2-TRANSISTOR FM TRANSMITTER

R1 270
R2, R5, R6 4k7
R3 10k
R4 100k
C1 1n
C2 5.6p
C3, C4 10u
C5 3-18p
L1, L2 5 turns of enamel coated magnet wire with an inside diameter of about 4mm
Mic Electret microphone
Q1, Q2 2N2222, 2N3904 or any other general-purpose NPN

Original source:

Electronic Circuits

Description:

While there are a plethora of similar 2-transistor schematics available, this one is above average. A major improvement over the little 1-transistor circuit that we've discussed previously, this transmitter consist of two stages. The first transistor is used to amplify audio, which means that the microphone is now much more sensitive to sound. The second one acts as an oscillator.

All in all, this is an interesting project for beginners and more experienced hobbyists alike. Use any stiff wire or telescope whip antenna, just make sure that it's not too long. Range should be about 100m or even more in the open. Stability is still a problem, though.

Problems:

The coils should be identical to ensure proper operation. Do not speak to closely to the microphone. It's so sensitive that you can easily overdrive the circuit.

Possible uses:

A reasonably good wireless microphone or baby monitor. This is a nice short-range FM transmitter, you could even use it in a homemade walkie-talkie.


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