使用變容管的優質調頻話筒（英文）,3V FM Transmitter for Short Distance - 88MHz to 108MHz

使用變容管的優質調頻話筒（英文）,3V FM Transmitter for Short Distance - 88MHz to 108MHz

關鍵字：使用變容管的優質調頻話筒（英文）

3V FM Transmitter for Short Distance - 88MHz to 108MHz

Description

Features of the transmitter:
Supply Voltage:+3V DC
Current: 21mA
Output Frequency: 88MHz - 108MHz
Modulation: FM
Frequency Shift: ±30KHz
Input: Electret microphone or other input audio source

The important part of the circuit is formed of the Colpitts type oscillator. C3,C4,C5,C6,CD1-CD2 and L1 determines the frequency. BF982 and dual gate MOSFET are ac tive parts in the oscillator. When the input impedance of the MOSFET gate inputs are high, LC tank is not affected. However transistors force the LC tank and cause phase shift.

Two driver stages are added to isolate the antenna from oscillator. First stage (BF199) amplifies the low signal of the oscillator and works as a constant load. The second stage (BFR90) amplifies the signal going through the antenna some more. A short copper wire can be used as an antenna here. Attaching a large antenna to this circuit is unnecessary because the output power is low.

Notes

Coil 1: Winding wire must be 1 mm thick and isolated. Number of turns: 3.5 . 5mm core must be used and the distance between each turn must be 1mm.

You can use BF199 instead of BFR90.

If you can't find the varicap diode, you can use two BB405 instead.

注意：下面兩張圖合并起來才是個完整電路哦