SOLENOIDAn electromagnetic device that changes electrical energy into mechanical motion; based
upon the attraction of a movable iron plunger to the core of an electromagnet .
SOLIDOne of the three states of matter; it has definite volume and shape (ice is a solid) .
SOLID-STATE DEVICEAn electronic device that operates by the movement of elections within a solid
piece of semiconductor material .
SONICPertaining to sounds capable of being heard by the human ear .
SOURCE(1) The object that produces the waves or disturbance. (2) The name given to them end of a
two-wire transmission line that is connected to a source . (3) The device which furnishes the
electrical energy used by a load .
SOURCE, MAINTENANCE, AND RECOVERABILITY CODE (SM & R CODE)Specifies
maintenance level for repair of components or assemblies .
SPACEAbsence of an RF signal in cw keying. Key-open condition or lack of data in communications
systems. Also a period of no signal .
SPACE CHARGEAn electrical charge distributed throughout a volume or space .
SPACE DIVERSITYReception of radio waves by two or more antennas spaced some distance apart
SPACE WAVERadio waves that travel directly from the transmitter to the receiver and remain in the
SPACINGThe condition in teletypewriter operation where a circuit is open and no current flows .
SPARK-GAP MODULATORA modulator that consists of a circuit for storing energy, a circuit for
rapidly discharging the storage circuit (spark gap), a pulse transformer, and a power source .
SPECIAL PURPOSE ELECTRONIC TEST EQUIPMENT (SPETE)Test equipment that is
specifically designed to generate, modify, or measure a range of electronic functions of a specific or
peculiar nature on a single system or equipment .
SPECIFIC GRAVITYThe ratio between the density of a substance and that of pure water at a given
SPECIFIC RESISTANCEThe resistance measured in ohms of a unit volume of a substance to the flow
of electric current. (The unit volume used is generally the circular mil-foot.) 
SPECTRUM(1) The entire range of electromagnetic waves arranged in order of their frequencies. (2)
The range of frequencies considered in a system .
SPECTRUM ANALYSISThe display of electromagnetic energy arranged according to wavelength or
SPECTRUM ANALYZERA test instrument that provides a visual display of the frequency distribution
of an RF signal such as a transmitter output .
SPIN VECTORIn a gyro, a vector representing the angular velocity of the gyro rotor. The spin vector
lies along the spin axis of the rotor .