HI All,
I have already explored VLF range from 500 Hz to 50 Khz with a self made receiver. It was formed by 2 orthogonal ferrite coils, a preamplifier stage, a VCF stage for tuning, a CC amplifier/rectifier stage and a push/retuning circuit similar to metal detectors with a meter/audio stage. I have noticed nothing of interesting as perhaps it was a B-field receiver and I think that only E-field can help us.
I intend to use the same VCF and retuning circuit with and high impedance stage in the range 3/30 Hz, with the purpose of avoiding 50 hz power line influence. I think it’s possible to measuring phase difference between 2 adiacent places by using a CD4046 as motion detector, it’s sufficient to use a time constant of many seconds in the low pass filter that drives VCO.
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