This 88-108 MHz FM Transmitter Beacon Broadcast circuit will address a connected audio accent on the FM advertisement bandage (88-108 MHz) which could acclimated for alien ascendancy or aegis purposes. Ambit draws about 30 mA from a 6-9 volt array and can be accustomed to about 100 yards. A 555 timer is acclimated to aftermath the accent (about 600 Hz) which abundance modulates a Hartley oscillator. A added JFET transistor absorber date is acclimated to abstract the oscillator from the antenna so that the antenna position and breadth has beneath aftereffect on the frequency. Fine abundance acclimation can be fabricated by adjusting the 200 ohm resistor in alternation with the battery.
Oscillator abundance is set by a 5 about-face broke inductor and 13 pF capacitor. The inductor was anguish about a #8 X 32 bolt (about 3/16 diameter) and again removed by unscrewing the bolt. The inductor was again streached to about a 3/8 inch breadth and broke abreast the center. The oscillator abundance should appear out about abreast the centermost of the bandage (98 MHz) and can be confused college or lower by hardly accretion or burden the inductor. A baby arresting diode (1N914 or 1N4148) is acclimated as a varactor diode so that the absolute accommodation in alongside with the inductor varies hardly at the audio amount appropriately causing the oscillator abundance to change at the audio amount (600 Hz).
The ramping waveform at pins 2 and 6 of the timer is activated to the antipodal biased diode through a ample (1 Meg) resistor so that the capacitance of the diode changes as the ramping voltage changes appropriately altering the abundance of the catchbasin circuit. Alternately, an audio arresting could be activated to the 1 Meg resistor to attune the oscillator but it may crave an added pullup resistor to about-face bent the diode. The N approach JFET transistors acclimated should be aerial abundance VHF or UHF types (Radio Shack #276-2062 MPF102) or similar.
Oscillator abundance is set by a 5 about-face broke inductor and 13 pF capacitor. The inductor was anguish about a #8 X 32 bolt (about 3/16 diameter) and again removed by unscrewing the bolt. The inductor was again streached to about a 3/8 inch breadth and broke abreast the center. The oscillator abundance should appear out about abreast the centermost of the bandage (98 MHz) and can be confused college or lower by hardly accretion or burden the inductor. A baby arresting diode (1N914 or 1N4148) is acclimated as a varactor diode so that the absolute accommodation in alongside with the inductor varies hardly at the audio amount appropriately causing the oscillator abundance to change at the audio amount (600 Hz).
The ramping waveform at pins 2 and 6 of the timer is activated to the antipodal biased diode through a ample (1 Meg) resistor so that the capacitance of the diode changes as the ramping voltage changes appropriately altering the abundance of the catchbasin circuit. Alternately, an audio arresting could be activated to the 1 Meg resistor to attune the oscillator but it may crave an added pullup resistor to about-face bent the diode. The N approach JFET transistors acclimated should be aerial abundance VHF or UHF types (Radio Shack #276-2062 MPF102) or similar.
