Abstract: A radio link is established between the portable receiver used by an operator to trace the underground portion of a utility and the transmitter which induces a magnetic signal in the utility. Circuitry in both transmitter and receiver allows the operator who is remote from the transmitter to interrogate the transmitter from the receiver for essential information and to control operating functions at the transmitter. Such operations as changing the transmission frequency of the generator, conserving batter power by switching the transmitter's frequency generator to and from a power saving standby mode during periods of non-use, checking on the power level of the battery, and determining if the transmission circuit is complete and unbroken can be effected without the necessity of the operator returning to the site of the transmitter.