18WuD2x

650 spot modulation • square-law meter
electron beam. Also see INTENSITY MODULA-
TION.
spot welding A method of electrical welding in
which the parts to be joined are held together,
overlapping, between the points of two electrodes,
between which a current is passed to heat the
parts at the spot of contact.
spot-wheel pattern A frequency-identifying wheel
pattern produced on an oscilloscope screen by intensity-modulating
a circular trace. The circular
trace is produced by applying a standardfrequency
signal to the horizontal and vertical input
terminals 90 degrees out of phase. A square-wave
signal of unknown frequency is applied to the intensity-modulation
(z-axis) input terminals. The
square wave chops the circle into a number of
bright sectors or spots. The unknown frequency
(fx) equals Nfs, where N is the number of spots in
the circle, and fs is the standard frequency. Compare
GEAR-WHEEL PATTERN.
sprat Acronym for small portable radar torch. A
portable radar unit that uses a Gunn diode to
generate microwave energy. The range is about
500 meters ( 1 ⁄3 mile).
spray coating 1. Applying a protective coat of insulating
material to a conductor or component by
spraying it with a liquid substance and allowing it
to dry. Compare DIP COATING. 2. The coat applied,
as defined in 1.
spreader 1. An insulator used to separate the
wires of an air-spaced transmission line. 2. Any
of the rods composing the supporting structure in
a cubical quad antenna.
spreading current In a semiconductor, current
caused by the movement of charge carriers by circuitous
routes, that is, in paths that deviate significantly
from straight lines.
spreading loss Energy lost during the transmission
of radiation.
spreading resistance In a semiconductor device,
the resistance that is a consequence of electrical
paths through material that is not along straight
lines between electrodes.
spread spectrum 1. A method of transmission in
which the occupied bandwidth of the signal is deliberately
increased, or spread out, over a much
wider range than it would normally occupy with
conventional modulation. 2. A signal transmitted,
as defined in 1.
spring coil See SOLENOID, 1.
spring contact See FLEXIBLE CONTACT.
sprite In video and animated computer graphics, a
brief insert, such as a little insect that scurries
across the screen, or a face that pops in and
smiles. It is used primarily for effect.
SPST Abbreviation of SINGLE-POLE/SINGLE-
THROW (switch or relay).
spurious emission From a radio or television
transmitter, an unintended and unwanted
output signal on a frequency other than the
fundamental signal frequency. It can be
generated by faulty modulation, amplification,
and/or oscillation.
spurious oscillation 1. Oscillation in a normally
nonoscillatory circuit. 2. In an oscillator, simultaneous
oscillation at a frequency other than the
normal one.
spurious response In a communications receiver,
a signal that appears to be on a certain frequency,
when, in fact, the received signal is not
on that frequency. It often results from inadequate
image rejection.
spurious-response ratio The ratio of the transmission
(or gain) of a circuit of a desired signal to its
transmission (or gain) for a spurious signal at the
same setting of the circuit (e.g., signal-to-image
ratio).
spurious sidebands In an amplitude-modulated
(AM) or single-sideband (SSB) radio signal, sideband
energy at frequencies outside the nominal
signal band, usually resulting from improper
modulation, inadequate filtering, improper envelope
clipping, or nonlinear amplification.
Sputnik The first orbiting artificial earth satellite.
It was launched by Russia (then known as the
Union of Soviet Socialist Republics) in 1957.
sputter 1. A layer of material obtained by sputtering
(see SPUTTERING, 1). 2. To carry out the process
of sputtering (see SPUTTERING, 1).
sputtering 1. A technique for electrically depositing
a film of metal on a metallic or nonmetallic
surface. In a vacuum chamber, the piece of metal
to be deposited is made the cathode of a highvoltage
circuit, with respect to a nearby anode
plate. The high voltage causes atoms to be ejected
from the surface of the cathode and strike the
surface of an object placed in their path, becoming
deposited on it as a film of cathode metal.
Compare EVAPORATION, 1. 2. The disintegration
of a vacuum-tube cathode through ejection of
surface atoms from the cathode by impinging
positive ions.
sq Abbreviation of SQUARE.
S Q band A section of the S BAND, from 2400 to
2600 MHz.
SQC Abbreviation of STATISTICAL QUALITY CON-
TROL.
SQR 1. Abbreviation of SQUARE ROOTER. 2. In
the BASIC computer-programming language, a
function that computes the square root of a positive
number.
S quad See SIMPLE QUAD.
square-law demodulator See SQUARE-LAW DE-
TECTOR.
square-law detector A detector whose output is
proportional to the square of the root-meansquare
(rms) value of the input. Also called
WEAK-SIGNAL DETECTOR.
square-law meter 1. A meter whose deflection is
proportional to the square of the quantity applied
to it. Also see CURRENT-SQUARED METER. 2. A
high-impedance electronic voltmeter, whose