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:
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.
