18WuD2x

adioactive element • radio-frequency choke 577
radioactive element A chemical element that is
RADIOACTIVE (e.g., uranium). Also called radioelement.
radioactive isotope See RADIOISOTOPE.
radioactive tracer A quantity of radioactive material
put into a system so that its path can be monitored
by means of a radiation detector. An
example is the introduction of radioactive barium
into the large intestine. The flow and concentration
of the barium gives an indication of the functioning
of the lower intestine.
radioactive transducer A pickup device for detecting
and measuring radioactivity (e.g., Geiger-
Mueller tube).
radioactivity counter See GEIGER COUNTER
and SCINTILLATION COUNTER.
radio altitude See RADAR ALTITUDE.
radio amateur An electronics hobbyist licensed to
operate two-way wireless communications stations
in various assigned frequency bands, without
receiving payment for services rendered.
Radio Amateur Civil Emergency System Abbreviation,
RACES. A civil-defense organization of licensed
amateur radio stations. Also see RADIO
AMATEUR.
radio astronomy The observation, study, and
analysis of radio-frequency electromagnetic emissions
from bodies or points in space, and the
study of these bodies through their radiations.
radioautograph See AUTORADIOGRAPH.
radio beacon 1. A radio transmitter of directionfinding
or guidance signals. 2. Also called radio
beam. The signals transmitted by a radio beacon,
as defined in 1.
radio beam 1. Antenna radiation focused in one
direction. 2. See RADIO BEACON, 2.
radiobiology A field of biology concerned with the
influence of radiant energy or radioactivity on living
organisms.
radio broadcast A radio transmission directed to
numerous, nonspecific receivers—especially by a
station in the broadcast service. Also called RA-
DIOCAST. Also see BROADCAST SERVICE, 1, 2.
radio car An automobile equipped with a two-way
radio.
radio carbon Radioactive carbon (i.e., carbon 14).
radiocast See RADIO BROADCAST.
radio channel A single, usually narrow radiofrequency
band within a larger band, in which
stations are authorized to transmit signals of a
specified type. Also see CHANNEL, 1; CHANNEL
SEPARATION; and CHANNEL WIDTH.
radiochemistry The chemistry of radioactive substances.
radio communication Wireless communication
carried on by means of radio-frequency electromagnetic
waves.
radio compass See DIRECTION FINDER.
radioconductor A substance or body whose electrical
conductivity is affected by radio waves, and
that can be used as a sensor of such waves.
radio control See REMOTE CONTROL.
radio direction finder See DIRECTION FINDER.
radio Doppler 1. A change in the frequency of a radio
signal emitted by a source having radial motion,
with respect to the receiver. 2. An electronic
device used to measure radial speed by means of
the Doppler effect at radio frequencies.
radio-electronics The branch of electronics specifically
involved with wireless communications.
radioelement See RADIOACTIVE ELEMENT.
radio engineer A trained professional skilled in the
physics and mathematics of radio communications,
and in the theory and application of basic
electronics engineering and related subjects. Also
see RADIO ENGINEERING.
radio engineering The branch of electronics engineering
devoted to the theory and operations of
radio communication.
radio field strength The intensity of radio waves
at a given point. Also see FIELD INTENSITY, 2
and RADIO MAP.
radio frequency Abbreviation, RF. 1. Consisting
of, or pertaining to, alternating currents at frequencies
above about 9 kHz (the lowest allocated
radio communications frequency). 2. Consisting
of, or pertaining to, electromagnetic fields whose
wavelengths are longer than those of infrared,
but shorter than about 33 kilometers (corresponding
to a frequency of 9 kHz). Also see RA-
DIO SPECTRUM.
radio-frequency amplifier 1. In a superheterodyne
circuit, the channel in which the incoming
signal is amplified. Compare INTERMEDIATE-
FREQUENCY AMPLIFIER. 2. Broadly, an amplifier
of radio-frequency signals.
radio-frequency choke Abbreviation, RFC. A lowinductance
coil used to block radio-frequency
(RF) alternating currents. Many RF chokes have
air cores; some have cores of ferrite or powdered
iron.
In
(General bipolar circuit)
+12 V
radio-frequency amplifier, 2
Out