Broadband Satellite Service Glossary



A/D Conversion – (analog-to-digital conversation) The process of converting a time-continuous analog signal to a sampled digital representation.

Adaptive – Refers to the ability of the DCLZ algorithm to “adapt” or change to accommodate differences in the type of data to be compressed.

Algorithm – Systematic means of describing a problem; a procedure for solving a problem in a finite number of steps.

Amplitude Shift Keying – A digital modulation format where information is conveyed in the amplitude of a carrier signal.

Amplifier – A device used to boost 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.

ANIK – The Canadian domestic satellite system that transmits Canadian Broadcasting Corporation’s (CSC) network feeds throughout the country. This system also carries long distance voice and data services throughout Canada as well as some transborder service to the U.S. and Mexico.

Antenna – A device for transmitting and receiving radio waves. Depending on their use and operating frequency, antennas can take the form of a single piece of wire, a di-pole a grid such as a yagi array, a horn, a helix, a sophisticated parabolic-shaped dish, or a phase array of active electronic elements of virtually any flat or convoluted surface.

Aperture – A cross sectional area of the antenna which is exposed to the satellite signal.

Apogee – The point in an elliptical satellite orbit which is farthest from the surface of the earth. Geosynchronous satellites which maintain circular orbits around the earth are first launched into highly elliptical orbits with apogees of 22,237 miles. When the communication satellite reaches the appropriate apogee, a rocket motor is fired to place the satellite into its permanent circular orbit of 22,237 miles.

Apogee Kick Motor (AKM) – Rocket motor fired to circulate orbit and deploy satellite into geostationary orbit.

Asymmetrical links – are ideal for data based communications such as web browsing due to the limited need for uplink and the high need for downlink to display pages. Ideally, bandwidth for web browsing should be assigned to the network asymmetrically as there should be little or no need to provide and pay for the same bandwidth for inbound delivery as is needed for the outbound. Unlike terrestrial networks, with satellite links it is possible to assign bandwidth exactly as required for each direction

Attenuation – The loss in power of electromagnetic signals between transmission and reception points.

Attitude Control – The orientation of the satellite in relationship to the earth and the sun.

Audio Subcarrier – The carrier between 5 MHz and 8 MHz containing audio (or voice) information inside of a video carrier.

Automatic Frequency Control (AFC) – A circuit which automatically controls the frequency of a signal.

Automatic Gain Control (AGC) – A circuit whic4h automatically controls the gain of an amplifier so that the output signal level is virtually constant for varying input signal levels.

Automatic Repeat Request (ARR) – Protocol for dealing with data words that are corrupted by errors whereby the receiving system requests a re-transmission of the word(s) in error.

AZ/EL Mount – Antenna mount that requires two separate adjustments to move from one satellite to another. (AZ: Azimuth, EL: Elevation).

Azimuth – The angle of rotation (horizontal) that a ground based parabolic antenna must be rotated through to point to a specific satellite in a geosynchronous orbit. The azimuth angle for any particular satellite can be determined for any point on the surface of the earth giver the latitude and longitude of that point. It is defined with respect to due north as a matter of easy convenience.



B-Mac – A method of transmitting and scrambling television signals. In such transmissions MAC (Multiplexed Analog Component) signals are time-multiplexed with a digital burst containing digitized sound, video synchronizing, authorization, and information.

Backhaul – A terrestrial communications channel linking an earth station to a local switching network or population center.

Backoff – The process of reducing the input and output power levels of a traveling wave tube to obtain more linear operation.

Amplitude Shift Keying – A digital modulation format where information is conveyed in the amplitude of a carrier signal.

Band Pass Filter – An active or passive circuit which allows signals within the desired frequency band to pass through but impedes signals outside this pass band from getting through.

Bandwidth – A measure of spectrum (frequency) use or capacity. For instance, a voice transmission by telephone requires a bandwidth of about 3000 cycles per second (3KHz). A TV channel occupies a bandwidth of 6 million cycles per second (6 MHz) in terrestrial Systems. In satellite based systems a larger bandwidth of 17.5 to 72 MHz is used to spread or “dither” the television signal in order to prevent interference.

Baseband – The basic direct output signal in an intermediate frequency based obtained directly from a television camera, satellite television receiver, or video tape recorder. Baseband signals can be viewed only on studio monitors. To display the baseband signal on a conventional television set a “modulator” is required to convert the baseband signal to one of the VHF or UHF television channels which the television set can be tuned to receive.

Baud – The rate of data transmission based on the number of signal elements or symbols transmitted per second. Today most digital signal

BCH – A type of block coding of data words named after the inventors Bose, Chaudhuri and Hocquenghem.

Beacon – Low-power carrier transmitted by a satellite which supplies the controlling 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 on the earth more precisely. Tighter beamwidths thus deliver higher levels of power and thus greater communications performance.

BER – Bit Error Rate – In a digital transmission, BER is the percentage of bits with errors divided by the total number of bits that have been transmitted, received or processed over a given time period. The rate is typically expressed as 10 to the negative power. For example, four erroneous bits out of 100,000 bits transmitted would be expressed as 4 x 10 -5, or the expression 3 x 10 -6 would indicate that three bits were in error out of 1,000,000 transmitted. BER is the digital equivalent to signal-to-noise ratio in an analog system.

BERT – Bit Error Rate Test – a procedure or device that measures the bit error rate of a transmission.

Bird – Slang for a communications satellite located in geosynchronous orbit.

Bit – A single digital unit of information

Bit Error Rate – The fraction of a sequence of message bits that are in error. A bit error rate of 10-6 means that there is an average of one error per million bits.

Bit Rate – The speed of a digital transmission, measured in bits per second.

Blanking – An ordinary television signal consists of 30 separate still pictures or frames sent every second. They occur so rapidly, the human eye blurs them together to form an illusion of moving pictures. This is the basis for television and motion picture systems. The blanking interval is that portion of the television signal which occurs after one picture frame is sent and before the next one is transmitted. During this period of time special data signals can be sent which will not be picked up on an ordinary television receiver.

Block Codes – A code with a fixed number of bytes.

Block Down Converter – A device used to convert the 3.7 to 4.2 KHz signal down to UHF or lower frequencies (1 GHz and lower).

Broad beam – A single large circular beam that covers a large geographic area.

Broadband – Describing transmission equipment and media that can support a wide range of electromagnetic frequencies; typically, the technology of Cable Antenna Television transmissions, as applied to data communications, that employs coaxial cable as the transmission medium and radio frequency carrier signals in the 50- to 500- MHz range; any communication channel with bandwidth greater than that of a voice-grade telecommunications channel; sometimes used synonymously with wideband.

Broadcast – The sending of one transmission to multiple users in a defined group (compare to unicast).

BUC – Block Up Conductor

Buffer – A temporary storage space in a computer system or subsystem; especially one that accepts data at one rate and delivers it at another (to coordinate subsystems that process data at different rates).

Business Television – Corporate communications tool involving video transmissions of information via satellite. Common uses of business television are for meetings, product introductions and training.

Byte – Digital word containing eight information bits (1’s or 0’s).



C Band – This is the band between 4 and 8 GHz with the 6 and 4 GHz band being used for satellite communications. Specifically, the 3.7 to 4.2 GHz satellite communication band is used as the down link frequencies in tandem with the 5.925 to 6,425 GHz band that serves as the uplink.

Carrier to Noise Ratio (C/N) – The ratio of the received carrier power and the noise power in a given bandwidth, expressed in dB. This figure is directly related to G/T and S/N; and in a video signal the higher the C/N, the better the received picture.

Carrier – The basic radio, television, or telephony center of frequency transmit signal. The carrier in an analog signal. is modulated by manipulating its amplitude (making it louder or softer) or its frequency (shifting it up or down) in relation to the incoming signal. Satellite carriers operating in the analog mode are usually frequency modulated.

Carrier Frequency – The main frequency on which a voice, data, or video signal is sent. Microwave and satellite communications transmitters operate in the band from 1 to 14 GHz (a GHz is one billion cycles per second).

Cassegrain Antenna – The antenna principle that utilizes a subreflector at the focal point which reflects energy to or from a feed located at the apex of the main reflector.

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. Television signals require a 6 MHz frequency band to carry all the necessary picture detail.

Channel Efficiency – In error correction, the ratio of the input information divided by the transmitted information plus code.

Circular Polarization – Unlike many domestic satellites which utilize vertical or horizontal polarization, the international Intelsat satellites transmit their signals in a rotating corkscrew-like pattern as they are down-linked to earth. On some satellites, both right-hand rotating and left-hand rotating signals can be transmitted simultaneously on the same frequency; thereby doubling the capacity of the satellite to carry communications channels.

Clamp – A video processing circuit that removes the energy dispersal signal component from the video waveform.

Clarke Orbit – That circular orbit in space 22,237 miles from the surface of the earth at which geosynchronous satellites are placed. This orbit was first postulated by the science fiction writer Arthur C. Clarke in Wireless World magazine in 1945. Satellites placed in these orbits, although traveling around the earth at thousands of miles an hour, appear to be stationary when viewed from a point on the earth, since the earth is rotating upon its axis at the same angular rate that the satellite is traveling around the earth.

C/No – Carrier-to-noise ratio measured either at the Radio Frequency (RF) or Intermediate Frequency (IF).

Coaxial Cable – A popular transmission medium usually consisting of one central wire conductor (two, for twin axial cable) surrounded by a dielectric insulator and encased in either a wire mesh or an extruded metal sheathing; coaxial cable comes in many varieties, depending on the degree of EMI shielding afforded and voltages and frequencies accommodated; common Community Antenna Television (Cable Antenna Television) transmission cable, typically supporting RF frequencies from 50 to about 500 MHz; also called coax.

Code Division Multiple Access (CDMA) – Method of combining multiple users on a given channel bandwidth using unique spreading codes, or hopping patterns to distinguish and given user.

Code Rate – In error correction, the ratio of information divided by information plus redundancy. Codes with a high code rate are desirable because they efficiently use the available channel for information transmission.

Codec – Coder/decoder system for digital transmission.

Coding Gain – In communications engineering, coding gain refers to the improvement in decibels (dB) that a particular code offers over other option. An improvement in coding gain can provide the designer with options such as reducing transmission power or bandwidth.

Co-Location – Ability of multiple satellites to share the same approximate geostationary orbital assignment frequently due to the fact that different frequency bands are used.

Color Subcarrler – A subcarrier that is added to the main video signal to convey the color information. In NTSC systems, the color subcarrier is centered on a frequency of 3.579545 MHz, referenced to the main video carrier.

Common Carrier – Any organization which operates communications circuits used by other people. Common carriers include the telephone companies as well as the owners of the communications satellites, RCA, Comsat, Direct Net Telecommunications, AT&T and others. Common carriers are required to file fixed tariffs for specific services.

Companding – A noise-reduction technique that applies single compression at the transmitter and complementary expansion at the receiver.

Composite Baseband – The unclamped and unfiltered output of the satellite receiver’s demodulator circuit, containg the video information as well as all transmitted subcarriers.

Compression – Any of several techniques that reduce the number of bits required to represent information in data transmission or storage (thus conserving bandwidth and/or memory), in which the original form of the information can be reconstructed; also called “compaction”.

Compression Ratio – The ratio of the number of original data bytes to the number of compressed data bytes.

Continuous Phase Frequency Shift Keying – (CPFSK) Digital modulation format where information is conveyed in the frequency of a carrier signal ensuring that the phase is continuous between symbol transitions.

Conus – Contiguous United States. Basically, all the states in the U.S. except Hawaii and Alaska.

Cross Modulation – A form of signal distortion in which modulation from one or more RF carrier(s) is imposed on another carrier.

CSU – Channel service unit. A digital interface device that connects end-user equipment to the local digital telephone loop. CSU is frequently coupled with DSU (see below) as CSU/DSU.

C/T – Carrier-to-noise-temperature ratio.



D/A Conversion – (digital-to-analog conversation) The process of converting a discrete time digital representation of a waveform to a continuous analog voltage equivalent.

D-TDMA – deterministic time division multiple access this technology simply takes TDMA and adds the ability to prioritize types of traffic. This will allow voice and video to be prioritized above data transfers to make the best use of the bandwidth. This technology is used in digital-advanced mobile phone system (D-AMPS) and Global System for Mobile communications (GSM). Packets are transmitted based on priorities established within the router which allow for VoIP and video teleconferencing to transmit first since they are real-time traffic.

DAMA Demand-Assigned Multiple Access – A highly efficient means of instantaneously assigning telephony channels in a transponder according to immediate traffic demands.

Data Coding – Operating on data with an algorithm to accomplish encryption, error correction, compression, or some other feature.

dBc – The level of a signal in dB relative to a wanted carrier signal level.

dBm – The level of a signal in dB relative to 1 m W (0 dBm).

DBS Direct broadcast satellite – Refers to service that uses satellites to broadcast multiple channels of television programming directly to home mounted small-dish antennas. (i.e. DIRECTV – The Dish Network)

dBi – The dB power relative to an isotropic source.

dBW The ratio of the power to one Watt expressed in decibels.

DC – (Data Compression) A method to encode data by eliminating redundancy. May be implemented in hardware or software.

Decibel (dB) – 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.

Declination – The offset angle of an antenna from the axis of its polar mount as measured in the meridian plane between the equatorial plane and the antenna main beam.

Decoder – A television set-top device which enables the home subscriber to convert an electronically scrambled television picture into a viewable signal.

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 satellite connection is very close on one-quarter of a second.

Demodulator – A satellite receiver circuit which extracts or “demodulates” the “wanted “signals from the received carrier.

Density – A measure of how much data is stored in a given area or linear sequence (track) on a specific medium. Density may be measured in Bits per inch or millimeter, in tracks per inch or millimeter, or in bits per square inch or millimeter.

DES – (Data Encryption Standard) A Scheme approved by the National Bureau of Standards that encrypts data for security purposes. DES is the data-communications encryption standard specified by Federal Information Processing Systems (FIPS) Publication 46.

Deviation – The modulation level of an FM signal determined by the amount of frequency shift from the frequency of the main carrier.

Differential Phase Shift Keying – (DPSK) Digital modulation format where information is conveyed in phase difference of a carrier signal between consecutive symbols.

Differentially Encoded Phase Shift Keying – (DEPSK) Digital modulation format where data is pre-coded to convey information in the change of state between consecutive bits, to overcome the phase ambiguity problem with coherent phase shift keying.

Digital Conversion – Technique of preparing 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 Audio Broadcasting – (DAB) The generic name given to the new generation of radio transmission using digitally encoded audio waveforms.

Digital Speech Interpolation DSI – A means of transmitting telephony. Two and One half to three times more efficiently based on the principle that people are talking only about 40% of the time.

Downlink – The satellite to earth half of a 2 way telecommunications satellite link. Often used to describe the receive dish end of the link

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 signal timing. DSU is frequently coupled with a CSU (see above) as CSU/DSU.

DTV – Digital Television

Dual Spin – Spacecraft design whereby the main body of the satellite is spun to provide altitude stabilization, and the antenna assembly is despun by means of a motor and bearing system in order to continually direct the antenna earthward. This dual-spin configuration thus serves to create a spin stabilized satellite.

Duplex Transmission – Capability for simultaneous data transmission between a sending station and a receiving station.

DVB – Digital Video Broadcast – This is an all digital as the name indicates, and was originally designed for broadcast video and has been modified to allow various types of traffic.

DVB-S – Digital Video Broadcast via satellite

DVB-C – Digital Video Broadcast via cable

DVB-RCS – Digital Video Broadcast, Return Channel via Satellite



E1 – Wide-area digital transmission facility used predominantly in Europe that carries data at a rate of 2.048 Mbit/s.

E3 – Wide-area digital transmission facility used predominantly in Europe that carries data at a rate of 34.368 Mbit/s.

Earth Station – The term used to describe the combination of antenna, low-noise amplifier (LNA), down-converter, and receiver electronics; used to transmit and receive a signal by satellite. Earth Station antennas vary in size from the 2 foot to 12 foot (65 centimeters to 3.7 meters) diameter.

Echo Canceller – An electronic circuit which attenuates or eliminates the echo effect on satellite telephony links. Echo cancellers are largely replacing obsolete echo suppressors.

Echo Effect – A time-delayed electronic reflection of a speaker’s voice. This is largely eliminated by modern digital echo cancellers.

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 – This term 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 were tilted to a point directly overhead, the satellite antenna would have an elevation of 90 degrees, depending on the offset of the antenna.

Encoder – A device used to electronically alter a signal so that it can only be viewed on a receiver equipped with a special decoder.

Encoding/Decoding – The process of organizing information into a particular format and then reconverting it for use; for pulse-code-modulated voice transmission, the generation of digital signals to represent quantified samples, and the subsequent reverse process.

EOL – End of Life of a satellite.

Equatorial Orbit – An orbit with a plane parallel to the earth’s equator.

ESC Engineering Service Circuit – The 300-3,400 Hertz voice plus teletype (S+DX) channel used for earth station-to-earth station and earth station-to-operations center communications for the purpose of system maintenance, coordination and general system information dissemination. In analog (FDM/FM) systems there are two S+DX channels available for this purpose in the 4,000-12,000 Hertz portion of the baseband. In digital systems there are one or two channels available which are usually convened to a 32 or 64 Kbps digital signal and combined with the earth station traffic digital bit stream. Modern ESC equipment interfaces with any mix of analog and digital satellite carriers, as well as backhaul terrestrial links to the local switching center.

Ethernet – A popular local area network design, the product of Xerox Corp., characterized by 10 Mbps baseband transmission over a shielded coaxial cable and employing CSMA/CD as the access control mechanism; standardized by the IEEE as specification IEEE 802.3; referring to the Ethernet design or as a compatible with Ethernet.



F/D Ratio of antenna focal length to antenna diameter. A higher ratio means a shallower dish.

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.

FEC – Forward Error Correction – It is a powerful technique for improving the performance of error-prone channels found in communication systems. It is a system of error control for data transmission where the receiving device has the capability to detect and correct any character or code block that contains fewer then a predetermined number of symbols in error. It is intended to improve the capacity of a channel by adding some carefully designed redundant information to the data being transmitted through the channel.

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 distribution 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.

Fiber Optic – Transmission technology in which modulated light wave signals., generated by laser or LED, are propagated along a typically glass or plastic medium, and then demodulated to electrical signals by a light-sensitive receiver.

Focal Length – Distance from the center feed to the center of the dish.

Focal Point – The area toward which the primary reflector dish directs and concentrates the signal received.

Footprint A map of the signal strength showing the EIRP contours of equal signal strengths 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, tends to decrease slowly as the spacecraft ages.

Forward Error Correction (FEC) – Adds unique codes to the digital signal at the source so errors can be detected and corrected at the receiver.

Frequency – The number of times that an alternating current goes through its complete cycle in one second of time. One cycle per second is also referred to as one hertz; 1000 cycles per second, one kilohertz; 1,000,000 cycles per second, one megahertz: and 1,000,000,000 cycles per second, one gigahertz.

Frequency Coordination – A process to eliminate frequency interference between different satellite systems or between terrestrial microwave systems and satellites. In the U.S. 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.

FTDMA – frequency time division multiple access – The FTDMA features a unique and patented two-dimensional satellite access scheme, which combines the TDMA slotted ALOHA and FDMA techniques. Remote terminals burst in randomly selected frequency channels at each transmission. Occasional high traffic sites are automatically off-loaded from the shared resources and have dedicated frequency channels allotted to them upstream communications are transmitted using a patented, proprietary technology – Frequency/Time Division Multiple Access, or FTDMA. Downstream transmissions, however, use the industry standard Digital Video Broadcast (DVB) carrier.

FSK – (Frequency Shift Keying) – Digital modulation format where information is conveyed in the frequency of a carrier signal.

FTP – File Transfer Protocol – A very common method of moving files between two Internet sites. FTP is a special way to login to another Internet site for the purposes of retrieving and/or sending files. There are many Internet sites that have established publicly accessible repositories of material that can be obtained using FTP, by logging in using the account name anonymous, thus these sites are called anonymous ftp servers.



G.711 – Describes the 64-kbps PCM voice coding technique. In G.711, encoded voice is already in the correct format for digital voice delivery in the PSTN or through PBXs. Described in the ITU-T standard in its G-series recommendations.

G.723 – Audio (Voice) Compression Protocol reducing the required bandwidth per call, per direction to 8 kbps using adaptive multi-rate wideband.

G.729 – Audio (Voice) Compression Protocol reducing the required bandwidth per call, per direction to 12 kbps using conjugate-structure algebraic-code-excited linear-predication.

Gain – A measure of amplification expressed in dB.

Geostationary – Refers to a geosynchronous satellite angle with zero inclination. so the satellite appears to hover over one spot on the earth’s equator.

Geostationary Orbit – circular orbits that are orientated in the plane of the earth’s equator. The satellite appears stationary.

Geosynchronous – The Clarke circular orbit above the equator. For a planet the size and mass of the earth, this point is 22,237 miles above the surface. Geosynchronous The Clarke circular orbit above the equator. For a planet the size and mass of the earth, this point is 22,237 miles above the surface.

Gigabyte – a unit of information equla to 1000 megabytes or 10^9 (1,000,000,000) bytes

Gigahertz (GHz) – One billion cycles per second. Signals operating above 3 Gigahertz are known as microwaves. above 30 GHz they are know as millimeter waves. As one moves above the millimeter waves signals begin to take on the characteristics of Iightwaves.

Global Beam An antenna down-link pattern used by the Intelsat satellites, which effectively covers one-third of the globe. Global beams are aimed at the center of the Atlantic, Pacific and Indian Oceans by the respective Intelsat satellites, enabling all nations on each side of the ocean to receive the signal. Because they transmit to such a wide area, global beam transponders have significantly lower EIRP outputs at the surface of the Earth as compared to a US domestic satellite system which covers just the continental United States. Therefore, earth stations receiving global beam signals need antennas much larger in size (typically 10 meters and above (i.e.30 feet and up). Gregorian Dual-reflector antenna system employing a paraboloidal main reflector and a concave ellipsoidal subreflector.

GMSK – (Gaussian Minimum Shift Keying) – Digital modulation format where information is conveyed in the frequency of a carrier signal, where the incoming data is first shaped with a Gaussian low-pass filter.

GSM – (Global System for Mobile Communication) – A cellular radio standard using digital GMSK modulation.

G/T – A figure of merit of an antenna and low noise amplifier combination expressed in dB. “G” is the net gain of the system and “T” is the noise temperature of the system. The higher the number, the better the system.



H.323 – is a protocol for the transmission of real-time audio, video and data information over packet switching-based networks. Such networks include IP-based (including the Internet), Internet packet exchange-based local area networks, enterprise networks and metropolitan and wide area networks. H.323 can also be applied to multipoint-multimedia communications. The technology provides a vast array of services which means it can be used in consumer, business and entertainment applications. H.323 is an essential element in ensuring that the compatibility of the mobile multimedia applications and services will be introduced with the implementation of third generation wireless technologies.

Headend Electronic control center – generally located at the antenna site of a CATV system – usually including antennas, preamplifiers, frequency converters, demodulators and other related equipment which amplify, filter and convert incoming broadcast TV signals to cable system channels.

Headers – Blocks of data written at the beginning of cartridges or files that contain specific identification information.

Hertz (Hz) – The name given to the basic measure of radio frequency characteristics. An electromagnetic wave completes a full oscillation from its positive to its negative pole and back again in what is known as a cycle. A single Hertz is thus equal to one cycle per second.

HNO – Host Network Operator, iDirect Host Network Operator

HTPC – Hyper Turbo Product Code is a TPC with an added parity correction code dimension.

HTTP – HyperText Transfer Protocol – The protocol for moving hypertext files across the Internet. Requires a HTTP client program on one end, and an HTTP server program on the other end. HTTP is the most important protocol used in the World Wide Web.

Hub The master station through which all communications to, from and between micro terminals must flow. in the future satellites with on-board processing will allow hubs to be eliminated as MESH networks are able to connect all points in a network together.



Inclination The angle between the orbital plane of a satellite and the equatorial plane of the earth.

Information Transport – Transferring electronic information or data via electronic, photonic, or any other mans. May be point to point or network, one or two way, also referred to as “communications” or “telecommunications” (same as data transport).

INMARSAT – The International Maritime Satellite Organization operates a network of satellites for international transmissions for all types of international mobile services including maritime, aeronautical, and land mobile.

Interference – Energy which tends to interfere with the reception of the desired signals, such as fading from airline flights, RF interference from adjacent channels, or ghosting from reflecting objects such as mountains and buildings.

IP – Internet Protocol – is the most basic protocol to communicate on the Internet. An IP number is a numerical address consisting of four numbers separated by periods. Each IP address uniquely identifies a certain computer on the Internet. The domain name is used to make using them easier.

IPSec – Internet Protocol Security – is a protocol suite for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session.

IRD – An integrated receiver and decoder for reception of a transmission of voice, video and data.

ISDN – Integrated Services Digital Network. A CCITT standard for integrated transmission of voice, video and data. Bandwidths include: Basic Rate Interface – BR (144 Kbps – 2 B & 1 D channel) and Primary Rate – PRI (1.544 and 2.048 Mbps).

Isotropic Antenna – A hypothetical omnidirectional point-source antenna that serves as an engineering reference for the measurement of antenna gain.

ITU – International Telecommunication Union.



Jammer – An active electronic counter-measures (ECM) device designed to deny intelligence to unfriendly detectors or to disrupt communications.

JPEG – ISO Joint Picture Expert Group standard for the compression of still pictures.



Ka Band – The frequency range from 18 to 31 GHz.

Kbps – Kilobits per second. Refers to transmission speed of 1,000 bits per second.

Kelvin (K) – The temperature measurement scale used in the scientific community. Zero K represents absolute zero, and corresponds to minus 459 degrees Fahrenheit or minus 273 Celsius. Thermal noise characteristics of LNA are measured in Kelvins.

Kilohertz (kHz) – Refers to a unit of frequency equal to 1,000 Hertz.

Klystron – A microwave tube which uses the interaction between an electron beam and the RF energy on microwave cavities to provide signal amplification. The klystron operates on principles of velocity modulation very similar to those in a TWT except that klystron interaction takes place at discrete locations along the electron beam. Common types of klystrons are the reflex klystron (an oscillator having only one cavity), two-cavity klystron amplifiers and oscillators, and multi-cavity klystron amplifiers.

Ku Band – The frequency range from 10.9 to 17 GHz.



L-Band – The frequency range from 0.5 to 1.5 GHz. Also used to refer to the 950 to 1450MHz used for mobile communications.

LAN – (Local Area Network) – A network of interconnected workstations sharing the resources of a single processor or server within a relatively small geographic area.

Latency – In a network, latency, a synonym for delay, is an expression of how much time it takes for a packet of data to get from one designated point to another. In some usages latency is measured by sending a packet that will be returned back to the sender and thus the round-trip time is considered the latency.

Leased Line – A dedicated circuit typically supplied by the telephone company.

Lights-Out Termination of satellite carrier.

Low Noise Amplifier (LNA) – This is the preamplifier between the antenna and the earth station receiver. For maximum effectiveness, it must be located as near the antenna as possible, and is usually attached directly to the antenna receive port. The LNA is especially designed to contribute the least amount of thermal noise to the received signal.

Low Noise Block Downconverter (LNB) – A combination Low Noise Amplifier and downconverter built into one device attached to the feed.

LNC – Low Noise Converter converters the incoming signal from the satellite (3.6 to 4.2 GHz in the c-band and 10.700 to 12.750 in ku-band) into a lower frequency (900 to 2150 MHz).

Lossless – Characteristic of data compression algorithms such that when compressed data is decompressed, it is identical to the form it had prior to compression.

Lossy – Characteristic of data compression algorithms in which compressed data may not decompress exactly to its original form. Lossy compression is typically capable of very high compression performance, and is used primarily on data which may be slightly changed without significant effect.



Margin – The amount of signal in dB by which the satellite system exceeds the minimum levels required for operation.

MCPC – Multi Channel per Carrier – This is a byproduct of SCPC combined with TDM (Time division Multiple) voice/data multiplexing that operates in a star configuration

Megabyte – a unit of information equal to 1000 kilobytes or 10^6 (1,000,000) bytes

Megahertz (MHz) – Refers to a frequency equal to one million Hertz, or cycles per second.

Mesh Topology – devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network. T he topology of a network whose components are all connected directly to every other component A group of nodes sharing a large number of interconnections, where the interconnections are graphically represented with lines, can be visualized as a mesh.

Microwave – Line-of sight, point-to-point transmission of signals at high frequency. Many CATV systems receive some television signals from a distant antenna location with the antenna and the system connected by microwave relay. Microwaves are also used for data, voice, and indeed all types of information transmission. The growth of fiber optic networks have tended to curtail the growth and use of microwave relays.

Microwave Interference – Interference which occurs when an earth station aimed at a distant satellite picks up a second, often stronger signal, from a local telephone terrestrial microwave relay transmitter. Microwave interference can also be produced by nearby radar transmitters as well as the sun itself. Relocating the antenna by only several feet will often completely eliminate the microwave interference.

Minimum Shift Keying (MSK) – Digital modulation format where information is conveyed in the frequency of a carrier signal with modulation index equal to half the symbol period.

Modulation – The process of manipulating the frequency or amplitude of a carrier in relation to an incoming video, voice or data signal.

Modulator – A device which modulates a carrier. Modulators are found as components in broadcasting transmitters and in satellite transponders. Modulators are also used by CATV companies to place a baseband video television signal onto a desired VHF or UHF channel. Home video tape recorders also have built-in modulators which enable the recorded video information to be played back using a television receiver tuned to VHF channel 3 or 4.

MPEG – The Motion Pictures Experts Group, the television industry’s informal standards group.

MPEG-2 – The agreed standard covering the compression of data (coding and encoding) for digital television.

MPEG-2 MP@HL – Main Provile at High Level – The agreed much higher bit-rate system adopted to provide high definition television in wide screen format.

Multicast – Multicast is a subset of broadcast that extends the broadcast concept of one to many by allowing “the sending of one transmission to many users in a defined group, but not necessarily to all users in that group.”

Multiplexing – Techniques that allow a number of simultaneous transmissions over a single circuit.



Noise – Any unwanted and unmodulated energy that is always present to some extent within any signal.

Noise Figure (NF) – A term which is a figure of merit of a device, such as an LNA or receiver, expressed in dB, which compares the device with a perfect device. NTSC – National Television Standards Committee A video standard established by the United States (RCA/NBC} and adopted by numerous other countries. This is a 525-line video with 3.58-MHz chroma subcarrier and 60 cycles per second.



OC-3 – A telecommunications standard for data rate speeds of 155 Mbits/second.

ON-OFF Keying (OOK) – Digital modulation format where information is conveyed by switching on and off a carrier signal.

Orbital Period – The time that it takes a satellite to complete one circumnavigation of its orbit.



Packet Switching – Data transmission method that divides messages into standard-sized packets for greater efficiency of routing and transport through a network.

Parabolic Antenna – The most frequently found satellite TV antenna, it takes its name from the shape of the dish described mathematically as a parabola. The function of the parabolic shape is to focus the weak microwave signal hitting the surface of the dish into a single focal point in front of the dish. It is at this point that the feedhorn is usually located.

Petabyte – a unit of information equal to 1000 gigabytes or 10^15 (1,000,000,000,000,000) bytes

Phase-Locked Loop (PLL) A type of electronic circuit used to demodulate satellite signals.

Point to Multipoint – a connection consisting of a central connection endpoint and other peripheral connection endpoints and in which data originating from the central connection endpoint are received by all other connection endpoints and data originating from the peripheral connection endpoints is received only by the central connection endpoint.

Point to point – This service requires the incorporation of an earth station as the HUB with connection to needed services. It incorporates various sites with a VSAT to communicate with the HUB.

Polarization – A technique used by the satellite designer to increase the capacity of the satellite transmission channels by reusing the satellite transponder frequencies. In linear cross polarization schemes, half of the transponders beam their signals to earth in a vertically polarized mode; the other half horizontally polarize their down links. Although the two sets of frequencies overlap, they are 90 degree out of phase, and will not interfere with each other. To successfully receive and decode these signals on earth, the earth station must be outfitted with a properly polarized feedhorn to select the vertically or horizontally polarized signals as desired. In some installations, the feedhorn has the capability of receiving the vertical and horizontal transponder signals simultaneously, and routing them into separate LNAs for delivery to two or more satellite television receivers. Unlike most domestic satellites, the Intelsat series use a technique known as left-hand and right-hand circular polarization.

Polarization Rotator – A device that can be manually or automatically adjusted to select one of two orthogonal polarizations.

Polar Mount – Antenna mechanism permitting steering in both elevation and azimuth through rotation about a single axis. While an astronomer’s polar mount has its axis parallel to that of the earth, satellite earth stations utilize a modified polar mount geometry that incorporates a declination offset.

Polar Orbit – An orbit with its plane aligned in parallel with the polar axis of the earth.

PSK Phase-Shift Key – It’s a form of phase modulation for digital signals, where the bits are quantified by various phase changes. It involves changing the phase of transmitted waveform instead of the frequency, these finite phase changes representing digital data. In its simplest form, a phase-modulated waveform can be generated by using the digital data to switch between two signals of equal frequency but opposing phase.

PTT – Post Telephone and Telegraph Administration Refers to operating agencies directly or indirectly controlled by governments in charge of telecommunications services in most countries of the world.

Pulse Code Modulation – A time division modulation technique in which analog signals are sampled and quantized at periodic intervals into digital signals. The values observed are typically represented by a coded arrangement of 8 bits of which one may be for parity.



Quality of Service (QoS) – QoS is the set of techniques to manage network resources. QoS enables you to provide better service to certain flows. This is done by either raising the priority of a flow or limiting the priority of another flow.

QPSK – Quadrature Phase Shift Keying System of modulating a satellite signal.

Quadrature Amplitude Modulation (QAM) – Digital modulation format where information is conveyed in the amplitude and phase of a carrier signal.



Rain Fade – Loss of signal at Ku or Ka Band frequencies due to absorption and increased sky-noise temperature caused by heavy rainfall.

Receiver (Rx) – An electronic device which enables a particular satellite signal to be separated from all others being received by an earth station, and converts the signal format into a format for video, voice or data.

Receiver Sensitivity – Expressed in dBm this tells how much power the detector must receive to achieve a specific baseband performance, such as a specified bit error rate or signal to noise ratio.

Redundancy – Extra bytes added to data that allows error detection and correction to occur; having backup equipment to ensure the minimal interruption.

RF – Radio Frequency

Router Network layer device that determines the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information.

RS – Reed Solomon Codes – are block-based error correcting codes with a wide range of applications in digital communications and storage. These codes are used to correct errors in many systems including storage devices, wireless or mobile communications, satellite communications, digital television, DVB, high-speed modems such as ADSL. The Reed-Solomon encoder takes a block of digital data and adds extra “redundant” bits. Errors occur during transmission or storage for a number of reasons (for example noise or interference, scratches). The Reed-Solomon decoder processes each block and attempts to correct errors and recover the original data. The number and type of errors that can be corrected depends on the characteristics of the code.

RS-Viterbi – Reed-Solomon/Viterbi coding technology

RTP – Real-time transport protocol – The Internet-standard protocol for the transport of real-time data, including audio and video. RTP is used in virtually all voice-over-IP architectures, for videoconferencing, media-on-demand, and other applications. A thin protocol, it supports content identification, timing reconstruction, and detection of lost packets.

RX – Short for receive



SAP – This protocol is used on NetWare networks to advertise available network services. For example, a NetWare server uses SAP to let other computers know that it’s offering up some shared files. This also stands for “Standard Accounting Program,” a program on which some large businesses run their accounting.

Scalar Feed – A type of horn antenna feed which uses a series of concentric rings to capture signals that have been reflected toward the focal point of a parabolic antenna.

Scrambler – A device used to electronically alter a signal so that it can only be viewed or heard on a receiver equipped with a special decoder.

SCPC – Single Channel Per Carrier

Selective Layer Encryption (SLE) – Encore Networks patented IPSec VPN solution to the VSAT industry called Selective Layer Encryption (SLE). SLE is designed to enhance VPN and work in tandem with PEP providing fully encrypted IPSec data.

SFD – Stauration Flux Density The power required to achieve saturation of a single repeater channel on the satellite. Sidelobe Off-axis response of an antenna.

Signal to Noise Ratio (S/N) – The ratio of the signal power and noise power. A video S/N of 54 to 56 dB is considered to be an excellent S/N, that is, of broadcast quality. A video S/N of 48 to 52 dB is considered to be a good S/N at the headend for Cable TV.

Simplex Transmission – Capability for transmission in only one direction between sending station and receiving station.

Single-Channel-Per-Carrier (SCPC) – A method used to transmit a large number of signals over a single satellite transponder.

Skew – An adjustment that compensates for slight variance in angle between identical senses of polarity generated by two or more satellites.

Slant Range – The length of the path between a communications satellite and an associated earth station.

Slot – That longitudinal position in the geosynchronous orbit into which a communications satellite is “parked”. Above the United States, communications satellites are typically positioned in slots which are based at two to three degree intervals.

S/N ratio – Signal-to-noise ratio

SNG – Satellite news gathering usually with a transportable uplink truck.

SOHO – Small Office, Home Office

Solar Outage – Solar outages occur when an antenna is looking at a satellite, and the sun passes behind or near the satellite and within the field of view of the antenna. This field of view is usually wider than the beamwidth. Solar outages can be exactly predicted as to the timing for each site.

Spectrum – The range of electromagnetic radio frequencies used in transmission of voice, data and television.

Spillover – Satellite signal that falls on locations outside the beam pattern’s defined edge of coverage.

Spin Stabilization – A form of satellite stabilization and attitude control which is achieved through spinning the exterior of the spacecraft about its axis at a fixed rate.

Splitter – A passive device (one with no active electronic components) which distributes a television signal carried on a cable in two or more paths and sends it to a number of receivers simultaneously.

Spot Beam – A focused antenna pattern sent to a limited geographical area. Spot beams are used by domestic satellites to deliver certain transponder signals to geographically well defined areas such as Hawaii, Alaska and Puerto Rico.

Spread Spectrum – The transmission of a signal using a much wider bandwidth and power than would normally be required. Spread spectrum also involves the use of narrower signals that are frequency hopped through various parts of the transponder. Both techniques produce low levels of interference Between the users. They also provide security in that the signals appear as though they were random noise to unauthorized earth stations. Both military and civil satellite applications have developed for spread spectrum transmissions.

SSL – Secured Sockets Layer – a protocol that transmits your communications over the Internet in an encrypted form. SSL ensures that the information is sent, unchanged, only to the server you intended to send it to. Online shopping sites frequently use SSL technology to safeguard your credit card information.

SSPA Solid state power amplifier – A solid state device that is gradually replacing Traveling Wave Tubes in satellite communications systems because they are lighter weight and are more reliable.

Star Topology – Network designed in the shape of a star, where all end points are connected to one central switching device, or hub. Star networks are easier to manage than ring topology but are slower because every message must pass through the central point.

Stationkeeping – Minor orbital adjustments that are conducted to maintain the satellite’s orbital assignment within the allocated “box” within the geostationary arc.

Subcarrier – A second signal “piggybacked” onto a main signal to carry additional information. In satellite television transmission, the video picture is transmitted over the main carrier. The corresponding audio is sent via an FM subcarrier. Some satellite transponders carry as many as four special audio or data subcarriers whose signals may or may not be related to the main programming.

SER – Symbol Error Rate – The probability of receiving a symbol in error (not to be confused with BER)

Symmetrical – or full duplex is for two way communications such as voice or any real time data.

Synchronization (Sync) – The process of orienting the transmitter and receiver circuits in the proper manner in order that they can be synchronized . Home television sets are synchronized by an incoming sync signal with the television cameras in the studios 60 times per second. The horizontal and vertical hold controls on the television set are used to set the receiver circuits to the approximate sync frequencies of incoming television picture and the sync pulses in the signal then fine tune the circuits to the exact frequency and phase.



T1 – The transmission bit rate of 1.544 millions bits per second. This is also equivalent to the ISDN Primary Rate Interface for the U.S. The European T1 or E1 transmission rate is 2.048 million bits per second.

T3 Channel (DS-3) In North America – A digital channel which communicates at 45.304 Mbps.

TCC – Turbo Convolutional Codes

TCP Acceleration – is the name of a series of techniques for achieving better throughput on an Internet connection than standard TCP achieves, without modifying the end applications.

TCP/IP – Transmission Control Protocol/Internet Protocol – the suite of communications protocols used to connect hosts on the Internet. TCP/IP uses several protocols, the two main ones being TCP and IPP. TCP/IP is built into the UNIX operating system and is used by the Internet, making it the de facto standard for transmitting data over networks. Even network operating systems that have their own protocols, such as Netware, also support TCP/IP

TDMA Time division multiple access – Refers to a form of multiple access where a single carrier is the shared by many users. Signals from earth stations reaching the satellite consecutively are processed in time segments without overlapping.

Terabyte – a unit of information equal to 1000 gigabytes or 10^12 (1,000,000,000,000) bytes

TI – Terrestrial Interference Interference to satellite reception caused by ground based microwave transmitting stations.

TPC – Turbo Product Codes – These codes have performance approaching the theoretical limit for any error correction code. TPC uses block codes solving multiple steps simultaneously, thereby achieving high data throughput in hardware. They do not suffer from the error floor at low BERs that have been attributed to other codes.

Transmitter – An electronic device consisting of oscillator, modulator and other circuits which produce a radio or television electromagnetic wave signal for radiation into the atmosphere by an antenna.

Transponder – A combination receiver, frequency converter, and transmitter package, physically part of a communications satellite. Transponders have a typical output of five to ten watts, operate over a frequency band with a 36 to 72 megahertz bandwidth in the L, C, Ku, and sometimes Ka Bands or in effect typically in the microwave spectrum, except for mobile satellite communications. Communications satellites typically have between 12 and 24 onboard transponders although the INTELSAT VI at the extreme end has 50.

TVRO – Television Receive Only terminals that use antenna reflectors and associated electronic equipment to receive and process television and audio communications via satellite. Typically small home systems.

Tweeking – The process of adjusting an electronic receiver circuit to optimize its performance.

TWT – Traveling-wave tube – A microwave tube of special design using a broadband circuit in which a beam of electrons interacts continuously with a guided electromagnetic field to amplify microwave frequencies.

TWTA – Traveling-wave-tube amplifier – A combination of a power supply, a modulator (for pulsed systems), and a traveling-wave tube, often packaged in a common enclosure.

TX – Short for Transmit

Synchronization (Sync) The process of orienting the transmitter and receiver circuits in the proper manner in order that they can be synchronized . Home television sets are synchronized by an incoming sync signal with the television cameras in the studios 60 times per second. The horizontal and vertical hold controls on the television set are used to set the receiver circuits to the approximate sync frequencies of incoming television picture and the sync pulses in the signal then fine tune the circuits to the exact frequency and phase.



Unicast – A unicast application transmits a copy of every packet to every receiver.

UNIX® – Operating system originally designed by AT&T for communicating multi-user, 32-bt minicomputers; has come into wide commercial acceptance because of its predominance in academia and its programming versatility. ATamp;&T System V Version 3 and Berkeley System Development Version 4.3 are currently popular.

Uplink – The earth station used to transmit signals to a satellite.



V.35 – ITU-T standard describing a synchronous, physical layer protocol used for communications between a network access device and a packet network. V.35 is most commonly used in the United States and in Europe, and is recommended for speeds up to 48 Kbit/s.

VAN – Value Added Network – A network whose services go beyond simple switching.

Viterbi Encoding/Decoding – is widely used for satellite and other noisy communication channels. There are two important components of a channel using Viterbi encoding: the Viterbi encoder (at the transmitter) and Viterbi Decoder (at the receiver). A Viterbi encoder includes extra information in the transmitted signal to reduce the probability of errors in the received signal that may be corrupted by noise.

VNO – Virtual Network Operator, iDirect VNO

VoIP – Voice over Internet Protocol – A technology for transmitting voice, such as ordinary telephone calls, over packet-switched data networks. Also called IP telephony.

VPN – Virtual Private Network – Network scheme in which portions of a network are connected via Internet, but information sent across the Internet is encrypted. The result is a “virtual network” which is also part of a larger network entity. This allows users to privately share private information over a public infrastructure. VPNs are often used to connect offices.

VSAT – Very small aperture terminal -Refers to small earth stations, usually in the 1.2 to 2.4 meter range. Small aperture terminals under 0.5 meters are sometimes referred to Ultra Small Aperture Terminals (USAT’s).

VSWR – Voltage Standing Wave Ratio – A measurement of mismatch in a cable, waveguide, or antenna system.



Waveguide – A metallic microwave conductor, typically rectangular in shape, used to carry microwave signals into and out of microwave antennas.

Wideband – A system in which multiple channels access a medium (usually coaxial cable) that has a large bandwidth, greater than that of a voice-grade channel; typically offers higher-speed data-transmission capability. Also see broadband.



X.25 – A set of packet switching standards published by the CCITT.