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ANALYSIS AND IMPROVEMENT OF THE PRIMARY FIELD WAVEFORM OF THE GROUND TEM METHOD *
Author(s) -
QIAN BIN
Publication year - 1987
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1111/j.1365-2478.1987.tb00813.x
Subject(s) - waveform , trailing edge , transmitter , electrical conductor , acoustics , signal edge , optics , electrical engineering , physics , voltage , transmission (telecommunications) , engineering , channel (broadcasting) , mechanics , analog signal
ABSTRACT Many ground TEM systems use an on‐off type of primary field waveform and measure the secondary field only in the transmitter off‐time, so as to realize the pure secondary field measurement. The width of the trailing edge of the primary pulses and the duration of the transmitter on‐time form a time‐constant (T c ) window. Most effective excitation is achieved if the target conductor has a T c falling into this window. To be able to measure in the transmitter on‐time, two primary field waveforms are proposed. The first is a series of unipolar pulses with identical steep ramps at both leading and trailing edges. Measurements made in the on‐time after the leading edges simply reduce the stacking time needed and power consumption by half. Also, long‐ T c conductors are better excited. The second is a series of bipolar pulses with long ramps as the leading edges and short ramps as the trailing edges. This waveform presents two different T c ‐windows at the same time and helps to improve the detection of long‐ T c conductors in the presence of short‐ T c ones.