Satellite Glossary of Terms

A...
Amplifier: A device used to boose the strength of an electronic signal.
Analog: A form of transmitting information characterized by continuously variable quantities, as opposed to digital transmission, which is characterized by discrete bits of information in numerical steps.  An analog signal is responsive to changes in light, sound, heat and pressure.
Analog-to-Digital Conversion (ADC): Process of converting analog signals to a digital representation.  DAC represents the reverse translation.
Antenna: A device for transmitting and receiving radio waves.
Aspect Ratio: The ratio of the width to the height of an image.

B...
Bandwidth: A measure of spectum (frequency) use or capacity.
Baud: The rate of data transmission based on the number of signal elements or symbols transmitted per second.  Today most digital signals are characterized in bits per second.
Beacon: Low-power carrier transmitted by a satellite which supplies the controllling engineers on the ground with a means of monitoring telemetry data, tracking the satellite or conducting propagation experiments.  This tracking beacon is usually a horn or omni antenna.
Beamwidth: THe angle or conical shape of the beam the antenna projects.  Large antennas have narrower beamwidths and can pinpoint satellites in space or dense traffic areas ont eh earth more precisely. Tighter beamwidths thus deliver higher levels of power and thus greater communications performance.
Bent Pipe Technology: Globalstar's (Bent Pipe Technology) allow the call to be first beamed up to the satellite and then retransmitted to a relatively close gateway.  The call is then sent through to its call destination through land-line or cellular networks.  The Globalstar Gateway carries out all the processing and switching of the calls rather than the satellite itself.  This improves the reliability of the call delivery.
Bird: Slang for a communications satellite located in geosynchronous orbit.
B-ISDN (Broadband ISDN): An ISDN (Integrated Services Digital Network) offering broadband capabilities.  B-ISDN is a CCITT-proposed service that may a) include interfaces operating at data rates from 150 to 600 Mb/s, b) use ATM (Asynchronous Transfer Mode) to carry all services over a single, integrated, high-speed packet-switched network, c) have LAN interconnection capability, d) provide access to a remote, shared disk server, e) provide voice/video/data teleconferencing, f) provide transport for programming services such as cable TV, g) probide single-user controlled access to remote video sources, h) handle voice/video telephone calls and i) access shop-at-home and other information services.
Bit: A single digital unit of information
Bit Rate: The speed of a digital transmission, measured in bits per second.
Broadband -->  See Wideband: A type of data transmission in which a single medium (wire) can carry several channels at once.
Broadcast: The sending of one transmission to multiple users in a defined group (compared to unicast).
BSS (Broadcasting Satellite Service)C-Band: Satellites operating in this band are spaced nene degrees apart in space, and normaly carry 16 transponders which operate at powers in excess of 100 watts. Typical receive antennas are 18 inches in diameter.  The United States has been allocated eight BSS orbital positions, of which three (101, 110 and 119 degrees) are the so-called prime "CONUS" slots from which a DBS provider can service the entire 48 contiguous states with one satellite.  A total of 32 DBS "channels" are available at each orbital position, which allows for delivery of some 250 video signals when digital compression technology is employed.

C...
Cache: A small fast memory which holds recently accessed data, designed to speed up subsequent access to the same data.  Most often applied to processor-memory access but also used for a lobal copy of data accessible over a network, etc.
CDMA: Code Division Multiple Access.  Refers to a multiple-access scheme where stations use spread-spectrum modulations and orthogonal codes to avoid interfering with one another.
Channel: A frequency band in which a specific broadcast signal is transmitted.  Channel frequencies are specified in the United States by the Federal Communications Commission.
Clarke Belt: The name given in hounor of Arthur C Clarke to the orbit 22,300 miles directly above the equator where satellites can maintain a stationary position in relation to the earth.  Also called geostationary orbit.

D...
Data Kit: A data kit is available for both the Globalstar and Iridium satellite phones.  The data kit consists of a data cable and CD which would allow the user to have dial up or direct Internet access through a serial port of a PC.
DBS: Direct broadcast satellite.  Refers to service tht used satellites to broadcast multiple channels of television programming directly to home mounted small-dish antennas.
Decibel: The standard unit used to express the ratio of two power levels.  It is used in communications to express either a gain or loss in power between the input and output devices.
Delay: The time it takes for a signal to go from the sending station through the satellite to the receiving station.  This transmission delay for a single hop satelltie connection is very close on one-quarter of a second.
Digital: Conversion of information into bits of data for transmission through wire, fiber optic cable, satellite or over air techniques.  Method allows simultaneous transmission of voice, data or video.
Digital Bit Stream: A continuously changing flow of digital information which is being transported over some transmission medium such as cable or on a satellite microwave frequency.
Digital Compression: A process by which complex sets of algorithms are employed to rearrange, reassemble and eliminate digital information from a data inventory in such a way that the amount of data (bits) to be stored or transported is reduced without a resulting lossof apparent resolution.
Docking Kit (Station): Spirit Wireless offers a docking kit which is a Car Kit mounted to a metal chassis, and modified to be portable.  Offered with a hard or soft case, external antenna, antenna cable, microphone for hands free operation, speaker and a cigarette lighter adapter.  The docking kit allows the user to easily move the phone from vehicle to vehicle with ease.  The magnetic low profile antenna included withthe unit would need to be located with an full view of the sky to get superior reception.
Downlink: The satellite to earth half of a 2 say telecommunications satellite link.  Often used to describe the receive dish end of the link.
DSL (Digital Subscriber Line): In ISDN, equipment that provides full-duplex service on a single twisted metallic pair at a rate sufficient to support ISDN basic access and additional framing, timing recovery and operational functions.  The physical termination of the DSL at the network end is the line termination; the physical termination at the customer end is the network termination.
DSU: Data Service Unit.  A device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as T1 or E1.  The DSU is also responsible for such functions as signel timing.  DSU is frequently coupled with a CSU (Channel service unit) as CSU/DSU.
Duplex Transmission: Capability for simultaneous data transmission between a sending station and a receiving station.
Duplex Satellite Modem: The GSP-1620 SDM provides 96 Kbps data service using the 48 LEO Globalstar satellite constellations.  The Direct Internet Access gives you connectivity to the Internet and email systems.  With this option you are not required to have an Internet Service Provider (ISP) Globalstar acts as your ISP.  The GSP-1620 SDM is a Hayes compatible modem.

E...
Earth Station: The term used to describe the combination or antenna, low-noise amplifier (LNA), down-converter, and receiver electronics used to receive a signal transmitted by a satellite.  Earth Station antennas vary in size from 2 foot to 12 foot (65 centimeters to 3.7 meters) diameter size used for TV reception to as large as 100 feet (30 meters) in diameter sometimes used for international communications.  The typical antenna used for INTELSAT communication today is 40 to 60 feet (13 to 18 meters).
Edge of Coverage: Limit of a satellite's defined service area.  In many cases, the EOC is defined as being 3 dB down from the signal level at beam center.  However, reception may still be possible beyond the 3dB point.
EIRP: Effective Isotropic Radiated Power - describes the strength of the signal leaving the satellite antenna or the transmitting earth station antenna, and is used in determining the C/N and S/N.  The transmit power value in units of dBW is expressed by the product of the transponder output power and the gain of the satellite transmit antenna.
Elevation: The upward tilt to a satellite antenna measured in degrees required to aim the antenna at the communications satellite.  When aimed at the horizon, the elevation angle is zero.  If it wee tilted to a point directly overhead, the satellite antenna would have an elevation of 90 degrees.
Encryption/Decryption: The action of disguising information so that it can be recovered relatively easily by persons who have the key, but is highly resistant to recovery by persons who do not have the key.  Encryption is accomplished by scrambling the bits, characters, works or phrases in the original message.
EOL: End of Life of a satellite.
Ethernet: A standard protocol (IEEE 802.3) for a 10 Mb/s baseband LAN (local area network) bus using carrier-sense multiple access with collision detection (CSMA/CD) as the access method, implemented at the Physical Layer in the ISO Open Systems Interconnection-Reference Model, establishing the physical characteristics of the CSMA/CD network.
Equatorial Orbit: An orbit with a plane parallel to the earth's equator.

F...
FCC: Federal Communications Commission - the national regularoty body for interstate telecommunications in the United States.  The commission consists of five members all nomited to a specific term by the President of the United States and confirmed by the Senate.  The current chairperson is William Kennard.  The authority for the commission is contained within the communications Act of 1934 as amended (most notably by the Telecommunications Act of 1996).
FDMA: Frequency Division Multiple Access.  Refers to the use of multiple carriers within the same transponder where each uplink has been assigned frequency slot and bandwidth.  This is usually employed in conjunction with Frequency Modulation.
Feed: This term has at least two key meanings within the field of satellite communications.  It is used to describe the transmission of video programming from a distrubution center.  It is also used to describe the feed system of an antenna.  The feed system may consist of a subreflector plus a feedhorn or a feedhorn only.
Feedhorn: The part of the satellite system that collects and focuses satellite signals reflected by the dish.
Fixed Site Satellite Phone: This unit is designed for use on a building.  When the customer needs a unit that will work inside a building, the fixed site satellite phone (GSP-2900) includes an antenna which would need to be installed outside with a clear view of the sky to get optimized signal performance.  The GSP-2900 fixed site unit allows you to have multiple extension line utilizing off the shelf analog desktop or cordless phone.
Footprint: A map of the signal strength showing the EIRP contours of equal signal strength as they cover the earth's surface.  Different satellite transponders on the same satellite will often have different footprints of the signal strength.  The accuracy of EIRP footprints or contour data can improve with the operational age of the satellite.  The actual EIRP levels of the satellite, however, thends to decrease slowly as the spacecraft ages.
Frequency Coordination: A process to eliminate frequency interface between different satellite systems or between terrestrial microwave systems and satellite.  In the US this activity relies upon a computerized service utilizing an extensive database to analyze potential microwave interference problems that arise between organizations using the same microwave band.  As the same C-band frequency spectrum is used by telephone networks and CATV companies when they are contemplating the installation of an earth station, they will often obtain a frequency coordination study to determine if any problems will exist.
FSS: The segment of Ku-band satellite service established by the FCc to be provided from medium power satellites.  These satellites are separated in orbit by at least 2 degrees.  RF signals are transmitted to FSS satellites in the 14 GHz to 14.5 GHz range and received from the satelltie in the 11.7 GHz to 12.2 GHz range.

G...
Gateway: A satellite gateway transmits and receives all traffic which is sent through terrestrial land-lind and cellular networks.  The Gateway carries out all the oprocessing and switching of the calls rather than the satellite itself.