7E Communications
   

Glossary Terms Beginning A

0-9 : A : B : C : D : E : F : G : H : I : J : K : L : M

N : O : P : Q : R : S : T : U : V : W : X : Y : Z

A
Ampere (or amp): measurement of electrical current.
AC
Alternating current: type of electrical current.
AC-3
See Dolby AC-3.
Access
The general term for the ability of a telecommunications user to make use of a network.
ADC
Analogue-to-digital conversion: process of converting analogue signals to a digital representation. DAC represents the reverse translation.
Ad hoc capacity
Capacity available for bookings on a temporary basis; see Occasional capacity.
ADPCM
Adaptive differential pulse code modulation.
Algorithm
Refers to the computational code used to compress or decompress a signal.
AM
Amplitude modulation.
Amplifier
Device used to increase the power of an electronic signal.
Amplitude modulation
Process where a baseband message signal modulates (alters) the amplitude and frequency of a high-frequency carrier signal, which is at a nominally fixed frequency, so that the carrier signal varies in amplitude.
Analogue
Signal which can take on a continuous range of values between a minimum and a maximum value; method of transmitting information by continuously variable quantities, as opposed to digital transmission, which is characterized by discrete 'bits' of information in numerical steps.
ANIK
Canadian domestic satellite system.
ANSI
American National Standards Institute (US).
Antenna
Device for transmitting and receiving radio waves; in SNG, the directional parabolic antenna used for satellite transmissions.
AOR
Atlantic Ocean Region: describes coverage area of a satellite.
Aperture
Cross-sectional area of a parabolic antenna.
Apogee
The point in a satellite's orbit when it is furthest away from the Earth.
Artifacts
Imperfections in a digital signal caused by the compression process.
ASI
Asynchronous serial interface: DVB compliant signal.
ATM
Asynchronous transfer mode: division of digital signals into small packets and transmitted in small, fixed-size data 'cells'.
Atmospheric losses
Losses caused by the travel of the signal through the atmosphere - encountered on both the uplink and the downlink.
Attenuation
Loss in power of electromagnetic signals between transmission and reception points.
Attitude control
Orientation of the satellite in relationship to the Earth and the Sun.
Audio sub-carrier
An extra carrier typically between 5 and 8 MHz carrying audio information on top of a video carrier.
Automatic frequency control
AFC: circuit which automatically controls the frequency of a signal.
Automatic gain control
AGC: circuit which automatically controls the gain of an amplifier so that the output signal level is virtually constant for varying input signal levels.
Availability
The percentage of time over a year that a satellite link will be received successfully. Not particularly applicable to SNG uplinks.
Azimuth
Angle of rotation (horizontal) that a parabolic antenna must be rotated through to point to a specific satellite in a geosynchronous orbit; the compass bearing of the satellite in the horizontal plane from a point on the Earth's surface.