A

ABR – Audio Broadcast Receiver. Term used by Radyne ComStream to identify a family of audio receive-only products such as the ABR200 and the ABR202.

Access – Service provided by local exchange carriers (or alternate access providers) that connects an inter-exchange carrier with its customers. Switched access provides such service over the public switched network; special access provides dedicated access for private-line services and sometimes at the closed end of switched services.

ADC – Analog-to-Digital Conversion. Process of converting analog signals to a digital representation. DAC is the reverse translation.

ADSL – Asymmetric Digital Subscriber Line. Broadband technology used over existing terrestrial wires to deliver high bandwidth to homes.

Affiliate – Independently owned broadcast station that contracts with a network to air that network's programming.

Airtime – Time at which an event is broadcast.

AM – Amplitude Modulation. Process in which baseband signal varies the amplitude or height of the carrier wave to create the desired information content.

Amplifier – Device used to boost the strength of an electronic signal.

Analog – Method of signal transmission in which information is relayed by continuously altering the waveform of the electromagnetic current. Compare with 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. Used in AM radio and most voice telephone circuits.

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

Antenna – 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 - Cross section of antenna exposed to the satellite signal.

Apogee - Point in an elliptical satellite orbit that is farthest from the surface of the earth. Geosynchronous satellites that 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.

ASIC - Application Specific Integrated Circuit. Integrated circuit designed for or by the end-user, specifically for a proprietary application.

ATM - High-speed packet switching technology. Information is organized into standard 53 byte cells. Data are sent character by character with a start and stop pulse for each one. These factors allow very efficient and extremely high throughput levels. Additionally, this high-speed information transfer allows dynamic allocation of bandwidth to meet the changing requirements of the user's applications automatically.

Attenuation - Loss in power of electromagnetic signals between transmission and reception points.

audio subcarrier - Carrier between 5 MHz and 8 MHz containing audio (or voice) information inside a video carrier.

B

Backhaul - Point-to-point transmission of television signals that will be further enhanced by commercial insertion, post production, then transmitted to the end user, cable system, or broadcast affiliate.

Bandwidth - Range of frequencies in a channel. Greater the bandwidth, the greater the capacity. Voice transmission by telephone requires a bandwidth of about 3000 cycles per second (3KHz); 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 television signals in order to prevent interference. Often used to state the capacity of analog circuits.

Baseband - Basic direct output signal in an intermediate frequency obtained directly from a television camera, satellite television receiver, or video tape recorder. Can be viewed only on studio monitors. Requires a modulator to convert the baseband signal to one of the VHF or UHF television channels in order to display on a conventional television set.

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 - Rate of data transmission based on the number of signal elements or symbols transmitted per second. Most digital signals are characterized in bits per second (bps) and five baud being roughly equivalent to one alphanumeric character.

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

Bird - Slang for communications satellite.

Bit - Single digital unit of information

Bit rate - Speed of a digital transmission measured in bits per second.

Block down converter - Device used to convert the 3.7 to 4.2 GHz signal down to UHF or lower frequencies (1 GHz and lower).

BPSK - Binary Phase Shift Keying. Digital modulation scheme used in transmission communications.

Bps - bits per second.

Broadband - Communications channel with a bandwidth broader than a voice-grade channel.

Broadcasting - Using the electronic media to reach a 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.

Byte - Eight binary digits, the same as eight bits.

C

C band - Band of frequencies used for satellite and terrestrial communications. Range of frequencies from 4 to 6 gigaHertz (billion cycles per second) is used by most communications satellites. 3.7 to 4.2 GHz satellite communication band is used as the downlink frequencies in tandem with the 5.925 to 6.425 GHz band that serves as the uplink. Requires larger ground antennas, usually twelve feet in diameter, for television reception.

Cable headend - point where cable TV systems receive programming for distribution across their network.

Carrier - Basic radio, television, or telephony center of frequency transmit signal. 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 - 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.

CATV - Community Antenna Television. System uses a single large antenna to supply a community or building with high-quality reception via cable.

CCIR - International Radio Consultative Committee.

CCITT - International Telegraph and Telephone Consultative Committee.

CDMA - Code division multiple access. Refers to a multiple-access scheme in which stations use spread-spectrum modulations and orthogonal codes to avoid interfering with one another.

Cellular telephone - Technology that serves mobile telephony. Operates at ultra-high frequency and uses a system of radio "cells" each a few miles across, which are interfaced by small, low-power radiotelephones.

Channel - 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. Also a telecommunications "pipe" of a given speed between two network locations. DS-0, DS-1 and DS-3 channels carry speeds of up to 64 kbps, 1.54 Mbps, and 45 Mbps, respectively.

Circuit - Connection of facilities that provides telecommunications service of a given type and speed between two or more points.

Circular polarization - Unlike many domestic satellites that use vertical or horizontal polarization, the international Intelsat satellites transmit their signals in a rotating corkscrew-like pattern as they are downlinked 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.

Clarke orbit - That circular orbit in space 22,237 miles from the surface of the earth at which geosynchronous satellites are placed. 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/N - Carrier to Noise Ratio. Ratio of received carrier power and noise power in a given bandwidth, expressed in dB. Directly related to G/T and S/N. In a video signal the higher the C/N, the better the received picture.

CO - Central Office. Building in which telephone companies locate their switching equipment and terminate their circuits. Synonym for Exchange.

Codec - Coder/decoder. Device that converts analog signals to digital signals or vice versa.

Co-location - Ability of multiple satellites to share the same approximate geostationary orbital assignment frequently because different frequency bands are used.

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

Compression - Means by which amount of bandwidth needed to transmit video or audio is reduced, thus increasing the capacity of a satellite transponder.

COMSAT - Communications Satellite Corporation, exclusive manager for INTELSAT.

Conditional access - Electronic method of limiting access to a service or services by an end-user. Conditional access methodologies exist in several industry standards such as NDC, Irdeto, etc.

Conus - Contiguous United States. All states except Alaska and Hawaii.

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

Custom product - Product designed and built by the vendor exclusively for the customer per the customer's specifications. Also called specialty product or application.

CW - Continuous Wave. Signal consisting of a single frequency.

D

DB - Decibel. Standard unit used to express the ratio of two power levels. Used in communications to express either a gain or loss in power between the input and output devices.

DBm - Decibel based on 1 milliwatt. Ratio of two power levels, in which the second is one milliwatt.

DBS - Direct Broadcast Satellite. Service that uses satellites to broadcast multiple channels of television programming directly to home mounted small-dish antennas.

DCE - Data Communications Equipment.

DDS - Digital Data Service. A 56 or 64kbps digital private line channel.

Decibel - see dB.

Declination - 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 - Television set-top device that enables a home subscriber to convert an electronically scrambled television picture into a viewable signal. Should not be confused with a digital coder/decoder known as a CODEC, which is used with digital transmissions.

Delay - Time it takes for a signal to go from sending station through satellite to receiving station. Delay for a single-hop satellite connection is approximately one-quarter of a second.

Demodulation - Process for retrieving an information signal that has been modulated onto a carrier.

Demodulator - Satellite receiver circuit that extracts or "demodulates" the wanted signals from the received carrier.

Deviation - Modulation level of an FM signal determined by amount of frequency shift from the frequency of the main carrier.

Diagnostic tests - Tests provided by the vendor, the customer, or a third party used to check equipment malfunctions and identify faulty components. At a minimum, the customer's diagnostic test is performed on each unit prior to installation. The same test can be performed on a unit that has been operating successfully in the event of a suspected failure.

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 communications technology permits higher transmission speeds and a lower error rate than analog technology. As an analog signal is received and amplified at each repeater station, any noise is also amplified. A digital signal, however, is detected and regenerated (not amplified), and any noise is lost unless it corresponds to a value that the regenerator interprets as a digital signal.

Dish - Slang for antenna.

DLM - Data line multiplexer (option).

Downlink - Process of receiving from a satellite. Also the dish used for reception.

DS-0 - Quantum unit of fiber-optic transmission capacity; a channel with a bandwidth of 64 Kbps, about the capacity used to carry a single voice conversation. DS-1 - Digital circuit with standardized operating characteristics and transmitting capacity equivalent to 24 voice-grade (64 Kbps) circuits (1.544 Mbps). Circuits are used to carry moderate volumes of traffic by both end users and carriers. DS-2 - Digital circuit with capacity equivalent of four DS-1 circuits (96 voice-grade circuits, 6.312 Mbps). Circuits are much less common than DS-1 or DS-3 circuits in the U.S., but are frequently used in Japan. DS-3 - Digital circuit with standardized operating characteristics and transmitting capacity equal to 28 DS-1 circuits (672 voice-grade circuits, 44.736 Mbps). Circuits are often used to carry high volumes of long-distance traffic or to provide resold DS-1 or voice-grade private-line service. Large companies also use DS-3s for internal communications. DSI - Digital Speech Interpolation. Means of transmitting telephony. Is about three times more efficient based on the principle that people are talking only about 40% of the time.

DSS® - Direct Satellite System. Proprietary DBS system from DIRECTV, Inc., used primarily in North America.

DVB - Digital Video Broadcast. Standard of direct-to-home transmission typical of all areas of the world outside of North America. Specifies system parameters for an "open" specification.

E

Earth station - 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.

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. Modern digital echo cancellers largely eliminate this.

Echo suppression - See echo canceller.

Edge of coverage - Limit of a satellite's defined service area. Defined as being 3 dB down from the signal level at beam center. Although reception may still be possible beyond the -3dB point.

EIRP - Effective Isotropic Radiated Power. Describes the strength of the signal leaving the satellite antenna or the transmitting earth station antenna. 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 - 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 tilted to a point directly overhead, the satellite antenna would have an elevation of 90 degrees.

Encoder - Device used to electronically alter a signal so it can only be viewed on a receiver equipped with a special decoder.

Encryption - Coding or otherwise scrambling transmission content, making it unusable or unseeable to viewers who do not have the specified decoding equipment. Primarily used for content security and to prevent signal theft.

End-to-end service - Inter-exchange service that extends from customer premises to customer premises, consisting of local loops on each end and an IXC leg in the middle.

Equatorial orbit - Orbit with a plane parallel to the earth's equator.

ESC - Engineering Service Circuit. 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 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 that 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.

F

FCC - Federal Communications Commission.

FDM - Frequency Division Multiplex.

FDMA - Frequency Division Multiple Access. Refers to the use of multiple carriers within the same transponder within which each uplink has been assigned frequency slot and bandwidth. Usually used in conjunction with Frequency Modulation.

FEC - Forward Error Correction. Technique that uses redundant information passed with the actual data to detect and correct errors without any retransmission of the data bits in error. Several standard FEC types exist within the communications systems produced by Radyne ComStream, including Trellis, Viterbi, Sequential, and Viterbi/Reed Solomon concatenated.

Feed - Transmission of video programming from a distribution center. Also, feed system of an antenna. Feed system may consist of a subreflector plus a feedhorn or a feedhorn only.

Feedhorn - 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)

Fiber optics - Technology that involves sending laser light pulses via glass strands to transmit digital information. Strands, although about the thickness of a human hair, have nearly unlimited capacity. Bundled in protective sheathing about the diameter of a human thumb, fiber can carry more information than copper cable the diameter of a utility pole.

FM - Frequency Modulation. Modulation method whereby the baseband signal varies the frequency of the carrier wave.

Focal length - Distance from the center feed to the center of the dish.

Focal point - Area toward which the primary reflector directs and concentrates the signal received.

Footprint - Map of signal strength showing EIRP contours of equal signal strengths as they cover the earth's surface. Different satellite transponders on the same satellite 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. Actual EIRP levels of the satellite, however, tends to decrease slowly as the spacecraft ages.

Frequency - Number of times an alternating current goes through its complete cycle in one second of time. One cycle per second is also referred to as one Hz; 1000 cycles per second, one KHz; 1,000,000 cycles per second, one MHz: and 1,000,000,000 cycles per second, one GHz.

Frequency coordination - Process to eliminate frequency interference between different satellite systems or between terrestrial microwave systems and satellites. In the U.S., relies on a computerized service using an extensive database to analyze potential microwave interference problems between organizations using the same microwave band. As the same C-band frequency spectrum is used by telephone networks and CATV companies, they often obtain a frequency coordination study to determine if any problems will exist.

FRU - Field Replaceable Unit. Term used to indicate an element of a system that can be replaced or added by a semiskilled end-user.

FSS - Fixed Satellite Service.

Full duplex - Transmission that occurs in both directions simultaneously over the communications media.

G

Gain - Measure of amplification expressed in dB.

GEO - Geosychronous Satellite. Satellite located at 22,282 miles above the equator that appears to be stationary from a fixed point on the earth. Round-trip time from the earth to the satellite and back is approximately 0.25 seconds. Typical frequency bands are C-Band (4-6 Ghz) and Ku-Band (12-14 Ghz).

Geostationary - Geosynchronous satellite angle with zero inclination so the satellite appears to hover over one spot on the earth's equator.

Geosynchronous - Clarke circular orbit above the equator. For the earth, this point is 22,237 miles above the surface.

GHz - Gigahertz. One billion cycles per second. Signals operating above 3 GHz are known as microwaves. Above 30 GHz they are known as millimeter waves. Above the millimeter rate, waves signals begin to take on lightwave characteristics.

Global beam - Antenna downlink pattern used by the Intelsat satellites and covers one-third of the globe. Beams are aimed at the center of the Atlantic, Pacific and Indian Oceans by the respective Intelsat satellites, which enables nations on both sides of the oceans 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 covering only the continental United States. Therefore, earth stations receiving global beam signals need antennas much larger in size.

GSO - Geosynchronous Orbit. Satellites in geosynchronous orbits around the earth in an area approximately 22,300 miles from the surface at the same rate that the earth turns, which allows them to complete one revolution every 24 hours.

Guard channel - Unused frequency space between television channels that prevents adjacent television channels from interfering with each other.

H

Half transponder - Method of transmitting two TV signals through a single transponder by reducing each TV signal's deviation and power level. Half-transponder TV carriers 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 includes antennas, preamplifiers, frequency converters, demodulators, and other related equipment to amplify, filter, and convert incoming broadcast TV signals to cable system channels.

HDTV - High Definition Television. Technical systems that provide a finer and wider TV picture, usually with twice as many scanning lines as standard TV.

HPA - High Power Amplifier. Equipment used to amplify signals.

Hub - Network operations center. All communications to, from, and between micro terminals must flow through the hub.

Hybrid satellite - Satellite that carries two or more different communications payloads; i.e., C-band and Ku-band.

Hz - Hertz. Basic measure of radio frequency characteristics. An electromagnetic wave completes a full oscillation from its positive to its negative pole and back in what is called a cycle. A single Hz is equal to one cycle per second.

I

IBS - INTELSAT Business Services.

IFRB - International Frequency Registration Board.

Inclination - Angle between the orbital plane of a satellite and the equatorial plane of the earth.

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

IntelliCasttm - Family of Radyne ComStream data broadcast receivers. Includes models 101, 401VR, and 801.

INTELSAT - International Telecommunications Satellite Organization. Agency that operates a network of satellites for international transmissions.

Interference - Energy that tends to interfere with the reception of 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. 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 - Hypothetical omni directional point-source antenna that serves as an engineering reference for the measurement of antenna gain.

ITU - International Telecommunication Union.

J

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

K

K - Kelvin. Temperature measurement scale used in the scientific community. Zero K represents absolute zero and corresponds to -459 degrees Fahrenheit or -273 Celsius. Thermal noise characteristics of LNA are measured in Kelvins.

Ka band - Frequency range from 18 to 31 GHz.

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

KHz - KiloHertz. Unit of frequency equal to 1,000 Hz.

Klystron - Type of high-power amplifier that uses a special beam tube.

Ku band - Frequency range from 10.9 to 17 GHz. Increasingly used by communications satellites. Requires smaller ground antennas, usually four feet in diameter.

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.

LAN - Local Area Network. Standard communications architecture, usually referring to computer communications.

LEO - Low Earth Orbit satellite. Satellites that are not stationary from a fixed point on earth and have the lowest orbit of all communication satellites. Must either be tracked or use a frequency band and access methodology that allows access to the satellite with a non-directional antenna. Most handset-to-satellite systems are based on LEO satellites using L-Band.

Leased line - Dedicated circuit typically supplied by the telephone company.

LNA - Low Noise Amplifier. 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. LNA contributes the least amount of thermal noise to the received signal.

LNB - Low Noise Block Down converter. Combination Low Noise Amplifier and down converter built into one device attached to the feed.

Local access - See local loop.

Local loop - Dedicated circuit between a customer premise and a CO. Sometimes used to include entrance facility service.

M

Margin - Amount of signal in dB by which the satellite system exceeds the minimum levels required for operation.

MATV - Master Antenna Television. Antenna system that serves a concentration of television sets such as in apartment buildings, hotels or motels.

Mbps - Megabits per second.

MCPC - Multiple Channels Per Carrier. Communications architecture that multiplexes channels of information in the time domain onto a single carrier (frequency domain).

MHz - Megahertz. Frequency equal to one million Hz, or cycles per second.

MEO - Medium Earth Orbit satellite. Satellite that is not stationary from a fixed point on earth and whose orbital path is between the LEOs and GEOs. MEOs must either be "tracked" or use a frequency band and access methodology that allows access to the satellite with a non-directional antenna.

Mesh - Network architecture wherein each node has the ability to communicate with every other node. In such a system, the number of potential communications paths = N * (N - 1) / 2

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. Also used for data, voice, and other types of information transmission.

Microwave interference - Interference that 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. Can also be produced by nearby radar transmitters and the sun. Relocating the antenna by only several feet often eliminates the interference.

MMDS - Multichannel Multipoint Distribution System. Terrestrial microwave system used to distribute high-bandwidth services to end-users at homes and offices. Advantage of MMDS over satellite-based services is in its ability to include local content programming.

Modem - Contraction of Modulator and Demodulator. Device used to convert digital data to and from a form for transmission over telephone circuits, terrestrial radio circuits, satellite circuits, etc.

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

Modulator - Device that modulates a carrier. Used as components in broadcasting transmitters and in satellite transponders. 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 to enable recorded video information to be played back using a television receiver tuned to VHF channel 3 or 4.

MORELOS - Mexican domestic communications satellite.

MOU - Memorandum of Understanding. Legal agreement used to set basic terms of a purchase or sale; usually not a firm contract.

MTBF - Mean Time Between Failures. Hours of use for all units of a specific type (time) divided by the number of confirmed failures for all units of that type (number of failures).

MUX - multiplexer. Device that both combines multiple data sources into a single data stream for transmission, and demultiplexes the single data stream into its composite forms.

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

N

NAB - National Association of Broadcasters.

Narrowband

Narrowcasting - Using electronic media to reach a specific audience.

NCTA - National Cable Television Association.

NIM - Network Interface Module. Term used by Radyne ComStream to indicate the front-end demodulator circuitry that converts L-band signals into a digital data stream.

NF - Noise Figure. Figure of merit of a device, such as an LNA or receiver, expressed in dB, which compares the device with a perfect device.

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

NRTC - National Rural Telecommunications Cooperative.

NTSC - National Television Standards Committee. Video standard established by the United States (RCA/NBC} and adopted by numerous other countries: 525-line video with 3.58-MHz chroma subcarrier and 60 cycles per second.

O

OEM - Original Equipment Manufacture.

One-way - Service provided from point-of-presence to point-of-presence in which transmission of the signal is in one direction only.

Open network - Network implemented to an industry-accepted standard. Typically refers to an Intelsat standard product.

Orbital period - Time it takes a satellite to complete one orbit.

P

Packet data - process in which stored data is transmitted in discrete units, called packets. Makes more efficient use of channel capacity and reliability of transfer.

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

PAL - Phase Alternation System. German-developed TV standard based upon 50 cycles. per second and 625 lines.

Parabolic antenna - Satellite TV antenna that is shaped like a parabola. Focuses 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.

PCM - Pulse Code Modulation.

PCS - Personal Communications System. See personal communications.

Personal communications - Use of wireless communications to extend telephone service to a person, regardless of location, rather than to a fixed location.

PLL - Phase-Locked Loop. Type of electronic circuit used to demodulate satellite signals.

Point-to-Point - Service provided between two Points-of-Presence/Customer Premise(s).

Point-to-Multipoint - Service provided one-way from one POP/Customer Premise to Multiple POPs/customer Premise.

POP - Point-Of-Presence. Location of an inter-exchange carrier's presence (i.e., equipment center) within a particular market.

Polarization - Design technique used 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 can receive vertical and horizontal transponder signals simultaneously, 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.

Polar orbit - Orbit with its plane aligned in parallel with the polar axis of the earth

POR - Pacific Ocean Region.

PPV - Pay-Per-View. Programs purchased by subscribers on a per-program rather than a per-month basis.

Private network - Network that is not implemented to an industry-accepted standard. Typically refers to a proprietary product that will not operate with another vendor's product.

Protocol - Set of standard procedures that permit devices to intercommunicate.

PSN - Public Telephone Network. Usually a common carrier such as a telephone company regulated by the FCC.

PSTN - Public Switched Telephone Network.

PTT - Postal Telephone and Telegraph. Operating agency in charge of telecommunications services, usually directly or indirectly controlled by a country's government. Many countries are privatizing their PTTS.

Pulse code modulation - Time division modulation technique in which analog signals are sampled and quantized at periodic intervals into digital signals. Values observed are typically represented by a coded arrangement of 8 bits of which one may be for parity.

Q

QPSK - Quadrature Phase Shift Keying. Digital modulation scheme used in transmission communications to allow increased sending capacity.

R

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

RBOC - Regional Bell Operating Company.

Receiver - See Rx.

Receiver sensitivity - Amount of power in dBm that a detector must receive to achieve a specific baseband performance, such as a specified bit error rate or signal to noise ratio.

Reseller - Carrier that purchases services of other carriers and retails the services to its customers.

Retrofit - Field upgrade that may be mandatory or selective. Mandatory retrofit means all field units must be upgraded to ensure reliable operation. Selective retrofit means that certain field units must be upgraded depending on the operating parameters.

RFI - Radio Frequency Interface. Denotes apparent disturbance or distortion to satellite signals.

Rx - Receiver. Electronic device that enables a particular satellite signal to be separated from all others being received by an earth station and converts signal format into a format for video, voice, or data.

S

Satellite - 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).

SCPC - Single Channel Per Carrier. Communications architecture that places one source of information onto a single carrier (frequency domain). Economical ways to get multiple signals on one transponder.

Simplex - Transmission that occurs in only one direction over the communications media.

Scrambling - Altering a video signal transmission so it cannot be received without an authorized operating decoder.

Shared hub - satellite communications operations center that is shared among several separate network users; often used for VSAT operations.

Slot - Longitudinal position in the geosynchronous orbit into which a communications satellite is positioned. Above the United States, communications satellites are typically positioned in slots based at two to three degree intervals.

SMATV - Satellite Master Antenna Television. Or private cable, a miniature cable system that receives programming by satellite and serves a housing complex or hotel.

S/N - Signal to Noise Ratio. 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.

SNMS - Simple Network Management System. Term used by ComStream for the network management system of its modems and earth stations product line.

Solar outage - Outage that occurs when 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. Timing of solar outages can be exactly predicted for each site.

Spectrum - 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.

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

Spot beam - 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 - Means of transmission in which information is carried encoded into discrete packages of information, then spread over a wide bandwidth for transmission to specific receivers which filter out the coded material.

SSPA - Solid State Power Amplifier. VSLI solid-state device that is gradually replacing traveling wave tubes in satellite communications systems because they are lighter weight and are more reliable.

Star network - Network configuration in which there is only one path between a central or controlling node and each endpoint node.

Stationkeeping - Minor orbital adjustments conducted to maintain the satellite's orbital assignment within the allocated area within the geostationary arc.

Subcarrier - Secondary signal paired with another the primary signal on the main carrier. For example, in satellite television transmission, the video picture is transmitted over the main carrier, and 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.

Sync - Synchronization. Process of orienting the transmitter and receiver circuits so that transmit in harmony. 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 tunes the circuits to the exact frequency and phase.

Switch - 1) Item of telecommunications equipment that accepts, routes and places, or forwards a call or other transmission. Includes LEC CO switches, IXC switches and PBXs. 2) Reconfiguration of electrical signals or television signals to different destinations.

T

T1 - Transmission bit rate of 1.544 millions bits per second. Also equivalent to the ISDN Primary Rate Interface for the U.S.

T3 - Digital channel that communicates at 45.304 Mbps. Available in North America.

Tariff - Usage fees charged for any given service.

Telephony - Transmission of speech to distant places.

TELESAT - Canadian domestic satellite operator.

Terrestrial - Earth, land, or ground-based telecommunications systems.

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

Transceiver - Combination of transmitter and receiver.

Transmitter - 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 - Combination receiver, frequency converter, and transmitter package, physically part of a communications satellite. Typical output is five to ten watts, operating over a frequency band with a 36 to 72 Mhz bandwidth in the L-, C-, Ku-, and sometimes Ka-Bands, or in the microwave spectrum, except for mobile satellite communications. Communications satellites typically have 12 to 24 onboard transponders.

TVRO - Television Receive Only. Antenna reflectors and associated electronic equipment to receive and process television and audio communications via satellite. Typically small home systems. Also known as downlink or backyard dish.

Two-way - Service provided by means of two simplex (one-way) circuits transmitting in opposite directions between the same two points, which may not synchronous.

TWTA - Traveling Wave Tube Amplifier. High-power RF slow wave amplifier commonly used in spacecraft transponders and earth station HPA equipment.

U

UHF - Ultra High Frequency. Band in the 500-900 MHz range, including TV channels 14 through 83.

Uplink - Transmitting to a satellite for relay. Also earth station used to transmit signals to a satellite.

V

Value-added service provider - Third party who leases capacity for resale.

VSAT - Very Small Aperture Terminal. Small earth stations, usually 1.2-2.4 meter diameter. Means of narrowcast transmission of video, voice, and data by SCPC to a satellite. Used in business applications. Small aperture terminals under 0.5 meters are sometimes called Ultra Small Aperture Terminals (USATs).

W

Wireless local loop - Term used to signify one of many forms of wireless technologies for "last mile" connectivity. Forms of wireless local loop include fixed, limited mobility, and full mobility, with varying numbers of subscribers supported in each category.

X

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

Y

Z