Controlled power source for underground line location

A transmitter for a line locator system that controls the electrical current, voltage or power applied to the target line is disclosed. Control of the electrical output of the transmitter can be achieved passively or by means of a feedback control system. A transmitter connected directly to a line can include an operator control and monitoring of current being supplied to a line to be located. Some transmitters include a current regulating circuit that controls current supplied to a line. In some transmitters, feedback controllers and feedback loops are used to regulate output current, voltage or power. Some control loops are based on monitoring currents in circuits; some control loops monitor power output from an inductive mode transmitter antenna. An inductively coupled transmitter with power output control is also disclosed.