"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.