OFF-LINE TEST EQUIPMENTEquipment that tests and isolates faults in modules or assemblies
removed from systems .
OHMThe 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
OHMIC VALUEResistance in ohms .
OHMMETERA meter used to measure resistance  .
OHM'S LAWThe 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 .
OHMS PER SQUAREThe resistance of any square area of thin film resistive material as measured
between two parallel sides .
OILCAN TUBEA 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 .
OMNIDIRECTIONAL ANTENNAAn antenna that radiates and receives equally in all directions
(nondirectional)  .
ON-LINE TEST EQUIPMENTContinuously monitors the performance of electronic systems .
OPAQUEThose substances that do not transmit (pass) any light rays; that is, the light rays are either
absorbed or reflected .
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 .
OPEN-ENDED LINEA transmission fine that has a terminating impedance that is infinitely large .
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 .
OPTICAL COUPLERA coupler composed of an LED and a photodiode and contained in a light-
conducting medium. Suitable for frequencies in the low-megahertz range .
OPTIMUM WORKING FREQUENCYThe most practical operating frequency that can be used with
the least amount of problems and is roughly 85 percent of the maximum usable frequency .
OPTOELECTRONIC DEVICESDevices that either produce or use light in their operation .
ORDER-WIRE CIRCUITA circuit between operators used for operations control and coordination .
ORGANIZATIONAL-LEVEL MAINTENANCE (SM & R CODE O)Responsibility of the user
OR GATEA gate that performs the logic OR function. It produces an output 1 whenever any or all of its
inputs is/are 1 .