Abstract: A receiver of pulsed phase modulated signals is disclosed. These signals are produced by switching a reactance on and off a power line. The receiver produces a sinusoidal current in phase with the current on the power line and a sinusoidal voltage nominally 90 degrees out of phase with the voltage on the power line. These sinusoids are multiplied together to produce a sinusoid of double the original frequency (which may be filtered out) and voltage levels (positive when the reactance is on line and negative when it is off). The absolute value difference between these voltage levels (if any) is used as an error voltage for feedback. The voltage sinusoid is modified by this feedback.

Abstract: A method of coding to provide command signals simultaneously to selected devices is disclosed. Each device is assigned a different power of the same integer. Commands are then signaled to the desired devices by sending a series of pulses, the total of which is the sum of the integer raised to the power of each the devices to be commanded. Thus if devices having powers of 0 and 3 are to be commanded, and the integer is 2, 9 pulses would be sent. (2.degree.=1, 2.sup.3 =8, 1+8=9). Each different total will signal a unique device or a unique combination of devices.

Abstract: A single pair of conductors in a drill cable in a borehole is used not only to transmit power into the hole, but to transmit control commands into the hole, and to communicate sensor data back up to the surface. A frequency for power and communication of 1 kHz is employed; but this is frequency modulated by deviation of about 5 percent to transmit commands down-hole. A different non-interfering phase modulation is used to send data back to the surface by causing a susceptance (preferably capacitive) to be connected across the supply cable to signify a binary pulse. The alteration in phase between current into the cable and potential across it is observed at the surface and the pulses so detected are processed by conventional data processing techniques.