circuit diagram of phone broadcaster is useful to hear the conversation between persons who use the telephone. This circuit doesn’t need additional power supply, as it is only need the power from the telephone line. The circuit has two sections, the automatic switching, and the FM transmitter.
The automatic switching consists of resistors R1-R3, variable resistor VR1 as the regulator, transistor T1 and T2, zener diode D2, and diode D1. R1 and VR1 is useful as an input voltage divider from the telephone line.
Parts list :
Resistor R1-R2, R4 : 47k ohm
Resistor R3 : 100 ohm
Resistor R5 : 22k ohm
Resistor R6 : 1M ohm
VR1 : 100k ohm
Diode D1 : 1N4001
Zener diode D2 : 24V, 400mA
Capacitor C1 : o.o1 uF
Capacitor C2 : 330 pF
Trimmer C3 : 50p
Capacitor C4 : 5.6 pF
Capacitor C5 : 10 pF
Transistor T1-T2 : BC548
Transistor T3 : BF494
Inductor L1 : 45rotation 36SWG in resistor carbon 1M 1W
Inductor L2 : 3 rotation 21 SWG 12mm diameter
Antenna
