OCTAL NUMBER SYSTEM - A number system based on powers of eight. This
system is used extensively in computer work .
OERSTED - A unit of magnetic field strength.
OFF-LINE TEST EQUIPMENT - Equipment that tests and isolates faults in
modules or assemblies removed from systems .
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 .
OHMIC VALUE - Resistance in ohms .
OHMMETER - A meter used to measure resistance .
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 .
OHMS PER SQUARE - The resistance of any square area of thin film resistive
material as measured between two parallel sides .
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 .
OMNIDIRECTIONAL ANTENNA - An antenna that radiates and receives equally in
all directions (nondirectional) .
ONLINE PROCESSING - Processing from terminals under the direct control of
a computer.
ON-LINE TEST EQUIPMENT - Continuously monitors the performance of
electronic systems .
OPAQUE - Those 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 LINE - A transmission fine that has a terminating impedance
that is infinitely large .
OPERATING SYSTEM - Software that controls the execution of programs. An
operating system may provide services such as input/output control and data management. It
may also provide job scheduling, memory allocation, and other general functions. It is
usually loaded by a bootstrap program.
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 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 .
OPTICAL TIME-DOMAIN REFLECTOMETER (OTDR) - A piece of test equipment used
to test a fiber-optic cable for such things as attenuation, localized losses, and defects.
It transmits an optical pulse (usually a laser) into the fiber-optic cable and analyzes
the resulting reflections in terms of amplitude versus distance.
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 .
OPTOELECTRONIC DEVICES - Devices that either produce or use light in their
operation .
ORDER-WIRE CIRCUIT - A circuit between operators used for operations
control and coordination .
ORGANIZATIONAL-LEVEL MAINTENANCE (SM & R CODE O) - Responsibility of
the user organization .
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 .
ORIGIN - The point on a graph where the vertical and horizontal axes cross
each other .
OSCILLATOR - An oscillator is a nonrotating device that produces
alternating current. The frequency is determined by the characteristics of the device .
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 .
OUTPUT - The magnitude of the reproduced signal voltage, usually measured
at the output of the reproduced amplifier.
OUTPUT END - The end of a transmission line that is opposite the source;
receiving end .
OUTPUT IMPEDANCE - The impedance that is presented to the load by the
transmission line and its source .
OVERDRIVEN - When the input signal amplitude is increased to the point
that the transistor goes into saturation and cutoff .
OVERMODULATION - A condition that exists when the peaks of the modulating
signal are limited .
OXIDE BUILD-UP - The accumulation of oxide or wear products as deposits on
the surface of heads and guides.
OXIDE LOADING - (1) A measure of the density with which oxide is packed
into a coating. (2) The weight of the oxide per unit volume of the coating.
OXIDE SHED - The loosening of particles of oxide from the tape coating
during use.
