Project 7 Mobile ELF/ULF recorder Whith ELF/ULF reception the disturbing magnetic fields from electrically powered engines are a mayjor problem that can spoil recordings made at home. Thus a recording system for mobile use is valuable, but there is not much hardware for this. A cassete recorder can be used, if the low frequency signals are modulated with a carrier in the audio range. Amplitude modulation is very prone to dropouts from the tape, frequency modulation is prone to the jitter from the motor, but phase modulation doesn't suffer from either. In order to regenerate the signal from the recording later, a reference tone must be recorded simultaneously. As the bandwidth of the signals to be recorded is very low, there is a possibility to cover signals from several receiving systems with one single audio channel of a mono cassette recorder.

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