Low EMW Frequency Detector

I came across this project because I wanted to prove the Schumann resonance (physicist - Winfried Otto Schumann) myself.

 

For detecting electromagnetic fields in this frequency region, antennas that focus on the magnetic part of the wave are better suited. This requires a larger coil (with a ferromagnetic core) followed by a low-noise amplifier.

The spectrum must then be scanned with an AD converter (USB sound card) with the appropriate frequency response (down to 1 Hz) and passed to a PC with FFT analysis.

The coil (detector) consists of a split winding (increase in the natural resonance) with copper lacquer wire, which results in a total of 16,000 turns. The core was a rod made of individual wires (70% nickel, 30% iron). To ensure that this structure is largely protected from moisture, the whole thing is installed in an aluminum tube and provided with a robust plug-in connection (XLR).

 

The signal is transmitted to the amplifier using a symmetrical microphone cable known from audio technology.

The resonant frequency of the detector is above the measuring range.

Three detectors (antennas) can be connected to the amplifier. Since it can be assumed that very large electromagnetic fields are present in the range of the 16.7Hz (railway network) and the 50Hz (power supply network), Notch filters are provided for these two frequencies. There are further filter options available with a LowPassFilter with a cut-off frequency of 48Hz and a HighPassFilter with a cut-off frequency of 4.4Hz.

The amplifier is powered by a built-in 12V battery, which can be charged from the outside via a 5.6mm/2.2mm plug.
Of course, it is important with such measuring amplifiers that the amplifier's own distortion products and noise are kept as low as possible. The components used are selected accordingly.

The necessary software for displaying and evaluating the measurement results is self-created and runs on Linux as well as Windows. All relevant parameters can be set here.