1-50
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].
OHMIC VALUE—Resistance in ohms [1].
OHMMETER—A meter used to measure resistance [3] [16].
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].
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 (OP AMP)—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].
ORDER-WIRE CIRCUIT—A circuit between operators used for operations control and coordination [17].
ORGANIZATIONAL-LEVEL MAINTENANCE (SM & R CODE O)—Responsibility of the user
organization [14].
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].
