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adiothermy • random feed 581
radiothermy See DIATHERMY.
radio thorium Radioactive THORIUM.
radiotracer See TRACER.
radio transceiver A RADIO RECEIVER and RADIO
TRANSMITTER built into a single unit, and generally
intended for use in two-way communication.
radio transmitter The complete apparatus that
generates radio-frequency power, modifies it with
the data needed for communication, and delivers
the product to an antenna for radiation into
space. Here, the radio transmitter is distinguished
from similar equipment: facsimile transmitter,
remote-control transmitter, telemetry
transmitter, television transmitter, etc.
radio-transparent material 1. A substance
through which radio waves pass with little or no
attenuation. 2. A substance through which
X rays, gamma rays, or high-speed subatomic
particles can pass with little or no attenuation.
radiotrician Acronym for radio electrician. See RA-
DIO SERVICE TECHNICIAN.
radio tube 1. A VACUUM TUBE used at radio frequencies.
2. A vacuum tube used as an amplifier,
local oscillator, detector, or mixer in an early radio
receiver.
radiovision See TELEVISION.
radio watch See WATCH.
radio waves Electromagnetic waves in the RADIO
SPECTRUM.
radio window That portion of the radio-frequency
electromagnetic spectrum that passes through
the atmosphere, rather than being refracted or
absorbed. The wavelength range is about 20 meters
to 5 millimeters, or 15 MHz to 60 GHz. The
lower limit of this range is affected by ionospheric
conditions. The upper frequency limit depends on
various factors, including relative humidity and
dust content of the air.
radium Symbol, Ra. A rare radioactive metallic
element. Atomic number, 88. Atomic weight,
226.025.
radius The straight-line distance from the center of
a circle or sphere to its periphery.
radius vector In spherical or polar coordinates, a
line segment drawn from the pole, or origin, and
representing the vector magnitude.
radix The number indicating the number of symbols
in a system of numerical notation, and the
powers of which give the place values of the system.
Thus, 10 is the radix of the decimal system,
and 2 is the radix of the binary system. Also
called BASE.
radix point In a number, the point (dot or period)
separating the integral and fractional digits. Its
specific name depends on the system of notation
involved: binary point, decimal point, etc.
radome A plastic shell housing a radar antenna—
especially aboard an aircraft.
radon Symbol Rn. A gaseous radioactive element
that results from the disintegration of radium.
Atomic number, 86. Atomic weight, 222.
rad/s Abbreviation of radians per second, the SI
unit of angular velocity.
rad/s 2 Abbreviation of radians per second squared,
the SI unit of angular acceleration.
radux A continuous-wave, low-frequency radionavigation
system. Position is determined by comparing
the phase of two signals sent from
different locations.
RAID Acronym for REDUNDANT ARRAY OF INDE-
PENDENT DISKS.
rainbow generator A test-signal generator that
produces a full color spectrum, a pattern resembling
the successive coloration of a rainbow, on
the screen of a color-television receiver. Also see
RAINBOW PATTERN.
rainbow pattern A test pattern for servicing a
color-television receiver. It consists of a full color
spectrum, thus taking its name from its resemblance
to a rainbow. Also see RAINBOW GENER-
ATOR.
RAM Abbreviation of RANDOM-ACCESS MEM-
ORY.
ramp A sawtooth wave with a linear rise and a
practically instantaneous decay; its name was
derived from its resemblance to an incline.
Amplitude
ramp
Time
ramp generator A test-signal generator that produces
sawtooth-wave signals. Also see RAMP.
R and D Abbreviation of research and development
or research and design. (Also, R&D.)
random access Abbreviation, RA. In computer and
data-processing operations, pertaining to storage
or memory in which data can be recovered in any
order.
random-access memory In computer and dataprocessing
systems, a memory providing access
time that is independent of the address.
random deviation Irregular RIPPLE.
random-fed antenna An antenna that uses RAN-
DOM FEED.
random feed A method of connecting a transmission
line to an antenna, wherein the feed point is
not necessarily at the center and not necessarily
at a current loop or voltage loop. This technique
is rarely used; it generally results in some radiation
from the feed line.