18WuD2x

S units • supermodulation 663
V 1
V 2
V 0
n
V 3 V c0 = − V 1
i = 1
summing amplifier
S units In radio (especially amateur radio), gradations
reflecting the strength of received signals.
Typically, a value of S9 (9 s-units), representing
“extremely strong signals,” is equal to a strength
of 50 microvolts. The next lower S unit (S8) is
6 dB lower in voltage (i.e., 25 microvolts); S7 is
12 dB below S9 (i.e., 12.5 microvolts), etc.
sun lamp An incandescent or fluorescent lamp with
high ultraviolet output, used in medicine for the
treatment of certain skin disorders. It can also be
used for skin tanning; most physicians discourage
habitual use of the lamps for this purpose.
sunlight lamp A lamp that produces visible light
whose spectral distribution is similar to that of
typical daylight. It generally produces more blue
and violet light than a conventional lamp. It is
sometimes used for indoor lighting in winter at
high latitudes, and/or to enhance plant growth.
sunlight-powered laser A laser whose action is
stimulated by sunlight collected by a system of
mirrors and lenses. The life of the device is long,
compared with that of conventional lasers.
sun-pumped laser See SUNLIGHT-POWERED
LASER.
sun relay See SUN SWITCH.
sunspot An area on the sun’s surface that is visible
as a dark, irregular region of variable size, generally
several thousand miles across. Sunspots are
believed to be comparatively cool regions associated
with solar magnetic disturbances. The number
of sunspots is correlated with the frequency
and intensity of solar flares (see SOLAR FLARE).
sunspot cycle Regular periodic variation of sunspot
activity. The time between peaks in activity
is approximately 11 years.
sun switch A photoelectric switch or relay actuated
by sunlight and used for various domestic
and industrial purposes, such as switching
lights, operating window shades, etc.
sup Abbreviation of SUPPRESSOR.
super Contraction of supersonic.
super- Prefix denoting over, above, greater than, or
higher than, with respect to size, value, or rank.
Compare SUB-.
superaudible frequency See ULTRASONIC FRE-
QUENCY.
superbeta transistor A transistor or transistor
combination, such as a Darlington pair (see
COMPOUND CONNECTION), that provides a very
high current amplification factor (beta).
Relative sunspot numbers
1970 1980 1990 2000
sunspot cycle
supercardioid microphone A microphone that is
highly sensitive in one direction and insensitive
in all other directions. The directional pattern is
similar to a CARDIOID PATTERN, but is exaggerated
along the axis of optimum response.
superconducting cable A cable in which superconductivity
is achieved by surrounding the cable
with liquid helium to lower its temperature to
near absolute zero.
superconductivity The virtual disappearance of
resistance in some metals cooled to temperatures
in the vicinity of absolute zero. Also see CRYO-
GENICS, CRYOSTAT, and CRYOTRON.
superconductor A material or device that displays
superconductivity.
super flatpack An integrated-circuit package of
the flatpack type having considerably more components
and leads than those in the conventional
flatpack.
superhet Contraction of superheterodyne.
superheterodyne circuit A circuit in which the incoming
signal in a first detector (or mixer) beats
with the signal of a local oscillator, resulting in a
lower (intermediate) frequency, which then is amplified
by an intermediate-frequency (IF) amplifier.
This IF signal is detected by a second
detector whose output is amplified by an audiofrequency
(AF) amplifier. Because the IF amplifier
operates at a single (fixed) frequency, it can be
adjusted for optimum selectivity and gain. Also
called superhet circuit.
superheterodyne receiver A radio or television receiver
using a SUPERHETERODYNE CIRCUIT.
superhigh frequency See RADIO SPECTRUM.
Supermalloy An alloy having a maximum permeability
of 10 6 .
supermodulation A type of amplitude modulation
(AM) in which one radio-frequency (RF) power
stage continuously generates the carrier, and a
second (usually identical) RF power stage is gated
into full operation at the proper instant by the audio
modulation to add additional RF power (corresponding
to 100% modulation) to the signal. At
the same time, the carrier amplitude is decreased
by the proper amount to fulfill the conditions of a