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signal area
4 Any electronic carrier of information, as distinct from
noise.
5 Standard visual symbols displayed on simple airfield.
signal area Plot of ground at simple airfield, usually
adjacent to tower, set aside and equipped for display of
ground-to-air signals (5) for informing pilots of aircraft
not equipped with radio, eg of circuit direction, local
hazards, prohibitions, etc.
signal data General term for elint output or for any
recorded (if possible quantified) information on received
signals (2).
signal flare Flare pyrotechnic whose use conveys known
meaning, eg two-star red.
signal frequency Frequency of transmitted carrier as
distinct from component parts, or received carrier as
distinct from intermediate frequency to which it is
converted.
signal generator Versatile oscillator capable of
outputting any desired RF or AF at any selected amplitude
and with output modulated to simulate actual
transmission.
signal intelligence General term for communications
intelligence plus electronic intelligence; art of detecting,
recording, analysing and interpreting all unknown or
hostile signals.
signalling lamp Usually means hand-held lamp [e.g.,
Aldis] capable of sending Morse.
signalman Authorized person using hands, wands
and/or lights to marshal aircraft on apron or elsewhere on
airport manoeuvring area.
signal pistol Projector of pyrotechnics, eg Very pistol.
signal rocket Pyrotechnic fired from launcher on
ground.
signal star Pyrotechnic of distinctive character emitted
from cartridge or signal pistol.
signal-to-noise ratio Ratio of amplitude of desired signal
to amplitude of noise signals at a given point in time
(DoD). Ratio, at selected point in circuit, of signal power
to total circuit noise power (ASCC). Number of dB by
which level of fully modulated signal at maximum output
exceeds noise level, all values being rms.
signature Characteristic pattern of target displayed by
detection and identification equipment (DoD, NATO
etc). Like thumb-print, * analysed with sufficient accuracy
can identify source as to type and even to specific
example of emitter. Can be EM (radar, IR, optical),
acoustic (eg SST boom *) or velocity (Doppler *).
significant obstacle Posing potential threat to aircraft.
significant tracks Tracks of aircraft or missiles which
behave in an unusual manner which warrants attention
and could pose a threat to a defended area (DoD, NATO).
significant turn Change of heading large enough for
explicit account to be taken operationally of reduction of
climb gradient.
significant weather Potentially dangerous to aviation.
Sigsec Signals security (USA).
SIGWX Significant weather [also Sigwr].
SIIDAS Sensor independent integrated defensive aids
suite.
SIIS Skills interactive information system.
s(i,k) Slope of sound pressure level; change between
⅓-octave SPLs at i-th band at k-th moment in time. Hence
∆s(i,k) = change in SPL slope, s´(i,k) is adjusted slope
Silver C
between adjacent adjusted bands, and - s¯(i,k) is average
slope (see noise).
SIL 1 Suomen Ilmailu Litto (Finnish Aeronautical
Society).
2 Site d’intégration lanceurs (F); launcher assembly
site.
3 System[s] integration laboratory.
4 Service information letter.
5 Speed interference level.
Silane Proprietary hypergolic liquid used to initiate
combustion of fuel [usually LH 2 ].
Silastic Proprietary range of silicone rubbers and
sealants including many resistant to hydrocarbon fuels.
SILC 1 Space-object identification in living colour.
2 Semiconductor IR laser countermeasure[s].
Silcodyne High-temperature hydraulic fluid for supersonic
aircraft, also called DP.47 (UK).
Silence Significantly lower community exposure to
aircraft noise and emissions.
Silencer Significantly lower aircraft noise for community
in Europe research [acronym] (EC).
silencer In piston-engine exhaust, common meaning.
silent target Non-emitting, ie no radio, radar, IR, laser,
TV or other detectable radiation.
silica Silicon dioxide, quartz, SiO 2 .
silica gel Numerous stable sols of colloidal particles,
some important as drying agents.
silicon Si, abundant versatile solid element with many
forms, eg dark crystal or brown powder; important in
alloys, in vast range of compounds and in pure crystalline
form as semiconductor; basis of major part of microelectronics.
Density 2.3, MPt 1,410°C.
silicon chip Popular name for microcircuit fabricated in
chip scribed from slice of single-crystal epitaxial silicon.
Formerly each chip contained devices and subcircuits,
today can be a complete equipment requiring only
packaging and human interfaces.
silicone Generalized term for polymeric organosiloxanes
of form (R 2 SiO) n , including elastomers,
rubbers, plastics, water-repellants and finishes, eg resins,
lacquers and paints.
silicone cork Relatively cheap ablator and heat
insulator, eg on Shuttle external tank.
silicon nitride Refractory ceramic, Si 3 N 4 ; increases
strength slightly to 1,200°C, good thermal shock
resistance becauase of small thermal expansion, and
resists many forms of chemical attack.
silk Parachute (colloq.), hence hit the *, take to the *.
SILL Strategic illuminator laser.
SilMU Silicon micro-machined electromechanical
system inertial measurement unit.
silo Missile shelter that consists of hardened vertical
hole in ground with facilities either for lifting missile to a
launch position or for direct launch from shelter.
Normally closed by hardened lid and provided with
shock-isolating missile supports.
silver Metallic element, Ag, density 10.5, MPt 962°C,
important in electronics, photography, joining metals,
cloud seeding and disposal of explosives and nerve gases.
silver ball Inceptor controlling Stovl engine nozzle[s]
(colloq.).
Silver bullet Procurement process for highly classified
items (US).
Silver C Intermediate certificate and badge for gliding,
616