This phone transmitter circuit is a very small telephone VHF Adjustable Voice Transmitter. When the alligator clips are connected anywhere along the pole wires or to the red and green wires of the telephone pair that runs from the jack on the outside of a home, thru the basement, up thru the walls, the phone transmitter circuit below transmits both sides of the conversation to a discrete location blocks away. It is primarily used in clandestine or spy operations. The polarity of the clips does not matter. The design of this phone transmitter circuit presents a very high impedance to the phone pair and virtually undetectable. When the high voltage ring signal is present, the neon bulb reacts acting as a voltage divider, thus lowering the input voltage to the circuit protecting it.
C1 tunes the unit to frequency. C2 trims the antenna for maximum power and radiation. Use a small flex wire antenna of about 18 inches.
L1 is made using # 20 copper wire. Use the smooth end of a 3/16 inch drill bit and air wind 3 tight turns.
The unit is monitored using a VHF 147 to 170 MHz wideband tunable receiver.