The amplification and magnetic tape recording of geomagnetic micropulsation signals

Abstract

This thesis describes instrumentation for amplifying and tape-recording geomagnetic micropulsation signals in the frequency range. 005 to .2 c/s. Signals are detected by an iron cored coil and amplified by a galvanometer amplifier using CdS light dependent resistors. The advantages and disadvantages of applying negative feedback to such an amplifier are considered, and the effect of feedback on frequency response is examined. The amplifier developed (which does not use feedback) is simple, economical, and reliable. Output voltage is 100 mv/gamma/c/s and drift is less than ± 2 mv. The magnetic tape recording system, comprising three signal channels and one time channel, uses amplitude modulated carrier recording which combines the wide dynamic range and simplicity of direct recording with the flat frequency response of F.M. Accuracy of reproduction is intermediate between F.M. and direct recording, being theoretically ± 2 or 3 %. Using slow speed recording techniques, the system will record the output signals from three galvanometer amplifiers for a period of three days eight hours. Dynamic range is about 50 dB and the accuracy of reproduction is ± 7 %. It is hoped that improvements to the tape deck will double the recording time available and improve the accuracy to ± 3 %.