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FM Beacon Broadcast Transmitter 88 108 MHz - This circuit will transmit a persistent sound tone on the FM show band (88-108 MHz) which could utilized for remote control or security purposes. Circuit draws around 30 mA from a 6-9 volt battery and can be gotten to around 100 yards. A 555 clock is utilized to deliver the tone (around 600 Hz) which recurrence adjusts a Hartley oscillator. A second JFET transistor cushion stage is utilized to disengage the oscillator from the reception apparatus so that the recieving wire position and length has less impact on the recurrence.

Fine recurrence alteration can be made by modifying the 200 ohm resistor in arrangement with the battery. Oscillator recurrence is set by a 5 turn tapped inductor and 13 pF capacitor. The inductor was twisted around a #8 X 32 fastener (around 3/16 width) and afterward evacuated by unscrewing the screw. The inductor was then streached to around a 3/8 inch length and tapped close to the middle.

FM Beacon Broadcast Transmitter Circuit Diagram

The oscillator recurrence ought to turn out some place close to the focal point of the band (98 MHz) and can be moved higher or lower by marginally extending or packing the inductor. A little flag diode (1N914 or 1N4148) is utilized as a varactor diode so that the aggregate limit in parallel with the inductor differs marginally at the sound rate consequently creating the oscillator recurrence to change at the sound rate (600 Hz).

The inclining waveform at pins 2 and 6 of the clock is connected to the turned around one-sided diode through a substantial (1 Meg) resistor so that the capacitance of the diode changes as the sloping voltage changes consequently adjusting the recurrence of the tank circuit. On the other hand, a sound sign could be connected to the 1 Meg resistor to adjust the oscillator yet it may require an extra pullup resistor to switch inclination the diode. The N channel JFET transistors utilized ought to be high recurrence VHF or UHF sorts (Radio Shack #276-2062 MPF102) or comparative.