RADAR - An acronym for RAdio Detecting And Ranging .
RADAR ALTIMETER - Airborne radar that measures the distance of the aircraft above the
ground.
RADAR BEAM - The space in front of a radar antenna where a target can be effectively
detected or tracked. Defined by areas that contain half or more of the maximum power
transmitted .
RADAR DETECTOR - A detector that, in its simplest form, only needs to be capable of
producing an output when rf energy (reflected from a target) is present at its input .
RADAR DISTRIBUTION SWITCHBOARD - An electrical switching panel used to connect inputs
from any of several radars to repeaters (indicators) .
RADAR MILE - Time interval (12.36 microseconds) for rf energy to travel out from a
radar to a target and back to the radar; radar nautical mile .
RADAR TEST SET - A combination of several test circuits and equipment used to test
various characteristics of a radar .
RADIATION FIELD - The electromagnetic field that radiates from an antenna and travels
through space .
RADIATION LOSSES - The losses that occur when magnetic lines of force about a conductor
are projected into space as radiation and are not returned to the conductor as the cycle
alternates .
RADIATION PATTERN - A plot of the radiated energy from an antenna .
RADIATION RESISTANCE - The resistance that if inserted in place of the antenna would
consume the same amount of power as that radiated by the antenna .
RADIO COMMUNICATIONS - The term describing teletypewriter, voice, telegraphic, and
facsimile communications. .
RADIO FREQUENCY (RF) - (1) Any frequency of electromagnetic energy capable of
propagation into space . (2) The frequencies that fall between 3 kilohertz and 300
gigahertz used for radio communications .
RADIO FREQUENCY CARRIER SHIFT - The system that uses a keyer to shift a radio frequency
signal above or below an assigned frequency. These shifts correspond to marks and spaces .
RADIO HORIZON - The boundary beyond the natural horizon in which radio waves cannot be
propagated over the earth's surface .
RADIO SET CONTROL UNIT - Equipment used to remotely control certain transmitter and
receiver functions .
RADIO WAVES - (1) A form of radiant energy that can neither be seen nor felt. (2) An
electromagnetic wave that is generated by a transmitter .
RADIX - Also called the base. The number of distinct symbols used in a number system.
For example, since the decimal number system uses ten symbols (0, 1, 2, 3, 4, 5, 6, 7, 8,
9), the radix is 10. In the binary number system, the radix is 2 because it uses only two
symbols (0, 1) .
RADIX POINT - Also called BINARY POINT, OCTAL POINT, DECIMAL POINT, and so forth,
depending on the number system .
RAM - Acronym for random-access memory.
RANDOM ACCESS - A method of accessing data (or instructions) without having to scan any
preceding information. Magnetic core, semiconductor, and bubble memories are considered
random access storage devices.
RANGE - The length of a straight line between a radar set and a target .
RANGE-GATE - A movable gate used to select radar echoes from a very short range
interval .
RANGE-HEIGHT INDICATOR - A radar display on which slant range is shown along the X axis
and height along the Y axis .
RANGE MARKER - A movable vertical pulse on an A-scope or a ring on a ppi scope used to
measure the range of an echo or to calibrate the range scale .
RANGE RESOLUTION - Ability of a radar to distinguish between targets that are close
together .
RANGES - The several upper limits a meter will measure as selectable by a switch or by
jacks; for example, a voltmeter may have ranges of 1 volt, 2.5 volts, 10 volts, 25 volts,
and 100 volts .
RANGE STEP - On an A-scope sweep, a vertical displacement used to measure the range of
an echo .
RAREFIED WAVE - A longitudinal wave that has been expanded or rarefied (made less
dense) as it moves away from the source .
RATE GYRO - A gyro used to detect and measure angular rates of change .
RATIO - The value obtained when one number is divided by another. This value indicates
the relative proportions of the two numbers .
RATIO DETECTOR - A detector that uses a double-tuned transformer to convert the
instantaneous frequency variations of the fm input signal to instantaneous amplitude
variations .
RATIO OF TRANSMITTED POWERS - The power ratio (fsk versus AM) that expresses the
overall improvement of fsk transmission when compared to AM under rapid-fading and
high-noise conditions .
RC CONSTANT - Time constant of a resistor-capacitor circuit; equal in seconds to the
resistance value in ohms multiplied by the capacitance value in farads .
RC DIFFERENTIATOR - An RC circuit in which the output is taken from the resistor .
RC FILTER - A filter used in applications where load current is low and constant, and
voltage regulation is not necessary .
RC INTEGRATOR - An RC circuit in which the output is taken from the capacitor .
RC NETWORK - A circuit containing resistance and capacitance arranged in a particular
manner to perform a specific function .
RC OSCILLATOR - An oscillator in which the frequency is determined by resistive and
capacitive elements .
REACTANCE - The opposition offered to the flow of an alternating current by the
inductance, capacitance, or both, in any circuit .
REACTANCE AMPLIFIER - A low-noise amplifier that uses a nonlinear variable reactance as
the active element instead of a variable resistance. Also called a parametric amplifier .
REACTANCE TUBE - A tube connected in parallel with the tank circuit of an oscillator.
Provides a signal that will either lag or lead the signal produced by the tank .
REACTANCE-TUBE MODULATOR - An fm modulator that uses a reactance tube in parallel with
the oscillator tank circuit .
READ/WRITE ERASE HEAD - A three-gap head (read, write, erase) on one body. Sometimes
the erase head is bolted to the read/write head.
READ/WRITE HEAD - A two-gap head (read, write) on one body.
REAL-TIME PROCESSING - A computer processing method in which data about a particular
event is entered directly into the computer as the event occurs and is immediately
processed so it can influence future processing.
RECEIVER - (1) The object that responds to the wave or disturbance. Same as DETECTOR .
(2) Equipment that converts electromagnetic energy into a visible or an audible form . (3)
In radar, a unit that converts rf echoes to video and/or audio signals .
RECEIVER SENSITIVITY - (1) The degree to which a receiver can usefully detect a weak
signal. (2) The lower limit of useful signal input to the receiver .
RECEIVER TRANSFER SWITCHBOARD - Equipment used to transfer receiver audio outputs to
remote control station audio circuits .
RECEIVING ANTENNA - The device used to pick up the rf signal from space .
RECEIVING END - See OUTPUT END .
RECEPTION - The instant when an electromagnetic wave passes through a receiver antenna
and induces a voltage in that antenna .
RECIPROCAL (OF A QUANTITY) - The value obtained by dividing the number 1 by that
quantity .
RECIPROCITY - The property of interchangeability of the same antenna for transmitting
and receiving .
RECORD - A group of related fields, all pertaining to the same subject.
RECORD BLOCK - Several records blocked together.
RECORD LENGTH - The number of characters in a record.
RECOVERY TIME - In a radar, the time interval between the end of the transmitted pulse
and the time when echo signals are no longer attenuated by the tr gap .
RECTIFIER - A device used to convert ac to pulsating dc .
RECTANGULAR-COORDINATE GRAPH - A graph in which straight-line axes (horizontal and
vertical) are perpendicular .
RED - The reference color of equipment that passes classified information, It normally
refers to patch panels .
REEL - The metal-, glass-, or plastic-flanged hub on which magnetic tape is wound.
REFERENCE LINE - The position of zero displacement in a wave .
REFERENCE POINT - A point in a circuit to which all other points in the circuit are
compared .
REFERENCE TAPE - A tape used as a reference against which the performances of other
tapes are compared.
REFLECTED WAVE - (1) The wave that reflects back from a medium. (2) The wave moving
back to the source from the termination of a transmission line after reflection has
occurred .
REFLECTING OBJECT - In radar a air or surface contact that provides an echo .
REFLECTION WAVES - Waves that are neither transmitted nor absorbed, but are reflected
from the surface of the medium they encounter .
REFLECTOR - The parasitic element of an array that causes maximum energy radiation in a
direction toward the driven element .
REFLEX KLYSTRON - A klystron with a reflector (repeller) electrode in the place of a
second resonant cavity used to redirect the velocity-modulated electrons back through the
cavity that produced the modulation . (2) A microwave oscillator that is tuned by changing
the repealer voltage .
REFRACTION - The changing of direction of a wave as it leaves one medium and enters
another medium of a different density .
REFRACTIVE INDEX - In a wave-transmission medium, the ratio between the phase velocity
in free space and in the medium .
REGENERATION - See FEEDBACK .
REGENERATIVE DETECTOR - A detector circuit that produces its own oscillations,
heterodynes them with an incoming signal, and deflects them .
REGENERATIVE FEEDBACK - The process by which a portion of the output signal of an
amplifying device is fed back in phase to reinforce the input. Also called POSITIVE
FEEDBACK .
REGULATOR - The section in a basic power supply that maintains the output of the power
supply at a constant level in spite of large changes in load current or input line voltage
.
RELATIVE BEARING - Bearing of a target measured in a clockwise direction from
"dead ahead" of a ship or plane .
RELAY - An electromagnetic device with one or more sets of contacts that change
position by the magnetic attraction of a coil to an armature .
RELUCTANCE - A measure of the opposition that a material offers to magnetic lines of
force .
REMANENCE - (1) The magnetic flux density that remains in a magnetic circuit after
removal of applied magnetomotive force. (2) Is not necessarily equal to residual flux
density.
REMOTE-CUTOFF TUBE - An electron tube in which the control grid wires are farther apart
at the centers than at the ends. This arrangement allows the tube to amplify large signals
without being driven into cutoff. This tube is also called a VARIABLE-MU TUBE .
REMOTE TERMINAL - A display terminal, such as a crt or other piece of equipment, which
is not located with the computer but is connected by a communications line. In a typical
online, real-time communications system, the remote device is usually a teletypewriter or
a crt visual display unit.
REMOVABLE FIXED DISK - A hard-disk device (usually) with only one hard-disk platter
that's used to record and retrieve data.
REPEATER - (1) Another name for an active satellite . (2) Also, a common name for
remote radar indicators.
REPELLER - Sometimes called a REFLECTOR. An electrode in a reflex klystron with the
primary purpose of reversing the direction of the electron beam .
REPERFORATOR - Equipment that converts the incoming tty signal and stores it on paper
tape .
REPRODUCTION - The process of converting electrical signals to sound waves. This sound
is speech, music, and so on .
REPULSION - The mechanical force tending to separate bodies having like electrical
charges or like magnetic polarity .
RERADIATION - The reception and retransmission of radio waves that is caused by
turbulence in the troposphere .
RESIDUAL MAGNETISM - Magnetism remaining in a substance after removal of the
magnetizing force .
RESISTANCE - (1) The opposition a device or material offers to the flow of current. The
effect of resistance is to raise the temperature of the material or device carrying the
current. (2) A circuit element designed to offer a predetermined resistance to current
flow. A resistance of 1 ohm will allow a current of 1 ampere to flow through it when a
potential of 1 volt is applied. .
RESISTIVITY - See SPECIFIC RESISTANCE. The reciprocal of conductivity .
RESISTOR - The electrical component that offers resistance to the flow of current. It
may be a coil of fine wire or a composition rod .
RESOLUTION (DYNAMIC RANGE) - The average peak-to-peak signal amplitude at the maximum
flux reversal divided by the average peak-to-peak signal amplitude at the minimum flux
reversal at the desired recording method.
RESOLVER - A rotary, electromechanical device used to perform trigonometric
computations by varying the magnetic couplings between its primary and secondary windings.
It is generally used in circuits that solve vector problems, such as analog computers and
conversion equipment. The resolver solves three different type problems: (1) Resolution -
separating a vector into two mutually perpendicular components; (2) Composition -
combining two components of a vector to produce a vector sum; and (3) Combination - the
process of resolution and composition taking place simultaneously .
RESONANCE - The condition in a circuit containing inductance and capacitance in which
the inductive reactance is equal and opposite to the capacitive reactance. This condition
occurs at only one frequency and the circuit in that condition is said to be in resonance
.
RESONANCE CHAMBER - See ECHO BOX .
RESONANT CIRCUIT - A circuit that contains both inductance and capacitance and is
resonant at one frequency (XL = XC) .
RESONANT FREQUENCY - That frequency in a given resonant circuit at which the inductive
and capacitive reactance values are equal and cancel each other .
RESONANT LINE - A transmission line that has standing waves of current and voltage .
REST FREQUENCY - The carrier frequency during the constant-amplitude portions of a
phase modulation signal .
REST POSITION - See REFERENCE LINE .
REST TIME (RT) - The time when there is no pulse; nonpulse time .
RESULTANT MAGNETIC FIELD - The magnetic field produced in a synchro by the combined
effects of the three stator magnetic fields .
RETENTIVITY - The ability of a material to retain its magnetism .
RETURN - The rf signal reflected back from a radar target; echo .
REVERBERATION - The multiple reflections of sound waves .
REVERSE AGC - The type of agc that causes an amplifier to be driven toward cut-off .
REVERSE BIAS - An external voltage applied to a diode or semiconductor junction to
reduce the flow of electrons across the junction. Also called BACK BIAS .
RF IMPEDANCE BRIDGE - A piece of test equipment used for measuring the combined
resistance and reactance of a component, piece of equipment, or system at rf frequencies.
RF RADIATION HAZARD - A health hazard caused by exposure to electromagnetic radiation
or high-energy particles (ions). Abbreviated RADHAZ .
RF (RADIO FREQUENCY) AMPLIFIER - An amplifier designed to amplify signals with
frequencies between 10 kilohertz (10 kHz) and 100,000 megahertz (100,000 MHz) .
RF (RADIO FREQUENCY) TRANSFORMER - A transformer specially designed for use with rf
(radio frequencies). An rf transformer is wound onto a tube of nonmagnetic material and
has a core of either powdered iron or air .
RGK - The symbol used to express the resistance between the grid and the cathode of an
electron tube .
RHEOSTAT - A variable resistor used for the purpose of adjusting the current in a
circuit .
RHO - Greek letter "rho" (r). Used in the field of electricity and
electronics to represent the specific resistance of a substance .
RHOMBIC ANTENNA - A diamond-shaped antenna used widely for long-distance,
high-frequency transmission and reception .
RIGID COAXIAL LINE - A coaxial line consisting of a central insulated wire (inner
conductor) mounted inside of a tubular outer conductor .
RIGIDITY - The tendency of the spin axis of a gyro wheel to remain in a fixed direction
in space if no force is applied to it .
RINGING - RF oscillations caused by shock excitation of a resonant circuit or cavity .
RING TIME - In radar, the time during which the output of an echo box remains above a
specified level .
RIPPLE FREQUENCY - The frequency of the ripple current. In a full-wave rectifier it is
twice the input-line frequency .
RIPPLE VOLTAGE - The alternating component of unidirectional voltage. (This component
is small compared to the direct component.)
RLC CIRCUIT - An electrical circuit that has the properties of resistance, inductance,
and capacitance .
RL DIFFERENTIATOR - An RL circuit in which the output is taken from the inductor .
RL INTEGRATOR - An RL circuit in which the output is taken from the resistor .
RMS - Abbreviation of root mean square .
ROM - Acronym for read-only memory.
ROOT MEAN SQUARE (RMS) - The equivalent heating value of an alternating current or
voltage, as compared to a direct current or voltage. It is 0.707 times the peak value of a
sine wave .
ROTARY CAP - A spark gap, similar to a mechanically driven rotary switch, used to
discharge a pulse-forming network .
ROTARY SWITCH - A multicontact switch with contacts arranged in a circular or
semicircular manner .
ROTATING FIELD - The magnetic field in a multiphase ac motor that is the result of
field windings being energized by out-of-phase currents. In effect, the magnetic field is
made to rotate electrically rather than mechanically .
ROTATING JOINT - A joint that permits one section of a transmission line or waveguide
to rotate continuously with respect to another while passing energy through the joint.
Also called a rotary coupler .
ROTATIONAL DELAY - The time required for the read/write head to find a specified record
on a disk, diskette, or drum once head positioning has occurred.
ROTOR - (1) The revolving part of a rotating electrical machine. The rotor may be
either the field or the armature, depending on the design of the machine . (2) The
rotating member of a synchro that consists of one or more coils of wire wound on a
laminated core. Depending on the type of synchro, the rotor functions similarly to the
primary or secondary winding of a transformer .
RPK - The symbol used to represent the resistance between the cathode and plate of a
tube .
RUNNING OPEN - The teletypewriter condition where the type hammer constantly strikes
the type box but does not print or move across the page .
RZ RECORDING - (See digital recording.)
