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Signal processing for a three-component transmitting (3CTx) electromagnetic device
(2021-04-23) Finlayson, Michael
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.