RF subterranean electrical resistance measuring appts. - has electrical and magnetic field sensors, superheterodyne signal processing and evaluation of amplitude and phases by sample=and=hold system

摘要

The appts. for measuring the specific electrical resistance of subterranean strata transmits 10 kHz to 2 MHz electromagnetic waves below the surface during, e.g., prospecting operations. The appts. has sensors (1,2) for detecting the components of the electric and magnetic fields respectively. The sensor signals are low-pass filtered (3,4) and individually mixed (5,6) as in superheterodyne reception followed by narrow-band filtering (13,14) of the mixer signals. After amplification (15,16) the mixer signals are processed by the evaluation stages (17,18,20) wherein the relative signal phase-shifts/amplitudes are determined with enhanced accuracy using a Sample and Hold system (19). USE/ADVANTAGE - Relatively simple construction and use of IF stages eliminates customary problems associated with RF signal processing. Has improved strata depth selectivity.