| 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). |
| Baseband |
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. |
| Beamwidth |
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 subreflector 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 downlinked 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 baseband
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 upconverts
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 downconversion
or a satellite modulator
before upconversion. |
| 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 Downconverter) |
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
downconverter. |
| 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
Inteference |
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. |
