SIGNALA general term used to describe any ac or dc of interest in a circuit; for example, input signal 
SIGNAL DISTORTIONAny unwanted change to the signal .
SIGNIFICANT SIDEBANDSThose sidebands with significantly large amplitude .
SILICONA metallic element which, in its pure state, is used as a semiconductor .
SILICON-CONTROLLED RECTIFIER (SCR)A semiconductor device that functions as an
electrically controlled switch .
SINE WAVE(1) The curve traced by the projection on a uniform time scale of the end of a rotating arm,
or vector. Also known as a sinusoidal wave . (2) The basic synchronous alternating waveform for all
complex waveforms .
SINGLE-ENDED MIXERSee UNBALANCED CRYSTAL MIXER .
SINGLE LINE DIAGRAMA diagram which shows, by means of single lines and graphic symbols, the
course of an electric circuit or system of circuits and the component devices or parts used therein .
SINGLE, STATIONARY-LOBE SCANNING SYSTEMAntenna (with a single, stationary beam) that
is rotated to obtain 360-degree coverage .
SINKSee OUTPUT END .
SKIN EFFECTThe tendency for alternating current to concentrate in the surface layer of a conductor.
The effect increases with frequency and serves to increase the effective resistance of the conductor 
SKIP DISTANCEThe distance from a transmitter to the point where the sky wave is first returned to
SKIP ZONEA zone of silence between the point where the ground wave becomes too weak for reception
and the sky wave is first returned to earth .
SKY WAVESRadio waves reflected back to earth from the ionosphere .
SLANT RANGESee RANGE .
SLIPThe difference between rotor speed and synchronous speed in an ac induction motor .
SLIP RINGSContacts that are mounted on the shaft of a motor or generator to which the rotor windings
are connected and against which the brushes ride . Devices for making electric connections between
stationary and rotating contacts.
SLOPE DETECTORA tank circuit tuned to a frequency, either slightly above or below an FM carrier
frequency, that is used to detect intelligence .
SLOTNarrow opening in a waveguide wall used to couple energy in or out of the waveguide. Also called
an aperture or a window .
SNAP-ACTINGChanging position quickly with the aid of a spring .