Acronym for "radio detection and
ranging" A system that measures
the distance and direction of
objects.
radioastronomy
Branch of astronomy that studies
the radio waves generated by
celestial bodies and uses these
emissions to obtain information
about them.
radio broadcast
Transmission of music, voice and
other information on radio
carrier waves that can be
received by the general public.
radio communication
Term used to describe the
transfer of information between
two or more points by use of
radio or electromagnetic waves.
radio-frequency amplifier
Amplifier having one or more
active devices to amplify radio
signals.
radio-frequency generator
Generator capable of supplying
RF energy at any desired
frequency in the radio-frequency
spectrum.
radio-frequency probe
Probe used in conjunction with
an AC meter to measure
radio-frequency signals.
RC
Abbreviation for "resistance
capacitance" also abbreviation
for "radio controled" as in "RC
model airplanes."
RC time constant
Product of resistance and
capacitance in seconds.
reactance
Symbol "X". Opposition to
current flow without the
dissipation of energy. Example:
The opposition provided by
inductance or capacitance to AC
current.
reactive power
Also called imaginary power or
wattless power. It is the power
value in "volt amps" obtained
from the product of source
voltage and source current in a
reactive circuit.
real number
Number having no imaginary part.
receiver
Unit or piece of equipment used
to receive information.
recombination
Process by which a conduction
band electron gives up energy
(in the form of heat or light)
and falls into a valence band
hole.
rectangular coordinates
A Cartesian coordinate of a
Cartesian coordinate system
whose straight-line axes or
coordinate planes are
perpendicular.
rectangular wave
Also known as a pulse wave. A
repeating wave that only
operates between two levels or
values and remains at one of
these values for a small amount
of time relative to the other
value.
rectification
Process that converts
alternating current to direct
current.
rectifier
Diode circuit that converts
alternating current into
pulsating direct current.
reed relay
Relay consisting of two thin
magnetic strips within a glass
envelope. When a coil around the
envelope is energized, the
relay's contacts snap together
making a connection between
leads attached to the reed
strips.
regenerative feedback
Positive feedback. Feedback from
the output of an amplifier to
the input such that the feedback
signal is in phase with the
input signal. Used to produce
oscillation.
regulated power supply
Power supply that maintains a
constant output voltage under
changing load conditions.
regulator
Device or circuit that maintains
a desired output under changing
conditions.
relay
Electromechanical device that
opens or closes contacts when a
current is passed through a
coil.
relative
Not independent. Compared with
or with respect to some other
measured quantity.
relaxation oscillator
Free running circuit that
outputs pulses with a period
dependent or one or more RC time
constants.
reluctance
Resistance to the flow of
magnetic lines of force.
remanence
Amount a material remains
magnetized after the magnetizing
force has been removed.
residual magnetism
Magnetism remaining in the core
of an electromagnet after the
coil current is removed.
resistance
Symbolized "R" and measured in
ohms. Opposition to current flow
and dissipation of energy in the
form of heat.
resistive power
Amount of power dissipated as
heat in a circuit containing
resistive and reactive
components. True power as
opposed to reactive power.
resistive temperature
detector
(RTD) Temperature detector
consisting of a fine coil of
conducting wire (such as
platinum) that will produce a
relatively linear increase in
resistance as temperature
increases.
receptivity
Measure of a material's
resistance to current flow.
resistor
Component made of material that
opposes flow of current and
therefore has some value of
resistance.
resistor color code
Coding system of colored stripes
on a resistor to indicate the
resistor's value and tolerance.
resonance
Circuit condition that occurs at
the frequency where inductive
reactance (XL)
equals capacitive reactance (XC).
reverse bias
Bias on a PN junction that
allows only leakage current
(minority carriers) to flow.
Positive polarity on the n-type
material and negative polarity
to the p-type material.
reverse breakdown voltage
Amount of reverse bias that will
cause a PN junction to break
down and conduct in the reverse
direction.
reverse current
Current through a diode when
reverse biased. An extremely
small current also referred to
as leakage.
reverse saturation
current
Reverse current through a diode
caused by thermal activity. This
current is not affected by the
amount of reverse bias on the
component, but does vary with
temperature.
RF
Abbreviation for "radio
frequency."
rheostat
Two terminal variable resistor
used to control current.
right angle triangle
Triangle having a 90° or square
corner.
ripple frequency
Frequency of the ripple present
in the output of a DC source.
ripple voltage
The small variations in Dc
voltage that remain after
filtering in a power supply.
rise time
Time for the leading edge of a
pulse to rise from 10% of its
peak value to 90% of its peak
value.
RL differentiator
An RL circuit whose output
voltage is proportional to the
rate of change of the input
voltage.
RL filter
Selective circuit of resistors
and inductors that offers little
or no opposition to certain
frequencies while blocking or
attenuating other frequencies.
RL integrator
RL circuit with an output
proportionate to the integral of
the input signal.
rms
Abbreviation for "root mean
square"
rms value
Rms value of an AC sine wave is
0.707 times the peak value. This
is the effective value of an AC
sine wave. The rms value of a
sine wave is the value of a DC
voltage that would produce the
same amount of heat in a heating
element.
roll-off rate
Rate of change in gain when an
amplifier is operated outside of
its bandwidth.
rotary switch
Electromechanical device that
has a rotating shaft connected
to one terminal capable of
making or breaking a connection
to one or more other terminals.
R-2R ladder
Network or circuit composed of a
sequence of L networks connected
in tandem. Circuit used in
digital to analog converters.
