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FM wireless microphone band regulator circuit

Published on Mar 14 2011 // DIY Telephone Circuits

FM wireless microphone band  regulator circuit

Previous "electronic newspaper" published some on the "FM wireless microphone," the circuit, although simple, but there are still many shortcomings. Not a short distance, that is, the noise, and now the author to introduce a simple structure, firing up to 200 meters away from the wireless microphone, the average beginner can produce success.
First, the circuit schematic (see below)
   The circuit consists of three parts: 1. Audio amplification part; 2. Part of high frequency oscillation; 3. Regulator section. MIC signal from the microphone into the base of transistor VT1, VT1 amplified by the audio signal by the high-frequency oscillation circuit C2 VT2 coupled to the base, and then by the antenna out. This circuit’s operating frequency between the 85 ~ 104MHz.
Second, the selection of components
  MIC selection of high sensitivity electret microphone, VT1 for the 9013H, ß = 125. VT2 is 2N3866; ß = 90, L1, L2 ? 0.71mm enamelled wire with an ordinary pen core, respectively, in the tightly wound 4 turns and 10 turns, C4, C5, C6 using ceramic capacitors, error ± 5%. Used LM7806 Three-terminal voltage regulator power supply, 9V batteries, circuit boards can be made.
Third, assembly and commissioning
   Circuit assembly is relatively simple, as long as no damage components, one can be successfully installed. After circuit weld, then weld up the antenna, antenna radio antenna with 0.5 m, when debugging at the microphone on the sound source, and then left the microphone 5 to 6 meters, turn on FM radio, adjust the Tuning knob, if is turbid received harmonic, adjust the oscillator coil L1 can opener spacing, L1 increased frequency spacing is large, and vice versa decreases with time is not received by the sound of harmonics.
  To increase the transmission power, can change the length of the transmitting antenna, or to replace 34D50 emission control transistor VT2, R4 resistor into 4.7kO, this time firing range can be further increased by about 100 meters.