Electronic Circuits and Diagram-Electronics Projects and Design

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Description.

The circuit presented her will transmit a audio tone in the FM  band.The circuit can be used as a tracking signal transmitter or a remote control transmitter.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.
The NE555 timer (IC1) is used for producing the audio tone.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.

Circuit diagram with Parts  list. 

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.

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