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VSAT Glossary



VSAT Glossary


Analog The representation of information in variable intensity and/or frequency by a continuous signal.
Antenna Equipment that sends and/or receives signals from a satellite.
Aperture A cross sectional area of an antenna exposed to the satellite signal.
Apogee The highest point in the satellite’s orbit (km); the point in the orbit of a satellite where it is farthest from the object about which it revolves.
ASCII (American Standards Code for Information Interchange) A code with seven information signals and one parity check signal.
Asynchronous Transmission Data transmission in which each information character or byte is individually synchronized, usually by the use of start or stop elements.
ATP Acceptance Test Procedure
Attenuation The loss in power of electromagnetic signals between transmission and reception points.
AZ-EL Mount Antenna mount that requires two separate adjustments-of azimuth and elevation-to move from one satellite to another.
Azimuth The angle between an antenna beam and the meridian plane, measured along a horizontal plane.
Bandwidth The range of frequencies utilized for the transmission of a signal or group of inter-related signals expressed in Hertz (Hz).
Baseband A video or audio signal transmitted at its original frequency.
BER (Bit Error Rate) The percentage of received bits that are in error during transmission; expressed as a number referenced to a power of ten.
Beamwidth The angular coverage of an antenna beam. Earth station beams are usually specified at the half-power (or -3 dB) point. Satellite beams are based on the area to be covered.
Bisync Binary Synchronous Communications (BSC).
Bit A single unit of information.
BPSK Binary Phase Shift Keying.
BTV (Business Television) Corporate communications tool involving video transmissions of information via satellite. Common uses of business television are for meetings, product introductions and training.
Carrier A continuous frequency capable of being modulated with a second data-carrying signal.
Cassegrain Antenna comprised of two reflectors, the parabolic reflector and an hyperbolic subreflector at the focus point, which reflects signals back into the feed.
C-Band Frequencies of approximately 4 to 6 GHz for satellite downlink and uplink transmission, respectively.
Channel Path for electrical communication between two facilities.
Circular Polarization A mode of transmission in which signals are downlinked in a rotating corkscrew pattern. A satellite’s transmission capacity can be doubled by using both right-hand and left-hand circular polarization.
CPU Central Processing Unit.
C/N (Carrier-to-Noise Ratio) Refers to the ratio of the satellite carrier (or signal) to noise level in a given channel. Usually measured in dB at the LNA output.
Colocation Placement of several satellites near each other in orbit. This allows a single fixed antenna to receive signals from all of the satellites without tracking.
DAMA Demand Assignment Multiple Access.
dB Decibel. A unit of signal measurement that expresses a ratio between two electrical signals or levels logarithmically.
dBW An expression of power in dB relative to one watt.
D/C (Down Converter) Equipment that performs frequency conversion to a lower (IF) band.
DCE Data Circuit Terminating Equipment.
Delay The time it takes for a signal to go from the sending station through the satellite to the receiving station.
Demodulator Equipment that converts the RF signal from the carrier into baseband signals (video, audio, or data) for further processing or amplification.
Digital The representation of information in binary form (ones and zeros), discontinuous in time.
Downlink Transmission of information from a satellite to earth for reception by earth stations.
DPSK Differential Phase Shift Keying.
Driver A software module that manages an I/O port to an external device.
DTE Data Terminal Equipment.
DTMF (Dual Tone Multifrequency) A method of signaling and basis for operation of push-button telephone sets.
Duplex Operation Method in which transmission is possible simultaneously in both directions of a telecommunications channel. Generally, two frequencies in radio communications are required.
Earth Station Any system (combination of satellite antenna, amplification, conversion, and reception electronics) that can either transmit to or receive signals from orbiting satellites.
Eclipse When a satellite passes through the line between the earth and the sun or the earth and another satellite.
EIRP (Effective Isotropic Radiated Power) Refers to measure of satellite signal strength on the ground.
Elevation The angle between an antenna beam and the horizontal plane.
Encoder Equiment that converts a baseband analog input into a digital data stream.
Encryption The process of coding, "scrambling," or altering a signal electronically so it can only be decoded by recipients who have the equipment and knowledge to reverse the encryption code.
F/D Ratio of antenna focal length to antenna diameter. A higher ration means a shallower dish.
FDMA (Frequency Division Multiple Access Refers to the use of multiple carriers within the same transponder where each uplink has an assigned frequency slot and bandwidth.
FEC (Forward Error Correction) A technique that ensures the transmitted message is received at the receiving end without error.
Feeds Device mounted at the focus point of the antenna that gathers signals reflected from the dish.
FEP Front End Processor.
Focal Length Distance from the feed to the center of the dish.
Footprint The area of the earth's surface that a satellite's signal is expected to cover. Shown as an EIRP contour map xpressed in dBW.
Gain Increased signal power usually the result of amplification; measured in decibels.
Geostationary Refers to a geosynchronous satellite angle with zero inclination, so the satellite appears to hover over one spot on the earth’s equator.
Geosynchronous Refers to the orbit in which the speed of a satellite’s orbit is synchronized with the speed of the earth’s rotation so that they are always positioned above the same spot on the earth. For this to occur, the satellite must be in orbit 22,300 miles over the equator, Most communications satellites are in geosynchronous orbit.
GHz (Gigahertz) One billion cycles per second.
G/T (Gain-to-Noise Temperature) Ratio of the gain of an antenna compared to the receive system noise temperature; expressed in dB per degree K.
Hertz (Hz) One cycle per second.
HPA (High-Power Amplifier) Earth station equipment that amplifies the transmit RF signal.
HPC (High-Power Converter) VSAT RF equipment that upconverts and amplifies transmit signals.
Hub The central earth station satellite transmission facility that is the focal point for communicating to remote locations within a satellite communications network.
IF (Intermediate Frequency) The frequency of a satellite receiver after downconversion or a satellite modulator before upconversion.
IFL (Interfacility Link) A cable that provides communication between the ODU and IDU.
I/O Input/Output
IP Internet Protocol.
kbps One thousand bits per second.
kHz (Kilohertz) One thousand cycles per second.
Ku-Band Frequencies approximately in the 12 to 14 GHz range for satellite reception and transmission, respectively.
LAN Local Area Network.
LLC Logical Link Control.
LNA (Low Noise Amplifier) Equipment that receives the satellite signal reflected by the antenna and amplifies it to the level needed by the satellite receiving equipment.
LNB (Low Noise Block Downconverter) Satellite receiving equipment that converts all signals from the LNA to the lower IF frequencies.
LNC (Low Noise Converter) Part of the earth station transmission subsystem consisting of an LNA and downconverter.
Mbps One million bits per second.
M&C (Monitor and Control) Equipment that monitors and controls Skystar network traffic and hub and VSAT equipment status.
MHz (Megahertz) One million cycles per second.
Modem (Modulator/Demodulator) Equipment that converts between digital data and audio tones for transmission and reception over analog channels.
Modulator Equipment that converts audio, video, or data signals (baseband) into an RF signal.
MSK Minimum Shift Keying.
MTBF (Mean Time Between Failure) Average length of time for which a system, or a component of a system, works without fault.
MTTR (Mean Time To Respond) Average time taken to arrive on site to correct a fault in a system or component.
Multiplexing A technique that combines multiple data channels on a single transmission channel.
MUX Multiplexer equipment.
Noise Extraneous and unwanted signal disturbances.
PA/TDMA Permanent Assignment Time Division Multiple Access.
POP Point of Presence.
POS Point of Sale.
Protocol Formal set of rules governing the format, timing, sequence, and error control of messages on a data network.
PSK Phase Shift Keying.
PVC Permanent Virtual Circuit.
QPSK Quadrature Phase Shift Keying.
RA Random Access.
RA/TDMA Random Access Time Division Multiple Access.
RF (Radio Frequency) The frequency range from 10 kHz to 100 GHz used for transmitting data, audio, or video.
Redundancy A secondary system of backup equipment that performs similarly to a primary system, thereby preventing network downtime and system outages.
Response Time The elapsed time between the end of an inquiry and the beginning of the response.
RFI Radio Frequency Interference.
RFT (Radio Frequency Terminal) Equipment including an antenna, U/C, D/C, HPA, and LNA which provides the up and down conversion of signals in a satellite-based network.
R/O (Receive Only) Referring to an earth station that receives transmissions only and does not transmit.
Routing The process of selecting the correct circuit path for a message.
SAC (Satellite Access Controller) Skystar equipment that contains the satellite transmission facility components and data network components.
SCPC Single Channel Per Carrier.
SDLC Synchronous Data Link Control.
SNA System Network Architecture.
S/N (Signal-to-Noise Ratio) Relative power of the signal to the noise in a channel.
SSPA (Solid-State Power Amplifier) A lower powered transmitter used for amplification of RF signals at a remote site.
SVC Switched Virtual Circuit.
Synchronous When characters or bits are transmitted at a fixed rate with the transmitting and receiving devices synchronized.
TCP/IP Transmission Control Protocol/Internet Protocol.
TDM Time Division Multiplexing.
TDMA (Time Division Multiple Access) Refers to a form of multiple access where a single carrier is time shared by many users. Signals from earth stations reaching the satellite consecutively are processed in time segments without overlapping.
Teleconference A meeting involving at least one uplink and a number of downlinks at different locations.
Telemetry The use of telecommunications for automatically indicating or recording measurements at a distance from the measuring instrument.
Terrestrial Inteference Interruptions in a satellite signal caused by high power land-based microwave links in the 4 GHz band.
Tracking Using earth-based equipment to follow a satellite’s position.
Transfer Orbit An intermediate elliptical orbit used to reach geosynchronous orbit, where the apogee is the same altitude as the final operating orbit.
Transponder The circuitry on a satellite that receives the uplink signal, amplifies it, then retransmits it as the downlink signal.
TWTA Traveling Wave Tube Amplifier. Satellite electronic components that provide power for the transponders (in watts).
U/C (Up converter) Equipment that performs frequency conversion to a higher (RF) band.
Uplink Transmission of information from an earth station to a geostationary communications satellite.
VSAT (Very Small Aperture Terminal) A small earth station, usually less than 2.4 meters, used for satellite communications.
X.25 Protocol; a set of packet switching standards.




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