Abstract: A vector positional display for use in an underground metal locating system for indicating the relative position of the underground metal with respect to a sensor array. The underground object functions as a RF transmitter, and the antenna array detects the transmitted signal. Commutation of the antenna array causes frequency modulation of the received signal which after demodulation can be used for identifying the direction of the object from the sensor array. A display slot counter accumulates count from a system clock, and resolution decoders determine field of view from the antenna array in locating the object. A zero crossing data probe triggers a display decoder which converts accumulated count to a format for energizing lights in the display unit.

Abstract: A system for locating underground or above ground metal and pipe objects includes a transmitter for generating an RF signal which is applied to the object which acts as a transmitter. An above-ground antenna array receives the RF signal transmitted by the underground object with a commutator for periodically and sequentially receiving signal from each antenna in the array, the commutator frequency modulating the received signal. A FM demodulator then demodulates the signal from the commutator and provides a Doppler effect frequency shift signal. A vector positional display then indicates position of the object based on the Doppler effect frequency shift signal relative to a reference signal.

Abstract: A metal locating system includes a first transmitter unit and a second receiver detector unit for locating an under and above ground radio frequency driven element such as a pipe. The first unit is a radio frequency transmitter operating at radio frequencies and coupled to the driven element as a loss line antenna. The receiver second unit is a switched diversity antenna connected to a radio FM receiver and a differential phase detection system. When the first unit is driven by the driven element, the second unit is able to detect and trace the position of the driven element relative to the switched diversity antenna.