18WuD2x

sea clutter • secondary frequency standard 613
sea clutter Collectively, the radar echoes that the
sea reflects.
seal 1. The point at which a lead or electrode enters
or leaves and is secured to an envelope, case,
or housing. Such a point is often tightly closed
against the passage of air in or out of the envelope.
2. To close off a circuit or component from
tampering.
sealed dry battery A set of electrochemical dry
cells that can be installed without concern for orientation
or position. Example: 9-volt “transistor
battery.”
sealed meter 1. A meter that is tightly closed
against the entry of moisture and foreign materials.
2. A meter that is locked or otherwise protected
against tampering.
sealing compound A substance (such as wax,
pitch, or plastic) used to enclose and protect electronic
devices.
search 1. To scan or sweep through a range of
quantities or through a region of interest. 2. To
examine (usually in some prescribed order) items
of information in a computer memory to find
those satisfying a given criterion.
search coil An inductive probe (exploring coil)
used to sample magnetic fields.
search oscillator A variable-frequency oscillator
used to locate and identify signals by the heterodyne
method.
search probe 1. See SEARCH COIL. 2. A capacitive
probe used to sample electric fields.
search radar A radar that displays a target almost
immediately after that target enters a scanned
area.
search time The time needed to test items during
a search (see SEARCH, 2).
sea return See SEA CLUTTER.
seasonal effects In ionospheric propagation, the
changes produced as a result of the revolution of
the earth around the sun. The path of the sun
across the sky, and the length of the day, are primarily
responsible for such effects.
seasonal static Atmospheric electrical interference,
most prevalent during the summer.
S E band A section of the S BAND extending from
1550 to 1650 MHz.
sec 1. Abbreviation of SECOND. 2. Abbreviation of
SECTION. (Also, sect.) 3. Abbreviation of SEC-
ONDARY. 4. Abbreviation of SECANT.
secant Abbreviation, sec. The trigonometric function
representing the ratio of the hypotenuse of a
right triangle to the adjacent side (c/b). The secant
is the reciprocal of the cosine; sec x = 1/cos x.
second 1. Abbreviation, s and sec. A unit of time.
The mean solar second is 1/86,400 of a mean solar
day, and is 1/60 minute or 1/3600 hour.
2. Symbol ("). A unit of arc measure. 1" = 1/3600
geometric degree.
secondaries See SECONDARY COLORS.
secondary 1. See SECONDARY WINDING. 2. See
SECONDARY STANDARD.
secondary battery See STORAGE BATTERY.
secondary calibration The calibration of an instrument,
based on a reference instrument calibrated
against an absolute source.
secondary capacitance 1. The distributed capacitance
of the secondary winding of a transformer
whose primary winding is unloaded. Compare
PRIMARY CAPACITANCE, 1. 2. A series or shunt
capacitance used to tune the secondary coil of a
radio-frequency transformer. Compare PRIMARY
CAPACITANCE, 2.
From
IF amp.
secondary capacitance, 2
Secondary
capacitance
To next
IF amp.
secondary cell See STORAGE CELL.
secondary circuit 1. The circuit associated with
the secondary winding of a transformer. 2. See
OUTPUT CIRCUIT.
secondary coil See SECONDARY WINDING.
secondary color 1. A color prepared by mixing two
primary colors. 2. In television operations, any
displayed color composed of two or more color
primaries.
secondary current The current flowing in the secondary
winding of a transformer. Also called
TRANSFORMER OUTPUT CURRENT. Compare
PRIMARY CURRENT.
secondary electron 1. The electron possessing the
lesser energy after a collision between two electrons.
Compare PRIMARY ELECTRON. 2. An
electron ejected by secondary emission.
secondary emission The action whereby electrons
in the atoms at the surface of a target are ejected
as a result of bombardment by a beam of (primary)
electrons. Thus, in an electron tube, electrons
from the cathode strike the plate with a
force that drives secondary electrons out of the
plate, into the surrounding space.
secondary emitter A source of secondary electrons
(e.g., the plate of an electron tube or a dynode
in a photomultiplier tube).
secondary failure The failure of a component or
circuit, resulting from the failure of some other
component. For example, the pass transistor in a
power supply might burn out, causing the output
voltage to increase; this increased voltage can
damage equipment connected to the supply.
secondary frequency standard A device for generating
signals of accurate frequency, but that does