OCTAL NUMBER SYSTEM A number system based on powers of eight. This system is used extensively in computer work [13].

OFF-LINE TEST EQUIPMENT Equipment that tests and isolates faults in modules or assemblies removed from systems [14].

OHM The unit of electrical resistance. That value of electrical resistance through which a constant potential difference of 1 volt across the resistance will maintain a current flow of 1 ampere through the resistance [1].

OHM'S LAW The current in an electrical circuit is directly proportional to the electromotive force in the circuit. The most common form of the law is E = IR, where E is the electromotive force or voltage across the circuit, I is the current flowing in the circuit, and R is the resistance of the circuit [1].

OHMIC VALUE Resistance in ohms [1].

OHMMETER A meter used to measure resistance [3] [16].

OHMS PER SQUARE The resistance of any square area of thin film resistive material as measured between two parallel sides [14].

OILCAN TUBE A type of planar tube, similar to the lighthouse tube, which has cooling fins. The oilcan tube is designed to handle large amounts of power at uhf frequencies [6].

OMNIDIRECTIONAL ANTENNA An antenna that radiates and receives equally in all directions (nondirectional) [10] [18].

ON-LINE TEST EQUIPMENT Continuously monitors the performance of electronic systems [14].

OPAQUE Those substances that do not transmit (pass) any light rays; that is, the light rays are either absorbed or reflected [10].

OPEN CIRCUIT (1) The condition of an electrical circuit caused by the breaking of continuity of one or more conductors of the circuit; usually an undesired condition. (2) A circuit that does not provide a complete path for the flow of current [1].

OPEN-ENDED LINE A transmission fine that has a terminating impedance that is infinitely large [10].

OPERATIONAL AMPLIFIER An amplifier designed to perform computing or transfer operations and that has the following characteristics: (1) very high gain, (2) very high input impedance, and (3) very low output impedance [8].

OPTICAL COUPLER A coupler composed of an LED and a photodiode and contained in a light- conducting medium. Suitable for frequencies in the low-megahertz range [7].

OPTIMUM WORKING FREQUENCY The most practical operating frequency that can be used with the least amount of problems and is roughly 85 percent of the maximum usable frequency [10].

OPTOELECTRONIC DEVICES Devices that either produce or use light in their operation [7].

OR GATE A gate that performs the logic OR function. It produces an output 1 whenever any or all of its inputs is/are 1 [13].

ORDER-WIRE CIRCUIT A circuit between operators used for operations control and coordination [17].

ORGANIZATIONAL-LEVEL MAINTENANCE Responsibility of the user organization [14].

ORIGIN The point on a graph where the vertical and horizontal axes cross each other [10].

OSCILLATOR An oscillator is a nonrotating device that produces alternating current. The frequency is determined by the characteristics of the device [9].

OUT-OF-CIRCUIT METER A meter that is not permanently installed in a circuit. Usually portable and self-contained, these meters are used to check the operation of a circuit or to isolate troubles within a circuit [3].

OUTPUT END The end of a transmission line that is opposite the source; receiving end [10].

OUTPUT IMPEDANCE The impedance that is presented to the load by the transmission line and its source [10].

OVERDRIVEN When the input signal amplitude is increased to the point that the transistor goes into saturation and cutoff [7].

OVERMODULATION A condition that exists when the peaks of the modulating signal are limited [12].