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Satellite Terminology


A device that enables an input signal to control a source of power, and thus is capable of delivering at its output a reproduction or analytic modification of the essential characteristics of the signal.

Amplitude Modulation
The process by which a continuous high frequency wave (carrier) is caused to vary in amplitude by the action of another wave containing information.

The most distant point from the center of the earth to an orbit around it.

Ascending chain
The fixing of telecommunications equipment used in the transmission of signals to the satellite.

A general term used to denote a decrease in signal magnitude in transmission from one point to another.

Attenuator range
A transponder gain adjustment in decibels.

The angle in the horizontal plane between a reference line and the horizontal projection of the line joining the two points. True north is used where no reference direction is stated.

Back off
The process of reducing the input and output power levels of a traveling wave tube to obtain more linear operation.

Difference between two frequencies. Frequency range used by a signal.

The band of frequencies occupied by the signal before it modulates the carrier frequency to form the transmitted line or radio signal.

Bit Error Rate (BER)

The rate of errors to the total number to the total number of bits being sent in a data transmission from one location to another.

BBoltzmann's constant
The number k that relates the average energy of a molecule to the absolute temperature of the environment. k is approximately k=1.38 x 10-23 joules/kelvin = -128.6 dBJ/K.

Binary phase shift keying. A form of modulation in which binary data is transmitted by changing the carrier phase by 180 degrees.

In general, wide bandwith equipment or systems that carry signals occupying a large portion of electromagnetic spectrum. A broadband communication system can simultaneously accomodate television, voice, data and many other services.

Bit Error Rate (BER).
Tasa de bits erróneos. Relación del número de bits erróneos al total de bits transmitidos en un determinado intervalo de tiempo.

Banda Ka.
Rango de frecuencias de 20 a 30 GHz utilizada para la transmisión/recepción de señales desde estaciones fijas y móviles.

Técnica de modulación digital por corrimiento de fase binario. La información digital se transmite cambiando la fase de la portadora 180°.


An operation directed to one or more slaves on one or more segments.

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-to-noise density ratio (C/No)
The ratio between the carrier and the noise density in a 1 Hz bandwidth. It is expressed in dB/Hz.

Carrier-to-noise ratio (CNR) (C/No)
The ratio of the powers of the carrier and the noise after specified bandlimiting and before any nonlinear process, such as amplitude limiting and detection. It is expressed in dB.

Cassegrain reflector antenna

A paraboloidal-reflector antenna with a convex subreflector, located between the vertex and the prime focus of the main reflector.

C Band
Frequency range from 3.7 to 6.4 GHz used for the transmission/reception of satellite fixed services and microwave signals.

Comité Consultif Internationale Télégraphique et Téléphone (International Consultative Comittee for Telephone and Telegraph). An advisory comittee established under the United Nations in accordance with the International Telecommunications Convention Article 13, to study and recommend solutions for questions on technical operation and tariffs.

International Radio Consultative Committee.

Code Division Multiple Access. Technique to access the satellite in which the signal is transmitted in a given bandwidth in certain periods of time through a transformattion code.

Center of box
Central point of the orbital location if it is viewed as an imaginary square in which the satellite drifts in any direction with a certain tolerance range.

An instruction represented in the control field of a protocol data unit (PDU) and transmitted by a logical link control (LLC). It causes the addressed LLCs to execute a specific data link control function.

Continous wave
Unmodulated signal.

Control Center
Systems and equipment that control the satellites, receive telemetry and transmit commands.

Portion of the Earth that is reached by the radiofrequency emitted by a satellite. Also known as service area.

Cross-pol isolation
The ratio of the wanted signal level to the unwanted signal level in the same receiver channel when the transmitting antenna is radiating nominally orthogonally polarized signals at the same frequency and power level.

Clean, unmodulated carrier wave.

Demand Asignation Multilple Access. Technique to access the satellite in which a bandwidth is shared by several stations in different lapses of time according to a transmission request and making it available to be used by other stations in the system dolo disponible para el uso de otras estaciones del sistema.

A standard unit for expressing the ratio between two parameters using logarithms to the base 10. Decibels provide a convenient format to express voltages or powers that range several orders of magnitude for a given system.

Decibels relative to carrier power level.

Decibels relative to the miliwatt expressed power.

Descending chain
The fixing of telecommunications equipment used in the reception of signals from the satellite.

Ratio of the energy per bit to that of the noise spectral density, in watts per hertz.

Earth station
A ground station designed to transmit to and to receive transmission from communication satellites.

Edge of coverage
Limit of a satellite's defined service area.

Effective Isotropic
Radiated Potency (EIRP) In a given direction, the gain of a transmitting antenna multiplied by the net power accepted by the antenna from the connected transmitter.

Elevation Angle
The 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 it were tilted to a point directly overhead, the satellite antenna would have an elevation of 90 degrees.

Expected operational life
The period of time a satellite is capable of rendering services.

Frequency Division Multiple Access. A method of providing multiple access to a communication satellite in which the transmissions from a particular earth station occupy a particular assigned frequency band. In the satellite the signals are simultaneously amplified and transposed to a different frequency band and retransmitted. The earth station identifies its receiving channel according to its assigned frequency band in the satellite signal.

Frequency band
Group of frequencies between given limits.

A figure of merit of an antenna and low noise amplifier combination expressed in dB. "G" is the net gain of the system and "T" is the noise temperature of the system. The higher the number, the better the system.

Geostationary satellite
A sophisticated electronic communications relay station orbiting 22,237 miles above the equator moving in a fixed orbit at the same speed and direction of the earth (about 7,000 mph east to west).

High Power Amplifier
A device that increases the power levels of a signal in the final stage before being transmitted to the satelllite.

Interference detection, analysis and eradication technique.

Intermodulation noise
Noise occurring when one or more signals go through a non-lineal device with very high input levels producing sporadic signals.

International Telecommunications Union.

Ka Band
Frequency range from 20 to 30 GHz used for transmission/reception of signals from fixed and mobile stations.

Ku Band
Frequency range from 11 to 18 GHz used for the transmission/reception of satellite fixed services and microwave signals.

Landing rights
Permission granted by the authority of a country to transmit signals from earth stations on its territory to a determined satellite.

L Band
Frequency range from 1 to 2 GHz, used in satellite mobile communications.

Low Noise Amplifier
A device that amplifies the satellite signal received through an antenna with a minimal noise contribution.

Modulated carrier
A signal that varies its amplitude, phase or frequency regarding a known reference according to the modulation technique used in the transmission.

Transmission from one point to multiple users of a determined group network, not necessarily to the whole of it.

Unwanted disturbances superimposed over a useful signal, which tend to obscure its information content.

Noise figure
The ratio of the total noise power per unit bandwidth delivered by the system into an output termination to the portion thereof engendered at the input frequency by the input termination, whose noise temperature is standard (290 kelvins) at all frequencies.

Noise power density
The noise power generated per bandwidth unit or in a determined reference bandwidth.

Occasional service
A service given on a determined date and time, on an irregular basis.

Orbital slot
It is the satellite position on the orbital arc. It is expressed on degrees (East/West) from the Greenwich meridian.

Phase shifting keying (PSK)
The form of phase modulation in which the modulating function shifts the instantaneous phase of the modulated wave among predetermined discrete values.

Position attenuator
A device that reduces the power at the input of the system. In a communications satellite, it reduces the sensibility in the reception. It is expressed on dB.

Pulse Code Modulation
The type of pulse modulation where the magnitude of the signal is sampled and each sample is approximated to a nearest reference level (quantizing). Then a code, which represents the reference level, is transmitted to the distant location.

Rain attenuation
Loss or reduction of power levels and polarization of the radioelectric waves due to rain or very dense clouds. It depends on a region's rainfall rate.

A process that calculates the exact position of a satellite.

A body which revolves around another body and which has a motion primarily and permanently determined by the force of attraction of this body.

Signal-to-noise ratio
The ratio of the value of the signal to that of the noise.

Single Channel per Carrier (SCPC)
A method used to transmit a large number of signals over a single satellite transponder.

Solar outages
Outage that occurs when the sun passes behind or near the satellite and within the field of view of the antenna. This field of view is usually wider than the beamwidth. Timing of solar outages can be exactly predicted for each site.

Space waste
Fabricated objects that travel around the Earth without any useful means.

Spin satellite
A satellite that is stabilized by the spin of one of its sections.

Station keeping
Range in which a satellite can move inside the imaginary square around its orbital slot.

Switchable coverage
Satellite hability to change its service area.

Time Division Multiple Access. A technique whereby earth stations communicate with each other on the basis of non-overlapping time sequenced bursts of transmission through a common satellite repeater.

Information from the satellite about its health and configuration.

Thermal noise
Noise occurring in electric conductors and resistors and resulting from the random movement of free electrons contained in the conducting material. The name derives from the fact that such random motion depends on the temperature of the material.

Transmisor locating system (TLS)
A system that finds radioelectric interference sources.

A transmitter-receiver facility, the fonction of which is to transmit signals automatically when the proper interrogation is received.

Triaxial satellite
A satellite that is stabilized through its three axis and tridirectional movements due to its thrusters.

Ultra small aperture terminal. Earth stations with antennas that have a diameter of less that 70 cm. They are used for satellite data transmission/reception.

Very small aperture terminal. Earth stations with antennas that have a diameter of 2.4 meters or less.

A system of material boundaries or structures for guiding electromagnetic waves.

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