A useful guide to avoid getting lost among the many acronyms
GLOSSARY
Abbreviations and jargon from the field of maritime satellite communication from A-Z
Glossary
A • B • C • D • E • F • G • H • I • J • K • L • M • N • O • P • Q • R • S • T • U • V • W • X • Y • Z
A
ACU
Antenna Control Unit
Aperture
The cross sectional area of an antenna, which is exposed to the satellite signal
Azimuth
The horizontal angle a parabolic antenna must be rotated to, in order to point to a specific satellite in the orbit. It is defined with respect due to north for an easier convenience.
B
Band Pass Filter
A circuit which allows only those signals within the desired frequency band to pass through.
Bandwidth
The width of the available frequency spectrum or capacity.
Beamwidth
The angle of the beam of the antenna for which the signal strength decreases no more than 3dB (half signal strength) in ratio to the maximum signal strength.
Bit Error Rate (BER)
The fraction of a sequence of message bits that are in error. A bit error rate of 106 means that there is an average of one error per million bits.
BUC
A Block Up Converter is used in the transmission (uplink) of satellite signals. It converts a band of frequencies from a lower frequency to a higher one. Modern BUCs convert from L band to Ku band, C band and Ka band.
C
Carrier Frequency
The main frequency on which a voice, data or video signal is sent.
Carrier to Noise Ratio (C/N)
The ratio of the received modulated carrier signal power (C) to the received noise power (N) in a given bandwidth, expressed in dB. The higher the C/N the better the signal quality.
Cassegrain Antenna
An antenna priciple that uses a subreflector at the focal point, which reflects the signal to or from a feed located at the apex of the main reflector.
C/T
Carrier-to-noise-temperature ratio.
CW
A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration.
D
dB
The decibel is a logarithmic unit of measurement that expresses the ratio between two power levels.
dBi
The dB power relative to an isotropic source.
dBW
The ratio of the power to one Watt expressed in decibel.
Delay
The time it takes for a signal to leave a sending station, pass the satellite and reach a receiving station.
Downlink
The path of a 2 way satellite communication from the satellite to earth.
E
EIRP
Equivalent Isotropic Radiated Power - describes the strength of the signal leaving the satellite antenna (product of the transponder output power and the gain of the satellite transmit antenna in dBW) and is used for determining the C/N and S/N.
Elevation
The vertical angle that a parabolic antenna has to set to point to a specific satellite in the orbit. Elevation is zero when the antenna points to the horizon.
ELS
Eastern Limit Switch.
F
F/D
Ratio of antenna focal length to antenna diameter.
Feed
The feed system of an antenna, which may consist of a subreflector plus a feed-horn or a feed-horn only.
Feed-horn
A satellite antenna component that collects the signal reflected from the main reflector (primary focused antenna) or the subreflector (cassegrain antenna) and channels this signal into the Low-Noise-Amplifier (LNA).
Footprint
Shows the EIRP contours of equal signal strengths as they cover the earth's surface.
FSK Transmitter
Frequency Shift Keying Transmitter.
G
Gain
The amplification of an antenna expressed in dB.
Geostationary
Orbital positions perpendicular to earth's equator where the satellite moves with the angular velocity of the rotation of the earth.
G/T
The Gain over Noise Temperature of a system, expressed in dB/K.
H
Hub
The main station through which all communications to, from and between micro terminals must flow.
I
INMARSAT
The INternational MARitime SATellites operates as a network for international transmissions for all type of international mobile services. Together, these satellites cover the most of the earth.
IF
Intermediate Frequency.
Isotropic antenna
A hypothetical omni-directional point-source antenna which serves as a reference for the measurement of antenna gain.
K
Ka-Band
The Ka-Band covers the frequencies of 29.5-30 GHz, i.e. wavelengths from slightly over one centimeter down to 0.75 centimeters. The Ka-Band is part of the K-Band of the microwave band of the electromagnetic spectrum.
Ku-Band
The frequency range from 10.7 to 18 GHz.
L
LLS
Lower Limit Switch.
LNB
Low Noise Block Converter.
LO
Local Oscillator.
Low Noise Amplifier (LNA)
The preamplifier between the antenna and the earth-station receiver which contributes the least amount of thermal noise to the received signal.
Low Noise Block / Converter (LNB / LNC)
A combination of a Low Noise Amplifier and a down-converter built into one device attached to the feed.
Margin
Is the difference between the level of the satellite system and the minimum levels required for operation.
O
OMT
Orthomodal Transductor.
Parabolic Antenna
An antenna whose shape is mathematically described as a parabola. The shape focuses the weak microwave signal into a focal point in the front of the dish where the feed-horn or a second reflector (subreflector) is located.
PLL
Phase Locked Loop.
Receiver
An electronic device which separates a particular satellite signal from all other received signals and converts it into a format for video, voice or data.
S
Sidelobe
Off-axis response of an antenna.
Signal to Noise Ratio (S/N)
The ratio of the signal power (S) to the noise power (N). The higher the S/N the better the signal quality.
Skew
The polarization axes of a geostationary satellite antenna are usually adjusted perpendicular to the equator. Because of the almost spherical shape of the earth, earth station antennas not located at the same longitude of the orbital position of the satellite have an inclination in polarization angle when looking to this satellite. The skew angle is the angle that has to be adjusted to compensate this difference in orientation.
Spot Beam
A focused antenna pattern of a satellite antenna sent to a limited geographical area, to deliver certain transponder signals to these defined areas.
T
Transmitter
An electronic device which modulates voice, video and data signals into electromagnetic waves and radiates them into the atmosphere by using an antenna.
Transponder
A combination of receiver, frequency converter and transmitter package which is physically part of a communication satellite. It operates over a frequency band of 36 to 72MHz bandwidth.
TVRO
Television Receive Only terminals that use antenna reflectors and electronic equipment to receive television and audio communication via satellite.
U
V
VSAT
Very Small Aperture Terminal. It is a two-way satellite ground station or a stabilized maritime VSAT antenna with a dish antenna that is smaller than 3 meters. The majority of VSAT antennas range from 75 cm to 1.2 m. Data rates range from 4 kbit/s up to 4 Mbit/s; some upgraded modules can even reach a max downlink of up to 16 Mbit/s.
W
WLS
Western Limit Switch.