miniature fm transmitter:

click here to enlarge schematic

parts:

Transmitter Parts:
R1, R4, R6	10K resistor
R2	1Meg resistor
R3	100K resistor
R5	100 ohm resistor
R7	1K resistor
C1, C2	0.1uf capacitor
C3	0.01uf capacitor
C4	4-40pf variable capacitor
C5	4.7pf capacitor
Q1, Q2	2N3904 transistor
L1	8-10 turns of 22gauge wire around non-conductive 1/4" diameter form
Elec Mike	Electret Mic

This miniature transmitter is easy to construct and it's transmissions can be picked up on any standard FM receiver. It has a range of up to 1/4 of a mile or more. It is great for room monitoring, baby listening, nature research, etc. L1 is 8 to 10 turns of 22 gauge hookup wire close wound around a non-conductive 1/4 inch diameter form, such as a pencil. C4 is a small, screw-adjustable, trimmer capacitor. Set your FM receiver for a clear, blank space in the lower end of the band. Then, with a non-conductive tool, adjust this capacitor for the clearest reception. A little experimenting and patience may be in order. Most of the parts' values are not critical, so you can try adjusting them to see what happens.