This is a design for the tracking transmitter of audio tone in FM band frequency. The circuit can be used a signal transmitter or remote control transmitter. The circuit is use only the available components. The range of the transmitter is 100 m in the distance using 9V power supply and with a matching antenna. The circuit is built by 555 timer IC for producing the audio tone and based on JFET as core the circuit. This is figure the circuit.
The operation of the circuit is 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. 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.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. 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 operation of the circuit is 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. 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.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. 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.
