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