BELOW 150 Hz
Weak signals are present also at very low frequencies, in ULF and ELF bands. For this band the horizontal polarization is better, because in vertical field the sferics are 30 dB higher than background noise, in wide band reception systems.


Strange signal at 26 and 74 Hz lasting about 3 minutes, spaced by 15 minutes. Received with horizontal loop connected directly to the MIC input of CT300, by 100m of twisted cable. Note the strong signal at 50 Hz, set at 0 dB in the spectrogram: the signal at 74 Hz is at -76dB and the background noise is -84 dB in 0.3 Hz passband. This signal is not seen over the mains, and remains unexplained. It is present 24h a day.


This spectrogram shows the 50 Hz with a noise in the first 25 seconds (probably generated from a periodical load on electrical line),  an 85 Hz tone (generated by the monitor of my PC at 100m distance), some statics, and weird signals at 6, 9 and 12 Hz (like tweeks but slower). Unexplained.


Comparison between electric antenna, vertical E field (T antenna) and magnetic antenna, horizontal E field (Horizontal loop) in a 2Hz-86Hz range. A difference of 30 db S/N ratio is evident. Signals at 67, 74, 82 and 86 Hz are only seen on the red trace (loop) and lost in the noise with the T. This difference is caused by overload of soundblaster input from statics signal in 3kHz-9kHz band: in this band the dynamic range of spherics can be more of 140dB! This effects isn't produced in horizontal field, where the level of spherics is very weak.

300899 for courtesy of SM6LKM

Spectrogram of 2-86Hz band send me in .wav file by SM6LKM, Johan BODIN; signal received in Sverige (2000Km far from me). The same strange signal at 26 and 74 Hz, detected with longwire antenna (inverted L, 15m up, 90m top) connected to Line Input of SoundBlaster.

300899 for courtesy of SM6LKM

Spectrum of the same signal. From the symmetry around 50 Hz line Johan guess that it is sidebands created by something modulating 24 Hz on the 50 Hz. Many thanks, Johan!

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