The circuit consists of three parts : 1. Audio amplification part; 2 . Some high-frequency oscillation ; 3 . Regulator part . Signal from the microphone MIC into the base of transistor VT1 , VT1 amplified by the audio signal through coupling to high-frequency oscillation circuit C2 VT2 base , and then fired out by the antenna . The circuit ‘s operating frequency between the 85 ~ 104MHz . Second , the selection of components MIC selected highly sensitive electret microphone , VT1 for the 9013H, ß = 125. VT2 to 2N3866; ß = 90, L1, L2 with ? 0.71mm enamelled wire core , respectively, in the ordinary ball-point pen tightly wound 4 turns and 10 turns , C4, C5, C6 using porcelain capacitors , error ± 5%. Used LM7806 Three-terminal regulator power supply with 9V batteries , circuit boards can be made . 3 , assembly and commissioning Circuit assembly is relatively simple, as long as the components without damage , an installation can be successful .
After soldering the circuit, solder the antenna , antenna, radio antenna of 0.5 meters , the microphone on the sound source when debugging Office , and then left the microphone 5 to 6 meters , turn on FM radio and tune Tuning knob , if Received was a turbid harmonic oscillation can be used screwdriver adjust the spacing between the coil L1 , L1 increased frequency of large space , otherwise reduce this time is not received with a harmonic sound. To increase the transmission power , can change the length of the transmitting antenna , or to replace 34D50 triode transmitting tubes VT2 , R4 resistor replaced 4.7kO, this time firing range can be further increased by about 100 meters.