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Telephone FM transmitter

Updated on November 7, 2012

Fixed telephone FM transmitter

There is this simple project that I want to share with you, dear readers. It is a simple telephone transmitter, which you can use, if you want to hear phone conversations on your stereo. This device is connected to the fixed line, and transmits the conversation over FM band, starting from the moment you pick up the phone handset. In addition, the user can also install a switch, with which the user can actually shut down the transmitter.

One of the best things is that the device doesn’t require external power source to work, because the voltage is supplied through the telephone line. As antenna I would advise you to use a straight copper line with approximately 10 centimeters length. You can use the circuit for whatever purpose you want. Use it wisely.

The parts list that you will have to buy is:

Q1 = 2N3904, NTE123A, BC107, PN100, 2N4401, 2N2222, etc.

Q2 = 2N3563, or NTE108, nothing else

D1-D4 = 1N4148, signal diode

Resistors, 1/4W, 5% tolerance:

R1 = 100 ohm (brown-black-brown)

R2 = 33K (orange-orange-orange)

R3 = 10K (brown-black-orange)

R4 = 47K (yellow-violet-orange)

R5 = 390 ohm (orange-white-brown)

C1 = 27pF, ceramic

C2 = 0.1uF (100nF), ceramic

C3 = 0.022uF, (22nF) ceramic, 100V type

C4 = 0.001uF, (1nF) ceramic

C5 = 5.6pF, ceramic

C6,C7 = 47pF, ceramic

C8 = 5-20pF trimmer cap

L1 = 15nH (nanoHenry), 6 turns of #22 enameled copper wire

L2 = 30nH, 8 turns of #22 enameled copper wire

L3 = 8nH, 6 turns of #22 tinned copper wire



The printed board
The printed board
Placing the elements on board
Placing the elements on board
The final looks
The final looks

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