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87-108MHz FM Wireless Microphone

87-108MHz FM Wireless Microphone

This FM wireless microphone is easy to build and has a useful range of transmission (over 300 meters outdoors). Despite its small number of components and an operating voltage of 3V to easily penetrate over three floors of an apartment building. You can tune anywhere on the FM band (87-108MHz) and its transmissions can be picked up at any point of view of the FM receiver.

The coil (L1) should be approximately 3 mm in diameter, 5 turns 0.61 mm copper wire. You can vary the Tx frequency by simply adjusting the distance between the coils. The antenna should be a half wavelength or quarter-time (100 MHz, 150 cm or 75 cm).

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