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A	ACM - Adaptive Coding and Modulation Changing modulation and encoding parameters in real time. When a return channel is available from each receiving site to the transmit site, DVB-S2 offers a powerful feature known as Adaptive Coding and Modulation (ACM). With ACM it is possible to dynamically modify the coding rate and modulation scheme for every single frame, according to the measured channel conditions where the frame is received. The return channel is used to dynamically report the receiving conditions at each receiving site. This technique provides exact channel protection and dynamic link adaptation to propagation conditions, targeting each individual receiving terminal. Acquisition Process by which the demodulator adjusts frequency, phase, gain, and code-word synchronization to match that of the incoming carrier. Adaptive Pulse Code Modulation (ADPCM) Is a common coding scheme used to convert voice traffic to a digital bit stream. More efficient than standard voice coding. Alphanumeric A combination of letters and numbers. Amplitude Modulation (AM) The baseband signal is caused to vary the amplitude or height of the carrier wave to create the desired information content. 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. ANMS Audio Network Management System. The software system used to configure and control a satellite-relayed audio broadcast system. An audio broadcast system consists of a hub, an uplink earth station, and one or more audio receivers located at remote sites. The ANMS software to manage the system comprises a set of Windows 3.1 applications: Message Router, Monitor and Control, Network Management, and Security. 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. Antenna Control Units (ACUs) Microprocessor-based terminals which are used to control the movements of a satellite antenna. 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. APSK 16/32-Ary Amplitude and Phase Shift Keying (16-APSK, 32-APSK) It is a digital modulation scheme that conveys data by changing, or modulating, both the amplitude and the phase of a reference signal. It combines both Amplitude-shift keying (ASK) and Phase-shift keying (PSK) to increase the number of bits modulated in one symbol (16-APSK 4 Bits per Symbol). 16-APSK and 32-APSK are standard modulation types in DVB-S2. ARF Alternate Recovery Facility. ASCII (American Standards Code for Information Interchange) A code with seven information signals and one parity check signal. ASTN Automotive Satellite Television Network. Asynchronous Transmission Data transmission in which each information character or byte is individually synchronized, usually by the use of start or stop elements. 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 Signal Audio signals consist of analog information such as music or voice. The audio signals may be either mono, dual mono (stereo), or joint stereo. Audio Subcarrier The carrier between 5 MHz and 8 MHz containing audio (or voice) information inside of a video carrier. Audio/Video Switcher (AVS) These devices are commonly used at video receive only sites to switch between various audio and video sources. The most common configuration is 10 inputs with one output. Autologoff A function that disables access to the ANMS after a prespecified time interval in which no user activity occurs. Automatic Frequency Control (AFC) A circuit which automatically controls the frequency of a signal. Automatic Gain Control (AGC) A circuit which automatically controls the gain of an amplifier so that the output signal level is virtually constant for varying input signal levels. Automatic Voltage Regulator (AVR) These are sometimes used at sites where the input AC power is poor and requires additional regulation. Axial Ratio A measure of circularity of polarization, related to a circular polarized antennas cross polarized antenna-mounted package. Converts the satellite receive band for input into the satellite receiver. AZ/EL Mount Antenna mount that requires two separate adjustments to move from one satellite to another; 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	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. Band A unit for designating a specific frequency or range of frequencies in the electromagnetic spectrum. 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. Basic Cable Channels received by cable subscribers at no extra charge, usually supported by advertising and small per-subscriber fees paid by cable operators. 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 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. Beacon Receiver Is used to receive the satellites beacon. The output of the beacon receiver is typically fed into the antenna controller. 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. 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. Bisync Binary Synchronous Communications (BSC). 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 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). Block Downconversion The use of a fixed frequency first local oscillator, to downconverter an entire satellite band to a lower intermediate frequency for subsequent tuning and demodulation. Block Error Rate The number of blocks with errors divided by the number of blocks of received data. BO Backoff of the power amplifier (not the common street usage), given as a negative number, an amount of power reduced to avoid saturating the input to a satellite transponder. Body-Stabilized The satellite control system which allows the entire body of the satellite to hold a fixed orientation (attitude) toward the earth. Also called three-axis stabilized. Boresight Axis of symmetry of a parabolic antenna. BPSK Binary Phase Shift Keying; a digital modulation scheme used in transmission communications. Broadcasting Using the electronic media to reach wide-area audience. Business Television Corporate communications tool involving video transmissions of information via satellite. Common uses of business television are for meetings, product introductions and training.
C	C Band C-Band is a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 3 to 8 GHz. It was the first frequency band allocated for commercial ground-to-satellite communications. EC (Extended C-Band) Sub-range of C-Band between 3625MHz and 4200MHz for reception and between 5850MHz and 6425MHz for transmission. SEC (Super-Extended C-Band) Sub-range of C-Band between 3400MHz and 4200MHz for reception and between 5850MHz and 6725MHz for transmission. RC (Russian C-Band) Sub-range of C-Band between 3650MHz and 4150MHz for reception and between 5975MHz and 6475MHz for transmission. PC (Palapa C-Band) Sub-range of C-Band between 3400MHz and 3640MHz for reception and between 6425MHz and 6725MHz for transmission. XC (XC-Band) Sub-range of C-Band between 4500MHz and 4800MHz for reception and between 6725MHz and 7025MHz for transmission. LMC (LMI EC-Band) Sub-range of C-Band between 3375MHz and 3950MHz for reception and between 5725MHz and 6475MHz for transmission. 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. Cellular Telephone The current technology that serves the majority of mobile telephone needs. It operates at ultra high frequency, and uses a system of radio "cells" each a few miles across which are interfaced by small, low-power radio-telephones. 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. Churn A cable industry term that takes account of subscriber connects, disconnects, upgrades and downgrades. 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. Clocking Use of clock pulses to control synchronization of data and control characters. C/No Carrier-to-noise ratio measured either at the Radio Frequency (RF) or Intermediate Frequency (IF) Coaxial Cable 1) Cable consisting of one or more tubes, each of which has a wire contained within and insulated from a surrounding conductor. Large numbers of individual circuits can be derived from a coaxial cable by means of carrier and multiplexing techniques. 2) an IF/RF transmission line consisting of a central conductor and a concentric outer conductor separated by a dielectric (nonconducting) material. Codec Coder/decoder system for digital transmission. Collocation 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. Common Fault An M&C message indicating that a device is not operating normally and identifying a specific category of failure. 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 A term used to denote reducing the amount of bandwidth needed to transmit video or audio, thus increasing the capacity of a satellite transponder. Configuration Template These templates control how the remote interprets relay signal information. The relay signals are used to control other devices (cartridge players, etc.) at the remote site. Continuous Wave (CW) A signal consisting of a single frequency. CPU Central Processing Unit. Cross Modulation A form of signal distortion in which modulation from one or more RF carrier(s) is imposed on another carrier. Crystal Controlled This term is used to describe a non-frequency agile up or down converter. These are used in situations where the system will not be changing frequencies. C/T Carrier-to-noise-temperature ratio.
D	DAMA Demand-Assigned Multiple Access - A highly efficient means of instantaneously assigning telephony channels in a transponder according to immediate traffic demands. Data Signal Data signals consist of various specialized transmissions like stock exchange ticker tape information, or intracompany traffic such as inventory, billing, or payroll. Data signals are multiplexed within the normal bandwidth of the channel outroute and output at the receiver to serial printers, another computer, or a similar device. DBS Direct broadcast satellite. Refers to service that uses satellites to broadcast multiple channels of television programming directly to home mounted small-dish antennas. dBi The dB power relative to an isotropic source. dBW The ratio of the power to one Watt expressed in decibels. DCE Data Circuit Terminating Equipment. 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. This should not be confused with a digital coder/decoder known as a CODEC which is used in conjunction with digital transmissions. DDS Direct digital synthesizer. Deemphasis Reinstatement of a uniform baseband frequency response following demodulation. 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. Demodulation The process for retrieving an information signal that has been modulated onto a carrier. Demodulator A satellite receiver circuit which extracts or "demodulates" the "wanted "signals from the received carrier. Deviation The modulation level of an FM signal determined by the amount of frequency shift from the frequency of the main carrier. 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 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. Dish Slang term for antenna. Diumal The orbital movement of a satellite where the spacecraft crosses the Earth's equator twice during each 24-hour period. Doppler Buffer Used to smooth out the periodic frequency variation in the received data rate caused by satellite motion. Doppler Effect A frequency shift which occurs due to the signal delays which take place as an inclined orbit satellite moves closer or further away from the receiving site. Doppler Shift Condition resulting from the slight drifting of satellites which occurs; the effect is a slight difference in data rate clocks at the receive and transmit sites. Downconversion Translation of frequency or a block of frequencies to a lower portion of the electromagnetic spectrum. Downconverter This commonly refers to a device that has an input of C- or Ku-Band and outputs 70 or 140 MHz. Other conversions are also possible. The output typically has a bandwidth of 36 MHz when 70 MHz is used and 72 MHz when 140 MHz is used. Downlink To receive from a satellite; also, the dish used for reception. Downlink Frequency The frequency at which the satellite broadcasts the combined channels to the receivers. 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. 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 Operation Method in which transmission is possible simultaneously in both directions of a telecommunications channel. Generally, two frequencies in radio communications are required. DVB-DSNG Digital Satellite Television. Satellite 1st generation is a standard used for satellite broadcasting by mobile units. DVB-S Digital Satellite Television. Satellite 1st generation is a standard used for satellite broadcasting. Standardised modulations are BPSK and QPSK with convolutional inner and Reed Solomon (e.g.188/204) outer coding. DVB-S2 DVB-S2 (Digital Satellite Television. Satellite 2nd generation) is an enhanced specification to replace the DVB-S standard, ratified by ETSI (EN 302307) in March 2005. DVB-S2 is based on the DVB-S and the DVB-DSNG standards. The system allows transmission / reception of audio?video and/or data streams, using QPSK or 8PSK or 16/32-APSK modulation with concatenated LDPC and BCH coding. A single FEC datagram may be 64800 bits (normal) or 16200 bits (short). Two new key features were added to DVB-S: VCM and ACM.
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 the.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 is today 13 to 18 meters or 40 to 60 feet. EC (Extended C-Band) Sub-range of C-Band between 3625MHz and 4200MHz for reception and between 5850MHz and 6425MHz for transmission. 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. Echo Suppression Refers to the cancellation of any reflected signals in a communications channel, maritime vessel portable terminals. Eclipse Period when the satellite passes into the Earth's (or Moon's) shadow, when power must be drawn from storage batteries. Eclipse protected Refers to a transponder that can remain powered during the period of an eclipse. 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. EI/Az (EI over Az) An antenna mount providing independent steering in azimuth and elevation. 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. Electromagnetic Spectrum The entire range of wavelengths of electromagnetic radiation-including visible light-which extend from gamma rays to microwaves and radio waves, all of which travel at the speed of light (186,000 miles per second or 300,000,000 meters per second). 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. Encoder A device used to electronically alter a signal so that it can only be viewed on a receiver equipped with a special decoder. 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. EOL End of Life of a satellite. Ephemersis Data This is data used to describe the orbit of a satellite. This data is used by antenna controllers to track satellites without having to monitor beacon signals. This method of tracking is referred to as Program Tracking. 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. Exciter This is a device that accepts as input audio and video signal and generates a FM modulated carrier in the band of interest. Extended Ku-Band Tx - between 13.75GHz and 14.25GHz.
F	Faraday Rotation When peak sunspot activity highly charges the Earth's ionosphere, the vectors of linearly-polarized satellite signals can be rotated or "twisted" through interaction with the Earth's atmosphere. F/D Ratio of antenna focal length to antenna diameter. A higher ratio means a shallower dish. FDM Frequency Division Multiplex. 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 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. Feedhorn A satellite TV receiving antenna component that collects the signal reflected from the main surface reflector and channels this signal into the low-noise amplifier (LNA) FEP Front End Processor. FM Frequency Modulation - A modulation method whereby the baseband signal varies the frequency of the carrier wave. FM Threshold That point at which the input signal power is just strong enough to enable the receiver demodulator circuitry successfully to detect and recover a good quality television picture from the incoming video carrier. Using threshold extension techniques, a typical satellite TV receiver will successfully provide good pictures with an incoming carrier noise ratio of 7db. Below the threshold a type of random noise called "sparkles" begins to appear in the video picture. In a digital transmission, however, signal is sudden and dramatically lost when performance drops under the threshold. Focal Length Distance from the center feed to the center of the dish. Focal Point The area toward which the primary reflector 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. Formats Formats are specific, user-determined combinations of the signals available on each channel (audio, data, and relay) that a receiver can be authorized to receive. Formats allow you to mask off those parts of the channel signal (audio, data, or relay) that you do not want the receiver to be able to process. 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. Frequency Reuse A technique which maximizes the capacity of a telecommunications satellite through the use of spatially-isolated beam antennas and/or the use of dual polarities. Frequency Shift Keying (FSK) A way in which binary levels are expressed with a shift in frequency. FRU - Field Replaceable Unit A circuit card containing a microcontroller that communicates with another on the monitor and control card; referred to as option cards.
G	Gain A measure of amplification expressed in dB. Gaussian Noise White noise uniform across the entire range of frequencies that is introduced into a transmission channel from the environment; may interfere with a carrier signal. Also referred to as background electrical noise. May be abbreviated as WGN (white Gaussian noise). 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 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 Equatorial (Clarke) Orbit (GEO) Unique orbit in which a body can remain essentially stationary elative to earth coordinates. Geosynchronous Orbit (GSO) Satellites in geosynchronous orbit travel around the earth in an area approximately 22,300 miles from the surface at the same rate that the earth turns, therefore completing one revolution every 24 hours. 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. 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. Guard Band An unused spectra of frequencies which lie above and below each transponder. The guard band helps to prevent adjacent communications signals from interfering with one another. Guard Channel Television channels are separated in the frequency spectrum by spacing them several megahertz apart. This unused space serves to prevent the adjacent television channels from interfering with each other.
H	Half Transponder A method of transmitting two TV signals through a single transponder through the reduction of each TV signal's deviation and power level. Half-transponder TV carriers each operate typically 4 dB to 7 dB below single-carrier saturation power. 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. 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. High Definition Television (HDTV) Various technical systems providing a finer and wider TV picture, usually with twice as many scanning lines as standard TV. High Power Amplifier (HPA) Equipment used to amplify signals. HPC (High-Power Converter) VSAT RF equipment that upconverts and amplifies transmit signals. 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. Hub Device Any device that resides at the hub site and which is directly controlled by the ANMS. Hybrid Satellite A satellite which carries two or more different communications payloads (i.e., C-band and Ku-band).
I J	I/O Input/Output IF (or i.f.) Intermediate Frequency (in a receiver). IM Intermodulation noise or distortion. The undesirable result when a non-linear amplifier is forced to carry multiple signals simultaneously. Inclination The angle between the orbital plane of a satellite and the equatorial plane of the earth. Indoor Unit (IDU) The indoor portion of a VSAT system. 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. INTELSAT The International Telecommunications Satellite Organization operates a network of satellites for international transmissions. 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. 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. JPEG ISO Joint Picture Expert Group standard for the compression of still pictures.
K	K-band The frequency spectrum 10.9 to 36 GHz. Ka Band The frequency range from 18 to 31 GHz. Ku-Band This symbol refers to "K-under" - in other words, the band directly below the K-band. In radar applications, it ranges from 10 to 18 GHz. The Sub-ranges variety for transmission only. For receive the range between 10.95 and 12.75GHz is used in satcom. Standard Ku-Band Tx - between 14.0GHz and 14.5GHz. Extended Ku-Band Tx - between 13.75GHz and 14.25GHz. Super-Extended Ku-Band Tx - between 13.75GHz and 14.50GHz. 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 type of high-power amplifier which uses a special beam tube. Ksps Thousand symbols per second.
L	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. Latitude The distance, expressed in degrees, from the Earth's equator to points north or south. The equator is assigned a value of 0 degrees: North and South poles are 90 degrees. Leased Line A dedicated circuit typically supplied by the telephone company. LHCP (or LCP) Left Hand Circular Polarization. LLC Logical Link Control. LMC (LMI EC-Band) Sub-range of C-Band between 3375MHz and 3950MHz for reception and between 5725MHz and 6475MHz for transmission. LNA Low Noise Amplifier - is a special type of amplifier used in communication systems to amplify signals captured by an antenna. LNB Low Noise Block - consists of a LNA and a downconverter with RF input and IF (normally L-band) output. LNC Low Noise Converter - consists of a LNA and a downconverter with RF input and IF output. Even if it is not an official standardization, "LNC" became the term for LNB`s used with Transceivers. LNF A combination of a feed, automatic polarizer and a low noise amplifier in a common package. LO Local Oscillator. Local Area Network (LAN) Standard communications architecture, usually referring to computer communications. Longitude The distance in degrees from one meridian to any other is defined in terms of degrees of longitude (Also see meridian and longitude). Look Angle The angle between the horizon and the amount an earth station antenna is tilted up to receive signals from, or send signals to, a satellite. Loopback Test in which the routing signal is directed only through the designated equipment or portions of the satellite link to isolate setup problems. Loop Timed System System using a single clock source for the entire point-to-point, round-trip circuit. This circuit extends from the master station through a satellite relay to a slave station and then back through a satellite to the master station. LOS Line of Sight. Low Earth Orbit (LEO) Satellites placed in orbit less than 22,300 miles above the earth. 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. Low Noise Converter (LNC) Part of the earth station transmission subsystem consisting of an LNA and downconverter. Low Power Satellite Satellite with transponder RF power below about 30 watts.
M	MAC (A, B, C, D2) Multiplexed analog component color video transmission system. Subtypes refer to the various methods used to transmit audio and data signals. Margin The amount of signal in dB by which the satellite system exceeds the minimum levels required for operation. Master Antenna Television (MATV) An antenna system that serves a concentration of television sets such as in apartment buildings, hotels or motels. Mbps One million bits per second. MCPC Multiple channels per carrier. Mean Time Between Failure (MTBF) Average length of time for which a system, or a component of a system, works without fault. Mean Time To Respond (MTTR) Average time taken to arrive on site to correct a fault in a system or component. Medium Power Satellite Satellite with transponder RF power in the region of 30 to 60 watts. Megahertz (MHz) Refers to a frequency equal to one million Hertz, or cycles per second. Meridians Lines circling from pole to pole which cross each of the 360 degrees which comprise the Earth's equator. MESH This is a system layout that allows all of the earth stations to communicate with all other earth stations in the network. 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. Modem (Modulator/Demodulator) Equipment that converts between digital data and audio tones for transmission and reception over analog channels. Modified Polar Mount A satellite antenna mount, the design of which has been created to track the geostationary satellite arc by means of a single antenna movement called the actuation. This design, which is based on the True Polar Mounts used by astronomers' telescopes, has two modified adjustments which correct for the closer distances of satellites versus celestial objects and the latitude for each receiving site. 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. Monitor and Control (M&C) Equipment that monitors and controls Skystar network traffic and hub and VSAT equipment status. MTBF Mean time between failures. Multiplexing Techniques that allow a number of simultaneous transmissions over a single circuit. MUX Multiplexer equipment.
N	Narrowcasting Using the electronic media to reach a specific audience. 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. Noise Temperature Noise measurement of a system, as the absolute temperature of a resistive source delivering equal noise power. Expressed in (degrees) Kelvin for C-band amplifiers. NTSC The typical video signal format commonly used in the US and Japan.
O P Q	Offset-Fed Antenna An antenna whose reflector forms only part of a paraboloid of revolution, usually excluding the pole or apex, such that a front feed causes no aperture blockage. Open Loop Mode in which communication is sent in one direction only from the controller to the slave; in this mode, the slave does not respond to the controller, nor does it send any type of messages informing the controller of commands received, nonexecuted commands, or error conditions. Orbit The path along which a communications satellite moves in relationship to the Earth's surface. This path can either be parallel to the Earth's polar axis (polar orbit), parallel to the Earth's equator (equatorial) or inclined. Orbital Period The time that it takes a satellite to complete one circumnavigation of its orbit. Orthogonal Mutually at right angles (e.g., horizontal and vertical polarization, or right and left-hand circular polarization). Outdoor Unit (ODU) The other major component of a remote VSAT electronics package. PA/TDMA Permanent Assignment Time Division Multiple Access. Packet Switching Data transmission method that divides messages into standard-sized packets for greater efficiency of routing and transport through a network. PAD Slang for satellite transponder channel attenuation, it is an electronic device that adds electrical resistance to a circuit to protect a transponder from signals that are too strong. PAL - Phase Alternation System The German developed TV standard based upon 50 cycles per second and 625 lines. PANDA This is a trade name used by Wegener to describe an audio compression scheme that is commonly used to transmit large numbers of audio subcarriers. 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. Passthrough A low-level mnemonic command sent to a selected device from the M&C application. PC (Palapa C-Band) Sub-range of C-Band between 3400MHz and 3640MHz for reception and between 6425MHz and 6725MHz for transmission. Personal Communications A term to describe the use of wireless communications to extend telephone service to a person, regardless of location, rather than to a fixed location. Phase-Locked Loop (PLL) A type of electronic circuit used to demodulate satellite signals. Planar Array Flat satellite antenna composed of a grid work of tiny resonant elements. PN Pseudonoise. Pointing Error The amount of difference between the direction in which the antenna is pointing, the beam focus or "boresight" of the antenna's main beam and the actual direction of the satellite. 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. Polling Periodic query of device status. Polling Rate The frequency at which the Message Router sends out polling messages to hub devices. Prime Focus The focal point of a paraboloid reflector. A feed system placed at that point. PROCS&OIs Procedures and Operating Instructions. Propagation Delay The delay from the time a signal is sent until it is received; caused by distance to and from the satellite. Protocol Any set of standard procedures that permits devices to intercommunicate. PSK Phase Shift Keying. 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. PVC Permanent Virtual Circuit. QPSK - Quadrature Phase Shift Keying System of modulating a satellite signal.
R	R/O (Receive Only) Referring to an earth station that receives transmissions only and does not transmit. RA Random Access. RA/TDMA Random Access Time Division Multiple Access. Radio Frequency Interference (RFI) A term used to denote apparent disturbance or disortion to satelite signals. Rain Outage Loss of signal at Ku or Ka Band frequencies due to absorption and increased sky-noise temperature caused by heavy rainfall. RC (Russian C-Band) Sub-range of C-Band between 3650MHz and 4150MHz for reception and between 5975MHz and 6475MHz for transmission. 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 A secondary system of backup equipment that performs similarly to a primary system, thereby preventing network downtime and system outages. Reed-Solomon Codec Block-oriented coding system that is applied on top of standard Viterbi coding to correct the bulk of the data errors that are not detected by the other coding systems, significantly reducing the bit error rates. Available as an option module card. Relay Relay (cue) signals are the binary (ON/OFF) controls carried by a channel that operates relay contacts within the receiver. Response Time The elapsed time between the end of an inquiry and the beginning of the response. RF Radio Frequency 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. RHCP (or RCP) Right-Hand Circular Polarization. Routing The process of selecting the correct circuit path for a message. RPM Revolutions Per Minute.
S	S-band Satellite downlinks in the region of 2.6 GHz. Satellite A sophisticated electronic communications relay station orbiting 22,237 miles above the equator moving in a fixed orbit at the same speed and direction of the earth (about 7,000 mph east to west). SAC (Satellite Access Controller) Skystar equipment that contains the satellite transmission facility components and data network components. Saturation Flux Density (SFD) This is a term used to describe the input sensitivity of a satellite. 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. SCC - Satellite Control Channel Generally used for monitoring purposes. Main application is monitoring and controlling remote earth station equipment from a central hub facility. SCPC Single channel per carrier. 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. SEC (Super-Extended C-Band) Sub-range of C-Band between 3400MHz and 4200MHz for reception and between 5850MHz and 6725MHz for transmission. Sidelobe Off-axis response of an antenna. Sidereal Time The period of the North-South motion of an inclined orbit satellite which is equivalent to 23 hours, 56 minutes, and 4 seconds in mean solar time. 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. Single Axis Tracking An antenna positioning system which requires one independent movement in either Declination or Elevation in order to maintain its acquisition of an inclined orbit satellite. 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. Snow A form of noise picked up by a television receiver caused by a weak signal. Snow is characterized by alternate dark and light dots appearing randomly on the picture tube. To eliminate snow, a more sensitive receive antenna must be used, or better amplification must be provided in the receiver (or both). Solar Array A network of solar cells which generate electricity when exposed to sunlight. Solar Eclipse When the earth shadows the satellite's solar array from the sun. 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. Sparklies Popular term for impulse noise spikes visible as black or white spots or streaks in the TV picture at CNR values close to threshold. Spectral Inversion Condition typically caused by RF equipment that uses the image of the modem's output spectrum instead of the true spectrum. (Note: There is nothing wrong with systems that do this; simply compensate for the condition.) Example: A 70 MHz modem IF output also contains a mirror-like image at -70 MHz: If the RF equipment is designed to use the -70 MHz image and the receive RF does not similarly invert the signal (that is, undo the inversion), then there is a spectral inversion and the signal cannot be recognized by the receiver. Spectrum The range of electromagnetic radio frequencies used in transmission of voice, data and television. Spherical Simple geometry for fee-steerable or multiple beam antenna. 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. Spin Stabilized The satellite control system which spins the body of the satellite while the antenna s rotated in the opposite direction in order to keep it pointed toward the earth. 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. SSPA Solid state power amplifier. A VSLI solid state device that is gradually replacing Traveling Wave Tubes in satellite communications systems because they are lighter weight and are more reliable. Standard Ku-Band Tx - between 14.0GHz and 14.5GHz. Stationkeeping Minor orbital adjustments that are conducted to maintain the satellite's orbital assignment within the allocated "box" within the geostationary arc. Step Track A tracking method used by many antenna controllers in which the antenna "follows" the satellite. Storage Orbit A predetermined orbit initiated during the launch phase. This orbit is calculated to take advantage of all natural forces impinging on the satellite - including solar winds and the effects of the gravitational fields of the Earth and Moon - so that as time goes on the inclination lessens without requiring any expenditure of station keeping fuel. At some predetermined time, the amount of inclination will reach zero degrees or actual geostationary operation. 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. Subsatellite Point The longitudinal point over the Earth's equator to which a communications satellite has been assigned by the international Frequency Registration Board of the ITU. Sun Outage When the sun passes behind a satellite in relation to the earth, and the sun's energy momentarily interferes with the satellite signals. Happens two times each year dring spring and fall equinox. Super-Extended Ku-Band Tx - between 13.75GHz and 14.50GHz. Superstation A local TV station whose signal is satellite delivered to cable systems and backyard antennas across the country. Synchronous When characters or bits are transmitted at a fixed rate with the transmitting and receiving devices synchronized. 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.
T	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. 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. Telemetry The use of telecommunications for automatically indicating or recording measurements at a distance from the measuring instrument. Telemetry, Tracking and Control (TT&C) Means of accessing the control systems in a spacecraft in order to position and configure the spacecraft; or the facility which monitors and controls the health of a satellite. Test Loop Translator (TLT) Test equipment used to simulate the performance of a satellite at the earth station. Three-Axis Stabilization A means of keeping a satellite stable and constantly pointed at a single point on the earth. Also known as body-stabilized. Threshold In an FM system, the value of CNR at which the linear relationship between CNR and demodulated signal SNR breaks down. (Also see Sparklies) Threshold Extension Techniques for reducing the CNR value at which threshold effects occur. TI - Terrestrial Interference Interference to satellite reception caused by ground based microwave transmitting stations. Timeout An M&C response message which means that the polled device did not respond within the allotted time period. Tracking Using earth-based equipment to follow a satellite's position. Transceiver A combination of transmitter and receiver, integrates a Power Amplifier (SSPA) and Up- and Downconverter in one single outdoor box, designed to interface with any 70/140MHz modem. It upconverts the 70/140MHz IF Input signal to the RF signal for transmission and downconverts the received from satellite RF signal to a 70/140MHz signal to use by demodulator. Transfer Orbit An intermediate elliptical orbit used to reach geosynchronous orbit, where the apogee is the same altitude as the final operating orbit. 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. Transponder Access Control System (TACS) Computer-controlled spectrum monitoring system that measures downlink signal parameters. 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. TWTA Traveling wave tube amplifier.
U V W	UHF The spectrum 300 MHz-3 GHz. Terrestrial broadcast television occupies 470-890 MHz. The 620-790 MHz band is allocated for community DBS downlinks in developing countries and remote areas. Upconverter A device used at an earth station to convert from 70 to 140 MHz to either C- or Ku-band frequencies. Uplink The earth station used to transmit signals to a satellite Uplink Frequency The frequency at which the earth station's uplink transmitter sends the combined channels to the satellite. UPS Uninterrupted Power Supply. VCM - Variable Coding and Modulation Optimizes the transmission parameters for various users. In DVB-S2 each frame that is transmitted, contains information on how that frame is modulated and coded in its header. A VCM capable demodulator will read this information from the header of each frame and use it to demodulate and decode that frame. This allows varying the modulation and coding parameters of each transmitted frame within the DVB-S2 stream since decoding is done on a frame-by-frame basis. A unique feature of the DVB-S2 standard is that multiple services can be transmitted on the same carrier, each using their own modulation scheme and coding rate. VCM is particularly powerful when different services do not need the same protection level or different services are intended for different stations with different average receiving conditions. Virtual Private Network (VPN) A Capability that allows users to create their own private information network. Viterbi A standard form of FEC decoding; the other standard form of FEC decoding is Sequential. Volatile Volatile memory; command Parameters that direct the modem to perform a real-time function or enter a test mode are stored in volatile memory and are not remembered by the CM701 after power is cycled or a reset. VSWR Voltage Standing Wave Ratio. A measurement of mismatch in a cable, waveguide, or antenna system. 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) Waveguide A metallic microwave conductor, typically rectangular in shape, used to carry microwave signals into and out of microwave antennas.
X Y Z	X.25 A set of packet switching standards published by the CCITT. XC (XC-Band) Sub-range of C-Band between 4500MHz and 4800MHz for reception and between 6725MHz and 7025MHz for transmission. XPOL Cross-Polarization; allows two separate signals, one vertical and the other horizontal, to exist on the same frequency and pass independently of each other. Yagi A communications antenna consisting of a main metal boom that supports numerous quarterwave elements. Used for reception of S-band TV signals from Arabsat.