|
|
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.
top
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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.
top
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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 |
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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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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 |
|
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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.
top
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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.
top
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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
|
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.
top
|
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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.
top
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| M |
|
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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
|