John Byrns wrote:

In article , Patrick Turner
wrote:


OK, I have taken a closer look at the analysis on the web page at this URL:
http://www.amwindow.org/tech/htm/diodedistortion.htm
and it is more screwed up than I thought.

snip a vastly complex and incomprehensible disputation of the
largely incomprehensible text and formulae at
http://www.amwindow.org/tech/htm/diodedistortion.htm

About all we want is low distortion detection, and it matters noe that we
cannot follow all this mathematical analysis.

Indeed, my original point was simply that the analysis on that web page,
which had been mentioned in this thread as being somehow relevant, was
actually totally irrelevant because it dealt with a square law detector,
not a linear diode peak envelope detector as is commonly used in
High-Fidelity AM receivers. It was then pointed out in this thread that
the conclusion of the web page did not agree with Treman's calculations
for the square law detector. My "incomprehensible disputation" was simply
to tie up the loose ends and show where the web page went wrong on its
square law detector analysis, which would still have been irrelevant to
High-Fidelity designs even if it had been done correctly.

As soon as my eyes see pages full of calculations, my mind goes into a fog....

I only like the test results of practical circuits.
I am only interested in what is proven to work, or not work.



There is no mention of the output voltages measured with respect to
the % of modulation.

I pointed out that very fact in my first post about this web page, that no
details were given of the operational under which the experimental results
were measured.

With respect to the square law detector analysis, the voltage level
doesn't matter, square law is square law irrespective of the carrier
level, so the distortion doesn't change with signal level in an ideal
square law detector, it only changes with the modulation percentage.

From the test circuit shown, there is no bias current flow in the diode
to keep it
turned on even
without an RF signal to demodulate.
This would also reduce thd.

You have still haven't enlightened us with some concrete information about
how much, if at all, your biased diode detector really helps reduce the
distortion of the diode peak envelope detector.

It should be *obvious* from the circuit!

A germanium diode once turned on with a bias current has a low variation in its
"on"
voltage, and is a far lower impedance rectifier than any tube rectifier which has a

varying plate resistance with Ia.
The Ge rectifier has the same "on voltage" during the charge peaks into the cap
or the RC time constant circuit.
Its possible to arrange a tube rectifier with a virtually constant current bias
from a suitable
CF driver tube, but why? a Ge diode is easier and better.

I haven't looked at
biased diodes as AM detectors myself, although I am given to understand
that the proper bias can reduce the distortion of a diode peak envelope
detector, but I am also given to understand that the proper bias is
dependent on signal level, which requires a complex circuit to cause the
bias to maintain the proper relationship to the signal level.

My circuit is as simple as it gets.
Hve the cathode of the CF at +50v, and have a 1M R to drain 0.05mA
through the diode. Much more current could be used.

This method means that detection of weak signal lower than the forward voltage
of the Ge diode of 0.27v peak approx are not subject to the non linear turn on
of the diode, ie, there is no clipping by the diode.

Although I
haven't seen it mentioned, I would assume that a very tight AGC circuit
would also serve to allow a fixed bias to be applied to the diode. I
would think that if a simple bias scheme such as yours really
significantly helped lower the detector distortion, we would have seen
more implementations of this idea in high quality receivers over the
years.

My methods have not been seen in 99% of old domestic tube radios because they
employ an extra tube or two, and two germanium diodes.
I would have been hanged by management in 1955 if I had insisted that
any extravagant use of tubes were to be employed.
The industry was dominated by lowest common denominator ideas.

There have certainly been plenty of expensive AM receivers built
over the years, that didn't skimp on the parts count, where an extra
resistor or two, to bias the diode wouldn't break the bank. That is not
to say that I haven't seen cheap transistor radios that had biased
detectors, but it never seemed to be actively pursued in the better AM
receivers of the tube era.

Transistor AM radios were a major step backwards for audio quality
in 99% of cases.
It went from bad to plain ****ehouse.

Quantity not quality was what dominated radios in old days.

If you wanted better sound, you bought a Quad AM tuner, which only
rich folks could afford.

95% of radio manufacturing was to produce lo-fi junk,
where 5% thd and 150 Hz to 2 kHz of bw was very very common, at a 1/2 watt of
output.
People just were not concerned about fidelity, it didn't help
the cricket or football scores, or make the news about the Suez Canal
crisis any better.


You could better make your point if you posted a couple of graphs for
distortion vs. signal level for a diode detector, with and without bias,
and for several modulation levels, maybe 80% and 100%.

My biased SS diode has lowest thd at high levels of signal.

But if you have a normally gronded last IF coil feeding a diode to 100pF
with a typical 1M discharge R to ground, then with low signals on weak stations,
the thd is appalling, and I thought such issues would be obvious to anyone
familiar with diode operation. No need for me to copy out
the wave form analysis I did, build a detector like I have and you won't be
dissapointed!





Nobody needs to know math involved with diode detectors
to get much lower thd than is realised in most old fashioned and
attrocious tube
detector stages in
conventional AM radios.

Well you are probably right about that, but for a completely different
reason than you have in mind.

I try to stick with what works well in practice, and discard all BS.....
I am too busy to be intellectual about bloomin diode detectors.

Patrick Turner.



Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

In article , Patrick Turner
wrote:

John Byrns wrote:

You have still haven't enlightened us with some concrete information about
how much, if at all, your biased diode detector really helps reduce the
distortion of the diode peak envelope detector.

It should be *obvious* from the circuit!

It's not, at least not to those among us, such as myself, who are not so clever.

My circuit is as simple as it gets.
Hve the cathode of the CF at +50v, and have a 1M R to drain 0.05mA
through the diode. Much more current could be used.

This method means that detection of weak signal lower than the forward voltage
of the Ge diode of 0.27v peak approx are not subject to the non linear turn on
of the diode, ie, there is no clipping by the diode.

Is what you are saying is that the diode in your circuit is always "turned on"?

Quantity not quality was what dominated radios in old days.

If you wanted better sound, you bought a Quad AM tuner, which only
rich folks could afford.

I have one of those "rich folks" Quads right here next to my computer, and
I guess those "rich folks" got taken as the Quad uses a common vacuum
diode detector, like a common kitchen radio, nothing special, the only
special care taken in the detector design seems to be that the audio
output is tapped way down on the diode load resistor to minimize negative
peak clipping.

You could better make your point if you posted a couple of graphs for
distortion vs. signal level for a diode detector, with and without bias,
and for several modulation levels, maybe 80% and 100%.

My biased SS diode has lowest thd at high levels of signal.

One would expect you to be an advocate of your on circuit, but how low is
the thd at high modulation levels?

But if you have a normally gronded last IF coil feeding a diode to 100pF
with a typical 1M discharge R to ground, then with low signals on weak
stations,
the thd is appalling, and I thought such issues would be obvious to anyone
familiar with diode operation. No need for me to copy out
the wave form analysis I did, build a detector like I have and you won't be
dissapointed!

Actually your wave form analysis would be very interesting to see indeed.
The impedance of the IFT is quite low at the harmonic frequencies in the
diode current wave form so the diode sees a low impedance drive at those
frequencies even without a cathode follower, and the filtering effect of
the IFT prevents the harmonics in the current pulses from reaching the
plate of the IF amplifier. See the discussion on page 1077 of the RDH4
relative to loading of the IFT secondary by the diode,although much more
comprehensive discussions can be found elsewhere.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article ,
(John Byrns) wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

You have still haven't enlightened us with some concrete
information about how much, if at all, your biased diode detector
really helps reduce the distortion of the diode peak envelope
detector.

It should be *obvious* from the circuit!

It's not, at least not to those among us, such as myself, who are not
so clever.

My circuit is as simple as it gets. Hve the cathode of the CF at
+50v, and have a 1M R to drain 0.05mA through the diode. Much more
current could be used.

This method means that detection of weak signal lower than the
forward voltage of the Ge diode of 0.27v peak approx are not
subject to the non linear turn on of the diode, ie, there is no
clipping by the diode.

Is what you are saying is that the diode in your circuit is always
"turned on"?

Snip

Congratulations for the continuation of one of the most retarded
threads I've yet read. Never heard of biasing a diode or being unable
to understand doing so is pretty pathetic. Electronics does not get any
simpler than this.

Why don't you cross post this to more news groups so more people can
have a laugh.

--
Telamon
Ventura, California

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

You have still haven't enlightened us with some concrete information about
how much, if at all, your biased diode detector really helps reduce the
distortion of the diode peak envelope detector.

It should be *obvious* from the circuit!

It's not, at least not to those among us, such as myself, who are not so clever.

My circuit is as simple as it gets.

See where the DC flows in my circuit, even without any IF signal present.


Hve the cathode of the CF at +50v, and have a 1M R to drain 0.05mA
through the diode. Much more current could be used.

This method means that detection of weak signal lower than the forward voltage
of the Ge diode of 0.27v peak approx are not subject to the non linear turn on
of the diode, ie, there is no clipping by the diode.

Is what you are saying is that the diode in your circuit is always "turned on"?

Indeed it is turned on all the time, and this stops the huge variation in 455 kHz
ripple
voltage with low level signals when the IF signal is very low, and the R of the RC
detector circuit is just taken to ground from a C which has a very low charge in it
when the signal is very low, as it is in a conventional circuit.



Quantity not quality was what dominated radios in old days.

If you wanted better sound, you bought a Quad AM tuner, which only
rich folks could afford.

I have one of those "rich folks" Quads right here next to my computer, and
I guess those "rich folks" got taken as the Quad uses a common vacuum
diode detector, like a common kitchen radio, nothing special, the only
special care taken in the detector design seems to be that the audio
output is tapped way down on the diode load resistor to minimize negative
peak clipping.

I don't recall what Quad have in their box, but on strong reception, but the mainly
conventional
circuit within does work fairly well enough for many people.
I like things to work better than "conventional", because this stands for lowest
common
denominator, which is plain substandard, imho.


You could better make your point if you posted a couple of graphs for
distortion vs. signal level for a diode detector, with and without bias,
and for several modulation levels, maybe 80% and 100%.

My biased SS diode has lowest thd at high levels of signal.

One would expect you to be an advocate of your on circuit, but how low is
the thd at high modulation levels?

Very low, compared to many other circuits.

Its difficult to measure because other thd effects swamp the thd of the detector.

To measure the accuracy of the detector, you need an AM signal
from a generator that itself has less than 0.01 % of thd in the envelope shape.

If an AM signal at say 1 MHz is applied to the RF input of a set,
then the mixer and IF tubes will impose some thd, and finally the detector
then adds its thd.
But from tests using a dual trace CRO with an input signal from a 455 kHz source,
so that the recovered audio is overlaid onto the wave form of the envelope,
I found it was impossible to see any thd with my detector idea up to several volts,
with any level of % modulation.
This method of inspecting the detector performance removes the need to
have a low distortion enevelope shape to begin with.

I might add that the CF buffer used for the detector was a 12AU7,
and its thd would be around 0.1% at 10 vrms output, simply
because of the thd of such a tube arranged the way it is.
If a 12AT7 were used, the open loop gain is higher, and the gain reduction much
more than 12AU7, so the thd would be perhaps 0.03% at 10v output.


But if you have a normally gronded last IF coil feeding a diode to 100pF
with a typical 1M discharge R to ground, then with low signals on weak
stations,
the thd is appalling, and I thought such issues would be obvious to anyone
familiar with diode operation. No need for me to copy out
the wave form analysis I did, build a detector like I have and you won't be
dissapointed!

Actually your wave form analysis would be very interesting to see indeed.

I drew up the wave forms I thought would appear, and sure enough they did appear
when I tested a typical circuit.

At very low signal levels, or where the % modulation approaches 100%, the 455 kHz
ripple voltage is very low, and when the 455 kHz signal is stringer, the ripple
voltage becomes much higher.
There is distortion in these goings on if the diodes Ra changes a lot, which is
does,
so a germanium diode which is turned on at all times by a DC flow prevents the
variations
one sees with a tube diode.



The impedance of the IFT is quite low at the harmonic frequencies in the
diode current wave form so the diode sees a low impedance drive at those
frequencies even without a cathode follower, and the filtering effect of
the IFT prevents the harmonics in the current pulses from reaching the
plate of the IF amplifier.

And if a CF buffer is used, the low impedance caused by diode current flows
are not seen by the IFT and IF pentode amp, so no distortion occurs.
The CF removes the thd caused by the diodes.

See the discussion on page 1077 of the RDH4
relative to loading of the IFT secondary by the diode,although much more
comprehensive discussions can be found elsewhere.

Indeed more exists elsewhere, but after thought about the problems,
I went my own way.

Patrick Turner.



Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

Telamon wrote:

In article ,
(John Byrns) wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

You have still haven't enlightened us with some concrete
information about how much, if at all, your biased diode detector
really helps reduce the distortion of the diode peak envelope
detector.

It should be *obvious* from the circuit!

It's not, at least not to those among us, such as myself, who are not
so clever.

My circuit is as simple as it gets. Hve the cathode of the CF at
+50v, and have a 1M R to drain 0.05mA through the diode. Much more
current could be used.

This method means that detection of weak signal lower than the
forward voltage of the Ge diode of 0.27v peak approx are not
subject to the non linear turn on of the diode, ie, there is no
clipping by the diode.

Is what you are saying is that the diode in your circuit is always
"turned on"?

Snip

Congratulations for the continuation of one of the most retarded
threads I've yet read. Never heard of biasing a diode or being unable
to understand doing so is pretty pathetic. Electronics does not get any
simpler than this.

Why don't you cross post this to more news groups so more people can
have a laugh.

Are you implying that those involved in this thread are retarded?
or mentally deficient?

I don't care that you have a good laugh.

I know that many ppl in the groups to whom this thread is being posted
don't have much of a clue about how AM radios work, let alone an FM set,
or its MPX stereo decoder, or let alone a TV set, or VCR, or CD player.

Hell, I damn well can't understand the schematic for the Space Shuttle,
and I knows the laughter over this must be deafening, but heck, I don't
care.

To many folks the simplest of concepts are difficult to understand,
and they restore their radios and amps using age old circuits
which perform woefully most of the time.
I am happy if I bring some simple alternative techniques for them to apply
if they want, but most won't, because the idea of drilling more tube socket

holes in an existing set is butchery.
I care for more fidelity, and to get it, serious butchery is required,
sometimes totally banishing the original old fashioned ideas altogether,
removing all vestige of the old maker's design, and placing my own label on
the chassis.

The old maker may have been delighted that he got the thd down to 5%, audio
bandwidth
from 150 Hz to 2 kHz, with some hum, but I wasn't.

Patrick Turner.




--
Telamon
Ventura, California

In article ,
Patrick Turner wrote:

Telamon wrote:

In article ,
(John Byrns) wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

You have still haven't enlightened us with some concrete
information about how much, if at all, your biased diode detector
really helps reduce the distortion of the diode peak envelope
detector.

It should be *obvious* from the circuit!

It's not, at least not to those among us, such as myself, who are not
so clever.

My circuit is as simple as it gets. Hve the cathode of the CF at
+50v, and have a 1M R to drain 0.05mA through the diode. Much more
current could be used.

This method means that detection of weak signal lower than the
forward voltage of the Ge diode of 0.27v peak approx are not
subject to the non linear turn on of the diode, ie, there is no
clipping by the diode.

Is what you are saying is that the diode in your circuit is always
"turned on"?

Snip

Congratulations for the continuation of one of the most retarded
threads I've yet read. Never heard of biasing a diode or being unable
to understand doing so is pretty pathetic. Electronics does not get any
simpler than this.

Why don't you cross post this to more news groups so more people can
have a laugh.

Are you implying that those involved in this thread are retarded?
or mentally deficient?

Yes, are you having trouble comprehending that?

--
Telamon
Ventura, California

In article ,
Patrick Turner wrote:

Telamon wrote:

In article ,
(John Byrns) wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

You have still haven't enlightened us with some concrete
information about how much, if at all, your biased diode detector
really helps reduce the distortion of the diode peak envelope
detector.

It should be *obvious* from the circuit!

It's not, at least not to those among us, such as myself, who are not
so clever.

My circuit is as simple as it gets. Hve the cathode of the CF at
+50v, and have a 1M R to drain 0.05mA through the diode. Much more
current could be used.

This method means that detection of weak signal lower than the
forward voltage of the Ge diode of 0.27v peak approx are not
subject to the non linear turn on of the diode, ie, there is no
clipping by the diode.

Is what you are saying is that the diode in your circuit is always
"turned on"?

Snip

Congratulations for the continuation of one of the most retarded
threads I've yet read. Never heard of biasing a diode or being unable
to understand doing so is pretty pathetic. Electronics does not get any
simpler than this.

Why don't you cross post this to more news groups so more people can
have a laugh.

Are you implying that those involved in this thread are retarded?
or mentally deficient?

I don't care that you have a good laugh.

.... and I don't care if you and Byrns look like idiots. The threads at
100 now and I'll check back in when it hits 500.

--
Telamon
Ventura, California

Telamon wrote:

Congratulations for the continuation of one of the most retarded
threads I've yet read. Never heard of biasing a diode or being unable
to understand doing so is pretty pathetic. Electronics does not get any
simpler than this.

John understands this stuff extremely well: I've argued detector issues
with him on rec.antiques.radio+phono in the past. John obviously doesn't
believe Patrick really understands what he's advocating.

Biased diode envelope detectors are *not* simple: I've used them for
x-ray spectroscopy with scintillation counters, and they are tricky
beasts. A biased diode is far from an ideal switch: its dynamic
resistance varies with instantaneous signal level, making the circuit
bandwidth vary rapidly. The mathematics of this are rather difficult.

I also think an emphasis on detector distortion under idealized test
conditions misses the real issues. The most annoying distortion on AM
signals doesn't come from the detector. Multipath, steep IF skirts, and
AGC all distort the modulation envelope. Perfect reproduction of such
distorted envelopes yields bad sound. I suspect that the great sound of
the old tube diode detectors actually results from their poor
reproduction of these sorts of envelope distortion (but this is a
difficult hypothesis to test).

In any case, my 1934 Stromberg-Carlson 58-T, with its weak AGC, poor
skirt selectivity, and a classic diode detector has the best sound of
any of my AM radios, both to my ears and my wife's. One receiver it
beats is my Drake R-8, which uses a very low distortion (active full
wave rectifier) envelope detector. Of course, the R-8 is a much better
DX machine, but that's a different issue.

-jpd

Are you implying that those involved in this thread are retarded?
or mentally deficient?

Yes, are you having trouble comprehending that?

I think you have a problem with basic human communication skills,
and the ability to define personal attributes in an appropriate manner.
I suspect nearly everyone here would agree.

It does not worry me in the least about whatever conclusions you have come to
over the issues I have just raised, or how you propose to remedy your
shortcomings.

But one thing seems certain, and its that you have not contributed much of
worth
which is relevant, helpful, interesting, informative or cheerful in the recent
discussions in this thread.

Patrick Turner.

Telamon wrote:
In article ,
Patrick Turner wrote:


Telamon wrote:



Are you implying that those involved in this thread are retarded?
or mentally deficient?


Yes, are you having trouble comprehending that?


Well yeah. Some ideas simply don't float well in the face of r.r.s