"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