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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
The process by which a continuous high frequency wave (carrier)
is caused to vary in amplitude by the action of another wave containing
The most distant point from the center of the earth to an orbit
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.
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.
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.
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.
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.
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
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
Noise occurring when one or more signals go through a non-lineal
device with very high input levels producing sporadic signals.
International Telecommunications Union.
Frequency range from 20 to 30 GHz used for transmission/reception
of signals from fixed and mobile stations.
Frequency range from 11 to 18 GHz used for the transmission/reception
of satellite fixed services and microwave signals.
Permission granted by the authority of a country to transmit signals
from earth stations on its territory to a determined satellite.
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.
A signal that varies its amplitude, phase or frequency regarding
a known reference according to the modulation technique used in
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.
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
A service given on a determined date and time, on an irregular
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
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.
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
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.
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.
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.
Fabricated objects that travel around the Earth without any
A satellite that is stabilized by the spin of one of its sections.
Range in which a satellite can move inside the imaginary square
around its orbital slot.
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.
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
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
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