job around a lot
> real smart designers.


But so many so called engineer designed radios were inspired mostly
by accountants, who hate the parts in radios because they cost money
to put there.
Engineers had pitched battles with accountants in company staff offices all the
time.

So it isn't too hard to build an AM radio with at least 10 kHz BW and low thd,
but it usually uses a couple more tubes the engineers of yesterday were
forbidden to use.
A superhet isn't rocket science, its schoolboy electronics, and any determined
person could build such a radio if they had the will, the tools, workshop, etc.
Sure, the old junk from hamfests does help the ability to experiment more
easily,
since things like IFTs can be tweaked and tried, and who cares if you
stuff one up?

Patrick Turner.


  #9  
Old June 17th 04, 05:59 PM
Jeffrey D Angus
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Default

Frank Dresser wrote:
> I think the fact that the synchrodyne never became at all popular as an AM
> radio detector in the tube era means something. If I recall correctly, I
> read that synchrodyne detectors would howl until they sync'd. Also, the
> phasing would have to be perfect to get good demodulation from normal double
> sideband AM.


Now appearing on alt.binaries.pictures.radio

Syncrhodyne three tube receiver from the April 1951 edition of
Radio News.

Jeff

--
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." Benjamin Franklin
"A life lived in fear is a life half lived."
Tara Morice as Fran, from the movie "Strictly Ballroom"

  #10  
Old June 17th 04, 08:04 PM
Chris Morriss
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In message >, Jeffrey D Angus
> writes
>Frank Dresser wrote:
>> I think the fact that the synchrodyne never became at all popular as an AM
>> radio detector in the tube era means something. If I recall correctly, I
>> read that synchrodyne detectors would howl until they sync'd. Also, the
>> phasing would have to be perfect to get good demodulation from normal double
>> sideband AM.

>
>Now appearing on alt.binaries.pictures.radio
>
>Syncrhodyne three tube receiver from the April 1951 edition of
>Radio News.
>
>Jeff
>


Many years ago, there was a series published in 'Wireless World' (might
even have been by John Linsley Hood) about the design of an AM
synchrodyne using transistors and linear ICs. It actually stripped off
the carrier from the incoming signal, and then limited and filtered this
to use as the source of the local oscillator. I believe the concept was
called 'Homodyne'.

As far as I know, the audio quality was excellent, but it couldn't tune
a weak signal close to a powerful one as the powerful one always
succeeded in becoming the LO for the demodulator.

Here in the UK, AM audio is filtered to 5kHz before it gets to the
modulator, so you wouldn't get any increase in audio bandwidth.


--
Chris Morriss
 




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