FM wireless microphone is very simple to build and has a useful transmission range (more than 300 meters in open air). Although a small component count and 3V operating voltage it will easily penetrate more than three floors of an apartment building. This may be found anywhere in the FM band (87-108MHz) and transmission can be picked up on any standard FM receiver.

The coil (L1) should be about 3mm in diameter with 5 turns of copper wire 0.61 mm. You can vary the Tx frequency by simply set the distance between the coils. Antenna should be half or a quarter of a long wavelength (100 MHz to 150 cm or 75 cm).

Place the transmitter about 10 feet from an FM radio. Set radio somewhere around 89-90 MHz wireless microphone fm

Parts list:

* T1,T2,T3: 2N2222 transistor
* R1: 10k 5%
* R2: 33k lin.
* R3: 12k 5%
* R4: 5.6k 5%
* R5: 2.2k 5%
* R6,R8: 47k 5%
* R7: 470 ohms 5%
* R9: 180 ohms 5%
* C1,C2: 47nF
* C3: 1nF
* C4: 33pF
* C5: 5.6pF
* C6: 8.2pF
* C7: 10nf
* L1: 3mm in diameter with 5 turns 0.61 mm copper wire
* K1: SPDT toggle switch
* Other parts: 2 AA battery holder, Electret microphone, antenna wire