Matching antenna to crystal radio
 

Hi Guys,
Assuming I have a tank circuit on a crystal radio with a Z at resonance of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.
If don't think that's what I want to do, tell me that too. :-)
MikeK

Matching antenna to crystal radio
 

On Sun, 14 Nov 2010 19:59:44 -0600, "amdx" wrote:

Hi Guys,
Assuming I have a tank circuit on a crystal radio with a Z at resonance of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.
If don't think that's what I want to do, tell me that too. :-)
MikeK


Hi Mike,

Try thinking backwards. How much current through your headphones/ear
pieces do you need to hear the signal you want? (This is assuming you
are not amplifying the signal, which if that's the case, what's the
point in building a xtal set?).

What is the impedance of your headphones/ear pieces? They will
dictate the "loaded Q" of your tank circuit.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
On Sun, 14 Nov 2010 19:59:44 -0600, "amdx" wrote:

Hi Guys,
Assuming I have a tank circuit on a crystal radio with a Z at resonance
of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.
If don't think that's what I want to do, tell me that too. :-)
MikeK


Hi Mike,

Try thinking backwards. How much current through your headphones/ear
pieces do you need to hear the signal you want? (This is assuming you
are not amplifying the signal, which if that's the case, what's the
point in building a xtal set?).

What is the impedance of your headphones/ear pieces? They will
dictate the "loaded Q" of your tank circuit.

73's
Richard Clark, KB7QHC
Hi Richard,
It all affects the loaded Q, the antenna, the diode, the audio matching
transformer and headphones.
I think the ideal is to impart maximum power to the tank circuit from the
antenna, now you have an
AC power supply with a known source impedance. Then pick your diode and
transformer match
your headphone for max power out...
I'm going through a mental exercise to build the most sensitive crystal
radio I can.
The best scenario would be to build a headphone with about a megaohm of
impedance
and eliminate the matching transformer losses. Here's one form that could
be modified.
http://www.hpfriedrichs.com/images-votc/gallows.jpg
If it's not self explanatory, you connect a stethoscope type headphone to
the tube that sticks out.
So to rephrase my question, how do I raise the impedance of an antenna to a
very high impedance
with minimum losses?
MikeK

Matching antenna to crystal radio
 

On Sun, 14 Nov 2010 23:58:47 -0600, "amdx" wrote:

http://www.hpfriedrichs.com/images-votc/gallows.jpg
If it's not self explanatory, you connect a stethoscope type headphone to
the tube that sticks out.

Not what I would call a megOhm Z candidate in any form as this is the
model for the commonplace 600 Ohm (telephone standard) to 1KOhm
headphone of antiquity. It uses a coil. You should be looking at
piezo.

So to rephrase my question, how do I raise the impedance of an antenna to a
very high impedance
with minimum losses?
MikeK

You could shorten the antenna to an inch or two for AM, but then it
would be shorter than your tank coil, and hence your tank coil should
be the antenna.

This was a toy commonly found in the late 50s when I got it for
Christmas. It was shaped like a Buck Rogers space ship with a ball
handled plunger as the nose cone that adjusted the ferrite in the core
of the coil (to be used as a tuner). Of course the longest wire was
the earphone lead (all of a foot or 18 inches which would still
constitute an extremenly high Z antenna that you seek).

I lived outside of San Francisco at the time, and AM stations were
unknown to it. However, I could get some Marine traffic like the
Coast Guard (I had a view of the Ocean from the hills around Pacific
Manor, now Pacifica).

Very uninspired performance to say the least.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

On 15 nov, 02:59, "amdx" wrote:
Hi Guys,
*Assuming I have a tank circuit on a crystal radio with a Z at resonance of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.
* If don't think that's what I want to do, tell me that too. :-)
* * * * * * * * * * * * * * * * * * *MikeK

Hello Mike,

Assuming you have a long wire outside and a ground provision, you may
use an inductive coupling. By changing the distance between the
antenna coil and the receiver coil, you modify the impedance
transformation.

Other method is capacitive coupling. Probably positioning the end of
the antenna wire close to the high impedance side of the tank circuit
will give the desired effect. Changing the distance changes the
coupling.

For inductive coupling, your receiver circuit can be floating, for
capacitive coupling, the receiver should be grounded.

By changing the coupling you can optimize for maximum selectivity
(with reduced sensitivity) or maximum sensitivity (with reduces
selectivity).

Regarding the antenna, assuming LW and AM reception, long combined
with high gives strongest signal, hence you can reduce the coupling to
get best selectivity.


Best regards,


Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me very likely

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
On Sun, 14 Nov 2010 23:58:47 -0600, "amdx" wrote:

http://www.hpfriedrichs.com/images-votc/gallows.jpg
If it's not self explanatory, you connect a stethoscope type headphone to
the tube that sticks out.

Not what I would call a megOhm Z candidate in any form as this is the
model for the commonplace 600 Ohm (telephone standard) to 1KOhm
headphone of antiquity. It uses a coil. You should be looking at
piezo.

Piezo is a candidate, but also on the table is a C shape laminated core
with a
small gap. The gap will be large enough that a small magnet will fit in it.
The magnet
is connected to a lever and on the other end is a diaphragm. The core will
be large
enough to hold thousands of turns. Possibly even a E I core with the a gap
milled in
the center leg for the magnet/lever assembly. A coil can be put on each of
the outer
legs. Not sure, but I think the center leg should be cone shaped to focus
the magnetic
field at the magnet. The magnet/lever assembly should have low mass.The
coils will
have taps for a va
Anyway that is the idea I'm working with at the moment.
Regarding piezos, I envision multiple piezo with a switching arrangement to
alter the impedance to match the impedance of the radio.


So to rephrase my question, how do I raise the impedance of an antenna to
a
very high impedance
with minimum losses?
MikeK

You could shorten the antenna to an inch or two for AM, but then it
would be shorter than your tank coil, and hence your tank coil should
be the antenna.

Trying to maximum signal for contest situations want a longer antenna.
Thanks, MikeK

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

"Wimpie" wrote in message
...
On 15 nov, 02:59, "amdx" wrote:
Hi Guys,
Assuming I have a tank circuit on a crystal radio with a Z at resonance of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.
If don't think that's what I want to do, tell me that too. :-)
MikeK

Hello Mike,

Assuming you have a long wire outside and a ground provision, you may
use an inductive coupling. By changing the distance between the
antenna coil and the receiver coil, you modify the impedance
transformation.

Other method is capacitive coupling. Probably positioning the end of
the antenna wire close to the high impedance side of the tank circuit
will give the desired effect. Changing the distance changes the
coupling.

Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me very likely
It seem a common method to couple the antenna is just a single series
variable capacitor. I don't know if this method couples maximum energy to
the radio. ??
Normally we transform our antenna to 50 ohms, in this case we would like
to see 1 million ohms, I'm not sure that can be done, and if it can the
losses
may be higher than having a mismatch.
Thanks, MikeK

Matching antenna to crystal radio
 

In article ,
says...
Hi Guys,
Assuming I have a tank circuit on a crystal radio with a Z at resonance of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.
If don't think that's what I want to do, tell me that too. :-)
MikeK



Put an alligator clip on the antenna lead and run it down the tank to
find max volume, then clip it on.

Matching antenna to crystal radio
 

"J. Todd" wrote in message
...
In article ,
says...
Hi Guys,
Assuming I have a tank circuit on a crystal radio with a Z at resonance
of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.
If don't think that's what I want to do, tell me that too. :-)
MikeK



Put an alligator clip on the antenna lead and run it down the tank to
find max volume, then clip it on.
Use a fork to scoop water out of a glass to satisfy your thirst.
I will work, just not well.
MikeK

Matching antenna to crystal radio
 

On Mon, 15 Nov 2010 09:17:30 -0600, "amdx" wrote:

C shape laminated core
with a
small gap. The gap will be large enough that a small magnet will fit in it.
The magnet
is connected to a lever and on the other end is a diaphragm.

This doesn't sound like a Crystal radio project at all. You describe
nothing that comes close to even 1KOhm, much less 1MOhm in load. Your
descriptions all use appeals to sensitivity, not impedance.

Trying to maximum signal for contest situations want a longer antenna.

This confounds your desire for higher Z. In the extreme (antenna of
several wavelengths and necessarily close to ground) will be less than
1KOhm. In the mid-range, could be hi-Z IFF it is a halfwave long. In
the conventional lengths, some may pose a moderately hi-Z (maybe
KOhms). None will exhibit the Z you anticipate for your Tank.

As I said, start thinking backwards from the power delivered to your
ear. Can you express that as a number? Not much point in the rest of
this if you cannot.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

On Mon, 15 Nov 2010 09:59:06 -0600, "amdx" wrote:

Put an alligator clip on the antenna lead and run it down the tank to
find max volume, then clip it on.
Use a fork to scoop water out of a glass to satisfy your thirst.
I will work, just not well.

Hi Mike,

Being facetious in the face of an answer that responds exactly to
what you want is not very smart.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
On Mon, 15 Nov 2010 09:59:06 -0600, "amdx" wrote:

Put an alligator clip on the antenna lead and run it down the tank to
find max volume, then clip it on.
Use a fork to scoop water out of a glass to satisfy your thirst.
I will work, just not well.

Hi Mike,

Being facetious in the face of an answer that responds exactly to
what you want is not very smart.

73's
Richard Clark, KB7QHC

Richard you are right, I read it wrong.
I thought he was just being smart because it's a crystal radio and he wanted
me
to just grab a alligator clip and connect the antenna ( I missed the taps
part)
I apologize J.Todd.
Connecting the antenna to taps on the coil is common, I don't believe this
method transfers maximum energy into the tank circuit, But I am open to more
info about that.
Also I expect any high performance crystal radio to be made with
litz wire, I suppose taps could be made to litz but I have looked at a lot
of
radios and don't recall ever seeing taps on a litz wire coil.
J.Todd I apologize for my smart alec remark.
MikeK

Matching antenna to crystal radio
 

On 15 nov, 16:23, "amdx" wrote:
"Wimpie" wrote in message

....
On 15 nov, 02:59, "amdx" wrote:

Hi Guys,
Assuming I have a tank circuit on a crystal radio with a Z at resonance of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.
If don't think that's what I want to do, tell me that too. :-)
MikeK

Hello Mike,

Assuming you have a long wire outside and a ground provision, you may
use an inductive coupling. *By changing the distance between the
antenna coil and the receiver coil, you modify the impedance
transformation.

Other method is capacitive coupling. *Probably positioning the end of
the antenna wire close to the high impedance side of the tank circuit
will give the desired effect. Changing the distance changes the
coupling.

Wim
PA3DJSwww.tetech.nl
without abc, PM will reach me very likely
*It seem a common method to couple the antenna is just a single series
variable capacitor. I don't know if this method couples maximum energy to
the radio. ??

Yes, with the correct value, it will.

*Normally we transform our antenna to 50 ohms, in this case we would like
to see 1 million ohms, I'm not sure that can be done, and if it can the
losses
may be higher than having a mismatch.
* * * * * * * * * * * Thanks, MikeK

Hello Mike,

Regarding the 1M Ohm impedance.
If you can make a tank circuit with 1MOhm impedance at resonance, you
can transform your antenna impedance to that value. You use your
resonant circuit as part of the impedance transformer. Even in case
of a ohmic 50 Ohms antenna impedance, you can transform this to 1 Mohm
(inductive or capacitive coupling). Maybe you have to combine the
coupling capacitor with a tap on the coil.

Regarding your detector.
In the detector circuit you transform a high impedance (around 1 MOhm)
to a lower impedance to find the sweet spot for your detector diode /
LF load combination.

If you have a simulator (for example SPICE type SW), you can model
your antenna as a voltage source in series with a capacitance (pF
range) and some resistance (1..100 Ohm range, depending on ground
provision).

By changing the coupling capacitance from the antenna to the top of
your resonant circuit, you can see what happens (in an .AC sweep).
You will see impedance transformation (that is more output voltage
than input voltage) and of course some detuning of your circuit
because of the additional capacitance.

If you want to do some hand calculation, search for: L impedance
transformation network.

Best regards,


Wim
PA3DJS
www.tetech.nl
please remove abc first in case of PM

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
On Mon, 15 Nov 2010 09:17:30 -0600, "amdx" wrote:

C shape laminated core
with a
small gap. The gap will be large enough that a small magnet will fit in
it.
The magnet
is connected to a lever and on the other end is a diaphragm.

This doesn't sound like a Crystal radio project at all. You describe
nothing that comes close to even 1KOhm, much less 1MOhm in load. Your
descriptions all use appeals to sensitivity, not impedance.

Trying to maximum signal for contest situations want a longer antenna.

This confounds your desire for higher Z. In the extreme (antenna of
several wavelengths and necessarily close to ground) will be less than
1KOhm. In the mid-range, could be hi-Z IFF it is a halfwave long. In
the conventional lengths, some may pose a moderately hi-Z (maybe
KOhms). None will exhibit the Z you anticipate for your Tank.

As I said, start thinking backwards from the power delivered to your
ear. Can you express that as a number? Not much point in the rest of
this if you cannot.

73's
Richard Clark, KB7QHC

Hi Richard,
I have probably confused things, I have 4 or 5 threads running at this
time.

The C core EI core thing is a starting attempt to build a speaker with a
high impedance
to eliminate the losses of a matching transformer. The whole excercise is to
build a crystal
radio that will eack out the most sensitivity.

1 picowatt to the earphone is a good number.

For sensitivity the starting point has got to be the tank circuit, you
want to build
an inductor with very high Q and then mate that to a good quality capacitor.
A Q of 1000 is possible over much of the AM BCB.
Can we agree on that?

Now you need to couple in energy from an antenna. If this is adjusted for
maximum power transfer, we have reduced the Q by 1/2 or Q=500.
Assuming a 240uh inductor and frequency of 1 Mhz the XL is 1507 ohms,
multiply that by the antenna loaded tank Q of 500 and we have an Rp =
753,500 ohms.
Does that work for you?

I think I found a good site for the antenna matching;
http://www.crystal-radio.eu/enantunittest1.htm


Now we need to detect and tranfer the signal to a transducer

I'll stop here till I get some feedback, I don't know my question anymore? \
:-)
Mike.

Matching antenna to crystal radio
 

"amdx" wrote in
:

....
Connecting the antenna to taps on the coil is common, I don't believe
this
method transfers maximum energy into the tank circuit, But I am open
to more info about that.

Well, you have to move beyond "believing" and do some analysis.

Broadly, adjusting the tap point, and retuning for maximum output is
finding the point of maximum power transfer for the given components and
source impedance.

I am quite skeptical (that is like "don't belive") that your scheme for
headphones is going to deliver what you suggest.

When I was a kid, these things here ALL used a crystal (or piezo)
earpiece, which has an impedance that looks like extreme R and a very
small shunt C, in all a very high impedance at audio frequencies of
interest.

Look at http://www.jaycar.com.au/productView.asp?ID=AS3305
&keywords=earpiece&form=KEYWORD for an example. (You probably will need
to fix the split URL. They also have a simple crystal radio kit in the
catalogue, no doubt suppliers in your country do also.

Traditionally, these were used with improvised smallish antennas, eg bed
iron, and that brought in too many stations. To obtain benefit from
enhanced sensitivity, you might need to be in a very quiet location, and
have extreme selectivity... both are practical issues.

Owen

Matching antenna to crystal radio
 

amdx wrote:


The C core EI core thing is a starting attempt to build a speaker with a
high impedance
to eliminate the losses of a matching transformer. The whole excercise is
to build a crystal
radio that will eack out the most sensitivity.

1 picowatt to the earphone is a good number.

You may want to make sure this enough to be audible. An iPod may output 30
milliwatts which is probably more than you would ever need/get. 1 picowatt
to a headphone may not be sufficient.


For sensitivity the starting point has got to be the tank circuit, you
want to build
an inductor with very high Q and then mate that to a good quality
capacitor. A Q of 1000 is possible over much of the AM BCB.
Can we agree on that?

Have you considered what Q=1000 does to the bandwidth of the received
signal?



Now you need to couple in energy from an antenna. If this is adjusted for
maximum power transfer, we have reduced the Q by 1/2 or Q=500.
Assuming a 240uh inductor and frequency of 1 Mhz the XL is 1507 ohms,
multiply that by the antenna loaded tank Q of 500 and we have an Rp =
753,500 ohms.
Does that work for you?

Won't both the antenna and the load serve to reduce the Q? You need to be
looking at how power is transferred from the antenna to the earphone. Trying
to optimize one part at a time may not yield the best result.



I think I found a good site for the antenna matching;
http://www.crystal-radio.eu/enantunittest1.htm


Now we need to detect and tranfer the signal to a transducer

I'll stop here till I get some feedback, I don't know my question anymore?
\
:-)
Mike.

Matching antenna to crystal radio
 

"Owen Duffy" wrote in message
...
"amdx" wrote in
:

...
Connecting the antenna to taps on the coil is common, I don't believe
this
method transfers maximum energy into the tank circuit, But I am open
to more info about that.

Well, you have to move beyond "believing" and do some analysis.

Broadly, adjusting the tap point, and retuning for maximum output is
finding the point of maximum power transfer for the given components and
source impedance.


I am quite skeptical (that is like "don't belive") that your scheme for
headphones is going to deliver what you suggest.

When I was a kid, these things here ALL used a crystal (or piezo)
earpiece, which has an impedance that looks like extreme R and a very
small shunt C, in all a very high impedance at audio frequencies of
interest.

Look at http://www.jaycar.com.au/productView.asp?ID=AS3305
&keywords=earpiece&form=KEYWORD for an example. (You probably will need
to fix the split URL. They also have a simple crystal radio kit in the
catalogue, no doubt suppliers in your country do also.

Traditionally, these were used with improvised smallish antennas, eg bed
iron, and that brought in too many stations. To obtain benefit from
enhanced sensitivity, you might need to be in a very quiet location, and
have extreme selectivity... both are practical issues.

Owen
Hey Owen,
Ok, so we find a tap that is the match to the antenna and then maximum
energy is
transferred across the turns from the tap to ground. And because those turns
are tightly coupled to the rest of the inductor the maximum energy is
transferred from
the antenna to the inductor.

The speaker build was a different thread but I'll pass along what started
me thinking.
http://www.hpfriedrichs.com/images-o...l/gallows1.jpg
and
http://www.hpfriedrichs.com/images-o...n/toms-ear.jpg
These are speakers that drive a stethoscope style headphone.
So I was thinking with a larger core so I could wind a high impedance
electromagnet and with new high flux magnets have something more sensitive
than conventional headphones.
Here's a concept drawing;
http://i395.photobucket.com/albums/p...hapedpoles.jpg

MikeK

Matching antenna to crystal radio
 

"joe" wrote in message
...
amdx wrote:


The C core EI core thing is a starting attempt to build a speaker with a
high impedance
to eliminate the losses of a matching transformer. The whole excercise is
to build a crystal
radio that will eack out the most sensitivity.

1 picowatt to the earphone is a good number.

You may want to make sure this enough to be audible. An iPod may output 30
milliwatts which is probably more than you would ever need/get. 1 picowatt
to a headphone may not be sufficient.

I can only go by what I have read on the crystal radio groups and they
say 1pw
is audable with very sensitive headphones..

For sensitivity the starting point has got to be the tank circuit, you
want to build
an inductor with very high Q and then mate that to a good quality
capacitor. A Q of 1000 is possible over much of the AM BCB.
Can we agree on that?

Have you considered what Q=1000 does to the bandwidth of the received
signal?

Ya, it would limit bandwidth. But to much Q is easy to solve and hard to
get.
That is only unloaded Q of the tank, adding the antenna brings that down to
Q=500.
Then comes the load from the detector and then the audio transducer
assembly.



Now you need to couple in energy from an antenna. If this is adjusted for
maximum power transfer, we have reduced the Q by 1/2 or Q=500.
Assuming a 240uh inductor and frequency of 1 Mhz the XL is 1507 ohms,
multiply that by the antenna loaded tank Q of 500 and we have an Rp =
753,500 ohms.
Does that work for you?

Won't both the antenna and the load serve to reduce the Q? You need to be
looking at how power is transferred from the antenna to the earphone.
Trying
to optimize one part at a time may not yield the best result.

Yes, absolutely. I think the optimization is in the tank circuit after
that
it is impedance matching.

MikeK


I think I found a good site for the antenna matching;
http://www.crystal-radio.eu/enantunittest1.htm


Now we need to detect and tranfer the signal to a transducer

I'll stop here till I get some feedback, I don't know my question
anymore?
\
:-)
Mike.

Matching antenna to crystal radio
 

On Mon, 15 Nov 2010 17:56:16 -0600, "amdx" wrote:

I can only go by what I have read on the crystal radio groups and they
say 1pw
is audable with very sensitive headphones..

Hi Mike,

You should consider their being very good at this then. 1 pW is the
lowest limit of hearing at 1KHz. No speaker/transducer is 100%
efficient. So, automatically, this claim you have read is suspect in
the highest degree.

Let's work these numbers further. The transducer elements you have
been describing may be sensitive, but that is not the same thing as
efficient. Given that they are ancient magnet and diaphram
constructions, they would be pushing the limits at 10%.

Further, your chosen power level of 1pW would not be heard but in a
very special anechoic chamber, and even then your heart and your
breath would be in competition as QRN. Speach as perceived to be at
normal quiet talking levels would be 40dB more powerful (and, again,
in a quiet surrounding like a library). This would be a normal
expectation of program content sound level.

Being generous (good efficiency and whispers at 1 meter in the
library), I would suspect that your receive power level would be
closer to 1nW and this would be straining things for a real listening
experience.

For sensitivity the starting point has got to be the tank circuit, you
want to build
an inductor with very high Q and then mate that to a good quality
capacitor. A Q of 1000 is possible over much of the AM BCB.
Can we agree on that?

Have you considered what Q=1000 does to the bandwidth of the received
signal?

Ya, it would limit bandwidth. But to much Q is easy to solve and hard to
get.
That is only unloaded Q of the tank, adding the antenna brings that down to
Q=500.
Then comes the load from the detector and then the audio transducer
assembly.

In the middle of the band, it would give you poor telephone audio
quality. However, many hams find it suitable for DX work.


Now you need to couple in energy from an antenna. If this is adjusted for
maximum power transfer, we have reduced the Q by 1/2 or Q=500.
Assuming a 240uh inductor and frequency of 1 Mhz the XL is 1507 ohms,
multiply that by the antenna loaded tank Q of 500 and we have an Rp =
753,500 ohms.
Does that work for you?

Good enough to pitch back and forth, much as your power level.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
On Mon, 15 Nov 2010 17:56:16 -0600, "amdx" wrote:

I can only go by what I have read on the crystal radio groups and they
say 1pw
is audable with very sensitive headphones..

Hi Mike,

You should consider their being very good at this then. 1 pW is the
lowest limit of hearing at 1KHz. No speaker/transducer is 100%
efficient. So, automatically, this claim you have read is suspect in
the highest degree.


Hi Richard,
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
MikeK


73's
Richard Clark, KB7QHC

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

Matching antenna to crystal radio
 

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

You have the diode to drive before the audio section and you want to match
the
diodes impedance.

Hi Mike,

This seems to wander the field when there are conflicting agendas on
the table. The wandering is due in large part to the absence of
specific numbers, and in this particular case, even the sense of
scale.

We have an audio Z match. We have a diode Z match. There is no sense
that if this is a high-Z or a low-Z for either/both/neither.

To this point, you have hewed to the commonplace magnetic speaker, and
from that I can only imagine that the problem with audio match is
transforming from a high (diode) Z to a low (speaker) Z. But from the
numbers, it would seem that both diode and speaker Zs are on par. I
could be wrong because this drift takes me into guessing.

Solve your problem and get a piezo headphone (or make one, this is the
tradition of Xtal radio, n'est pas?). They have to exhibit at least
10KOhm if not a bajillion ohms. If there isn't enough current to fire
the diode, Guess What? Slap a sacrificial resistor across the piezo
leads!

Radio Shack sells (or used to the last time I bought one) two or three
inch barium titanate ceramic disks that are offered as buzzer elements
(or rob a clock alarm for its buzzer - these things are a drug on the
market).

* * * * * * * * * * *

Now, if you only return to complain that the Hi-Z phones cause a
problem somewhere else; then I would recommend you abandon circuit
design and take up the study of math employing figures of merit. Such
assignments of merit are subjective, of course, but then you get to
own your personal solution. Discussion that follows this satisfactory
conclusion then enters the appropriate arena of philosophical or
religious controversy. This will certainly garner far more
participation in this group.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
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.

Every time you change frequency you change source resistance.
XL times Q equals source resistance, Q changes with frequency,
and XL changes with frequency.
Also when you change to a different station with a different signal strength
you change the current through the diode, this changes the resistance the
diode
presents to the tank.

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?

I don't know what that is derived from.


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?).

There are dozens of diodes to pick from, depends on the tank Z
and signal strength. I don't know what you mean when you say there aren't
many variables, there are many, many!
Coil Type (solenoid, spider, 3D solenoid)
Coil Form Material, paper, PVC, polypropylene, etc.
Wire type, solid, Litz
Antenna Match technique, Tap, cap tune, inductance coupling
Diodes, Diodes, Diodes
Audio, Transformer matching , high impedance piezo, sound powered
headphones, crystal earphone, horn driver.

Here's some more info on the diode selection and why.
Richard I'm well aware of your great knowledge (not being facetious)
and my lack of math and knowledge on this, but I'm to the point where
it seems you are not willing to learn new information. It seems you already
know it all. This especially in regards to the idea that the diodes
characterists
are very important to losses in the radio.
I think one of these pages has a graph showing a diode not matched to the
current available has a 33db loss.
Here's more diode info.
http://www.crystal-radio.eu/endiodes.htm
http://www.bentongue.com/xtalset/17Is_n/17Is_n.html
http://www.klimaco.com/HAMRADIOPAGES/xtal_how_to.htm

I do appreciate your time and the discusion, I did learn from it.
I'm going to take a few days off.
Sincerely, MikeK




73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

In article ,
Richard Clark wrote:

We have an audio Z match. We have a diode Z match. There is no sense
that if this is a high-Z or a low-Z for either/both/neither.

Richard-

We have a diode detector, which is nonlinear. If you allow a filter
capacitor on its output, there is current flow only on alternate RF
voltage peaks, in order to charge up the capacitor for the amount lost
to the audio load during the cycle. Its effect on circuit Q may be a
fraction of the total, also consisting of coil Q and input circuit
matching.

Therefore you want the diode connected to the high end of the coil, not
transformed to a lower impedance point on the coil.

Load impedance will affect audio level, so should be kept high for that
reason. However there may be some value of load that produces the
greatest audio output voltage. If too high, the filter capacitor would
charge to the peak of the modulation waveform and stay there.

Worst case is a low impedance audio load and no filter capacitor. Half
of the RF waveform is essentially cut off, leaving a peak-to-peak value
of one half the open circuit value. Since energy is extracted from the
circuit during the conduction cycle, the effect on Q should be
approximately the same as if a resistor having the same peak-to-peak
effect was connected across the circuit, disregarding the RMS value of a
half-sine waveform.

Fred
K4DII

Matching antenna to crystal radio
 

On Wed, 17 Nov 2010 09:17:51 -0600, "amdx" wrote:

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.

Every time you change frequency you change source resistance.
XL times Q equals source resistance, Q changes with frequency,
and XL changes with frequency.

Hi Mike,

There are a number of problems here. Q is strictly a function of
RESISTANCE and nothing else.

What you call source resistance, when using the math you provide, is
actually source impedance. Impedance embraces resistance and is
solely resistance when reactance is gone - such as at resonance.
However, it would seem that the Xtal Radio community treats reactance
as resistance interchangeably.

That is fine to a point, but it introduces serious problems in the
usage of the term "match" as there are actually several types of
"matching" and each has its peculiarity (only peculiar when you are
unfamiliar with the other types).

It is a given that you are going to have to change either Xc or Xl if
you are going to tune to another frequency. This alters the circuit
Z, certainly; and for the AM band you have a 3:1 variation from band
end-to-end.

Also when you change to a different station with a different signal strength
you change the current through the diode, this changes the resistance the
diode
presents to the tank.

Without numbers, this is like anticipating worry about your MPG
driving up a hill in comparison to driving down the same hill. Yes, a
wild variation, but do you give up cars and start walking instead?
Some of these "concerns" sound like they come from the AVC needy. I
thought Xtal Radio folks would man up and get with the program.



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?).

There are dozens of diodes to pick from, depends on the tank Z
and signal strength.

No, actually you've either mis-read the intent (which is certainly a
problem with that author's hodge-podge writing style) or you've read
too many written sources that each only see part of the elephant.
"It's a snake! We need something bulky."
"It's a wall! We need something slim."
"It's thin and flappy! We need something sturdy."

The problem with the diode is in its forward current and reverse
current. If they are about the same, you don't have a rectifier. This
would be a weak signal problem. The forward current defines the
series resistance of the diode and how much that is in comparison to
the load defines the efficiency. You want more current to lower the
diode resistance to increase the efficiency. Unfortunately this
demands you have a higher source voltage that offers less current
(Catch-22).

However, this problem is strictly for a low Z load like a magnetic
speaker - and thus enters the consternation over competing agendas
that gives everyone the fits that seems they enjoy agonizing over when
the solution is obvious. I will touch on that next:

I don't know what you mean when you say there aren't
many variables, there are many, many!
Coil Type (solenoid, spider, 3D solenoid)
Coil Form Material, paper, PVC, polypropylene, etc.

Those are non-starters for those who love to struggle in hope against
reality.

Wire type, solid, Litz

Ah yes, the magic Litz wire that is the salvation. The solution for
the problem that doesn't matter. You do this because you can, not
because you need to. And then you return to life with the car still
in the ditch (but you changed the air in the tires).

Antenna Match technique, Tap, cap tune, inductance coupling

This has been long figured out. For nearly a century.

Diodes, Diodes, Diodes

Whose solution is found in:

Audio, Transformer matching , high impedance piezo, sound powered
headphones, crystal earphone, horn driver.

Whose choice is obvious in hi impedance.

Like I said, there are not that many variables, until you find someone
on a soap box with a stump speech about the invidious dereliction of
design introduced with the Philips head screw. The advantages of the
Bristol head anyone?

Do not confuse the multitude of competing and contradicting factors as
the multitude of variables.

Introduce figure of merit to the discussion and argue about that. If
that gets resolved, the solution will pop right out.

Here's some more info on the diode selection and why.
Richard I'm well aware of your great knowledge (not being facetious)
and my lack of math and knowledge on this, but I'm to the point where
it seems you are not willing to learn new information.

There is no new information. It is a niche application you are
talking about, not new science. The niche has its concerns and they
are impacted by issues that are rarely a problem for the standard
usage of the components you mention, but there have been no new
devices introduced in this discussion. I see nothing innovative. In
fact, the discussion is so in-bred it lacks coverage outside of a
clubbish mainstream. I will offer something new below that is
actually quite old.

It seems you already
know it all. This especially in regards to the idea that the diodes
characterists
are very important to losses in the radio.

I have designed at the extreme edges of component characteristics,
true. More often in regard to temperature variation, mechanical
vibration, noise, accuracy, resolution, speed, bandwidth, linearity -
all that went towards continuous service in a largish orange box in
some jets.

I have studied diodes to no end, especially LEDs and photodetectors.
Talk about marginal signal detection and loss. I started with 1n34s
being used as varactors back in the late 60s. PIN and Tunnel diodes
followed. There is a world of non-linear devices out there. I
especially like the surgistor and posistor. Any reports of their use
in Xtal sets?

I have maintained a number of audio standards and measurement devices.
I have had to repair detectors that measured absolute value voltage
out to 7 places, the same issues arose there too. Small currents?
Like those that rise continuously through the air in femto-ampere
levels? You would need polonium treated probes to measure them (or
just use the anti-static record brushes of the 1970s).

I think one of these pages has a graph showing a diode not matched to the
current available has a 33db loss.
Here's more diode info.
http://www.crystal-radio.eu/endiodes.htm
http://www.bentongue.com/xtalset/17Is_n/17Is_n.html
http://www.klimaco.com/HAMRADIOPAGES/xtal_how_to.htm

This stuff merely shows the agony of counter trending data. In other
words select the optimal Is and you get trash Rd - and vice versa.
Reporting the numbers doesn't solve the problem however.

* * * * * * * *

In this offered discussion there is nothing of how the pioneers
managed it with galena crystals and cat whiskers. That data for
comparison is starkly absent in this and their discussion.

My Fourth Edition of "Standard Handbook for Electrical Engineers"
(1915) offers Coherers and Magnetic detectors. The coverage is
likewise absent of these alternatives.

"Section 21-289 Contact Rectifiers. The rectifiers most frequently
consist of a contact between a fine wire and some variety of mineral.
Among the minerals frequently use are iron pyrites, galena, silicon,
and molybdenite. In other forms, two crystals are used in contact,
such as zinkite with chaleopyryte or bornite, or silicon with metallic
arsenic.
"For detecting the direct-current pulses, head telephones of from
1,000 to 3,000 Ohms resistance are ordinarily used."

Returning to the obscure references, for magnetic detectors, consider:
http://en.wikipedia.org/wiki/Magnetic_detector
for the coherer, consider
http://en.wikipedia.org/wiki/Coherer

* * * * * * *

You might want to reflect that this thread has not been about matching
an antenna to a crystal radio at all. That topic was rather easily
and quickly answered by J. Todd. Loss is defined by wire resistance
and the proximity of objects to the tank.

The match from the Tank is similarly simple - once you define the
load. Loss is defined by wire resistance and the proximity of objects
to the tank.

The load is presented as its two native components: the detector and
the headset.

The detector is the variable of concern, it is defined by the current
necessary to drive the headset, everything surrounding the detector
has to conform to its choice. The loss is defined by the ratio of the
detector resistance to the load resistance plus that diode resistance.

The headset is defined by a power level you identified as one picowatt
delivered to the ear. I think we can agree that was very generous.
The loss is defined by the transducer efficiency.

This is the genesis of figure of merit, and that is your solution.

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

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?

Ok One more, with a little help I figured it out.
It has to to with the Thermal Voltage of the diode.
Vt=KT/q
with k=1.38E-23 and q=1.6E-19. T is absolute temperature in degrees Kelvin,
k is Boltzmann's constant and q is the charge of an electron. VT is close
to 0.025 volts at 20 degrees Celsius.

With a slightly increased temperature the .025 is raised to .0257,
and .0257 / 1 nanoamp =25,700,000
Thanks, MikeK

Matching antenna to crystal radio
 

On Wed, 17 Nov 2010 14:57:22 -0500, Fred McKenzie
wrote:

In article ,
Richard Clark wrote:

We have an audio Z match. We have a diode Z match. There is no sense
that if this is a high-Z or a low-Z for either/both/neither.

Hi Fred,

The subtext of that observation was the lack of numbers.
Quantification will aid immensely and give perspective to the direness
of the problem.

We have a diode detector, which is nonlinear. If you allow a filter
capacitor on its output, there is current flow only on alternate RF
voltage peaks, in order to charge up the capacitor for the amount lost
to the audio load during the cycle. Its effect on circuit Q may be a
fraction of the total, also consisting of coil Q and input circuit
matching.

This is dangerously close to decoupling the problem by looking at
minutia. Q is the ratio of power in to power consumed.

Therefore you want the diode connected to the high end of the coil, not
transformed to a lower impedance point on the coil.

Your detector placement serves the consumption side and consumption -
listening to program content - is the whole point of detection.

Preserving Q does not serve that goal.

Load impedance will affect audio level, so should be kept high for that
reason.

Audio level "should" follow power applied, be it low voltage high
current (a speaker); or high voltage low current (a piezo). Preserving
power levels while changing its form is the purpose transduction.

However there may be some value of load that produces the
greatest audio output voltage. If too high, the filter capacitor would
charge to the peak of the modulation waveform and stay there.

What you describe is a clamp, not a filter; but point is well taken.
What you have is the wrong balance of charge time to discharge time.
In other words, you have selected the wrong detector for the chosen
transducer, or vice-versa. Choose both to complement each other.

Consider, what would be lost if you clipped out that pesky cap?

73's
Richard Clark, KB7QHC

Matching antenna to crystal radio
 

"Richard Clark" wrote in message
...
On Wed, 17 Nov 2010 09:17:51 -0600, "amdx" wrote:

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.

Every time you change frequency you change source resistance.
XL times Q equals source resistance, Q changes with frequency,
and XL changes with frequency.

Hi Mike,

There are a number of problems here. Q is strictly a function of
RESISTANCE and nothing else.

Ya, loss resistance of the tank.
Can you agree that it varies with frequency?


What you call source resistance, when using the math you provide, is
actually source impedance. Impedance embraces resistance and is
solely resistance when reactance is gone - such as at resonance.

The tank is used at resonance, so yes, source resistance.

However, it would seem that the Xtal Radio community treats reactance
as resistance interchangeably.

Not so!


That is fine to a point, but it introduces serious problems in the
usage of the term "match" as there are actually several types of
"matching" and each has its peculiarity (only peculiar when you are
unfamiliar with the other types).

Are you getting at conjugate match?

It is a given that you are going to have to change either Xc or Xl if
you are going to tune to another frequency. This alters the circuit
Z, certainly; and for the AM band you have a 3:1 variation from band
end-to-end.

So your in agreement that Rp is not fixed?

Also when you change to a different station with a different signal
strength
you change the current through the diode, this changes the resistance the
diode
presents to the tank.

Without numbers, this is like anticipating worry about your MPG
driving up a hill in comparison to driving down the same hill. Yes, a
wild variation, but do you give up cars and start walking instead?
Some of these "concerns" sound like they come from the AVC needy. I
thought Xtal Radio folks would man up and get with the program.

No pick a different diode.

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?).

There are dozens of diodes to pick from, depends on the tank Z
and signal strength.

No, actually you've either mis-read the intent (which is certainly a
problem with that author's hodge-podge writing style) or you've read
too many written sources that each only see part of the elephant.
"It's a snake! We need something bulky."
"It's a wall! We need something slim."
"It's thin and flappy! We need something sturdy."

The problem with the diode is in its forward current and reverse
current. If they are about the same, you don't have a rectifier. This
would be a weak signal problem. The forward current defines the
series resistance of the diode and how much that is in comparison to
the load defines the efficiency. You want more current to lower the
diode resistance to increase the efficiency. Unfortunately this
demands you have a higher source voltage that offers less current
(Catch-22).

However, this problem is strictly for a low Z load like a magnetic
speaker - and thus enters the consternation over competing agendas
that gives everyone the fits that seems they enjoy agonizing over when
the solution is obvious. I will touch on that next:

I don't know what you mean when you say there aren't
many variables, there are many, many!
Coil Type (solenoid, spider, 3D solenoid)
Coil Form Material, paper, PVC, polypropylene, etc.

Those are non-starters for those who love to struggle in hope against
reality.

Wire type, solid, Litz

Ah yes, the magic Litz wire that is the salvation. The solution for
the problem that doesn't matter. You do this because you can, not
because you need to. And then you return to life with the car still
in the ditch (but you changed the air in the tires).

Can you wind a coil with a Q over 1000 with solid wire?

Antenna Match technique, Tap, cap tune, inductance coupling

This has been long figured out. For nearly a century.

Diodes, Diodes, Diodes

Whose solution is found in:

Audio, Transformer matching , high impedance piezo, sound powered
headphones, crystal earphone, horn driver.

Whose choice is obvious in hi impedance.

Like I said, there are not that many variables, until you find someone
on a soap box with a stump speech about the invidious dereliction of
design introduced with the Philips head screw. The advantages of the
Bristol head anyone?

Do not confuse the multitude of competing and contradicting factors as
the multitude of variables.

Introduce figure of merit to the discussion and argue about that. If
that gets resolved, the solution will pop right out.

Here's some more info on the diode selection and why.
Richard I'm well aware of your great knowledge (not being facetious)
and my lack of math and knowledge on this, but I'm to the point where
it seems you are not willing to learn new information.

There is no new information. It is a niche application you are
talking about, not new science. The niche has its concerns and they
are impacted by issues that are rarely a problem for the standard
usage of the components you mention, but there have been no new
devices introduced in this discussion. I see nothing innovative. In
fact, the discussion is so in-bred it lacks coverage outside of a
clubbish mainstream. I will offer something new below that is
actually quite old.

It seems you already
know it all. This especially in regards to the idea that the diodes
characterists
are very important to losses in the radio.

I have designed at the extreme edges of component characteristics,
true. More often in regard to temperature variation, mechanical
vibration, noise, accuracy, resolution, speed, bandwidth, linearity -
all that went towards continuous service in a largish orange box in
some jets.

I have studied diodes to no end, especially LEDs and photodetectors.
Talk about marginal signal detection and loss. I started with 1n34s
being used as varactors back in the late 60s. PIN and Tunnel diodes
followed. There is a world of non-linear devices out there. I
especially like the surgistor and posistor. Any reports of their use
in Xtal sets?

I have maintained a number of audio standards and measurement devices.
I have had to repair detectors that measured absolute value voltage
out to 7 places, the same issues arose there too. Small currents?
Like those that rise continuously through the air in femto-ampere
levels? You would need polonium treated probes to measure them (or
just use the anti-static record brushes of the 1970s).

I think one of these pages has a graph showing a diode not matched to the
current available has a 33db loss.
Here's more diode info.
http://www.crystal-radio.eu/endiodes.htm
http://www.bentongue.com/xtalset/17Is_n/17Is_n.html
http://www.klimaco.com/HAMRADIOPAGES/xtal_how_to.htm

This stuff merely shows the agony of counter trending data. In other
words select the optimal Is and you get trash Rd - and vice versa.
Reporting the numbers doesn't solve the problem however.

* * * * * * * *

In this offered discussion there is nothing of how the pioneers
managed it with galena crystals and cat whiskers. That data for
comparison is starkly absent in this and their discussion.

My Fourth Edition of "Standard Handbook for Electrical Engineers"
(1915) offers Coherers and Magnetic detectors. The coverage is
likewise absent of these alternatives.

"Section 21-289 Contact Rectifiers. The rectifiers most frequently
consist of a contact between a fine wire and some variety of mineral.
Among the minerals frequently use are iron pyrites, galena, silicon,
and molybdenite. In other forms, two crystals are used in contact,
such as zinkite with chaleopyryte or bornite, or silicon with metallic
arsenic.
"For detecting the direct-current pulses, head telephones of from
1,000 to 3,000 Ohms resistance are ordinarily used."

Returning to the obscure references, for magnetic detectors, consider:
http://en.wikipedia.org/wiki/Magnetic_detector
for the coherer, consider
http://en.wikipedia.org/wiki/Coherer

* * * * * * *

You might want to reflect that this thread has not been about matching
an antenna to a crystal radio at all. That topic was rather easily
and quickly answered by J. Todd. Loss is defined by wire resistance
and the proximity of objects to the tank.

The match from the Tank is similarly simple - once you define the
load. Loss is defined by wire resistance and the proximity of objects
to the tank.

The load is presented as its two native components: the detector and
the headset.

The detector is the variable of concern, it is defined by the current
necessary to drive the headset, everything surrounding the detector
has to conform to its choice. The loss is defined by the ratio of the
detector resistance to the load resistance plus that diode resistance.

The headset is defined by a power level you identified as one picowatt
delivered to the ear. I think we can agree that was very generous.
The loss is defined by the transducer efficiency.

This is the genesis of figure of merit, and that is your solution.

73's
Richard Clark, KB7QHC

I think you finally got it Richard.
Thanks, MikeK :-)

Matching antenna to crystal radio
 

*Use a fork to scoop water out of a glass to satisfy your thirst.
I will work, just not well.
* * * * * * * * MikeK


True, but operating crystal radios is much like sailing.

Maybe multiple taps is not that bad an idea.

- I never saw a crystal radio optimized for such a small tuning ration
that the LC had a fixed impedance. A 1-to-3 tuning ratio is quite
normal, and tank impedance will therefore vary considerably.

- On medium wave the impedance of the electrically very short wire
antenna will vary, but not that much. It will stay probably in the
order of a kiloohm or more. On shortwave it will swing considerably.

- If the receiver has to resolve different stations or at least
clearly separate different SW broadcast bands (to listen to the most
powerful broadcaster in each band, more is not doable), it may make
sense to reduce the loading below optimum energy transfer at the
resonant frequency.

This suggests that a coil with multiple taps could be useful. If the
radio has a tapped coil and 3 croc clips (one each for the tuning cap,
antenna, and detector) the user has to optimize over 3 dimensions in,
and 2 dimensions out - wanted signal level and interference.

Great fun, but not easy.

The human ear is not linear and tends to be a bad level measuring
instrument. It helps if the radio also has a microamp-meter to make
relative linear comparisons in total signal level. A 50uA meter may
have a DC resistance of 2kohm and load about the same as a magnetic
headset, but a 500uA may be sensitive enough and load less.

The combination of separate improvements that the ear alone could not
judge may in the end be considerable.

A digital voltmeter would be so high impedance as to be practically
invisible even at very high impedances too, but it has a battery
powered DC amplifier. IMO it is aesthetically incongruent with a RF-
powered radio.

Matching antenna to crystal radio
 

On Nov 15, 1:26*am, Wimpie wrote:
On 15 nov, 02:59, "amdx" wrote:

Hi Guys,
*Assuming I have a tank circuit on a crystal radio with a Z at resonance of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.
* If don't think that's what I want to do, tell me that too. :-)
* * * * * * * * * * * * * * * * * * *MikeK

Hello Mike,

Assuming you have a long wire outside and a ground provision, you may
use an inductive coupling. *By changing the distance between the
antenna coil and the receiver coil, you modify the impedance
transformation.

Other method is capacitive coupling. *Probably positioning the end of
the antenna wire close to the high impedance side of the tank circuit
will give the desired effect. Changing the distance changes the
coupling.

For inductive coupling, your receiver circuit can be floating, for
capacitive coupling, the receiver should be grounded.

By changing the coupling you can optimize for maximum selectivity
(with reduced sensitivity) or maximum sensitivity (with reduces
selectivity).

Regarding the antenna, assuming LW and AM reception, long combined
with high gives strongest signal, hence you can reduce the coupling to
get best selectivity.

Best regards,

Wim
PA3DJSwww.tetech.nl
without abc, PM will reach me very likely

I like your very practical advice here, Wim. For Mike, as Wim noted
in another post, you can simulate this in Spice quite easily. While
you're playing with it in Spice, you might also look at two high-Q
tanks, tuned to the same frequency, with a non-zero coupling
coefficient between the inductors. Excite the first with a voltage
generator in series with the RLC tank, or a current source across it,
and observe the frequency response at the second tank. Vary the
coefficient of coupling between the coils and notice how small it is
to get critical coupling. If you use LTSpice, you can use a .step
statement to run a set of simulations over a range of k values, for
example.

The flip side of this is that in LC filters that are very narrow-band
that you design assuming no coupling among the resonators, expect to
have to work some to insure that there really is no coupling among
them in your implementation! Sometimes it gets difficult to shield
well enough between adjacent resonators to get the performance you
want.

Cheers,
Tom

Matching antenna to crystal radio
 

On Nov 15, 1:59*am, "amdx" wrote:
Hi Guys,
*Assuming I have a tank circuit on a crystal radio with a Z at resonance of
1.5 megaohms.
How would I make an antenna and extract maximum signal and keep the Z at
750,000 ohms.

I did take part in the discussion of matching, but I am afraid you are
off by several orders of magnitude regarding the impedance value.

Say you shoot for resonance at 1 MHz: a 2.5 mH inductor (already
impractically large) and a 10 pf capacitor (already impossibly small)
will resonate close to 1 MHz but have an impedance of 16 kilohm or so,
100 times lower than your assumption.

For 10 MHz, it would be 1 pF and 250uH, again for 16 kohm.

In practical circuits the impedance is typically in the order of
300-2000 ohm.

A typical old-style mediumwave tuning capacitor has a maximum
capacitance of 360 pF to tune about 520 kHz at 850 ohm with a 260 uH
coil.

Assuming you use a much smaller than usual 100pF variable, say 130 pF
including tray capacitance in the coil, at the bottom of the band you
will need 760hH, and get 2.5 kiloohm.

On shortwave, let's say yo want to tune a lowest frequency of 6MHz
with only 60pF all included - again, nobody does that - you need 12uH
inductance but only get 450 ohm impedance.