Telamon wrote:

In article , Bill
wrote:

You used to have a web page with the radios you restored. Still have it?

Yes, http://www.sparkbench.com Most of the sets have tubes and SW so
its "on topic" for this crossposting.
:-)


Here I was all worried what was going to happen to rec.radio.shorwave
since the Bryant hiatus.

Don't worry unless you have a Llloyd and Bryant hiatus at the same time.

-BM

On 15 Jun 2004 07:43:12 -0500, Dan wrote:

On Tue, 15 Jun 2004 05:44:35 GMT, Telamon
wrote:

In article ,
Jon Noring wrote:

I'm the one who started and cross-posted the related topics (of
building a tube-based AM receiver) to the three newsgroups, including
rec.radio.shortwave.

Nevertheless, I believe the threads are sufficiently on-topic to
r.r.s. to not warrant some pro-active effort to try to stop.

I've sent a complaint to your news provider. We will see if they think
the same way you do.

I just sent two complaints to about Telamon trying
to disrupt an on-topic discussion. I suggest everyone involved in
this thread do the same. Include a complete, abusive or threatening
messsage from Telamon including headers. They're not hard to find.

Dan
Grundig S800, S650, S700, YB400, YB550PE
Degen DE1102, Kaito KA1102
Drake R8, Radio Shack DX-440
E. H. Scott 23 tube Imperial Allwave in Tasman cabinet (1936)

I just sent 50 complaints to . Heh heh. That'll get their attention about the troll.

Dan wrote:

On Tue, 15 Jun 2004 05:44:35 GMT, Telamon
wrote:

In article ,
Jon Noring wrote:

I'm the one who started and cross-posted the related topics (of
building a tube-based AM receiver) to the three newsgroups, including
rec.radio.shortwave.

Nevertheless, I believe the threads are sufficiently on-topic to
r.r.s. to not warrant some pro-active effort to try to stop.

I've sent a complaint to your news provider. We will see if they think
the same way you do.

I just sent two complaints to about Telamon trying
to disrupt an on-topic discussion. I suggest everyone involved in
this thread do the same. Include a complete, abusive or threatening
messsage from Telamon including headers. They're not hard to find.

Heck, post it again!

Telamon can't help it - he's bucking to be the next Fuhrer! "Post this! Don't
post that! Don't disagree with me otherwise you are a troll!". I would just
bet that he does a wonderful goose-step while trying to re-write FAQ's.

Keep on posting, guys! It's all part of the hobby.

Regards

John Barnard

Jeffrey D Angus wrote:

Telamon wrote:

In article ,
Jeffrey D Angus wrote:

Telamon wrote:

I don't care about your opinion and did not ask for it. I don't care if
other people posting from the other rec.antiques.radio+phono or
rec.audio.tubes think as you do.

I'm not interested in a debate about cross posting.

I have made a repeated, polite requests for this to stop so are you guys
from rec.antiques.radio+phono or rec.audio.tubes going to behave or not?

Please respond as to whether you will stop or not that's all I want to
know.

This is it guys I'm not asking again.

Can we have that in writing?

'Cause the simple answer is we ain't going to stop cross posting
just because YOU have YOUR knickers in a knot.


You a moron or something? Did I speak to you or did you READ it.

What a bozo.

You posted to a public forum. As a matter of fact, you CROSS posted
the three groups, including the one I normally read. RAR+P.

You did not address your posting to anyone in particular, other than
the people in RAT and RAR+P.

However, you specifically asked if "we" were going to stop. The
answer is no.

The simple fact is that nobody really gives a damn what you think.

Flame all you want.

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"

Curmudgeon,

Since you are using a "Forged Header" )
.. . . Will Anybody Listen ?

ho, Ho. HO ! - Makes One Wonder ~ RHF
..
..
= = = curmudg@eon (Curmudgeon) wrote in message
= = = ...
On 15 Jun 2004 07:43:12 -0500, Dan wrote:

On Tue, 15 Jun 2004 05:44:35 GMT, Telamon
wrote:

In article ,
Jon Noring wrote:

I'm the one who started and cross-posted the related topics (of
building a tube-based AM receiver) to the three newsgroups, including
rec.radio.shortwave.

Nevertheless, I believe the threads are sufficiently on-topic to
r.r.s. to not warrant some pro-active effort to try to stop.

I've sent a complaint to your news provider. We will see if they think
the same way you do.

I just sent two complaints to about Telamon trying
to disrupt an on-topic discussion. I suggest everyone involved in
this thread do the same. Include a complete, abusive or threatening
messsage from Telamon including headers. They're not hard to find.

Dan
Grundig S800, S650, S700, YB400, YB550PE
Degen DE1102, Kaito KA1102
Drake R8, Radio Shack DX-440
E. H. Scott 23 tube Imperial Allwave in Tasman cabinet (1936)

I just sent 50 complaints to .
Heh heh. That'll get their attention about the troll.
..

On 16 Jun 2004 11:46:14 -0700, (RHF) wrote:

Curmudgeon,

Since you are using a "Forged Header" )
. . . Will Anybody Listen ?

ho, Ho. HO ! - Makes One Wonder ~ RHF

Forged header? How does one forge headers when sending email? Inquiring minds want to know oh 3L33T 1.

.
.
= = = curmudg@eon (Curmudgeon) wrote in message
= = = ...
On 15 Jun 2004 07:43:12 -0500, Dan wrote:

On Tue, 15 Jun 2004 05:44:35 GMT, Telamon
wrote:

In article ,
Jon Noring wrote:

I'm the one who started and cross-posted the related topics (of
building a tube-based AM receiver) to the three newsgroups, including
rec.radio.shortwave.

Nevertheless, I believe the threads are sufficiently on-topic to
r.r.s. to not warrant some pro-active effort to try to stop.

I've sent a complaint to your news provider. We will see if they think
the same way you do.

I just sent two complaints to about Telamon trying
to disrupt an on-topic discussion. I suggest everyone involved in
this thread do the same. Include a complete, abusive or threatening
messsage from Telamon including headers. They're not hard to find.

Dan
Grundig S800, S650, S700, YB400, YB550PE
Degen DE1102, Kaito KA1102
Drake R8, Radio Shack DX-440
E. H. Scott 23 tube Imperial Allwave in Tasman cabinet (1936)

I just sent 50 complaints to .
Heh heh. That'll get their attention about the troll.
.

It is hard to believe that the distortion of a reasonably designed diode
detector is anywhere near "a few percent", as simple diode detectors were
used in the modulation monitors used by AM broadcast stations in times
gone by,

Take a look at RDH4 page 1073.

Even with extreme design precautions you can't get much better than about 2%
(see page 1080-1081).

To work, a diode detector has to "cut-off" for 1/2 the carrier cycle. This
requires that the diode always go through the "knee". A tube diode has a
voltage to the three-halves characteristic. A semiconductor diode has an
exponential characteries. Expand into a Taylor series, and look at the
first couple of terms. Distortion! Diodes as "multipliers" can be made better.

I'll look for the analysis.

BTW, if you trickle current in a tube diode and keep the signal small, you
have built a "square-law" detector. Not a diode detector. You can also see
this in the Taylor series.

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

Steven Swift wrote:

Take a look at RDH4 page 1073.

Even with extreme design precautions you can't get much better than about 2%
(see page 1080-1081).

To work, a diode detector has to "cut-off" for 1/2 the carrier cycle. This
requires that the diode always go through the "knee". A tube diode has a
voltage to the three-halves characteristic. A semiconductor diode has an
exponential characteries. Expand into a Taylor series, and look at the
first couple of terms. Distortion! Diodes as "multipliers" can be made better.



How about a synchronous detector? You need to recreate the station
carrier locally
(phase lock loop) and then feed that and the station signal into a
multiplier circuit
(maybe a dual control pentode or pentagrid tube, like a 6AS6 or 6CS6, or
tubes
used for chroma demod in color TV sets). No diode non linearity issues.

There is an op-amp circuit that is supposed to create a "perfect"
rectifier or diode
function. Use an op-amp fast enough, and maybe that can detect AM
signals well?
The op-amp circuit has one diode connected directly from the inverting
input to
the output, and another diode facing the other direction same
connections except
it has a resistor in series. Non-inverting input tied to ground. Ran a
simulation of
this using a 6AL5 for the diodes, and got about 2% distortion (mostly
2nd harmonic).
Also tried 1N34 geraninium diodes and it was really awful. So it looks
to not do
any better than an envelope detector...

Someone mentioned "Syncrodyne" radios. Is that the same thing, or
similar to, as
a syncronous AM detector?

Robert Casey wrote:

Steven Swift wrote:

Take a look at RDH4 page 1073.

Even with extreme design precautions you can't get much better than about 2%
(see page 1080-1081).

To work, a diode detector has to "cut-off" for 1/2 the carrier cycle. This
requires that the diode always go through the "knee". A tube diode has a
voltage to the three-halves characteristic. A semiconductor diode has an
exponential characteries. Expand into a Taylor series, and look at the
first couple of terms. Distortion! Diodes as "multipliers" can be made better.



How about a synchronous detector? You need to recreate the station
carrier locally
(phase lock loop) and then feed that and the station signal into a
multiplier circuit
(maybe a dual control pentode or pentagrid tube, like a 6AS6 or 6CS6, or
tubes
used for chroma demod in color TV sets). No diode non linearity issues.

There is an op-amp circuit that is supposed to create a "perfect"
rectifier or diode
function. Use an op-amp fast enough, and maybe that can detect AM
signals well?
The op-amp circuit has one diode connected directly from the inverting
input to
the output, and another diode facing the other direction same
connections except
it has a resistor in series. Non-inverting input tied to ground. Ran a
simulation of
this using a 6AL5 for the diodes, and got about 2% distortion (mostly
2nd harmonic).
Also tried 1N34 geraninium diodes and it was really awful. So it looks
to not do
any better than an envelope detector...

Someone mentioned "Syncrodyne" radios. Is that the same thing, or
similar to, as
a syncronous AM detector?

A very very accurate diode detector can be made with an RF opamp,
a shunt FB input network and a diode feeding a cap so that the audio level at the
cap
tries to follow the input signal.
Any sag in the audio level causes the opamp to turn on more with its high gain...
The same deal is used for driving meter circuits with great precision,
and at any F.
It could be done with tubes, its just more difficult, but thd way below that high
2%
is possible with a diode RC circuit fed from a CF stage, where the diode has a
CCS fed through it to stop the forward 'on' voltage varying much with signal input
level.

Patrick Turner.

Even with extreme design precautions you can't get much better than about 2%


See http://n2.net/k6sti/dist.jpg . This is a screen shot of my HP
3580A spectrum analyzer looking at the output of an old Knight tube
tuner. I radiated a signal into the tuner from a small loop connected
to my HP 8640B signal generator modulated 90% with 1 kHz. The vertical
scale is 10 dB/div and the horizontal scale is 500 Hz/div. You can see
the harmonics of the 1 kHz tone in the mid -50 dB region. Their RMS
sum is about -50 dB, roughly 0.3% THD.

I had lowered the tuner's detector load resistor to maximize
modulation acceptance (clipping at high modulation index due to
capacitive loads), but otherwise the circuit is stock. I tuned the
tuner by ear for lowest distortion.

Brian

"Steven Swift" wrote in message
...

Hey, don't worry about the rrs gripers. We've discussed detectors there
before, and we will again.



Take a look at RDH4 page 1073.

Even with extreme design precautions you can't get much better than about
2%
(see page 1080-1081).

This guy calculates 0.4% distortion at 50% modulation and 1.6% distortion at
100% modulation.

http://www.amwindow.org/tech/htm/diodedistortion.htm

In a typical diode detector test circuit he measured 0.32% distortion at 50%
modulation and 2% distortion at 100% modulation.



To work, a diode detector has to "cut-off" for 1/2 the carrier cycle. This
requires that the diode always go through the "knee". A tube diode has a
voltage to the three-halves characteristic. A semiconductor diode has an
exponential characteries. Expand into a Taylor series, and look at the
first couple of terms. Distortion! Diodes as "multipliers" can be made
better.


How would a precision rectifier do?


I'll look for the analysis.

BTW, if you trickle current in a tube diode and keep the signal small, you
have built a "square-law" detector.

It's been my impression that the "knee" area of the curve is the
"square-law" area of the curve. Again, it's my impression that the crystal
set guys use foreward bias to get their detectors out of the "square-law"
area of the diode's curve in order to maximize sensitivity and minimize
distortion.


Not a diode detector. You can also see
this in the Taylor series.

Steve

Why isn't a forward biased diode not a diode detector?

Frank Dresser

Brian wrote:

Even with extreme design precautions you can't get much better than about 2%

See http://n2.net/k6sti/dist.jpg . This is a screen shot of my HP
3580A spectrum analyzer looking at the output of an old Knight tube
tuner. I radiated a signal into the tuner from a small loop connected
to my HP 8640B signal generator modulated 90% with 1 kHz. The vertical
scale is 10 dB/div and the horizontal scale is 500 Hz/div. You can see
the harmonics of the 1 kHz tone in the mid -50 dB region. Their RMS
sum is about -50 dB, roughly 0.3% THD.

I had lowered the tuner's detector load resistor to maximize
modulation acceptance (clipping at high modulation index due to
capacitive loads), but otherwise the circuit is stock. I tuned the
tuner by ear for lowest distortion.

Brian

Many old radios have the secondary of the last IFT connected at one end to a
diode's
anode, with the cathode grounded, and then the other end to a 100pF,
47k, 100pF CRC filter, and then usually 1M or 470k to ground to
drain the current from the C, so the audio is retrieved, but the IF is shunted.
Sometimes the 1M is a volume control track, and there is DC flow down the track,
and after some time this DC causes the vol control to be annoyingly noisy.
Its the cheapest way to make an AM detector.

I have found its far better to have a fixed resistor to ground after the first
100pF, then
followed by the 47k and another 100 pF, and then 0.1 uF and volume control,
so the volume control isn't subject to DC.

The value of the resistance used to drain current out of the first 100pF to ground

is fairly critical for low distortion, yet it is chosen empirically.
But I suggest owners of average superhets rewire their detection ciruits as I
have suggested,
but that they also monitor the wave form on a CRO, or analyser,
and adjust DC drain R to get lowest thd.
Often this detector R causes cut off of the wave form, which sounds very bad,
but the right value of R will reduce the thd to a minimum, and R often will be
only 220k.
Methinks the effect is that the power being absorbed into the detector
is reflected as a load on the pentode plate circuit which drives the
IFT in the first place, and thus the tube sees the most optimal load for least
thd.
But a more exact explanation I cannot think of, all I know is that
my above recommended circuit makes many horrid sounding AM radios sound
one heck of a lot better.

The best and most linear operation of the IF pentode depends on the bias voltage,
whether or not its a vari-mu tube or not, and the load, so a few varaibles
are involved.

In my radio which uses a 6BX6/EF80, which is a sharp cut off, or linear
pentode, there is fixed bias, current FB with an unbypassed Rk, and some R damping

on the IFT, and I have carefully tried to make the IF amp as linear as possible,
and not affected by the loading effect of a diode and filter circuit.

The last IF coil is grounded at one end and feeds a CF tube, which then powers the
diode
and RC circuit, and the linearity of such a set up is much better than when the
source impedance is a high impedance, ie, the plate resistance of the pentode.

The diode is a germanium type and has a small DC bias current flow from the
cathode of the CF,
even when its not got any applied signal, so when a signal envelope is applied,
the value of the ripple
IF voltage barely changes, so variations in % modulation don't cause
very much difference in thd; its low all the time.

Patrick Turner.

Why isn't a forward biased diode not a diode detector?

Frank Dresser

It can be a detector.
The germanium diodes can have a tiny current to keep about
0.25 volts across them even with no signal.
the presence of a carrier with modulation or no modulation will cause a ripple
voltage into a cap, just like the signal at a power supply rectifier.

The ripple voltage is created by a small % of the 455kHz signal cycle
charging the C1 of the filter.

The amplitude of the carrier voltage varies at a slow speed of audio, and the
ripple voltage
stays the same value, and the detector audio signal closely follows the
shape of the modulation, ie, the audio is recovered linearly.

If you don't have any idle current in the diode, and drive the diode
off the end of a grounded IFT coil, then the ripple voltage varies a lot at low
signal,
when the R discharging the C1 of the filter has very little voltage across it.
So low level signals are very distorted by cut off distortion on the audio
cycles.

Patrick Turner.

But a more exact explanation I cannot think of, all I know is that
my above recommended circuit makes many horrid sounding AM radios sound
one heck of a lot better.


See http://n2.net/k6sti/ma.htm for more.

Brian

A very very accurate diode detector can be made with an RF opamp,
a shunt FB input network and a diode feeding a cap so that the audio level at the
cap
tries to follow the input signal.
Any sag in the audio level causes the opamp to turn on more with its high gain...
The same deal is used for driving meter circuits with great precision,
and at any F.


Pat, can you direct me to a schematic of such? Can't quite visualize
the circuit.

Thanks, Bob.

Brian wrote:

But a more exact explanation I cannot think of, all I know is that
my above recommended circuit makes many horrid sounding AM radios sound
one heck of a lot better.

See http://n2.net/k6sti/ma.htm for more.

Brian

Thankyou for that web reference on modulation acceptance.
The writer's conclusions on how to reduce the limiting effects of
a detector with low modulation % acceptance confirm what I discovered on my
own.

The audio output might reduce more than 1 dB, but 3 dB isn't a worry since
most
tube AM radios produce huge signal output levels.

Unfortunately, the above reference is encoded with Opera,
and unless you have Opera installed on one's PC, one cannot read the saved
file, which is a complete PITA!

Patrick Turner.

Robert Casey wrote:






A very very accurate diode detector can be made with an RF opamp,
a shunt FB input network and a diode feeding a cap so that the audio level at the
cap
tries to follow the input signal.
Any sag in the audio level causes the opamp to turn on more with its high gain...
The same deal is used for driving meter circuits with great precision,
and at any F.


Pat, can you direct me to a schematic of such? Can't quite visualize
the circuit.

Thanks, Bob.

Looks like I will have to scan a few of my paper files of schematics and post them.
But old man time is the catcher, I have to earn a living too...

The AM tuner I found the accurate detector was the Playmaster AM Tuner kit of 1982,
as designed by John Clarke and published in Electronics Australia , dec 1982.

It has the IF signal from the last IFT going to a 3k3 which feeds the input of a
CA3100 chip,
which has its other input grounded.
The output of the chip has an OA90 diode to the output.
The output has a 3k3 taken back to the live input of the CA3100, and that's all there
is to it,
not even any filter caps; I made a mistake before by saying there was.
There is a compensation cap of 8.2 pF between pins 1&8 of the CA3100, which I think
may have many equivalents, and be easily sourced.
Supply is +/- 15 volts.

This is to recover the audio, which is a positive going voltage.
To get a negative going AVC voltage, a second diode and 3k3 is used
with the diode pointing the other way.
Simple!

The last IFT has only one tuned circuit and its secondary
is a small winding to make a fair impedance transformation to drive the low
3k3 input impedance of the detector.



Patrick Turner.

Patrick Turner writes:

Unfortunately, the above reference is encoded with Opera,
and unless you have Opera installed on one's PC, one cannot read the saved
file, which is a complete PITA!

Patrick Turner.

It is standard HTML, maybe you are using a non-compliant browser.

No encoding at all.

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

Hi,

Unfortunately, the above reference is encoded with Opera,
and unless you have Opera installed on one's PC, one cannot read the saved
file, which is a complete PITA!

Patrick Turner.

It is standard HTML, maybe you are using a non-compliant browser.

No encoding at all.

Steve.

That's right, Opera doesn't "encode" anything. Whether it's a saved
file or a cache file, it has the original extension and can be opened
by whatever program is normally used.

73, Alan

Steven Swift wrote:

Patrick Turner writes:

Unfortunately, the above reference is encoded with Opera,
and unless you have Opera installed on one's PC, one cannot read the saved
file, which is a complete PITA!

Patrick Turner.

It is standard HTML, maybe you are using a non-compliant browser.

No encoding at all.

Non-compliant?
I am not sure what that means in geek-speak.

I once tried to instal the free version of Opera to replace Netscape,
which I still use.
I didn't like the Opera because it was riddled with adverts,
and wasn't free, and I went back to NS.
But every now and then something I try to save in my files is saved
under the 'O' banner, and any attempt I make here to open it again
results in my having to start Opera, which I have uninstalled.
Remnants of OPera have stayed behind on my PC, and were probably programmed to
do so, and Opera won't get my patronage.
So I just delete the saved item, and go without.
Its only happened twice, and I sure don't know much about PCs which are a PITA
sometimes.
I was led to assume that perhaps the item I had tried to save had come prepared
by
someone using Opera, that seems to be a silly assumption.

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

In article , Patrick Turner
wrote:

Steven Swift wrote:

Patrick Turner writes:

Unfortunately, the above reference is encoded with Opera,
and unless you have Opera installed on one's PC, one cannot read the saved
file, which is a complete PITA!

Patrick Turner.

It is standard HTML, maybe you are using a non-compliant browser.

No encoding at all.

Non-compliant?
I am not sure what that means in geek-speak.

I once tried to instal the free version of Opera to replace Netscape,
which I still use.
I didn't like the Opera because it was riddled with adverts,
and wasn't free, and I went back to NS.
But every now and then something I try to save in my files is saved
under the 'O' banner, and any attempt I make here to open it again
results in my having to start Opera, which I have uninstalled.
Remnants of OPera have stayed behind on my PC, and were probably programmed to
do so, and Opera won't get my patronage.
So I just delete the saved item, and go without.
Its only happened twice, and I sure don't know much about PCs which are a PITA
sometimes.
I was led to assume that perhaps the item I had tried to save had come
prepared
by
someone using Opera, that seems to be a silly assumption.


More likely it was prepared by someone using "AppleWorks". By what means
are you saving the file in Netscape?


Regards,

John Byrns


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

John Byrns wrote:

In article , Patrick Turner
wrote:

Steven Swift wrote:

Patrick Turner writes:

Unfortunately, the above reference is encoded with Opera,
and unless you have Opera installed on one's PC, one cannot read the saved
file, which is a complete PITA!

Patrick Turner.

It is standard HTML, maybe you are using a non-compliant browser.

No encoding at all.

Non-compliant?
I am not sure what that means in geek-speak.

I once tried to instal the free version of Opera to replace Netscape,
which I still use.
I didn't like the Opera because it was riddled with adverts,
and wasn't free, and I went back to NS.
But every now and then something I try to save in my files is saved
under the 'O' banner, and any attempt I make here to open it again
results in my having to start Opera, which I have uninstalled.
Remnants of OPera have stayed behind on my PC, and were probably programmed to
do so, and Opera won't get my patronage.
So I just delete the saved item, and go without.
Its only happened twice, and I sure don't know much about PCs which are a PITA
sometimes.
I was led to assume that perhaps the item I had tried to save had come
prepared
by
someone using Opera, that seems to be a silly assumption.

More likely it was prepared by someone using "AppleWorks". By what means
are you saving the file in Netscape?

I just clicked 'save as' and selected the appropriate listed file in my
W98 list under Windows Explorer, like I have done on so many other
things with no problems.
A couple of things have somehow listed themselves with the opera 'O' sign,
and I can't get them to save in some other icon, so I just
said to myself I wasn't meant to be able to save that one,
and since I can't open it, I deleted it.
Life isn't perfect, and I don't know everything, and some things don't work out,
and I am too busy to worry too much.....

Patrick Turner.



Regards,

John Byrns

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

"Patrick Turner" wrote in message
...


John Byrns wrote:

In article , Patrick Turner
wrote:

Steven Swift wrote:

Patrick Turner writes:

Unfortunately, the above reference is encoded with Opera,
and unless you have Opera installed on one's PC, one cannot read
the saved
file, which is a complete PITA!

Patrick Turner.

It is standard HTML, maybe you are using a non-compliant browser.

No encoding at all.

Non-compliant?
I am not sure what that means in geek-speak.

I once tried to instal the free version of Opera to replace Netscape,
which I still use.
I didn't like the Opera because it was riddled with adverts,
and wasn't free, and I went back to NS.
But every now and then something I try to save in my files is saved
under the 'O' banner, and any attempt I make here to open it again
results in my having to start Opera, which I have uninstalled.
Remnants of OPera have stayed behind on my PC, and were probably
programmed to
do so, and Opera won't get my patronage.
So I just delete the saved item, and go without.
Its only happened twice, and I sure don't know much about PCs which
are a PITA
sometimes.
I was led to assume that perhaps the item I had tried to save had come
prepared
by
someone using Opera, that seems to be a silly assumption.

More likely it was prepared by someone using "AppleWorks". By what
means
are you saving the file in Netscape?

I just clicked 'save as' and selected the appropriate listed file in my
W98 list under Windows Explorer, like I have done on so many other
things with no problems.
A couple of things have somehow listed themselves with the opera 'O' sign,
and I can't get them to save in some other icon, so I just
said to myself I wasn't meant to be able to save that one,
and since I can't open it, I deleted it.
Life isn't perfect, and I don't know everything, and some things don't
work out,
and I am too busy to worry too much.....



You should be able to right click on that file, and tell it to open with
some other (Netscape or IE) application. Is there something about the file
extension that is different from most? (Perhaps Opera laid claim to .htm
files where your normal browser claims .html, or vice versa). If this is the
case you can go into your IE and reset what opens that extension by default.

A couple of things have somehow listed themselves with the opera 'O' sign,
and I can't get them to save in some other icon, so I just
said to myself I wasn't meant to be able to save that one,
and since I can't open it, I deleted it.
Life isn't perfect, and I don't know everything, and some things don't
work out,
and I am too busy to worry too much.....


You should be able to right click on that file, and tell it to open with
some other (Netscape or IE) application.

I tried to open with IE, but no go.

Is there something about the file
extension that is different from most? (Perhaps Opera laid claim to .htm
files where your normal browser claims .html, or vice versa). If this is the
case you can go into your IE and reset what opens that extension by default.

I have only had this happen with two web pages/files I have tried to save.
Why not all the rest?
I only know about triodes....

Next tinme it happens, I'll fiddle round a bit more....

Patrick Turner.

In rec.antiques.radio+phono Patrick Turner wrote:
I once tried to instal the free version of Opera to replace Netscape,
which I still use.
I didn't like the Opera because it was riddled with adverts,
and wasn't free, and I went back to NS.
But every now and then something I try to save in my files is saved
under the 'O' banner, and any attempt I make here to open it again
results in my having to start Opera, which I have uninstalled.
Remnants of OPera have stayed behind on my PC, and were probably programmed to
do so, and Opera won't get my patronage.

In this case, your uninstall procedure was broken, and you should just
point the registry settings for .html files to netscape again. Maybe
netscape can even do that itself (the procedure is referred to as
setting it as default browser).

---
Met vriendelijke groet,

Maarten Bakker.

Patrick Turner said:

I once tried to instal the free version of Opera to replace Netscape,
which I still use.
I didn't like the Opera because it was riddled with adverts,
and wasn't free, and I went back to NS.

Dunno about Opera, but I use Mozilla to my utmost satisfaction.
Very good popup- and cookie management.
See www.mozilla.org for more details. Free, also.

--
Sander deWaal
Vacuum Audio Consultancy

In article , (Steven
Swift) wrote:

It is hard to believe that the distortion of a reasonably designed diode
detector is anywhere near "a few percent", as simple diode detectors were
used in the modulation monitors used by AM broadcast stations in times
gone by,

Take a look at RDH4 page 1073.

The problem with this is that the RDH4 doesn't even give the operating
parameters for the detector that is discussed on page 1073. The RDH4 is
sort of a light weight book that tries to cover everything from soup to
nuts, and hence can't cover much of anything in any depth.

Even with extreme design precautions you can't get much better than about 2%
(see page 1080-1081).

To work, a diode detector has to "cut-off" for 1/2 the carrier cycle.

The typical diode detector is probably "cut-off" for considerably more
than "1/2 the carrier cycle" due to the effects of the peak hold
capacitor.

This requires that the diode always go through the "knee". A tube diode has
a voltage to the three-halves characteristic. A semiconductor diode has an
exponential characteries. Expand into a Taylor series, and look at the
first couple of terms. Distortion! Diodes as "multipliers" can be made better.

I'm not exactly sure what a "Taylor series" is, but it has been my
understanding that a rigorous mathematical analysis of the diode peak
envelope detector, including the effects of source impedance driving it,
and the peak hold capacitor, is essentially intractable. Something like
the "Taylor series" could probably be used to analyze an averaging type of
diode detector, but typically the diode is used as an envelope peak
detector because the peak hold capacitor improves the linearity of the
detector, except at high modulation percentages, when the modulation
frequency is too high, and the carrier frequency is too low. Most people
think the capacitor is there to filter RF out of the demodulated audio,
but that is only a serendipitous secondary effect.

The RDH4 avoids these problems by using static curves for the diode peak
envelope detector at various static carrier levels, as on page 1075, and
then plotting the diode load line on these curves and calculating the
distortion by graphical means. Notice that the distortion of the example
detector plotted on page 1075 can be considerably reduced by increasing
the average carrier level above the 10 volt peak level used in the
example, but the RDH4 is aimed at cost effective home radio designs, and
higher drive levels for the diode cost money. The distortion comes from
operation in the lower left corner of the graph on page 1075. I thought
lowering the diode load resistor slightly, in addition to increasing the
drive voltage, would also improve the distortion, but when I tried it I
found it didn't seem to work, I don't know if this is because a lower load
resistance doesn't decrease distortion, or if I simply scaled the values
off the graph incorrectly, I will have to recheck my work again in a
couple of days. I do know that you can't go too low with the diode load
resistance, or the linearizing effect of the peak hold capacitor will be
negated, but I assumed that would occur at a considerably lower load
resistance than I tried.


Regards,

John Byrns


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

John Byrns wrote:

In article , (Steven
Swift) wrote:

It is hard to believe that the distortion of a reasonably designed diode
detector is anywhere near "a few percent", as simple diode detectors were
used in the modulation monitors used by AM broadcast stations in times
gone by,

Take a look at RDH4 page 1073.

The problem with this is that the RDH4 doesn't even give the operating
parameters for the detector that is discussed on page 1073. The RDH4 is
sort of a light weight book that tries to cover everything from soup to
nuts, and hence can't cover much of anything in any depth.

Even with extreme design precautions you can't get much better than about 2%
(see page 1080-1081).

To work, a diode detector has to "cut-off" for 1/2 the carrier cycle.

The typical diode detector is probably "cut-off" for considerably more
than "1/2 the carrier cycle" due to the effects of the peak hold
capacitor.

This requires that the diode always go through the "knee". A tube diode has
a voltage to the three-halves characteristic. A semiconductor diode has an
exponential characteries. Expand into a Taylor series, and look at the
first couple of terms. Distortion! Diodes as "multipliers" can be made better.

I'm not exactly sure what a "Taylor series" is, but it has been my
understanding that a rigorous mathematical analysis of the diode peak
envelope detector, including the effects of source impedance driving it,
and the peak hold capacitor, is essentially intractable. Something like
the "Taylor series" could probably be used to analyze an averaging type of
diode detector, but typically the diode is used as an envelope peak
detector because the peak hold capacitor improves the linearity of the
detector, except at high modulation percentages, when the modulation
frequency is too high, and the carrier frequency is too low. Most people
think the capacitor is there to filter RF out of the demodulated audio,
but that is only a serendipitous secondary effect.

The RDH4 avoids these problems by using static curves for the diode peak
envelope detector at various static carrier levels, as on page 1075, and
then plotting the diode load line on these curves and calculating the
distortion by graphical means. Notice that the distortion of the example
detector plotted on page 1075 can be considerably reduced by increasing
the average carrier level above the 10 volt peak level used in the
example, but the RDH4 is aimed at cost effective home radio designs, and
higher drive levels for the diode cost money. The distortion comes from
operation in the lower left corner of the graph on page 1075. I thought
lowering the diode load resistor slightly, in addition to increasing the
drive voltage, would also improve the distortion, but when I tried it I
found it didn't seem to work, I don't know if this is because a lower load
resistance doesn't decrease distortion, or if I simply scaled the values
off the graph incorrectly, I will have to recheck my work again in a
couple of days. I do know that you can't go too low with the diode load
resistance, or the linearizing effect of the peak hold capacitor will be
negated, but I assumed that would occur at a considerably lower load
resistance than I tried.

Indeed RDH4 says a lot about detectors for home radio sets.
In practice, designs were based on a lowest common denominator
approach and sets were limited by careless nitwit accountants who
hated giving the mostly poor buying public any hope of
receiving their AM with any fidelity by denying them enough tubes required for
fidelity.

The RDH4 message starts on page 1072 and continues labouriously
and tediously to 1082,
where grid leak and other types of detectors are explained up to p1087.
If anyone understands all RDH4 has to say on detectors, they deserve an
Honary Degree in Old Fashioned Radio Theory.

The use of a cathode follower after the last IFT secondary to buffer the
detection loading effects on the preceeding IF amp is good practice,
and it allows a germanium diode to be driven with a low impedance,
rather than the waffly high impedance of the anode circuit of the IF amp anode
circuit,
and the resonant impedances of the IFT.

The the sec winding of the last IF can be biased at +30v
from a resistance divider and bypass cap to 0V,
and the live end of the winding biases the CF at 30v, and the cathode
of the CF will be at say 33v, and if you have a load R of 22k to OV,
the CF idle current is 1.5 mA.
1/2 a 12AU7 is an ideal CF tube.

The diode anode is directly connected to the CF cathode
and the diode cathode is connected to 1M to oV,
so an idle bias current of 0.033mA to OV flows in the 1M resistor.
One connects a 270 pF cap across the 1M and that is the RC
circuit which is charged by positive going pulses at 455 kHz, when such a signal is
applied.
Relatively slow variations in the DC level across the 270 pF,
ie, the positive and negative going audio voltages from the positive half of the AM
envelope shape
are allowed to occur due to the discharging of the 270 pF
by what is effectively a near constant current in the 1M resistor, because
peak voltage levels across the 270 pF may only vary
from 33v at no signal to a range of peak voltages from
26v to 40v when the input IF signal is strong, and about what to be expected
from normal operation from local stations using
the middle range of AVC control.

The filtering of 455 kHz ripple voltage from the stream of audio
is easily achived with a following 100k and 47 pF RC filter, and the
audio applied to a second CF, or a low gain first audio amp,
which of course is the other 1/2 of the 12AU7.
Such a detector works very well.

AVC can be generated by having a small cap of say 47 pF connected off the
cathode of the first CF which feeds a second germanium diode's anode
and where its cathode is taken to 0V.
The existing tube diodes in an existing duo diode-pentode IFamp
can be used to make AVC voltage.
The AVC is led away from the diode's anode with 1M to the usual AVC circuit.
I have used such a cap and diode connected from the
IF amp anode without increasing the audio distortion too much.


Patrick Turner.

In article , Patrick Turner
wrote:

Indeed RDH4 says a lot about detectors for home radio sets.
In practice, designs were based on a lowest common denominator
approach and sets were limited by careless nitwit accountants who
hated giving the mostly poor buying public any hope of
receiving their AM with any fidelity by denying them enough tubes required for
fidelity.

The RDH4 message starts on page 1072 and continues labouriously
and tediously to 1082,
where grid leak and other types of detectors are explained up to p1087.
If anyone understands all RDH4 has to say on detectors, they deserve an
Honary Degree in Old Fashioned Radio Theory.

The nearly 11 pages that the RDH4 devotes to diode detectors is only
enough space to give a superficial once over. In "Radio Receiver Design"
Sturley gives the subject of diode detectors in excess of 38 pages,
allowing for considerably more depth in the analysis and design
information presented for diode detectors. The RDH4 is a good source for
getting the initial idea of a topic, but you really need to look to other
sources for in depth information.

The use of a cathode follower after the last IFT secondary to buffer the
detection loading effects on the preceeding IF amp is good practice,
and it allows a germanium diode to be driven with a low impedance,
rather than the waffly high impedance of the anode circuit of the IF amp
anode circuit, and the resonant impedances of the IFT.

Can you explain what the advantage of driving the diode with a cathode
follower is? I understand the advantages of following the diode detector
with a cathode follower to isolate it from AC loading effects, but I have
not come across any suggestion that a very low impedance drive is
especially beneficial.


Regards,

John Byrns


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

John Byrns wrote:

In article , Patrick Turner
wrote:

Indeed RDH4 says a lot about detectors for home radio sets.
In practice, designs were based on a lowest common denominator
approach and sets were limited by careless nitwit accountants who
hated giving the mostly poor buying public any hope of
receiving their AM with any fidelity by denying them enough tubes required for
fidelity.

The RDH4 message starts on page 1072 and continues labouriously
and tediously to 1082,
where grid leak and other types of detectors are explained up to p1087.
If anyone understands all RDH4 has to say on detectors, they deserve an
Honary Degree in Old Fashioned Radio Theory.

The nearly 11 pages that the RDH4 devotes to diode detectors is only
enough space to give a superficial once over. In "Radio Receiver Design"
Sturley gives the subject of diode detectors in excess of 38 pages,
allowing for considerably more depth in the analysis and design
information presented for diode detectors. The RDH4 is a good source for
getting the initial idea of a topic, but you really need to look to other
sources for in depth information.

The use of a cathode follower after the last IFT secondary to buffer the
detection loading effects on the preceeding IF amp is good practice,
and it allows a germanium diode to be driven with a low impedance,
rather than the waffly high impedance of the anode circuit of the IF amp
anode circuit, and the resonant impedances of the IFT.

Can you explain what the advantage of driving the diode with a cathode
follower is? I understand the advantages of following the diode detector
with a cathode follower to isolate it from AC loading effects, but I have
not come across any suggestion that a very low impedance drive is
especially beneficial.

The low impedance output of the CF means the charge currents are supplied
to the RC circuit by the diode with a minimum of series losses,
and better linearity.

Meanwhile the CF imput impedance is extremely high,
and low capacitance, and had almost no effect on the
IFT.
And then if one does want to damp the tuned IFT circuits, a fixed resistance of 100k

can be used which won't adversly load the anode circuit of the IF amp.

Try my idea, you'll like it.

Sure RDH4 may appear to be superficial to some folks, but at times its plain
longwinded.
Its a source of info and inspiration, and like the Bible, full of great ideas,
which should be taken with a grain of salt, but not so much as to
turn yourself into a thoughtless pillar of salt, and have you blindly following the
scriptures
without question.

Patrick Turner.





Regards,

John Byrns

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

In article , Patrick Turner
wrote:

John Byrns wrote:

The use of a cathode follower after the last IFT secondary to buffer the
detection loading effects on the preceeding IF amp is good practice,
and it allows a germanium diode to be driven with a low impedance,
rather than the waffly high impedance of the anode circuit of the IF amp
anode circuit, and the resonant impedances of the IFT.

Can you explain what the advantage of driving the diode with a cathode
follower is? I understand the advantages of following the diode detector
with a cathode follower to isolate it from AC loading effects, but I have
not come across any suggestion that a very low impedance drive is
especially beneficial.

The low impedance output of the CF means the charge currents are supplied
to the RC circuit by the diode with a minimum of series losses,
and better linearity.

I guess I wasn't specific enough in my question, what I was wondering was
specifically how a cathode follower between the IFT and the diode provides
"better linearity"? It's not obvious that the "series losses" would be
reduced enough to justify an extra tube if the linearity isn't improved.

Meanwhile the CF imput impedance is extremely high,
and low capacitance, and had almost no effect on the IFT.
And then if one does want to damp the tuned IFT circuits, a fixed
resistance of 100k

This thread was about wideband High-Fidelity receivers where a properly
designed IFT is going to require some extra loading to achieve the require
bandwidth, why not take advantage of the natural loading provided by the
diode detector rather than adding an extra resistor to the circuit to do
the job, not to mention the extra tube? I don't follow your reasoning at
all when you say "a fixed resistance of 100k" "won't adversly load the
anode circuit of the IF amp"? Why should a diode detector load the anode
circuit of the IF amp any more adversely than an equivalent resistor?


Regards,

John Byrns


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

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

The use of a cathode follower after the last IFT secondary to buffer the
detection loading effects on the preceeding IF amp is good practice,
and it allows a germanium diode to be driven with a low impedance,
rather than the waffly high impedance of the anode circuit of the IF amp
anode circuit, and the resonant impedances of the IFT.

Can you explain what the advantage of driving the diode with a cathode
follower is? I understand the advantages of following the diode detector
with a cathode follower to isolate it from AC loading effects, but I have
not come across any suggestion that a very low impedance drive is
especially beneficial.

The low impedance output of the CF means the charge currents are supplied
to the RC circuit by the diode with a minimum of series losses,
and better linearity.

I guess I wasn't specific enough in my question, what I was wondering was
specifically how a cathode follower between the IFT and the diode provides
"better linearity"? It's not obvious that the "series losses" would be
reduced enough to justify an extra tube if the linearity isn't improved.

In my scheme, the diode is germanium which is forward biased with a small idle
current
from the cathode, and this DC drain does not create a load on the IF amp,
but it does remove the non linear turn on voltage of the diode.
The IF ripple voltage is low, so audio voltage recovered from an envelope is
nearly as high as sen on the envelope.

The variation in ripple voltage during a cycle of audio is low, so linearity
is better.



Meanwhile the CF imput impedance is extremely high,
and low capacitance, and had almost no effect on the IFT.
And then if one does want to damp the tuned IFT circuits, a fixed
resistance of 100k

This thread was about wideband High-Fidelity receivers where a properly
designed IFT is going to require some extra loading to achieve the require
bandwidth, why not take advantage of the natural loading provided by the
diode detector rather than adding an extra resistor to the circuit to do
the job, not to mention the extra tube?

Because the loading by a diode doesn't occur to the whole envelope signal like a
purely resistive
load, and the diode only conducts on the peaks of the IF waves.

I don't follow your reasoning at
all when you say "a fixed resistance of 100k" "won't adversly load the
anode circuit of the IF amp"? Why should a diode detector load the anode
circuit of the IF amp any more adversely than an equivalent resistor?

See above.

I will try to post some radio circuits at ABSE and ABPR tonight.

Patrick Turner.



Regards,

John Byrns

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

In article , Patrick Turner
wrote:

John Byrns wrote:

I guess I wasn't specific enough in my question, what I was wondering was
specifically how a cathode follower between the IFT and the diode provides
"better linearity"? It's not obvious that the "series losses" would be
reduced enough to justify an extra tube if the linearity isn't improved.

In my scheme, the diode is germanium which is forward biased with a small idle
current
from the cathode, and this DC drain does not create a load on the IF amp,
but it does remove the non linear turn on voltage of the diode.

That may well be, but diode bias is a different issue than using a cathode
follower, which isn't necessary to provide bias to the diode when such is
desired.

The IF ripple voltage is low, so audio voltage recovered from an envelope is
nearly as high as sen on the envelope.

The variation in ripple voltage during a cycle of audio is low, so linearity
is better.

Short of a filter, which some detector circuits use, there is always some
IF frequency ripple voltage, and the ripple voltage drops to near zero at
negative modulation peaks. How does your circuit eliminate this
variation?

Meanwhile the CF imput impedance is extremely high,
and low capacitance, and had almost no effect on the IFT.
And then if one does want to damp the tuned IFT circuits, a fixed
resistance of 100k

This thread was about wideband High-Fidelity receivers where a properly
designed IFT is going to require some extra loading to achieve the require
bandwidth, why not take advantage of the natural loading provided by the
diode detector rather than adding an extra resistor to the circuit to do
the job, not to mention the extra tube?

Because the loading by a diode doesn't occur to the whole envelope
signal like a
purely resistive
load, and the diode only conducts on the peaks of the IF waves.

The fact that the diode only conducts on the peaks is of little
consequence to the IF amplifier tube because of the filtering or
"flywheel" effect of the IFT.


Regards,

John Byrns


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

John Byrns wrote:

In article , Patrick Turner
wrote:

John Byrns wrote:

I guess I wasn't specific enough in my question, what I was wondering was
specifically how a cathode follower between the IFT and the diode provides
"better linearity"? It's not obvious that the "series losses" would be
reduced enough to justify an extra tube if the linearity isn't improved.

In my scheme, the diode is germanium which is forward biased with a small idle
current
from the cathode, and this DC drain does not create a load on the IF amp,
but it does remove the non linear turn on voltage of the diode.

That may well be, but diode bias is a different issue than using a cathode
follower, which isn't necessary to provide bias to the diode when such is
desired.

The IF ripple voltage is low, so audio voltage recovered from an envelope is
nearly as high as sen on the envelope.

The variation in ripple voltage during a cycle of audio is low, so linearity
is better.

Short of a filter, which some detector circuits use, there is always some
IF frequency ripple voltage, and the ripple voltage drops to near zero at
negative modulation peaks. How does your circuit eliminate this
variation?

Meanwhile the CF imput impedance is extremely high,
and low capacitance, and had almost no effect on the IFT.
And then if one does want to damp the tuned IFT circuits, a fixed
resistance of 100k

This thread was about wideband High-Fidelity receivers where a properly
designed IFT is going to require some extra loading to achieve the require
bandwidth, why not take advantage of the natural loading provided by the
diode detector rather than adding an extra resistor to the circuit to do
the job, not to mention the extra tube?

Because the loading by a diode doesn't occur to the whole envelope
signal like a
purely resistive
load, and the diode only conducts on the peaks of the IF waves.

The fact that the diode only conducts on the peaks is of little
consequence to the IF amplifier tube because of the filtering or
"flywheel" effect of the IFT.

Regards,

John Byrns

I have posted the schematic of the AM radio I use
at ABSE & ABPR, its the 2nd item in the post "AM recievers and tuners,2."

My schematic has AC loading of the detector circuit in the form of a volume control.

It also has the AGC voltage also derived off the CF, something I had forgotten I'd
modded two years after
I'd originally built the set in 1998.
The positive and negative going voltages derived from the envelope are both taken
from the
samne side of the envelope, the positive going side, and the AGC rectifier has only
33 pF
and its distortion effect on the audio detector's 270 pF cap is quite negligible.
I must have fpound quite enough AGC voltage was generated from this point.

The set does not have as good AGC as one with AGC applied to both the
the mixer and IF amp.
If I were to make a DV amp with two darlington connected pnp transistors, the effect

of the AGC on the one RF tube to which it is applied would be much better.


Another circuit I used in a revised Trio for a client has the output of the
audio detector going to 120k and 47 pF filter after the 270 pF detector cap,
then direct connected to another CF to avoid any loading of the detect circuit.
This allows detection of enormous envelope voltages with very low distortion.

The 1M2 plus 270 pF may seem to have too large a time constant for
detection of large voltages of 10 kHz audio, and inded that is the case
if one wants to detect 35 vrms of audio.
But there is never this much 10 kHz signal in an audio signal where there are high
average levels
at lower F.

The discharge rate of the 1M2 used with 270pF is fast enough to get
more than about 1 vrms of clean 10 kHz modulation .

All diode-RC detectors have reduced undistorted audio output voltage capability
as the frequency rises.

Patrick Turner.




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

In article ,
"Frank Dresser" wrote:

"Steven Swift" wrote in message
...

Hey, don't worry about the rrs gripers. We've discussed detectors there
before, and we will again.



Take a look at RDH4 page 1073.

Even with extreme design precautions you can't get much better than about
2%
(see page 1080-1081).

This guy calculates 0.4% distortion at 50% modulation and 1.6% distortion at
100% modulation.

http://www.amwindow.org/tech/htm/diodedistortion.htm

In a typical diode detector test circuit he measured 0.32% distortion at 50%
modulation and 2% distortion at 100% modulation.


The analysis on this web page is complete nonsense, at least for the type
of diode detector we are discussing here. We are concerned with
High-Fidelity envelope detectors, while the web page analyzes a perfect
square law detector. It starts the analysis of by giving the complete
diode equation, but then quickly says we will forget that and consider the
diode to be a perfect square law device, and not only that, but that it
will be used in some sort of unspecified circuit that maintains the
perfect square law response for the complete detector. I didn't check all
the math after the perfect square law assumption was made, but I will
assume he got it all correct. This type of analysis may have some
application to crystal set design, but not to the type of detectors we are
discussing.

He did compare his results with the results from a test circuit, but I
could find no indication of the signal level he made the measurements at,
perhaps I missed that. Even though the test circuit did include an RC
network type load as used in a peak detector, if he made the measurements
at low levels in the square law region of the diode, the capacitor would
not cause the diode to act as a linear peak detector.

The whole analysis on this web page is too simplistic and is irrelevant to
the subject at hand.


Regards,

John Byrns


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

"John Byrns" wrote in message
...

The analysis on this web page is complete nonsense, at least for the type
of diode detector we are discussing here. We are concerned with
High-Fidelity envelope detectors, while the web page analyzes a perfect
square law detector. It starts the analysis of by giving the complete
diode equation, but then quickly says we will forget that and consider the
diode to be a perfect square law device, and not only that, but that it
will be used in some sort of unspecified circuit that maintains the
perfect square law response for the complete detector. I didn't check all
the math after the perfect square law assumption was made, but I will
assume he got it all correct. This type of analysis may have some
application to crystal set design, but not to the type of detectors we are
discussing.

He did compare his results with the results from a test circuit, but I
could find no indication of the signal level he made the measurements at,
perhaps I missed that. Even though the test circuit did include an RC
network type load as used in a peak detector, if he made the measurements
at low levels in the square law region of the diode, the capacitor would
not cause the diode to act as a linear peak detector.

The whole analysis on this web page is too simplistic and is irrelevant to
the subject at hand.


Regards,

John Byrns

He came up with actual numbers, which is more than most do. Anyway, I also
noticed that there was no mention of the actual voltages the detector was
being driven at.

As far as the square law stuff goes, Terman says a the distortion of a true
square law detector will be m/4. So 80% modulaton will result in 20%
distortion. He might have derived that number, I don't remember. I do
remember the bigger point, that is, that operation in the square law region
is to be minimized for AM radio detectors.

Although I do remember reading that any part of a diodes curve can be
characterized as part of a parabola. I don't know if that's really true or
not, or if I'm actually remembering it correctly. But such an assumption
works fine with the usual rules of diode detectors. Run the diode at a
reasonably high voltage to minimize operation below the knee area of the
curve. Run the diode into a reasonably high resistance to minimize the
effects of the variation in the straighter part of the curve. Keep the DC
and AC resistances in balance.

Frank Dresser

In article ,
"Frank Dresser" wrote:

"John Byrns" wrote in message
...

The analysis on this web page is complete nonsense, at least for the type
of diode detector we are discussing here. We are concerned with
High-Fidelity envelope detectors, while the web page analyzes a perfect
square law detector. It starts the analysis of by giving the complete
diode equation, but then quickly says we will forget that and consider the
diode to be a perfect square law device, and not only that, but that it
will be used in some sort of unspecified circuit that maintains the
perfect square law response for the complete detector. I didn't check all
the math after the perfect square law assumption was made, but I will
assume he got it all correct. This type of analysis may have some
application to crystal set design, but not to the type of detectors we are
discussing.

He did compare his results with the results from a test circuit, but I
could find no indication of the signal level he made the measurements at,
perhaps I missed that. Even though the test circuit did include an RC
network type load as used in a peak detector, if he made the measurements
at low levels in the square law region of the diode, the capacitor would
not cause the diode to act as a linear peak detector.

The whole analysis on this web page is too simplistic and is irrelevant to
the subject at hand.


Regards,

John Byrns

He came up with actual numbers, which is more than most do. Anyway, I also
noticed that there was no mention of the actual voltages the detector was
being driven at.

As far as the square law stuff goes, Terman says a the distortion of a true
square law detector will be m/4. So 80% modulaton will result in 20%
distortion. He might have derived that number, I don't remember.

Yes, that's exactly what I thought, given the analysis methodology he
seemed to be using on the web page, the distortion seemed way too low to
me. You have inspired me to take a closer look and see exactly what he
did, and where he went wrong, or if I have just misinterpreted his
methodology. I will report back in a few days time.

I do
remember the bigger point, that is, that operation in the square law region
is to be minimized for AM radio detectors.

Exactly, which is why I said that the apparent square law analysis given
on the web page was "complete nonsense" in the context of a High-Fidelity
AM receiver.

Although I do remember reading that any part of a diodes curve can be
characterized as part of a parabola.

Yes, I think that is essentially correct.

I don't know if that's really true or
not, or if I'm actually remembering it correctly. But such an assumption
works fine with the usual rules of diode detectors. Run the diode at a
reasonably high voltage to minimize operation below the knee area of the
curve. Run the diode into a reasonably high resistance to minimize the
effects of the variation in the straighter part of the curve. Keep the DC
and AC resistances in balance.

Some people say there is no "knee" in the diode curve, which follows from
your observation "that any part of a diodes curve can be characterized as
part of a parabola."

There is one more thing that contributes to linear operation of a diode
detector, and that is the peak hold capacitor. As long as the capacitor
charges to the peak envelope voltage, the shape of the diode curve getting
there doesn't matter much, whereas if you take the output of the raw diode
and average it by putting it through a low pass filter, then the curvature
of the diode characteristic greatly affects the linearity of the output.
Of course even with the peak hold capacitor there are still problems at
very low signal levels, and also with high negative modulation, and the
peak hold capacitor does introduce problems of its own like tangential
clipping when the modulation at high frequencies is high.


Regards,

John Byrns


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

In article ,
(John Byrns) wrote:

In article ,
"Frank Dresser" wrote:

"John Byrns" wrote in message
...

The whole analysis on this web page is too simplistic and is irrelevant to
the subject at hand.

He came up with actual numbers, which is more than most do. Anyway, I also
noticed that there was no mention of the actual voltages the detector was
being driven at.

As far as the square law stuff goes, Terman says a the distortion of a true
square law detector will be m/4. So 80% modulaton will result in 20%
distortion. He might have derived that number, I don't remember.

Yes, that's exactly what I thought, given the analysis methodology he
seemed to be using on the web page, the distortion seemed way too low to
me. You have inspired me to take a closer look and see exactly what he
did, and where he went wrong, or if I have just misinterpreted his
methodology. I will report back in a few days time.

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.

The analysis starts with the Shockley diode equation, and then the
exponential power series equivalent to the Shockley equation is stated as
equation #2. At this point the author "examines" the second power
component of the equation, not quite making it clear that is all he is
going to examine, and will base the entire analysis on only the second
power component of the diode characteristic. An equation for the output
of a square law diode is given as equation #4, which is derived by
squaring the equation representing a carrier AM modulated by a single
tone. Equation #4 actually represents the V/I characteristic of a square
law diode, and does not necessarily represent the output of such a diode,
but we will accept it as such for the purposes of this analysis.

After considerable mathematical manipulation and six more equations the
author comes to the final diode output in equation #9, and after low pass
filtering to eliminate the carrier and carrier terms in the output he
comes to equation #10 which represents the demodulated signal output from
the detector. The author's equation #10 is:

(10) m(t) = (m**2)/4 + m*cos wmt + (m**2)/8[cos 2wmt]

The authors derivation of equation #9 from equation #4 was too convoluted
for me to easily follow, so I did my own derivation which required only
two intermediate steps rather than the 5 steps the author required, my
result for equation #10 was:

(10) m(t) = 1/2 + (m**2)/4 + m*sin wmt - (m**2)/4[cos 2wmt]

Neglecting the sin in place of cos for the main modulation term, and the
sign on the second harmonic term, we notice that the author lost the DC
term somewhere, and his second harmonic term is half of mine with an 8 in
the denominator rather than the 4 I derived. These differences could be
due to errors in my derivation, which often happen on the first pass, but
considering that my distortion result, discussed next, is the same as
Terman's, it seems likely that 4 is the correct value for the denominator
of the second harmonic term. I plan to eventually try to plow through the
authors derivation of equation #9 to see where he made his errors.

The error in the denominator would only account for a factor of two in the
distortion percentage, but he compounds the error when he calculates
distortion as power ratio rather than a voltage ratio which I believe is
conventional.

Taking the ratio between the amplitude of the fundamental, m*cos wmt, and
the amplitude of the second harmonic, (m**2)/8[cos 2wmt] and squaring the
author comes up with his equation #12 for percent distortion:

(12) THD (%) = (((m**2)/8)**2)/(m**2)) * 100, or ((m**2)/64) *100

which yields 1% distortion at 80% modulation and 1.5625% distortion at
100% modulation.

My version of equation #12, based on the ratio of the fundamental, m*sin
wmt, and the amplitude of the second harmonic, (m**2)/4[cos 2wmt] becomes:

(12) THD (%) = ((m**2)/4)/m) * 100, or (m/4) *100

which yields 20% distortion at 80% modulation and 25% distortion at 100%
modulation. These results show distortion more than an order of magnitude
greater than the distortion figures calculated on the web page. Note that
my result is in agreement with Terman's result at 80% modulation, as
quoted above, which leads me to suspect that I didn't make any serious
mathematical errors in my derivation. The errors in the web page author's
analysis stem from two sources, first the amplitude of the second harmonic
term is too small by a factor of two due to an error or some sort in the
derivation of the equation. The second cause of the error is due to the
fact that the web page author expresses distortion as a power ration
rather than the conventional voltage ratio.

Now of course all this is for a perfect square law detector, which does
not apply to what we have been talking about, which is a peak envelope
detector. The peak envelope detector which is considerably more difficult
to analyze, which probably explains why the author of the web page didn't
even try, and some authorities have gone so far as to say the problem is
so complex that it is basically intractable to rigorous mathematical
analysis.

I hope I didn't make too many typos in this, please let me know if I did
so I can correct them when I post the results of my analysis of exactly
where the author's derivation went wrong.


Regards,

John Byrns


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

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.

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

But anyway, a table at the conclusion of the article
gives the thd at various %m, :-

Modulation
Index (%) THD
(%)
10 1.02
25 0.08
50 0.32
100 2.0
150 6.3

Table 2 - Measured Total
Harmonic Distortion Versus
Modulation Index

But we dunno what the output voltages are, and no doubt the
thd results would be very different if the output voltage was 10v instead of say 1v
at 10% modulation, especially with a solid state diode.

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.

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.

Patrick Turner

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.

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. 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. 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. 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.

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%.

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.


Regards,

John Byrns


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