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Glossary of Satellite Terms and Acronyms

 

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


A


Access

Service
provided by local exchange carriers (or alternate access providers)
that connects an interexchange 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.

air
time

Time
at which an event is broadcast.

AM

Amplitude
Modulation. Process in which base band 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 wave form 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. Geo synchronous 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.

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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.

base
band


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 base band 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.

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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
head end

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 radio-telephones.

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 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.

Clarke
orbit

That
circular orbit in space 22,237 miles from the surface of the earth
at which geo synchronous 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 geo
stationary 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.

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.

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D

DAMA


Demand-Assigned Multiple Access. Protocol used to share bandwidth
in a time division mode. Typically used in a packet-switched environment
when large amounts of data are to be transferred. Is a highly
efficient means of instantaneously assigning telephony channels
in a transponder according to immediate traffic demands. Also
applicable in a circuit-switched environment. Usually characterized
by allowing each user a variable slot of time on a demand (or
request) basis.

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.

DBR

Data
Broadcast Receiver.

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.

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. DS-3s are also used by large companies 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.

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E


E1

European
equivalent of T1 or the transmission rate of 2.048 million bits
per second.

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. This
is largely eliminated by modern digital echo cancellers.

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 unseable 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 base band. 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.

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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 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
sub reflector plus a feed horn or a feed horn only.

feed
horn


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 base band
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.

FSS

Fixed
Satellite Service.

full
duplex

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

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G

gain


Measure of amplification expressed in dB.

GEO

Geo
synchronous 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).

geo
stationary


Geo synchronous satellite angle with zero inclination so the satellite
appears to hover over one spot on the earth’s equator.

geo
synchronous


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 light wave 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

Geo
synchronous Orbit. Satellites in geo synchronous 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.

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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.

head
end


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.

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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.

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.

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

JPEG


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 Kelvin

Ka
band


Frequency range from 18 to 31 GHz.

Kbps


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

kHz

Kilo
Hertz. 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.

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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
loop

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

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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

Multi
channel 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 base band 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.

MTBF

Mean
Time Between Failure. 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 de multiplexes the single data
stream into its composite forms.

multiplexing

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

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n

NAHUELSAT

Argentina
domestic communications satellite, Ku band.

Narrowband
/ narrowcasting

Using
electronic media to reach a specific audience.

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 un-modulated energy that is always present to
some extent within any signal.

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.

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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 a industry-accepted standard. Typically refers
to an Intelsat standard product.

orbital
period

Time it
takes a satellite to complete one orbit.

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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
feed horn 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 feed horn to select the vertically or
horizontally polarized signals as desired. In some installations,
the feed horn 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

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 permits 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.

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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 C, Ku or Ka Band frequencies due to absorption
and increased sky-noise temperature caused by heavy rainfall.

receiver

See
Rx.

receiver
sensitivity


Amount of power in dBm that a detector must receive to achieve
a specific base band 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.

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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 geo synchronous 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 head end for Cable TV.

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 beam width. 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.

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. VLSI 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.

station
keeping


Minor orbital adjustments conducted to maintain the satellite’s
orbital assignment within the allocated area within the geo stationary
arc.

sub
carrier


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 sub carrier. Some satellite
transponders carry as many as four special audio or data sub carriers
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.

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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.

TDMA


Time Division Multiple Access. Form of multiple access in which
a single carrier is shared by many users. When signals from earth
stations reach the satellite, they are processed in time segments
without overlapping. Typically used in a packet switched environment
when small or moderate amounts of data are to be transferred.
Also applicable in a circuit switched environment.

telephony

Transmission
of speech to distant places.

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.

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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.

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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).

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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.

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X

X.25

A set of
packet switching standards published by the CCITT.

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Y



Z


 

 

 

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