18WuD2x

eadthrough • receiver front end 585
then be detected, and the jamming signal
adjusted accordingly.
read time The period during which data is being
transferred from a computer storage unit.
read-write channel In computer operations, a
channel over which activity between a central
processing unit and a specific peripheral occurs.
read-write head An electromagnetic transducer
used for both reading and writing data. See READ
and WRITE.
read-write memory 1. A small data storage bank
for short-term use. The contents of the memory
are easily changed. 2. See RANDOM ACCESS
MEMORY.
real address See ABSOLUTE ADDRESS.
real axis The axis of the real-number component of
a COMPLEX NUMBER (i.e., the horizontal axis in
an ARGAND DIAGRAM).
real component The real-number part of a COM-
PLEX NUMBER.
real image The image formed on a screen when
rays from the object converge on passing through
a lens. Compare VIRTUAL IMAGE.
Object
Lens
real image
Screen
Image
real number A number in the category that includes
zero, all rational numbers, and all irrational
numbers. Also see COMPLEX NUMBER,
IMAGINARY NUMBER, IRRATIONAL NUMBER,
and RATIONAL NUMBER.
real power The apparent power multiplied by the
power factor in an alternating-current circuit
containing reactance. Real power is the difference
between the apparent power and the reactive
power. Actual radiated or dissipated power cannot
exceed the real power.
real time Pertaining to the operation of a computer,
communications, or data processing system in
which events are represented or acted on as they
occur. Data is processed as it becomes available,
usually through the use of time-sharing, directaccess
storage devices, and remote terminals.
real-time clock A device that produces periodic
signals that reflect the interval between events. It
is sometimes used to indicate time of day.
rear end The low-frequency portion of a superheterodyne
receiver (i.e., the intermediatefrequency
amplifier, second detector, and
audio-frequency amplifier). Compare FRONT END.
rear projection A method of big-screen television
picture reproduction. The image is focused onto a
translucent, flat surface. The viewer is positioned
on the side of the screen opposite to the projecting
beam.
Reaumur scale A thermometer scale on which zero
is the freezing point of water and 80 degrees is the
boiling point of water. Compare ABSOLUTE
SCALE, CELSIUS SCALE, FAHRENHEIT SCALE,
and RANKINE SCALE.
rebecca The airborne interrogator in the British
REBECCA-EUREKA SYSTEM.
rebecca-eureka system A British 90-milehovering
radar navigation system that consists of
an airborne interrogator (rebecca) and a ground
transponder beacon (eureka).
rebroadcast The retransmission of a radio broadcast
simultaneously by a station other than the
originator. Also see AUTOMATIC RELAY STATION.
rebroadcast station See AUTOMATIC RELAY STA-
TION.
recalescence During the cooling of a metal, the
sudden release of heat. Also see RECALESCENT
POINT. Compare DECALESCENCE.
recalescent point In a metal whose temperature is
being lowered from a higher value, the temperature
at which heat is suddenly released. Compare
DECALESCENT POINT.
recall Abbreviation, RCL. In computers and calculators,
an instruction that brings material from
the memory for examination or use. The opposite
instruction is STORE.
receiver 1. A device or system operated at the destination
end of a communication link; it accepts a
signal and processes or converts it for local use.
Also see specific entries for various types of receiver.
2. The earpiece of a telephone. 3. A radio
broadcast-band tuner integrated with a generalpurpose
preamplifier and power amplifier, and
containing standard jacks for input and output of
audio signals to and from peripheral equipment.
receiver detector In a wireless communications or
broadcast receiver, a circuit that extracts the information
from the signal. The design depends on
the type of emission to be received. See also DIS-
CRIMINATOR, ENVELOPE DETECTOR, PHASE-
LOCKED LOOP, PRODUCT DETECTOR, RATIO
DETECTOR.
receiver dynamic range A quantitative measure of
the ability of a wireless receiver to maintain a
fairly constant output, and yet to maintain its
rated sensitivity, in the presence of signals ranging
from very weak to extremely strong. This figure is
specified in decibels. It is typically 100 dB or more
in a well-engineered communications receiver.
receiver front end The portion of a wireless communications
or broadcast receiver consisting of
the first radio-frequency (RF) amplifier, and often
also including bandpass filters between this amplifier
and the antenna. The dynamic range and
sensitivity of a receiver are determined by the performance
of this stage. These two characteristics
are among the most important for any receiver.