Abstract: An automatic gain control (AGC) system for use in line locators that detect concealed conductors is presented. The AGC system includes determining an AGC signal from a reference sensor and processing signals from one or more observed sensors utilizing the AGC signal. The reference sensor is located farther from the concealed conductor than the observed sensors. The AGC system can be implemented in analog form or can include a digital AGC determination in a microprocessor.

Abstract: An electromagnetic field sensing apparatus used for locating and determining the distance to buried conductive conduits including at least two receptor means, each adapted to receive a signal from the conduit and produce an output voltage proportional to the signal received, and also including a calibrating coil, with known relative coupling to the receptor means, and capable of inducing calibrating signals therein. Computing means are employed to calculate the relative sensitivities of each said receptor means using the voltage signals induced therein by the calibrating coil, and said known relative coupling relationships. The computing means further uses the output voltages from said receptor means, induced therein by the signal radiating from the conductive conduit, and said relative sensitivities to calculate the distance to and location of the conduit. Display means are provided to indicate this distance and location.