AI-8
RADIATION RESISTANCE—The resistance, which if inserted in place of an antenna, would consume
the same amount of power as that radiated by the antenna.
RADIO FREQUENCIES—Electromagnetic frequencies that fall between 3 kilohertz and 300 gigahertz
and are used for radio communications.
RADIO HORIZON—The boundary beyond the natural horizon in which radio waves cannot be
propagated over the earth's surface.
RADIO WAVE—(1) A form of radiant energy that can neither be seen nor felt. (2) An electromagnetic
wave generated by a transmitter.
RAREFIED WAVE—A longitudinal wave that has been expanded or rarefied (made less dense) as it
moves away from the source.
RECEIVER—The object that responds to a wave or disturbance. Same as detector.
RECEIVING ANTENNA—The device used to pick up an rf signal from space.
RECEIVING END—See OUTPUT END.
RECIPROCITY—The property of interchangeability of the same antenna for transmitting and receiving.
RECTANGULAR-COORDINATE GRAPH—A graph in which straight-line axes (horizontal and
vertical) are perpendicular.
REFERENCE LINE—The position a particle of matter would occupy if it were not disturbed by wave
motion.
REFLECTED WAVE—(1) The wave that reflects back from a medium. (2) Waves traveling from the
load back to the generator on a transmission line. (3) The wave moving back to the sending end of a
transmission line after reflection has occurred.
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.
REFRACTION—The changing of direction as a wave leaves one medium and enters another medium of
a different density.
RERADIATION—The reception and retransmission of radio waves caused by turbulence in the
troposphere.
RESONANCE—The condition produced when the frequency of vibrations are the same as the natural
frequency (of a cavity). The vibrations reinforce each other.
RESONANT LINE—A transmission line that has standing waves of current and voltage.
REST POSITION—See REFERENCE LINE.
REVERBERATION—The multiple reflections of sound waves.
