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Glossary of Satellite Terms |
ACTS
Advanced Communications Technology Satellite. A NASA experimental satellite project to demonstrate the use of the Ka-Band (30/20 GHz) services.
Amplifier
A device used to boost the strength of an electronic
signal.
Amplitude Modulation (AM)
The baseband signal is caused to vary the amplitude or
height of the carrier wave to create the desired information content.
Analog
A form of transmitting information characterized by continuously
variable quantities, as opposed to digital transmission, which is characterized
by discrete bits of information in numerical steps. An analog signal is
responsive to changes in light, sound, heat and pressure.
Analog-to-Digital Conversion (ADC)
Process of converting analog signals to a digital representation.
DAC represents the reverse translation.
ANIK
The Canadian domestic satellite system that transmits
Canadian Broadcasting Corporation's (CSC) network feeds throughout the
country. This system also carries long distance voice and data services
throughout Canada as well as some transborder service to the U.S. and Mexico.
Antenna
A device for transmitting and receiving radio waves.
Depending on their use and operating frequency, antennas can take the form
of a single piece of wire, a di-pole a grid such as a yagi array, a horn,
a helix, a sophisticated parabolic-shaped dish, or a phase array of active
electronic elements of virtually any flat or convoluted surface.
Aperture
A cross sectional area of the antenna which is exposed
to the satellite signal.
Apogee
The point in an elliptical satellite orbit which is farthest
from the surface of the earth. Geosynchronous satellites which maintain
circular orbits around the earth are first launched into highly elliptical
orbits with apogees of 22,237 miles. When the communication satellite reaches
the appropriate apogee, a rocket motor is fired to place the satellite
into its permanent circular orbit of 22,237 miles.
Apogee Kick Motor (AKM)
Rocket motor fired to circulate orbit and deploy satellite
into geostationary orbit.
Apstar (Asia-Pacific Star)
Name of the Chinese satellite system which carries commercial video services in
the region.
Arabsat
This is the Arabsat Satellite Organization and its is headquartered in Riyadh,
Saudi Arabia. It provides regional telecommunications services for the Middle
East region.
AsiaSat
A satellite system covering the Asia mainland.
Asynchronous Communications
Stream of data routed through a network as generated, rather than in organized
message blocks. Most personal computers send data in this format. (See ATM)
Asynchronous Transfer Mode (ATM)
This is the new form of super-fast packet switching operating at speeds in
the Gigabits/second.
Attenuation
The loss in power of electromagnetic signals between
transmission and reception points.
Attitude Control
The orientation of the satellite in relationship to the
earth and the sun.
Audio Subcarrier
The carrier between 5 MHz and 8 MHz containing audio
(or voice) information inside of a video carrier.
Automatic Frequency Control (AFC)
A circuit which automatically controls the frequency
of a signal.
Automatic Gain Control (AGC)
A circuit which automatically controls the gain of an
amplifier so that the output signal level is virtually constant for varying
input signal levels.
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-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 Pass Filter
An active or passive circuit which allows signals within
the desired frequency band to pass through but impedes signals outside
this pass band from getting through.
Bandwidth
A measure of spectrum (frequency) use or capacity. For
instance, a voice transmission by telephone requires a bandwidth of about
3000 cycles per second (3KHz). A TV channel occupies a bandwidth of 6 million
cycles per second (6 MHz) in terrestrial Systems. In satellite based systems
a larger bandwidth of 17.5 to 72 MHz is used to spread or "dither" the
television signal in order to prevent interference.
Baseband
The basic direct output signal in an intermediate frequency
based obtained directly from a television camera, satellite television
receiver, or video tape recorder. Baseband signals can be viewed only on
studio monitors. To display the baseband signal on a conventional television
set a "modulator" is required to convert the baseband signal to one of
the VHF or UHF television channels which the television set can be tuned
to receive.
Baud
The rate of data transmission based on the number of
signal elements or symbols transmitted per second. Today most digital 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.
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.
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).
BPSK (Binary Phase Shift Keying)
A digital modulation technique in which the carrier phase can have one of
two possible values, namely 0 degrees or 180 degrees.
Broad beam
A single large circular beam that covers a large geographic area
Broadcast
The sending of one transmission to multiple users in a defined group (compare to unicast).
BSS (Broadcast Satellite Service)
This is the ITU designation but DBS or Direct Broadcast Service is more commonly used term in the satellite industry.
Business Television
Corporate communications tool involving video transmission of information via
satellite.
Common uses of business television are for meetings, product introductions and
training.
Buttonhook Feed
A shaped piece of waveguide directing signal from the feed to the LNA behind the
antenna.
Bypass
Use of satellite, local area network, wide area network or metropolitan area
network as an alternative transmission facility.
C Band
This is the band between 4 and 8 GHz with the 6 and 4
GHz band being used for satellite communications. Specifically, the 3.7
to 4.2 GHz satellite communication band is used as the down link frequencies
in tandem with the 5.925 to 6,425 GHz band that serves as the uplink.
Carrier
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).
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.
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.
CATV
Originally meant Community Antenna Television. Independent smaller companies in
rural communities would build a large television receiving antenna on a
nearby mountain to pick up the weak TV signals from a distant metropolis. These
signals were amplified, modulated onto television channels and sent along a
coaxial cable strung from house to house.
CCITT (now TSS)
Comite Consultatif Internationale de Telegraphique et Telephonique.
International body, associated with the ITU, which establishes worldwide
standards for telecommunications. Reorganized to include CCIR (radio standards
group) and renamed TSS (Telecommunications Standardization Sector).
CDMA
Code division multiple access. Refers to a multiple-access
scheme where stations use spread-spectrum modulations and orthogonal codes
to avoid interfering with one another.
Channel
A frequency band in which a specific broadcast signal
is transmitted. Channel frequencies are specified in the United States
by the Federal Communications Commission. Television signals require a
6 MHz frequency band to carry all the necessary picture detail.
CIF
Common Intermediate Format. A compromise television display format adopted by
the CCITT which is relatively easy to derive from both PAL and NTSC.
Circular Polarization
Unlike many domestic satellites which utilize vertical
or horizontal polarization, the international Intelsat satellites transmit
their signals in a rotating corkscrew-like pattern as they are down-linked
to earth. On some satellites, both right-hand rotating and left-hand rotating
signals can be transmitted simultaneously on the same frequency; thereby
doubling the capacity of the satellite to carry communications channels.
Clamp
A video processing circuit that removes the energy dispersal
signal component from the video waveform.
Clarke Orbit
That circular orbit in space 22,237 miles from the surface
of the earth at which geosynchronous satellites are placed. This orbit
was first postulated by the science fiction writer Arthur C. Clarke in
Wireless World magazine in 1945. Satellites placed in these orbits, although
traveling around the earth at thousands of miles an hour, appear to be
stationary when viewed from a point on the earth, since the earth is rotating
upon its axis at the same angular rate that the satellite is traveling
around the earth.
C/No or C/kTB
Carrier-to-noise ratio measured either at the Radio Frequency
(RF) or Intermediate Frequency (IF).
Coaxial Cable
A transmission line in which an inner conductor is surrounded by an outer
conductor or shield and separated by a nonconductive dielectric.
Codec
Coder/decoder system for digital transmission.
Co-Location
Ability of multiple satellites to share the same approximate
geostationary orbital assignment frequently due to the fact that different
frequency bands are used.
Color Subcarrler
A subcarrier that is added to the main video signal to
convey the color information. In NTSC systems, the color subcarrier is
centered on a frequency of 3.579545 MHz, referenced to the main video carrier.
Common Carrier
Any organization which operates communications circuits
used by other people. Common carriers include the telephone companies as
well as the owners of the communications satellites, RCA, Comsat, Direct
Net Telecommunications, AT&T and others. Common carriers are required
to file fixed tariffs for specific services.
Companding
A noise-reduction technique that applies single compression
at the transmitter and complementary expansion at the receiver.
Composite Baseband
The unclamped and unfiltered output of the satellite
receiver's demodulator circuit, containg the video information as well
as all transmitted subcarriers.
Compression Algorithms
Software that allows codecs to reduce the number of bits required for data
storage or transmission.
COMSAT
The Communications Satellite Corporation (part of Lockheed Martin) which serves
as the U.S. Signatory to INTELSAT and INMARSAT.
Conus
Contiguous United States. In short, all the states in
the U.S. except Hawaii and Alaska.
Cross Modulation
A form of signal distortion in which modulation from
one or more RF carrier(s) is imposed on another carrier.
CSU
Channel service unit. A digital interface device that connects end-user equipment to the local digital telephone loop. CSU is frequently coupled with DSU (see below) as CSU/DSU.
C/T
Carrier-to-noise-temperature ratio.
DAMA
Demand-Assigned Multiple Access - A highly efficient
means of instantaneously assigning telephony channels in a transponder
according to immediate traffic demands.
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.
De-BPSK
Differential Binary Phase Shift Keying
De-QPSK
Differential Quadrature Phase Shift Keying.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.
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.
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.
Discriminator
A type of FM demodulator used in satellite receivers.
Dithering
he process of shifting the 6-MHz satellite-tv signal up and down the 36-MHz
satellite transponder spectrum at a rate of 30 times per second (30 Hertz). The
satellite signal is "dithered" to spread the transmission energy out
over a band of frequencies far wider than a terrestrial common carrier microwave
circuit operates within, thereby minimizing the potential interference that any
one single terrestrial microwave transmitter could possibly cause to the
satellite transmission.
Down-Converter
That portion of the Fixed Satellite Service (FSS) television receiver that
converts the signals from the 4-GHz microwave range to (typically) the more
readily used baseband or intermediate frequency (IF) 70-MHz range.
Downlink
The satellite to earth half of a 2 way telecommunications satellite link. Often used to describe the recieve dish end of the link.
DSU
Data service unit. A device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as T1 or E1. The DSU is also responsible for such functions as signal timing. DSU is freqnetly coupled with a CSU (see above) as CSU/DSU.
DTV
Digital Television
Dual Spin
Spacecraft design whereby the main body of the satellite
is spun to provide altitude stabilization, and the antenna assembly is
despun by means of a motor and bearing system in order to continually direct
the antenna earthward. This dual-spin configuration thus serves to create
a spin stabilized satellite.
Duplex Transmission
Capability for simultaneous data transmission between a sending station and a receiving station.
DVB
Digital Video Broadcasting - The European-backed project to harmonise adoption of digital video.
E1
Wide-area digital transmission facility used predominantly in Europe that carries data at a rate of 2.048 Mbit/s.
E3
Wide-area digital transmission facility used predominantly in Europe that carries data at a rate of 34.368 Mbit/s.
Earth Station
The term used to describe the combination 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.
Eclipse
When a satellite passes through the line between the earth and the sun or the
earth and the moon.
Eclipse Protected
Refers to a transponder that can remain powered during the period of an eclipse.
El/Az
An antenna mount providing independent adjustments in elevation and azimuth.
Edge of Coverage
Limit of a satellite's defined service area. In many
cases, the EOC is defined as being 3 dB down from the signal level at beam
center. However, reception may still be possible beyond the -3dB point.
EIRP
Effective Isotropic Radiated Power - This term describes
the strength of the signal leaving the satellite antenna or the transmitting
earth station antenna, and is used in determining the C/N and S/N. The
transmit power value in units of dBW is expressed by the product of the
transponder output power and the gain of the satellite transmit antenna.
Elevation
The upward tilt to a satellite antenna measured in degrees
required to aim the antenna at the communications satellite. When. aimed
at the horizon, the elevation angle is zero. If it were tilted to a point
directly overhead, the satellite antenna would have an elevation of 90
degrees.
Encoder
A device used to electronically alter a signal so that
it can only be viewed on a receiver equipped with a special decoder.
Energy Dispersal
A low-frequency waveform combined with the baseband signal prior to modulation,
to spread the FM signal's peak power across the available transponder bandwidth
in order to reduce the potential for creating interference to ground-based
communications services.
EOL
End of Life of a satellite.
Equatorial Orbit
An orbit with a plane parallel to the earth's equator.
ESC
Engineering Service Circuit - The 300-3,400 Hertz voice
plus teletype (S+DX) channel used for earth station-to-earth station and
earth station-to-operations center communications for the purpose of system
maintenance, coordination and general system information dissemination.
In analog (FDM/FM) systems there are two S+DX channels available for this
purpose in the 4,000-12,000 Hertz portion of the baseband. In digital systems
there are one or two channels available which are usually convened to a
32 or 64 Kbps digital signal and combined with the earth station traffic
digital bit stream. Modern ESC equipment interfaces with any mix of analog
and digital satellite carriers, as well as backhaul terrestrial links to
the local switching center.
Eutelsat
The European Telecommunications Satellite Organization which is headquartered in
Paris, France. It provides a satellite network for Europe and parts of North
Africa and the Middle East.
FCC (Federal Communications Commission)
The U.S. federal regulatory body, consisting of five members, one of who is
designated chairman, appointed by the President and confirmed by the Senate,
which regulates interstate communications under the Communications Act of 1934.
F/D
Ratio of antenna focal length to antenna diameter. A
higher ratio means a shallower dish.
FDMA
Frequency division multiple access. Refers to the use
of multiple carriers within the same transponder where each uplink has
been assigned frequency slot and bandwidth. This is usually employed in
conjunction with Frequency Modulation.
Feed
Feedhorn FM - Frequency Modulation Focal Length
Focal Point
Footprint
Forward Error Correction (FEC)
Frequency
Frequency Coordination
Frequency Reuse Gain
GE Americon
Geostationary Transfer Orbit Geosynchronous
Gigahertz (GHz)
Global Beam
Gregorian Dual-reflector antenna system employing a paraboloidal
main reflector and a concave ellipsoidal subreflector.
Globalstar G/T
Guard Channel
Half Transponder
Headend
Heliosynchronous Orbit
High Frequency (HF)
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.
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).
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.
Distance from the center feed to the center of the dish.
The area toward which the primary reflector directs and
concentrates the signal received.
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.
Adds unique codes to the digital signal at the source
so errors can be detected and corrected at the receiver.
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.
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.
A technique which maximizes the capacity of a communications satellite through
the use of sp
A measure of amplification expressed in dB.
This is a large U.S. corporation providing satellite systems for domestic
communications. Has ownership in some international satellites.
Geostationary
Refers to a geosynchronous satellite angle with zero
inclination. so the satellite appears to hover over one spot on the earth's
equator.
This orbit is in the equatorial plane. This type of orbit has an elliptical
form, with a perigee at 200 km and an apogee at 35870 km.
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.
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.
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).
A mobile satellite system that deployes a network of 48 satellites to
create a global voice and data service. This system is backed by Qualcomm,
Loral, and Alcatel.
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.
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...H...
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.
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.
At an altitude of 600 to 800 km and situated in a quasi-polar plane. The
satellite is permanently visible
HEO
Highly Elliptical Orbit. This is type of orbit used by the Russian Molniya
Satellite system. It is also referred to as
Extremely Elliptical Orbit (EEO).
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.
Radio frequencies within the range of 3,000 to 30,000 kilohertz. HF radio is
known as
High-Power Satellite
Satellite with 100 watts or more of transponder RF power.
Hour Angle
Steering direction of a polar mount. An angle measured in the equatorial plane
between the antenna beam and the meridian plane.
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.
Hughes Galaxy IBS
IFRB Inclination
INMARSAT
INTELSAT
Interference
Inter Satellite Link - ISL
A domestic U.S. satellite system which provides a range of telecommunications
services.
I...I...
INTELSAT Business Services.
International Frequency Registration Board of the ITU - International
Telecommunications Union. The IFRB regulates the allocation of satellite
orbital locations.
The angle between the orbital plane of a satellite and
the equatorial plane of the earth.
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.
The International Telecommunications Satellite Organization
operates a network of satellites for international transmissions.
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.
Radio or optical communications links between satellites. They serve to
interconnect constellations of satellites.
INTERSPUTNIK
The international entity formed by the Soviet Union to provide international
communications via a network of Sovie
IRD
An integrated receiver and decoder for reception of a transmission of voice, video and data.
Iridium Satellite System
This was a 66 satellite network designed for mobile telephone use and is now
defunct.
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).
ISO Isotropic Antenna
ITU
Jammer - JPEG
Ka Band
Kbps
Kelvin (K)
Kilohertz (kHz)
Klystron
Ku Band
L-Band
Leased Line
Low Noise Amplifier (LNA)
Low Noise Block Downconverter (LNB)
Low Noise Converter (LNC)
Low-Power Satellite MAC (A, B, C, D2)
Margin
Master Antenna Television (MATV)
Medium-Power Satellite Megahertz (MHz)
Microwave
Microwave Interference
Modem Modulator
Molniya
The Russian domestic
satellite system which operated with highly elliptical satellites which
overlooked the high latitudes of the territories of the USSR. MPEG
MPEG-2
MPEG-2 MP@HL
Multiple Access Multiplexing
Mux NAB The U.S. agency which
administers the American space program, including the deployment of commercial
and military satellites via a fleet of space shuttle vehicles. Noise Figure (NF)
NTIA NTSC - National Television Standards Committee
OFTEL Packet Switching
PAL - Phase Alternation System
Parabolic Antenna
PBS (Public Broadcasting System)
A domestic USA
television and radio broadcast network. Polarization
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
Polar Mount
Polar Orbit
Pulse Code Modulation
QPSK Rain Outage
Receiver (Rx)
Receiver Sensitivity
RF Adaptor Router
Satellite
Satellite Terminal Scalar Feed
Scrambler
Secam
SFD - Stauration Flux Density
Sidelobe
Signal to Noise Ratio (S/N)
SILVO Single-Channel-Per-Carrier (SCPC)
Single Sideband (SSB) Skew
Slant Range
Slot
SMATV (Satellite Master Antenna System) SNG
Snow
Solar Outage
Sparklies Spectrum
Spillover
Spin Stabilization
Splitter
Spot Beam
Spread Spectrum
SSMA Stationkeeping
Subcarrier
Subsatellite Point Synchronization (Sync)
T1
T3 Channel (DS-3)
Teleconference The name of the U.S.
proposed LEO satellite system that would deploy 840 satellites for global telecommunications
services. The AT&T
Corporation has maintained its trademark for the Telstar name and currently
operates its domestic satellite system under the Telstar name. Transfer Orbit Transponder
Transponder Hopping TSS Turnkey TVRO
Tweeking
TWT (Traveling-wave tube)
TWTA (Traveling-wave-tube amplifier)
Ultra-high Frequency (UHF) Uplink
USAT V.35
Van Allen radiation belts
VSAT
VSWR
International Standards Organization. Develops standards such as JPEG and MPEG.
Closely allied with the CCITT.
A hypothetical omnidirectional point-source antenna that
serves as an engineering reference for the measurement of antenna gain.
International Telecommunication Union.
J...J...
An active electronic counter-measures (ECM) device designed to deny intelligence to unfriendly detectors or to disrupt communications.
ISO Joint Picture Expert Group standard for the compression
of still pictures.
K...K...
The frequency range from 18 to 31 GHz.
Kilobits per second. Refers to transmission speed of
1,000 bits per second.
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.
Refers to a unit of frequency equal to 1,000 Hertz.
A microwave tube which uses the interaction between an electron beam and the RF energy on microwave cavities to provide signal amplification. The klystron operates on principles of velocity modulation very similar to those in a TWT except that klystron interaction takes place at discrete locations along the electron beam. Common types of klystrons are the reflex klystron (an oscillator having only one cavity), two-cavity klystron amplifiers and oscillators, and multi-cavity klystron amplifiers.
The frequency range from 10.9 to 17 GHz.
The frequency range from 0.5 to 1.5 GHz. Also used to
refer to the 950 to 1450MHz used for mobile communications.
A dedicated circuit typically supplied by the telephone
company.
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.
A combination Low Noise Amplifier and downconverter built
into one device attached to the feed.
A combination Low Noise Amplifier and down converter built into one
antenna-mounted package.
Low Orbit
At an altitude of 200 to 300 km this orbit is used for certain types of
scientific or observation satellites, which can
Satellite with transmit RF power below 30 watts.
Multiplexed analog component color video transmission
system. Subtypes refer to the various methods used to transmit audio and
data signals.
The amount of signal in dB by which the satellite system
exceeds the minimum levels required for operation.
An antenna system that serves a concentration of television
sets such as in apartment buildings, hotels or motels.
Satellite generating transmit power levels ranging from 30 to 100 watts.
Refers to a frequency equal to one million Hertz, or
cycles per second.
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.
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.
A communications device that modulates signals at the transmitting end and
demodulates them at the receiving end.
Modulation
The process of manipulating the frequency or amplitude
of a carrier in relation to an incoming video, voice or data signal.
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.
The Moving Pictures Experts Group, the television industry's informal standards group.
The agreed standard covering the compression of data (coding and encoding) for digital television.
Main Provile at High Level - The agreed much higher bit-rate system adopted to provide high definition television in wide screen format.
The ability of more than one user to have access to a transponder.
Multiple System Operator (MSO)
A company that operates more than one cable television system.
Multipoint Distribution System (MDS)
A common carrier licensed by the FCC to operate a broadcast-like
omnidirectional microwave transmission facility within a given city typically
carrying television signals
Multicast
Multicast is a subset of broadcast that extends the broadcast concept of one to many by allowing "the sending of one transmission to many users in a defined group, but not necessarily to all users in that group."
Techniques that allow a number of simultaneous transmissions
over a single circuit.
A Multiplexer. Combines several different signals (e.g. video, audio, data) onto
a single communication channel for transmission. Demultiplexing separates each
signal at the receiving end.
National Association of Broadcasters.
NASA (National Aeronautics and Space Administration)
NASDA
National Space Development Agency of Japan.
NCTA
National Cable Television Association.
Noise
Any unwanted and unmodulated energy that is always present
to some extent within any signal.
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.
The National Telecommunications and Information Administration is a unit of the
Department of Commerce that address U.S. government telecommunications policy,
standards setting and radio spectrum allocation.
Nutation Damping
The process of correcting the nutational effects of a spinning satellite
which are similar in effect to a wobbling top. Active nutation controls use
thruster jets.
A video standard established by the United States (RCA/NBC}
and adopted by numerous other countries. This is a 525-line video with
3.58-MHz chroma subcarrier and 60 cycles per second.
The Office of Telecommunications of the United Kingdom government. This unit a
part of the Department of Industries regulates telecommunications in the United
Kingdom.
Orbital Period
The time that it takes a satellite to complete one circumnavigation
of its orbit.
Data transmission method that divides messages into standard-sized
packets for greater efficiency of routing and transport through a network.
The German developed TV standard based upon 50 cycles.per
second and 625 lines.
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.
Perigee
The point in an elliptical satellite orbit which is closest to the surface of
the earth.
Perigee Kick Motor (PKM)
Rocket motor fired to inject a satellite into a geostationary transfer orbit
from a low earth orbit especially that of a STS or Shuttle-based orbit of 300 to
500 miles altitude.
Period
The amount of time that a satellite takes to complete one revolution of its
orbit.
Phase Alternation System (PAL)
A European color television system incompatible with the US NTSC television
system.
Phase-Locked Loop (PLL)
A type of electronic circuit used to demodulate satellite signals.
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.
A device that can be manually or automatically adjusted
to select one of two orthogonal polarizations.
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.
An orbit with its plane aligned in parallel with the
polar axis of the earth
Protected-Use Transponder
A satellite transponder provided by the common carrier to a programmer with a
built-in insurance policy. If the protected-use transponder fails, the common
carrier guarantees the programmer that it will switch over to another
transponder, sometimes pre-empting some other non-protected programmer from the
other transponder.
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.
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.
Quadrature Phase Shift Keying is a digital modulation technique in which the
carrier phase can have one of four
Loss of signal at Ku or Ka Band frequencies due to absorption
and increased sky-noise temperature caused by heavy rainfall.
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.
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.
An add-on modulator which interconnects the output of the satellite television
receiver to the input (antenna
terminals) of the user's television set. The RF adaptor converts the
baseband video signal coming from the satellite receiver to a radio frequency RF
signal which can be tuned in by the television set on VHF channel 3 or 4.
Network layer device that determines the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information.
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).
A receive-only satellite earth station consisting of an antenna reflector
(typically parabolic in shape), a feedhorn, a low-noise amplifier (LNA), a down
converter and a receiver.
SAW (Surface Acoustic Wave)
A type of steep-skirted filter used in the baseband or IF section of
satellite reception and transmission equipment.
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.
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.
A color television. system developed by the French and
used in the USSR. Secam operates with 625 lines per picture frame and 50
cycles per second, but is incompatible in operation with the European PAL
system or the U.S. NTSC system.
The power required to achieve saturation of a single repeater channel on the satellite.
Off-axis response of an antenna.
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.
An organization formed in the mid 1980's to monitor frequency re-use.
Simplex Transmission
Capability for transmission in only one direction between sending station and receiving station.
A method used to transmit a large number of signals over
a single satellite transponder.
A form of amplitude modulation (AM) whereby one of the sidebands and the AM
carrier are suppressed.
An adjustment that compensates for slight variance in
angle between identical senses of polarity generated by two or more satellites.
The length of the path between a communications satellite
and an associated earth station.
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.
The adding of an earth station to a MATV system to receive satellite programs.
Satellite news gathering usually with a transportable uplink truck.
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 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.
A form of satellite television "snow" caused by a weak signal. Unlike
terrestrial VHF and UHF television snow which appears to have a softer texture,
sparklies are sharper and more angular noise "blips". As with
terrestrial reception, to eliminate sparklies, either the satellite antenna must
be increased in size, or the low noise amplifier must be replaced with one which
has a lower noise temperature.
The range of electromagnetic radio frequencies used in
transmission of voice, data and television.
Satellite signal that falls on locations outside the
beam pattern's defined edge of coverage.
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.
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.
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.
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.
Spread spectrum multiple access. Refers to a frequency multiple access or
multiplexing technique.
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.
Minor orbital adjustments that are conducted to maintain
the satellite's orbital assignment within the allocated "box" within the
geostationary arc.
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.
The unique spot over the earth's equator assigned to each geostationary
satellite.
Superband
The frequency band from 216 to 600 MHz, used for fixed and mobile radios and
additional television channels on a cable system.
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.
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.
In North America, a digital channel which communicates at 45.304 Mbps.
An electronic multilocation, multiperson conference using audio, computer,
slow-scan, or full-rate video systems.
Teledesic
Telstar
Terrestrial TV
Ordinary "over the air" VHF (very high frequency) and UHF (ultrahigh
frequency) television transmissions which are usually limited to an effective
range of 100 miles or less. Terrestrial tv transmitters operate at frequencies
between 54 megahertz and 890 megahertz, far lower than the l4/l2 and 6/4 billion
hertz (gigahertz) microwave frequencies used by satellite transponders.
Three-Axis Stabilization
Type of spacecraft stabilization in which the body maintains a fixed attitude
relative to the
orbital track and the earth's surface. The reference axes are roll, pinch,
and yaw, by nautical analogy.
Threshold Extension
A technique used by satellite television receivers to improve the signal-to
noise ratio of the receiver by approximately 3 db (50%). When using small
receive-only antennas, a especially equipped receiver with a threshold extension
feature can make the difference between obtaining a decent picture or no picture
at all.
Thruster
A small axial jet used during routine stationkeeping activities. These are often
fueled bydrazine or bi-propellant. In time ion-engines will probably replace
such thrusters.
TI - Terrestrial Interference
Interference to satellite reception caused by ground based microwave
transmitting stations.
A highly elliptical orbit which is used as an intermediate stage for placing
satellites into geostationary 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.
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.
A single TDMA equipped earth station can extend its capacity by having access to
several down-link beams by hopping from one transponder to another. In such a
configuration the number of available transponders must be equivalent to the
square of the number of beams that are interconnected or cross-strapped.
Telecommunications Standardization Sector. The world standards setting
organization resulting from the combination of the CCITT (Consultative Committee
on Telephony and Telegraphy) and the CCIR (Consultative Committee on
International Radio).
Refers to a system that is supplied, installed and sometimes managed by one
vendor or manufacturer.
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.
The process of adjusting an electronic receiver circuit
to optimize its performance.
A microwave tube of special design using a broadband circuit in which a beam of electrons interacts continuously with a guided electromagnetic field to amplify microwave frequencies.
A combination of a power supply, a modulator (for pulsed systems), and a traveling-wave tube, often packaged in a common enclosure.
Officially the band of frequencies ranging from 300 to 3000 MHz. In television
use, refers to the set of frequencies starting at 470 MHz, The UHF channels are
designated as 14 through 70.
Unicast
A unicast application transmits a copy of every packet to every receiver.
The earth station used to transmit signals to a satellite
Ultra Small Aperture Terminal. This refers to very small terminals for DBS
and other satellite applications where the terminal can be very small (under 50
cms).
ITU-T standard describing a synchronous, physical layer protocol used for communications between a network access device and a packet network. V.35 is most commonly used in the United States and in Europe, and is recommended for speeds up to 48 Kbit/s.
These are two high level radiation belts discovered by an Explorer Satellite
designed by Dr. Van Allen of Cal Tech. These belts which are highly destructive
to communications satellites consists of two belts of highly charged particles
and high energy neutrons.
VBI
Vertical blanking interval.
Vertical Interval Test Signal
A method whereby broadcasters add test signals to the blanked portion of the
vertical interval. Normally placed on lines 17 through 21 in both field one and
two.
Very High Frequencies (VHF)
The range of frequencies extending from 30 to 300 MHz; also television channels
2 through 13.
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)
Voltage Standing Wave Ratio. A measurement of mismatch
in a cable, waveg