Circuit Lake

Electronic Project and Circuit Collection

Telephone FM Transmitter

07/29/2011 Category: Analog, Project, Transmitter, Wireless

This project can transmits phone conversation up to 30 metres (100 feet) to an ordinary FM receiver. You can experiment to get greater transmission range away from the phone line by adding an aerial (about 150 cm of 26 gauge wire) to the collector of T2 (see circuit below).

Phone FM transmitter

To use phone transmitter, you need to attaches it in series to one of your phone lines. When there is a signal on the line (that is, when you pick up the handset) the circuit will transmit the conversation a short distance. In particular it will radiate from the phone line itself.

This passive device doesn’t need a battery. It uses the signal on the phone line for power. No aerial is needed – it feeds back the RF signal into the phone line which radiates it in the FM band. The frequency of transmission may be adjusted by the trimcap.


Telephone FM Transmitter Schematic Diagramclick for larger image

Part List
Telephone FM Transmitter Part List

Phone FM Transmitter
Project Detail and Documentation