SATELLITE COMMUNICATIONS GLOSSARY
The following terms and definitions will help familiarize you with your Satellite solution.
ANTENNA – A device for transmitting and receiving signals. An antenna is part of an Earth Station.
AMPLIFIER – An amplifier is a device that increases the power of a signal by use of an external energy source.
APERTURE – The cross-sectional portion of the satellite antenna that transmits and receives the signal.
ATTENUATION – Signal loss due to cabling, or reduction of signal strength due to atmospheric conditions.
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 given the latitude and longitude of that point. It is defined with respect to due north as a matter of easy convenience.
BACKHAUL – A terrestrial communications channel linking an earth station antenna to a local switching network or population center.
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).
BLOCK UP CONVERTER (BUC) – The transmitter for a satellite antenna. It converts a band from a lower frequency to a higher frequency, and performs power amplification, normally located directly at the satellite antenna input, or close to it.
CHANNEL – A Channel is a frequency band in which a specific broadcast signal is transmitted. Channel frequencies are specified in the United States by the Federal Communications Commission. The higher the frequency, the higher the gain that can be achieved with smaller antenna sizes. Higher frequency bands are more susceptible to rain fade.
DOWNLINK – The link from the satellite down to the Earth Station.
EARTH STATION – The ground equipment that transmits and receives electromagnetic waves, also referred to as a parabolic antenna.
FDMA – Frequency Division Multiple Access. A way of sharing a channel by assigning different frequencies to different users.
FOOTPRINT – The area of the Earth’s surface from which an Earth Station can transmit to or receive from a particular satellite.
GAIN – A measure of amplification expressed in decibels.
GEOSTATIONARY EARTH ORBIT (GEO) – Satellites orbiting at 35,786 km (22,282 mi) above the equator in the same direction and speed as the earth rotates on its axis, making them appear as fixed in the sky.
FREQUENCY BANDS – Internationally, frequencies are divided into well-defined bands. For satellites, the relevant bands are:
L-Band – As defined by IEEE std 521, the frequency range from 1 to 2 GHz. The L-band term is also used to refer to the 950 to 1450MHz frequency range used for mobile communications. L-band is used for Mobile Satellite Services and offers good penetration through adverse weather conditions and foliage.
C-Band – The frequency range from 3.7 to 6.2 GHz. Transmissions are less affected by atmospheric conditions such as snow and rain. However, C-band transmissions have low power, so Earth Stations must be rather large to compensate dish size. Applications include public switched networks and Internet trunking.
X-Band – The frequency range from 8.0 – 12.0 GHz. The X-band frequency enables high power operations with very small terminals. Applications include COTM, manpacks, emergency communications and airborne and shipboard platforms. X-band is also less vulnerable to rain fade and adjacent satellite side lobe interference than other frequencies.
Ku-Band – The frequency range from 11.7 to 14.5 GHz. Ku-band has higher power than C-band allowing for smaller dishes to be used. However, the higher frequency of Ku-band makes it more susceptible to adverse weather conditions than C-band. Applications include VSAT, rural telephony, satellite news gathering, videoconferencing, and multimedia.
Ka-Band – The frequency range from 17.7 to 21.2 GHz. Has a higher power than Ku-band allowing for smaller dishes to be used and therefore, will be used for high-bandwidth interactive services such as high-speed Internet, videoconferencing, and multimedia applications. Ka-band transmissions are more sensitive to poor weather conditions than Ku-band.
HUB – The master station through which all communications, to, from and between terminals must flow.
KBPS – Kilobits per second. Refers to transmission speed of 1,000 bits per second. KHZ KiloHertz. One KiloHertz is the equivalent of one thousand Hertz, or one thousand cycles per second. Used to measure frequency and bandwidth.
LAN – Local Area Network. A geographically localized network.
LATENCY—The time it takes for a signal to go from the sending station through the satellite to the receiving station. All stationary satellites are located 22,300 miles above the equator. This means that the round trip is 90,000 miles or more. The speed of light is 186,000 MPH, so the time it takes for a round trip is about 500 milliseconds (1/2 second).
LINEAR/PLANE POLARIZATION – Polarization of an electromagnetic wave in which the electric vector at a fixed point in space remains pointing in a fixed direction, although varying in magnitude. With satellites, the planes are referred to horizontal polarization or vertical polarization and allows for frequency re-use on the satellite for more bandwidth capability.
LOW EARTH ORBIT (LEO) -Satellites orbiting from 160- 2,000km above the earth and will take approximately 1.5 hours for a full orbit, which only covers a portion of the earth’s surface at any time.
LOW NOISE AMPLIFIER (LNA) – A preamplifier between the satellite 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. This boosts the desired signal while adding as little noise or distortion as possible.
LOW NOISE BLOCK DOWNCONVERTER (LNB) – A combination of Low Noise Amplifier and downconverter built into one device attached to the feed. It is used for the downlink satellite transmission by converting a band from a higher frequency to a lower frequency. This is simply the receiver on a satellite dish.
MODEM – A piece of network equipment containing a modulator and demodulator for receiving or transmitting satellite signals.
MEDIUM EARTH ORBIT (MEO) – Satellites located above LEO and below GEO satellites, typically traveling in an elliptical orbit over the North and South Pole or in an equatorial orbit.
MHZ – MegaHertz. One MegaHertz is equivalent of one million Hertz, or one million cycles per second. Used to measure frequency and bandwidth.
POLARIZATION – A technique used by satellite operators to reuse the satellite transponder frequencies when transmitting these signals to Earth. Two methods are possible: linear and circular. To successfully receive and decode these signals on earth, the antenna must be outfitted with a properly polarized linear or circular feedhorn to select the signals as desired.
RAIN FADE – The reduction of satellite signal strength due to rainfall.
ROUTER – A physical device joining multiple networks together by forwarding IP packets based on network layer information and enabling applications such as VoIP, video and data.
SATELLITE – Communications satellites orbit the earth and transmit and receive radio signals from earth stations. Satellite Receiver—A receiver designed for a satellite reception system, which receives modulated signals from an LNA or LNB and converts them into their original audio, video, or data form.
SPOT BEAM – A satellite beam with concentrated geographic coverage.
TDMA – Time Division Multiple Access. A way of sharing a channel by assigning different time slots to different users.
TELEPORT – A Telecommunications Hub, or Super Hub, which provides access to communications satellites and other long-distance media.
TERMINAL – One of the communications stations that receives, processes, and transmits signals between itself and a satellite.
TRANSPONDER – A device located on board the satellite which receives signals uplinked from an earth station and amplifies and transmits them back to earth on a difference frequency.
UPLINK – The link from the earth station up to the satellite.
VSAT – Very small aperture terminal. Refers to small earth stations, with antennas usually in the 1.2 to 2.4 meter range. Small aperture terminals under 0.5 meter are sometimes referred to Ultra Small Aperture Terminals (USAT’s)