Matching antenna to crystal radio
 

On Mon, 15 Nov 2010 19:22:37 -0600, "amdx" wrote:

What do you think of this guys numbers and methodology?
He says he can hear .0078 pw with a Adastra Model: 952-207
http://www.crystal-radio.eu/enluidsprekertest.htm

Hi Mike,

Where did the search for hi-Z go when this 16Ohm speaker was hauled
out for listening? OK, sure, it is all a matter of making a match - I
can go with that.

Let's do the math and see where that leads us for the specification
offered:
SPL @ 1W/1m: 112.5dB

When driven by .0078 pw we find ourselves 140dB below the 1 Watt that
yields 112.5 dB SPL heard at 1 meter. That translates to -27.5dB re
the absolute lowest level of hearing.

OK, supposing you are not 1 meter away from that speaker? I can well
anticipate that you would expect the stethoscope lead comes in to
rescue this claim. Does it get us to within 1mM of the cone to make
up the difference? Your ear can not get that close (maybe a cM) and
the volume of air in the tube makes it worse (unless we are using an
Hemholz resonator, and at that, the program material goes out the
window).

Being generous and saying the claim is off by 1 decimal place still
has us sitting in an anechoic chamber. No one has that kind of bucks
for a hobby pursuit except Bill Gates. Even then, this is about the
threshold of hearing for a juvenile. Is your scribbler 17 years old?
I can well imagine you, like myself, even that age out - 3 to 4 times
over. Program content is going to depress these readings by roughly
5dB for age and another 5 to 10dB for frequency variation.

If you want to copy 1WPM CW at 1KHz, this may fly (if you are buried
alone in a cave in South America). Who transmits A3 modulated CW
(yes, a contradiction in acronyms where CW commonly means morse code)
these days?

So, on the commonsense side of this, no that myth is busted.

The author explores efficiency and states:
The efficiency is 7.03µW / 56.8µW = 0.123
Which was my generous offering in an earlier posting (however, the
author stipulates this is a total conversion efficiency for both
speakers).

Going further we observe:
The efficiency is quite varying with different frequencies, at 1 kHz there was a peak.
At other frequencies the efficiency is lower.
This can be caused by resonances in the speakers, because this situation with two speakers connected is quite different from the normal use.
Normal use indeed (what I call listening to program content). There
is every chance that the coupled speakers were driven at a hemholz
resonance. Using the scope probe as a crude ruler, the volume of air
looks to be close to a half wave long.

Note the leading stipulation again:
The efficiency is quite varying with different frequencies
.... indeed.

I have had a hearing test in specially designed chambers, employing a
test that eliminates guessing when the sound is, or is not there. I've
even designed testing systems that use that methodology for measuring
Army helicopter pilot alertness. The psychological pressure of
expecting to hear a faint sound can drive results that are impossible
to replicate without that testing protocol.

Think you could follow the chain of reasoning here to cross-check the
other transducers' performance? If it is on par, then you can trust
the testing methodology. If my back-of-the-napkin calculations are
off, this will reveal it.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
On Mon, 15 Nov 2010 19:22:37 -0600, "amdx" wrote:

What do you think of this guys numbers and methodology?
He says he can hear .0078 pw with a Adastra Model: 952-207
http://www.crystal-radio.eu/enluidsprekertest.htm

Hi Mike,

Where did the search for hi-Z go when this 16Ohm speaker was hauled
out for listening? OK, sure, it is all a matter of making a match - I
can go with that.

Give me a break will ya?
You had said, "As I said, start thinking backwards from the
power delivered to your ear. Can you express that as a number? "
I inserted 1pw.
You then said "this claim you have read is suspect in the highest degree."
So then I find a reference that says .0078pw which is even 12db less than
the claim that is "suspect in the highest degree"
That's how I brought up a 16 ohm speaker.
Richard I'm not disagreeing with you, I'm learning here, I don't have the
knowledge or the math skills to do that. I end up looking up sources, such
as minimum hearing threshold and going to online converters to try and
follow your descriptions, which I appreciate. :-)

I'm exploring other ways that could eliminate
losses. The transformer he would use to transform the 16 ohm speaker
to 1.62 Mohm has about 1.5 db of loss. If I had a 1.62 Mohm speaker
with eqivalent sensitivity to his 16 ohm speaker, I would have a
1.5db gain. Not major but helpful in the search to cut lossses.

Let's do the math and see where that leads us for the specification
offered:
SPL @ 1W/1m: 112.5dB

When driven by .0078 pw we find ourselves 140dB below the 1 Watt that
yields 112.5 dB SPL heard at 1 meter. That translates to -27.5dB re
the absolute lowest level of hearing.


Hmm... seems to match what I found for minimum hearing threshold.


OK, supposing you are not 1 meter away from that speaker? I can well
anticipate that you would expect the stethoscope lead comes in to
rescue this claim. Does it get us to within 1mM of the cone to make
up the difference? Your ear can not get that close (maybe a cM) and
the volume of air in the tube makes it worse (unless we are using an
Hemholz resonator, and at that, the program material goes out the
window).

I don't know but I suspect he just held the Adastra driver up to his ear
for his tests.

Being generous and saying the claim is off by 1 decimal place still
has us sitting in an anechoic chamber. No one has that kind of bucks
for a hobby pursuit except Bill Gates. Even then, this is about the
threshold of hearing for a juvenile. Is your scribbler 17 years old?
I can well imagine you, like myself, even that age out - 3 to 4 times
over. Program content is going to depress these readings by roughly
5dB for age and another 5 to 10dB for frequency variation.


Ya I'm on the upper end on SPL needed for perception.


If you want to copy 1WPM CW at 1KHz, this may fly (if you are buried
alone in a cave in South America). Who transmits A3 modulated CW
(yes, a contradiction in acronyms where CW commonly means morse code)
these days?

So, on the commonsense side of this, no that myth is busted.

The author explores efficiency and states:
The efficiency is 7.03µW / 56.8µW = 0.123
Which was my generous offering in an earlier posting (however, the
author stipulates this is a total conversion efficiency for both
speakers).

Going further we observe:
The efficiency is quite varying with different frequencies, at 1 kHz there
was a peak.
At other frequencies the efficiency is lower.
This can be caused by resonances in the speakers, because this situation
with two speakers connected is quite different from the normal use.
Normal use indeed (what I call listening to program content). There
is every chance that the coupled speakers were driven at a hemholz
resonance. Using the scope probe as a crude ruler, the volume of air
looks to be close to a half wave long.

Note the leading stipulation again:
The efficiency is quite varying with different frequencies
... indeed.

I have had a hearing test in specially designed chambers, employing a
test that eliminates guessing when the sound is, or is not there. I've
even designed testing systems that use that methodology for measuring
Army helicopter pilot alertness. The psychological pressure of
expecting to hear a faint sound can drive results that are impossible
to replicate without that testing protocol.

Think you could follow the chain of reasoning here to cross-check the
other transducers' performance? If it is on par, then you can trust
the testing methodology. If my back-of-the-napkin calculations are
off, this will reveal it.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

Let's do the math and see where that leads us for the specification
offered:
SPL @ 1W/1m: 112.5dB

When driven by .0078 pw we find ourselves 140dB below the 1 Watt that
yields 112.5 dB SPL heard at 1 meter. That translates to -27.5dB re
the absolute lowest level of hearing.

Hi Richard.
Near the bottom of this page http://www.crystal-radio.eu/entrafounit1.htm
The author relates this about the use of his 1.62 Mohm input impedance
transformer driving the Adastra 16 ohm driver.

"when I connect a driver unit to the output of the transformer unit, a
1 kHz test tone on the transformer unit input with a amplitude of
1 mV peak-peak can be easily heard."

So, 1 mv peak to peak is .0003535V rms. V^2/R so .3535^2/ 1.62Mohm =7.7 x
10^-14
Or 0.077pw.
Hmm... that is a factor of 1 decimal unit from his earlier claim.
Or did I make the mistake???
Could this measurement have been made with a x10 scope probe and not noted
in recording of the measurement?
That would increase the power to 0.77pw, getting very close to the minimum
threshold
of hearing.
Inquiring minds want to know.
MikeK

Matching antenna to crystal radio
 

On Tue, 16 Nov 2010 08:42:04 -0600, "amdx" wrote:

Hi Richard.
Near the bottom of this page http://www.crystal-radio.eu/entrafounit1.htm
The author relates this about the use of his 1.62 Mohm input impedance
transformer driving the Adastra 16 ohm driver.

"when I connect a driver unit to the output of the transformer unit, a
1 kHz test tone on the transformer unit input with a amplitude of
1 mV peak-peak can be easily heard."

So, 1 mv peak to peak is .0003535V rms. V^2/R so .3535^2/ 1.62Mohm =7.7 x
10^-14
Or 0.077pw.
Hmm... that is a factor of 1 decimal unit from his earlier claim.
Or did I make the mistake???
Could this measurement have been made with a x10 scope probe and not noted
in recording of the measurement?
That would increase the power to 0.77pw, getting very close to the minimum
threshold
of hearing.
Inquiring minds want to know.
MikeK

Hi Mike,

As you have allowed, error can wriggle into any part of the
computational chain and slip us a 10dB hit, or a 10dB bonus.

I've calibrated laboratory grade Brüel & Kjær microphones and the
process is not done in one sitting.

Here is a very good, online calculator that you should play with:
http://www.ajdesigner.com/phpsound/s...sure_level.php
I asked you for a base power, there is also the matter of distance
from that power source to the ear drum, also the volume of air
involved. By using a combination of these offered equations, you can
(with scrupulous note-taking) find out all the cogent details.

I won't go into the matter of the perception of sound, and the
variation in that with the difference in transverse or longitudinal
sound pressure waves. However, as the word perception is now
introduced; when human senses enter the world of measurement,
measurement becomes vastly more complex (simply because we can fool
ourselves into believing anything). Eliminating the observational
bias is an enormous task.

A simple observation flows from that. Take those two speakers,
face-to-face. I mentioned they constructed a tuned hemholz resonator.
Connect your ear tube to that column. The Q of that resonator is
going to take any ambient noise, select out the resonant frequency and
amplify it. Guess what? You get to hear a signal that was never
applied to the leads! Belief can make for a tenacious trap.

Returning to J. Todd's post:
Put an alligator clip on the antenna lead and run it down the tank to
find max volume, then clip it on.
Gives you absolutely EVERYTHING you need. And, frankly, I am
surprised about your source material bemoaning the transformation loss
of using a transformer to connect their speaker to the Tank.

Consider that the Tank is, as it suggests, the repository of all the
power available to you (a "gas tank" as it were). That same Tank is
ALSO a universal matching unit. Along the length of the coil (let's
pretend that you can connect alligator clips to any point along the
length of that wire) you have a new Z transform of the entire circuit.
Basically from extreme hi-Z to extreme lo-Z and all Zs in between. The
detector/filter/speaker goes to the point that best matches (pun
intended) its Z (or some dozen or two dozen Ohms) and the antenna goes
to its own value Z (some thousands of Ohms) along the length of the
coil. You already have a transformer, what is the need of a lossy,
second unit?

Of course, these connections are going to perturb the Tank and move it
from its rest point. So is any other form of connection. The trick
is to accept this and design that into the final product.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
On Tue, 16 Nov 2010 08:42:04 -0600, "amdx" wrote:

Hi Richard.
Near the bottom of this page http://www.crystal-radio.eu/entrafounit1.htm
The author relates this about the use of his 1.62 Mohm input impedance
transformer driving the Adastra 16 ohm driver.

"when I connect a driver unit to the output of the transformer unit, a
1 kHz test tone on the transformer unit input with a amplitude of
1 mV peak-peak can be easily heard."

So, 1 mv peak to peak is .0003535V rms. V^2/R so .3535^2/ 1.62Mohm =7.7 x
10^-14
Or 0.077pw.
Hmm... that is a factor of 1 decimal unit from his earlier claim.
Or did I make the mistake???
Could this measurement have been made with a x10 scope probe and not noted
in recording of the measurement?
That would increase the power to 0.77pw, getting very close to the
minimum
threshold
of hearing.
Inquiring minds want to know.
MikeK

Hi Mike,

As you have allowed, error can wriggle into any part of the
computational chain and slip us a 10dB hit, or a 10dB bonus.

If you have time could you verify the 1 decimal point error that
his own numbers show. It is in the 4th to the last line on this page.
Near the bottom of this page http://www.crystal-radio.eu/entrafounit1.htm
I have contacted him once for clearification of steps on one of his pages.
He has remove his email from some pages and says he can't answer email, he
also
closed his online store.
I don't want to contact him again unless I'm sure that a correction should
be made.

Regarding 10db errors, I have physicist friend that worked for sonics
company,
he found their reference equipment in the water tank had a +10db error.
He reported that to his superior by showing that a transducer he designed
had more
output than the input.
The superior was very happy the design, the superior didn't get the jist of
what my
friend was trying to show him.


I've calibrated laboratory grade Brüel & Kjær microphones and the
process is not done in one sitting.

Here is a very good, online calculator that you should play with:
http://www.ajdesigner.com/phpsound/s...sure_level.php
I asked you for a base power, there is also the matter of distance
from that power source to the ear drum, also the volume of air
involved. By using a combination of these offered equations, you can
(with scrupulous note-taking) find out all the cogent details.

I won't go into the matter of the perception of sound, and the
variation in that with the difference in transverse or longitudinal
sound pressure waves. However, as the word perception is now
introduced; when human senses enter the world of measurement,
measurement becomes vastly more complex (simply because we can fool
ourselves into believing anything). Eliminating the observational
bias is an enormous task.

Perception may have been a bad word to introduce but even if you call it
threshold of hearing you still have the same problems you point out.

Placebo,
Can you say Power Balance Bracelet, homeopathic medicine, magnetic
shoe inserts or the best one Magic Female Relaxant Fragrance also called
"The Relationship Extender" because it can help you to settle differences,
and allow you to happily co-exist with a woman even at the most difficult
of times. :-)


A simple observation flows from that. Take those two speakers,
face-to-face. I mentioned they constructed a tuned hemholz resonator.
Connect your ear tube to that column. The Q of that resonator is
going to take any ambient noise, select out the resonant frequency and
amplify it. Guess what? You get to hear a signal that was never
applied to the leads! Belief can make for a tenacious trap.

Returning to J. Todd's post:
Put an alligator clip on the antenna lead and run it down the tank to
find max volume, then clip it on.
Gives you absolutely EVERYTHING you need. And, frankly, I am
surprised about your source material bemoaning the transformation loss
of using a transformer to connect their speaker to the Tank.

First,
I'll rephrase what I think you meant to say, I am surprised about YOU
bemoaning the source material transformation loss of using a transformer
to connect their speaker to the Tank.
Even I worded that poorly, but are you suggesting I should not work for
1.5db?

Second,
Tapping down on the tank coil may not work as well as first thought.
You still have diode characteristics to overcome, and as you tap down the
voltage
also decreases. I throw this out not fully aware of how lower voltage, lower
impedance affects the diode characterists, but I know the characteristics
will
change with current. I"ll add the contest guru's that I have noted use high
impedance taps to the detector. Although depending on signal strength they
switch in diodes that better match the current the radio signal is
delivering.



Consider that the Tank is, as it suggests, the repository of all the
power available to you (a "gas tank" as it were). That same Tank is
ALSO a universal matching unit. Along the length of the coil (let's
pretend that you can connect alligator clips to any point along the
length of that wire) you have a new Z transform of the entire circuit.
Basically from extreme hi-Z to extreme lo-Z and all Zs in between. The
detector/filter/speaker goes to the point that best matches (pun
intended) its Z (or some dozen or two dozen Ohms) and the antenna goes
to its own value Z (some thousands of Ohms) along the length of the
coil. You already have a transformer, what is the need of a lossy,
second unit?

Still hyave concern about diode characteristics.

Thanks, MikeK


Of course, these connections are going to perturb the Tank and move it
from its rest point. So is any other form of connection. The trick
is to accept this and design that into the final product.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

Here is some more info for you guys to chew on...

http://www.midnightscience.com/downl...es/anatomy.pdf

Matching antenna to crystal radio
 

On Tue, 16 Nov 2010 14:38:12 -0600, "amdx" wrote:

First,
I'll rephrase what I think you meant to say, I am surprised about YOU
bemoaning the source material transformation loss of using a transformer
to connect their speaker to the Tank.

Why?

Even I worded that poorly, but are you suggesting I should not work for
1.5db?

Why start with a 1.5dB deficit when the Tank is already there to do
the work of matching at no loss?

Second,
Tapping down on the tank coil may not work as well as first thought.

You are going to have to explain that better, because what follows
doesn't.

You still have diode characteristics to overcome, and as you tap down the
voltage
also decreases. I throw this out not fully aware of how lower voltage, lower
impedance affects the diode characterists, but I know the characteristics
will
change with current.

Changed voltage / changed current = changed Z

That's why the Tank is also called a transformer. You could displace
that function into a secondary, lossy transformer, but the same thing
will happen insofar as your last complaint. In other words, you can
add more loss and get the same grief.

I"ll add the contest guru's that I have noted use high
impedance taps to the detector. Although depending on signal strength they
switch in diodes that better match the current the radio signal is
delivering.

Do they offer a case for fumbling through a selection of diodes? At
first blush, the best is going to be the best - hands down.

Still hyave concern about diode characteristics.

Name one characteristic that presents a concern.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
On Tue, 16 Nov 2010 14:38:12 -0600, "amdx" wrote:

First,
I'll rephrase what I think you meant to say, I am surprised about YOU
bemoaning the source material transformation loss of using a transformer
to connect their speaker to the Tank.

Why?

I was trying to make sure I understood what you said, that's all.


Even I worded that poorly, but are you suggesting I should not work for
1.5db?

Why start with a 1.5dB deficit when the Tank is already there to do
the work of matching at no loss?

You have the diode to drive before the audio section and you want to match
the
diodes impedance. Tapping down will allow you to match diode impedance, but
I'm not sure tapped down is where you will find the best diode efficiency.
Your response to my "not sure " is anticipated. :-)


Second,
Tapping down on the tank coil may not work as well as first thought.

You are going to have to explain that better, because what follows
doesn't.


You still have diode characteristics to overcome, and as you tap down the
voltage also decreases.

"Here's a quote from Ben Tongue's webpage;
Many times the question is asked, "What is the best diode to use?" The
answer depends on the specific RF source resistance and audio load impedance
of the Crystal Set in question. At low signal levels the RF input
resistance and audio output resistance of a detector diode are equal to
25,700,000*n/Is Ohms (current in nA). For minimum detector power loss at
very low signal levels with a particular diode, all one has to do is
impedance match the RF source resistance to the diode and impedance match
the diodes' audio output resistance to the headphones by using an
appropriate audio transformer. The lower the Is of the diode, the higher
will be the weak signal sensitivity (volume) from the Crystal Set, provided
it is properly impedance matched to it's circuit (see article #1). This
does not affect strong signal volume. There is one caveat to this, however.
It is assumed that the RF tuned circuits and audio transformer losses don't
change. This can be hard to accomplish. It is assumed that the Rs, diode
junction capacitance, n and reverse leakage are reasonable. If the diode
you want to use has a higher Is than the optimum value, tap it down on the
tuned circuit. If the diode you want to use has a lower Is than the optimum
value, change the tank circuit to one with a higher L and lower C so that
the antenna impedance can be transformed to a higher value and repeat step
#1. "

And yes I note the "tap it down" which is used to match the impedance of the
diode.

Changed voltage / changed current = changed Z

That's why the Tank is also called a transformer. You could displace
that function into a secondary, lossy transformer, but the same thing
will happen insofar as your last complaint. In other words, you can
add more loss and get the same grief.

I"ll add the contest guru's that I have noted use high
impedance taps to the detector. Although depending on signal strength they
switch in diodes that better match the current the radio signal is
delivering.

Do they offer a case for fumbling through a selection of diodes? At
first blush, the best is going to be the best - hands down.

See above.
And yes they sometimes multiple diodes on there radio.

Still hyave concern about diode characteristics.

Name one characteristic that presents a concern.

Saturation current and
axis-crossing resistance equal to Rr
Sorry that's two, but their related.

See Ben's Page http://www.bentongue.com/xtalset/4opd_xfr/4opd_xfr.html

Thanks, MikeK


73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

On Tue, 16 Nov 2010 12:47:02 -0800, Jim wrote:

Here is some more info for you guys to chew on...

http://www.midnightscience.com/downl...es/anatomy.pdf

Thanx Jim,

It seems to be a more complete analysis. I will give it more time
later.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

On Tue, 16 Nov 2010 19:19:09 -0600, "amdx" wrote:

Why start with a 1.5dB deficit when the Tank is already there to do
the work of matching at no loss?

You have the diode to drive before the audio section and you want to match
the
diodes impedance. Tapping down will allow you to match diode impedance, but
I'm not sure tapped down is where you will find the best diode efficiency.
Your response to my "not sure " is anticipated. :-)

Hi Mike,

Unfortunately your response is not an answer. Your response suffers
equally for the proposed additional transformer - and you have added
loss for no net forward movement to the solution.

Second,
Tapping down on the tank coil may not work as well as first thought.

You are going to have to explain that better, because what follows
doesn't.


You still have diode characteristics to overcome, and as you tap down the
voltage also decreases.

"Here's a quote from Ben Tongue's webpage;
Many times the question is asked, "What is the best diode to use?" The
answer depends on the specific RF source resistance and audio load impedance
of the Crystal Set in question.

At first blush I have to ask, "How many source resistances are there
to be found for a Xtal radio?" I am not under the impression you have
much flexibility in that regard.

At low signal levels the RF input
resistance and audio output resistance of a detector diode are equal to
25,700,000*n/Is Ohms (current in nA).

25 million WHAT?

For minimum detector power loss at
very low signal levels with a particular diode,

If it were a "particular" diode, it would seem giving it a part number
would lend authenticity to this report.

Well, the rest reads about like an oath to motherhood and apple pie.

Do they offer a case for fumbling through a selection of diodes? At
first blush, the best is going to be the best - hands down.

See above.
And yes they sometimes multiple diodes on there radio.

I am less than whelmed.

Still hyave concern about diode characteristics.

Name one characteristic that presents a concern.

Saturation current and
axis-crossing resistance equal to Rr
Sorry that's two, but their related.

See Ben's Page http://www.bentongue.com/xtalset/4opd_xfr/4opd_xfr.html

Frankly, it looks like spaghetti math. If it suits you, then there is
a number that will supply the optimal solution - that is the nature of
math, after all. However, too much of this looks circular, especially
when I see complexity piled on top of loss just to return to the same
problem.

However, what it all boils down to is that you have to live with
whatever diode you select, and you shift the tap for the best
performance (not many variables left in the game of Xtal radios, is
there?).

73's
Richard Clark, KB7QHC