This is a circuit for lighting detector circuit that is using a VLF receiver tuned to 300 kHz designed to detect the crackle of approaching lightning. A bright lamp flashes in synchronize with the lightning bolts indicating the proximity and intensity of the storm. This is the figure of the circuit;
This circuit is the simple receiver which consists of a tuned amplifier driving a modified flasher circuit. The flasher is biased to not flash until a burst of RF energy, amplified by the 2N3904, is applied to the base of the 2N4403. The receiver standby current is about 350 micro amps which is nothing at all to a couple of D cells, hardly denting the shelf life. Of course, the stormier it gets, the shorter the battery life.
Adjust the potentiometer until the regular flashing just stops. (Use a multi-turn trimmer.) When properly adjusted, the lamp will occasionally flash when large motors or appliances switch on and off and an approaching storm will give quite a show. Obviously, tune-up is a bit more difficult during stormy weather. Adjust the pot with no antenna if lightning is nearby. Tune an AM radio to the bottom of the dial to monitor the pulses that the lightning detector is receiving. This lightning detector is not so sensitive that it will flash with every crackle heard on the radio but will only flash when storms are nearby. Increased sensitivity may be achieved by increasing the antenna length. The experienced experimenter may wish to add another gain stage after the first by duplicating the 2N3904 circuitry including capacitor coupling with the addition of a 47 ohm emitter resistor to reduce the gain somewhat.
1 comments:
Consider coupling the output to a current amplifier which could energise a solenoid to open circuit contacts in a telephone line thus minimising transients destroying the modem. Of course the gap would need to be wide.
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