Simple Telephone Transmitter

This is a simple design circuit for transmitter. This circuit is very useful for transmit telephone conversations. This circuit is work using based on transistor. Here’s the simple project circuit.

When the telephone receiver is on - hook to the line voltage of about 48 volts. R7 preset is adjusted to 24.7 V between the cathode of D2 and ground. In voltage Zener diode D2 will be in the breakdown and the transistor T1 will conduct. This makes the transistor T2 is OFF. When the receiver is off - hook, the line voltage drops to about 11 volts. This makes the transistor T1 is OFF and then T2 is ON. The T2 is switched ON condition will give way to the DC transistor T3 which is used in the FM transmitter. Transistor T3 is the cable as a common emitter radio frequency oscillator. In simple words the transistor T2 functions as ON / OFF switch for this oscillator. Modulated signal will be available to collectors of transistors T3 and id fed to the antenna signal through a capacitor C5. To L2 makes 3 changes of 21 SWG enameled copper wire on a plastic 12 mm. For the antenna, use a 1 meter insulated copper wire. Capacitor C3 can be 50pF trimmer.