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 dipole 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.
Backhaul
A terrestrial communications channel linking an earth
station to a local switching network or population centre.
Bandwidth
How much data you can send through a connection. Usually
measured in bits-per-second. A full page of English text is
about 16,000 bits. Sometimes it refers to thousands of bytes per
sec (kB), the page referred to would be 2Kb.
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.
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.
DAMA
Demand-Assigned Multiple Access - A highly efficient means
of instantaneously assigning telephony channels in a transponder
according to immediate traffic demands.
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.
DVB
Digital Video Broadcasting - The European-backed project to
harmonise adoption of digital video.
Earth Station
The term used to describe the combination or antenna,
low-noise receive a signal transmitted by a satellite. Earth
Station antennas vary in size from the.2 foot to 12 foot (65
centimetres 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.
Firewall
A special computers set up on a network to prevent intruders
from stealing or destroying confidential files.
Footprint
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.
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.
Internet
A worldwide network of networks, the Internet is not an
online service and has no real central "hub." Rather,
it is a collection of millions of networks, online services, and
single-user components as well as Web servers and email
services.
ISP
Internet Service Provider. A company that provides an
Internet connection.
Intranet
Internal systems, based on Internet technology, designed to
connect the members of a specific closed-user group. An Intranet
is a private Internet: a private network, usually a LAN or WAN,
that enables the use of Internet based applications in a secure
and private environment.
Ku Band
The frequency range from 10.9 to 17 GHz.
Router
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.
Server
A server is a computer that handles requests for data,
e-mail, web pages, file transfers, and other network services
from other computers
SSPA
Solid state power amplifier. A VSLI solid state device that
is gradually replacing Travelling Wave Tubes in satellite
communications systems because they are lighter weight and are
more reliable.
Transponder
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.
Uplink
The earth station used to transmit signals to a satellite.
VSAT
Very Small Aperture Terminal. An earth station, used for the
reliable transmission of data, video, or voice via
geo-stationary satellite, with a relatively small dish-antenna
(often 2.4m or 3.8m in diameter).
WAN
Wide Area Network. Two or more local area networks joined
over any geographical distance.
Wireless Network / WiFi
This uses low power microwave radio to link one or more
groups of users together, or to provide a link between two
buildings. It can span several kilometres point to point but
cannot be used where trees are in the way (water in the leaves
absorb the radio signal). WiFi hotspots cover an area of a
hundred metres radius using multiple channels to provide
multi-user access to a central Internet access point.
