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.
Schematic
Parts
R1__________180 Ohm 1/4 W Resistor
R2__________12K 1/4 W Resistor
C1__________330pf Capacitor
C2__________12pf Capacitor
C3__________471pf Capacitor
C4__________22pf Capacitor
Q1__________2SA933 Transistor
D1,D2,D3,D4_1SS119 Silicon Diode
D5__________Red LED
S1__________SPDT Switch
L1__________Tuning Coil
MISC________Wire, Circuit Board.
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 goe sto the phone(s), as well as the red wire from OUT2.
4. The antenna is a piece of thin (22 AWG) wire about 5 inches long.
5. All capacitors are rated for 250V or greater.
6. 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 not needed.
7. If you have problems with the LED burning out, then add a 300 ohm 1/4W resistor in series with it.