Saturday, October 08, 2011

FM crystal radio

I'm back!...Along with the lousy photos and the rusty English...

Having already build a lot of receivers with different approaches I have never tried FM with a "crystal" radio. Now is the time.

This is a simple circuit and honestly I wasn't expecting much performance but is fun and helps getting some momentum for future builds.

I can only get two very faint stations and with an external amp based on an LM386, my "crystal" earpiece I guess is not crystal....

My implementation

The schematic was "borrow" from here. Go on, see the original and nice implementations on that site.

Original schematic from the author site

L: 5 Turns of 1mm silver wire on an "Edding 3000" pen (around 12mm), diode connects to 2.5 turn (half the coil), spacing is around 2mm
D: OA90 or 1N34 (not sure, it wasn't marked) I tried several glass diodes and results were similar.
R: 150 K
C3: 18p
C1: 82p
C2: used one trimmer of 25p (80pf on the original schematic)
Antenna was around 25cm of wire and the 2 station's received are less than 8 km from the shack.

Have fun.