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