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Thunderstorm Predictor(2N3906)

2017-08-10 22:59  
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This article describes Thunderstorm Predictor (2N3906). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: 2N3906.

Sure, listening toVHFFM has great advantages over MW/LW AM from the old days — now we have bright stereo free from interference, fading and noise! However, your FM radio will no longer predict the arrival of a thunderstorm as did the AM radio many years ago-reliably and hours before the trouble was upon you! The crux is that AM detection will faithfully reproduce the effects of lightning and other massive static discharges approaching in a very simple way: they’re audible as slight crackling noises in the loudspeaker, almost irrespective of the tuning of the radio! Assuming no AM radio is available anymore, a dedicatedVLFreceiver tuned to about 300 kHz can faithfully detect the crackle of approaching lightning.

The simple receiver shown here consists of a loosely tuned amplifier driving a kind of flasher circuit that blinks anLEDin synchronicity with the lightning bolts. The frequency and intensity of theLEDactivity indicates the intensity and distance of the storm respectively. Looking at the circuit diagram, theLEDdriver is not biased to flash until a burst of RF energy, amplified by T1, arrives at the base of T2. The receiver works off 3 volts and has a negligible standby current of about 350 microamperes which will hardly dent the shelf life of a couple of 1.5-V D-size cells. T2 and T3 form a monostable generator triggered by sudden drops in T1’s collector voltage.

Figure:1 Thunderstorm Predictor Circuit Diagram

Figure 1 Thunderstorm Predictor Circuit Diagram

Preset P1 is adjusted until theLEDremains off when you’re sure there’s no thunderstorm around for a few hundred miles. The value of theLEDseries resistor is subject to experimentation andLEDcurrent. L2, C1 and the antenna are coarsely tuned for resonance at about 300 kHz. Frequency-wise, lightning is a fairly broadband phenomenon so any tuning to between 200 and 400 kHz will be fine for the circuit but make sure you’re not accidentally tuned to a nearbyVLFtransmitter! The input signal is obtained from a 70-cm long piece of stiff wire, with coil L1 inserted for impedance matching and lengthening the antenna electrically.

 

 


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