FM TRACKING TRANSMITTER

1. The circuit presented her will transmit a audio tone in the FM  band.
2. The circuit can be used as a tracking signal transmitter or a remote control transmitter.
   
3. The circuit uses only easily available components and any one can build this.The transmitter has a range of 100m @ 9V supply, with a matching antenna.
   
4. The NE555 timer (IC1) is used for producing the audio tone.
5. The first JFET(Q1) is wired as a Hartley oscillator which is frequency modulated by the audio tone.The second(Q2) JFET is wired as a buffer to isolate the oscillator based on Q1 from the antenna.
   
6. The diode D1 is used as a varactor here.The diode is reverse biased by the ramping voltage produced at the pin 6&2 of the IC1.
7. This results in the change of junction capacitance of reverse biased diode , which in turn alters the frequency of the oscillator to attain the frequency modulation.

          NOTES:

• The inductor L1 can be made by winding 5 turns of  18 SWG enameled copper wire on a 3/8 inch long, 3/16 inch diameter plastic tube .The coil must be tapped at the center.
• The antenna can be a 20cm long wire.
• The circuit can be powered from a 9V battery.
• POT R6 can be used to adjust the transmission power.