Analog
The representation of information in variable intensity and/or frequency by a
continuous signal.
Antenna
Equipment that sends and/or receives signals from a satellite.
Aperture
A cross sectional area of an antenna exposed to the satellite signal.
Apogee
The highest point in the satellite’s orbit (km); the point in the orbit of a
satellite where it is farthest from the object about which it revolves.
ASCII (American Standards Code for Information Interchange)
A code with seven information signals and one parity check signal.
Asynchronous Transmission
Data transmission in which each information character or byte is individually
synchronized, usually by the use of start or stop elements.
ATP
Acceptance Test Procedure
Attenuation
The loss in power of electromagnetic signals between transmission and reception
points.
AZ-EL Mount
Antenna mount that requires two separate adjustments-of azimuth and elevation-to
move from one satellite to another.
Azimuth
The angle between an antenna beam and the meridian plane, measured along a
horizontal plane.
Bandwidth
The range of frequencies utilized for the transmission of a signal or group of
inter-related signals expressed in Hertz (Hz).
Base band
A video or audio signal transmitted at its original frequency.
BER (Bit Error Rate)
The percentage of received bits that are in error during transmission; expressed
as a number referenced to a power of ten.
Beam width
The angular coverage of an antenna beam. Earth station beams are usually
specified at the half-power (or -3 dB) point. Satellite beams are based on the area to be
covered.
Bisync
Binary Synchronous Communications (BSC).
Bit
A single unit of information.
BPSK
Binary Phase Shift Keying.
BTV (Business Television)
Corporate communications tool involving video transmissions of information via
satellite. Common uses of business television are for meetings, product introductions and
training.
Carrier
A continuous frequency capable of being modulated with a second data-carrying
signal.
Cassegrain
Antenna comprised of two reflectors, the parabolic reflector and an hyperbolic
sub reflector at the focus point, which reflects signals back into the feed.
C-Band
Frequencies of approximately 4 to 6 GHz for satellite downlink and uplink
transmission, respectively.
Channel
Path for electrical communication between two facilities.
Circular Polarization
A mode of transmission in which signals are down linked in a rotating corkscrew
pattern. A satellite’s transmission capacity can be doubled by using both right-hand
and left-hand circular polarization.
CPU
Central Processing Unit.
C/N (Carrier-to-Noise Ratio)
Refers to the ratio of the satellite carrier (or signal) to noise level in a
given channel. Usually measured in dB at the LNA output.
Colocation
Placement of several satellites near each other in orbit. This allows a single
fixed antenna to receive signals from all of the satellites without tracking.
DAMA
Demand Assignment Multiple Access.
dB
Decibel. A unit of signal measurement that expresses a ratio between two
electrical signals or levels logarithmically.
dBW
An expression of power in dB relative to one watt.
D/C (Down Converter)
Equipment that performs frequency conversion to a lower (IF) band.
DCE
Data Circuit Terminating Equipment.
Delay
The time it takes for a signal to go from the sending station through the
satellite to the receiving station.
Demodulator
Equipment that converts the RF signal from the carrier into base band signals
(video, audio, or data) for further processing or amplification.
Digital
The representation of information in binary form (ones and zeros), discontinuous
in time.
Downlink
Transmission of information from a satellite to earth for reception by earth
stations.
DPSK
Differential Phase Shift Keying.
Driver
A software module that manages an I/O port to an external device.
DTE
Data Terminal Equipment.
DTMF (Dual Tone Multifrequency)
A method of signaling and basis for operation of push-button telephone sets.
Duplex Operation
Method in which transmission is possible simultaneously in both directions of a
telecommunications channel. Generally, two frequencies in radio communications are
required.
Earth Station
Any system (combination of satellite antenna, amplification, conversion, and
reception electronics) that can either transmit to or receive signals from orbiting
satellites.
Eclipse
When a satellite passes through the line between the earth and the sun or the
earth and another satellite.
EIRP (Effective Isotropic Radiated Power)
Refers to measure of satellite signal strength on the ground.
Elevation
The angle between an antenna beam and the horizontal plane.
Encoder
Equiment that converts a baseband analog input into a digital data stream.
Encryption
The process of coding, "scrambling," or altering a signal
electronically so it can only be decoded by recipients who have the equipment and
knowledge to reverse the encryption code.
F/D
Ratio of antenna focal length to antenna diameter. A higher ration means a
shallower dish.
FDMA (Frequency Division Multiple Access
Refers to the use of multiple carriers within the same transponder where each
uplink has an assigned frequency slot and bandwidth.
FEC (Forward Error Correction)
A technique that ensures the transmitted message is received at the receiving end
without error.
Feeds
Device mounted at the focus point of the antenna that gathers signals reflected
from the dish.
FEP
Front End Processor.
Focal Length
Distance from the feed to the center of the dish.
Footprint
The area of the earth's surface that a satellite's signal is expected to cover.
Shown as an EIRP contour map xpressed in dBW.
Gain
Increased signal power usually the result of amplification; measured in decibels.
Geostationary
Refers to a geosynchronous satellite angle with zero inclination, so the
satellite appears to hover over one spot on the earth’s equator.
Geosynchronous
Refers to the orbit in which the speed of a satellite’s orbit is
synchronized with the speed of the earth’s rotation so that they are always
positioned above the same spot on the earth. For this to occur, the satellite must be in
orbit 22,300 miles over the equator, Most communications satellites are in geosynchronous
orbit.
GHz (Gigahertz)
One billion cycles per second.
G/T (Gain-to-Noise Temperature)
Ratio of the gain of an antenna compared to the receive system noise temperature;
expressed in dB per degree K.
Hertz (Hz)
One cycle per second.
HPA (High-Power Amplifier)
Earth station equipment that amplifies the transmit RF signal.
HPC (High-Power Converter)
VSAT RF equipment that up converts and amplifies transmit signals.
Hub
The central earth station satellite transmission facility that is the focal point
for communicating to remote locations within a satellite communications network.
IF (Intermediate Frequency)
The frequency of a satellite receiver after down conversion or a satellite
modulator before up conversion.
IFL (Interfacility Link)
A cable that provides communication between the ODU and IDU.
I/O
Input/Output
IP
Internet Protocol.
kbps
One thousand bits per second.
kHz (Kilohertz)
One thousand cycles per second.
Ku-Band
Frequencies approximately in the 12 to 14 GHz range for satellite reception and
transmission, respectively.
LAN
Local Area Network.
LLC
Logical Link Control.
LNA (Low Noise Amplifier)
Equipment that receives the satellite signal reflected by the antenna and
amplifies it to the level needed by the satellite receiving equipment.
LNB (Low Noise Block Down converter)
Satellite receiving equipment that converts all signals from the LNA to the lower
IF frequencies.
LNC (Low Noise Converter)
Part of the earth station transmission subsystem consisting of an LNA and
down converter.
Mbps
One million bits per second.
M&C (Monitor and Control)
Equipment that monitors and controls Skystar network traffic and hub and VSAT
equipment status.
MHz (Megahertz)
One million cycles per second.
Modem (Modulator/Demodulator)
Equipment that converts between digital data and audio tones for transmission and
reception over analog channels.
Modulator
Equipment that converts audio, video, or data signals (baseband) into an RF
signal.
MSK
Minimum Shift Keying.
MTBF (Mean Time Between Failure)
Average length of time for which a system, or a component of a system, works
without fault.
MTTR (Mean Time To Respond)
Average time taken to arrive on site to correct a fault in a system or component.
Multiplexing
A technique that combines multiple data channels on a single transmission
channel.
MUX
Multiplexer equipment.
Noise
Extraneous and unwanted signal disturbances.
PA/TDMA
Permanent Assignment Time Division Multiple Access.
POP
Point of Presence.
POS
Point of Sale.
Protocol
Formal set of rules governing the format, timing, sequence, and error control of
messages on a data network.
PSK
Phase Shift Keying.
PVC
Permanent Virtual Circuit.
QPSK
Quadrature Phase Shift Keying.
RA
Random Access.
RA/TDMA
Random Access Time Division Multiple Access.
RF (Radio Frequency)
The frequency range from 10 kHz to 100 GHz used for transmitting data, audio, or
video.
Redundancy
A secondary system of backup equipment that performs similarly to a primary
system, thereby preventing network downtime and system outages.
Response Time
The elapsed time between the end of an inquiry and the beginning of the response.
RFI
Radio Frequency Interference.
RFT (Radio Frequency Terminal)
Equipment including an antenna, U/C, D/C, HPA, and LNA which provides the up and
down conversion of signals in a satellite-based network.
R/O (Receive Only)
Referring to an earth station that receives transmissions only and does not
transmit.
Routing
The process of selecting the correct circuit path for a message.
SAC (Satellite Access Controller)
Skystar equipment that contains the satellite transmission facility components
and data network components.
SCPC
Single Channel Per Carrier.
SDLC
Synchronous Data Link Control.
SNA
System Network Architecture.
S/N (Signal-to-Noise Ratio)
Relative power of the signal to the noise in a channel.
SSPA (Solid-State Power Amplifier)
A lower powered transmitter used for amplification of RF signals at a remote
site.
SVC
Switched Virtual Circuit.
Synchronous
When characters or bits are transmitted at a fixed rate with the transmitting and
receiving devices synchronized.
TCP/IP
Transmission Control Protocol/Internet Protocol.
TDM
Time Division Multiplexing.
TDMA (Time Division Multiple Access)
Refers to a form of multiple access where a single carrier is time shared by many
users. Signals from earth stations reaching the satellite consecutively are processed in
time segments without overlapping.
Teleconference
A meeting involving at least one uplink and a number of downlinks at different
locations.
Telemetry
The use of telecommunications for automatically indicating or recording
measurements at a distance from the measuring instrument.
Terrestrial Interference
Interruptions in a satellite signal caused by high power land-based microwave
links in the 4 GHz band.
Tracking
Using earth-based equipment to follow a satellite’s position.
Transfer Orbit
An intermediate elliptical orbit used to reach geosynchronous orbit, where the
apogee is the same altitude as the final operating orbit.
Transponder
The circuitry on a satellite that receives the uplink signal, amplifies it, then
retransmits it as the downlink signal.
TWTA
Traveling Wave Tube Amplifier. Satellite electronic components that provide power
for the transponders (in watts).
U/C (Up converter)
Equipment that performs frequency conversion to a higher (RF) band.
Uplink
Transmission of information from an earth station to a geostationary
communications satellite.
VSAT (Very Small Aperture Terminal)
A small earth station, usually less than 2.4 meters, used for satellite
communications.
X.25
Protocol; a set of packet switching standards.
| 
