Signal processing for a three-component transmitting (3CTx) electromagnetic device
Date
2021-04-23
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Abstract
When a three-component transmitter (3CTx) transmits simultaneously from all three
transmitters, the signal measured in a receiver coil will be the sum of the three primary and
secondary fields. In order to interpret the data, it is necessary to separate the signals from each
transmitter. In a numerical experiment utilizing time-domain type sources, a synthesized signal
comprised of the sum of three transmitter signals, a powerline signal and a low-frequency noise
signal was created. Frequency spectra showed that for multiple specific combinations of base
frequencies it is possible for the harmonics to be unique (not overlapping) and hence identifiable.
For these combinations, the transmitter signals can be separated using a stacking filter in the
time-domain. One specific combination is 30 Hz, 32.5 Hz, and 35 Hz for the three transmitters,
when the powerline is operating at 60 Hz. The secondary fields generated by these three base
frequencies were modelled using a wire-loop. Analyzing the response in three off-time and five
on-time windows, it was determined that the maximum differences caused by having three
different base frequencies are predictable and correctable. Thus, building and field testing the
3CTx is practical.
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Keywords
Geophysics, electromagnetics, transmitter development, signal separation