Here is a simple transmitter that when connected to a phone line,
will transmit anything on that line (execpt the dial tone) to any FM
radio. The frequency can be tuned from 88 to about 94Mhz and the
range is about 200 feet. It is extremely easy to build and is
therefore a good, useful beginner project.
1. L1 is 7 turns of 22 AWG wire wound on a 9/64 drill bit. You
may need to experiment with the number of turns.
2. By stretching and compressing the coils of L1, you can change
the frequency of the transmitter. The min frequency is about 88 Mhz,
while the max frequency is around 94 Mhz.
3. The green wire from the phone line goes to IN1. The red
wire from the phone line goes to IN2. The green wire from OUT1 goes
to the phone(s), as well as the red wire from OUT2.
antenna is a piece of thin (22 AWG) wire about 5 inches long.
5. All capacitors are rated for 250V or greater.
The transmitter is powered by the phone line and is on only when the
phone is in use. S1 can be used to turn the transmitter off if it is
7. If you have problems with the LED burning
out, then add a 300 ohm 1/4W resistor in series with it.
Part Total Qty. Description
R1 1 180 Ohm 1/4 W Resistor
R2 1 12K 1/4 W Resistor
C1 1 330pF Capacitor
C2 1 12pF Capacitor
C3 1 471pF Capacitor
C4 1 22pF Capacitor
Q1 1 2SA933 Transistor
D1,D2,D3,D4 4 1SS119 Silicon Diode
D5 1 Red LED
S1 1 SPDT Switch
L1 1 Tuning Coil
MISC 1 Wire, Circuit Board