eCircuitbook

Parts List:

R1,R3 = 100K


R2 = 10K


R4 = 470 ohm


C1,C4 = 470pF


C2,C3 = 4.7µF, 16V, electrolytic


C5,C6 = 4.7pF


C7 = 4-40pF trimmer cap (optional, see text)


L1 = 1µH


Q1,Q2 = 2N2222, NPN transistor


Mic = Electret Microphone


B1 = 9 Volt, Alkaline battery

Notes:

Nothing critical here. To get a bit of tuning out of the coil you could put a 4-40pF trimmer capacitor (optional) parallel over the 1 µH coil, L1.


C1/C4 and C5/C6 are ceramic capacitors, preferably NPO (low noise) types. C2/C3 are electrolytic or can be tantalum types.


The antenna is nothing more than a piece of 12" wire or a piece of piano wire from 6" to 12".

To find the signal on your receiver, make sure there is a signal coming into the microphone, otherwise the circuit won't work. I use an old mechanical alarm clock (you know, with those two large bells on it). I put this clock by the microphone which picks up the loud tick-tock. I'm sure you get the idea... Or you can just lightly tap the microphone while searching for the location of the signal on your receiver.