Abstract: A transmitter (12) has an output (13) adapted to be connected across an alternating current power line (AC1, AC2) at a point remote from an appliance (24) to be controlled. The transmitter generates one pulse per cycle of the alternating current. The pulse phase has a predetermined value with respect to the alternating current. A receiver (21) is adapted to be connected across the power line to couple the line to the appliance. When the receiver detects transmitter generated pulses during phase windows occurring each alternating current cycle, power is applied from the line to the appliance for the remainder of such alternating current cycle. The transmitter has an adjustment (14) that permits the phase of the transmitter generated pulses to be modulated and the receiver has an adjustment (26) that permits the position of the phase windows relative to the alternating current to be changed. The transmitter generated pulses and the phase windows occur only on every other half cycle of the alternating current.