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Access Control

A means of controlling access privileges when dealing with encrypted material.  All of the functions required to encrypt a signal and authorize subscribed individuals singly or in groups.

Access Control Center

The facility that controls encryption protocols and decoder authorization information.  This information is then transferred to the encryption system and broadcast to the network.

Access Control Processor

A circuit found within IRT's (integrated receiver/transcoders) and IRD's (integrated receiver/decoders) which processes the authorization information embedded within an encrypted signal..

Algorithms

A programmed set of mathematical formulas that perform a specific function.  Computer environments use algorithms to process information.

Amplitude Modulation (AM)

The baseband signal at a given frequency is caused to vary in height (amplitude).  This variation of the carrier wave height allows the creation of the desired information content.

Amplifier

A device used to increase the strength of an electronic signal.

Analog

A means of transmitting information via a modulated carrier wave.  Analog information content is inserted into the modulation using changes in continuously variable quantities such as light, sound, heat and pressure.

Analog-to-Digital Conversion (ADC)

The conversion of analog type signals to a digital format.   The reverse transition, Digital-to-Analog is known as (DAC).

ANIK

The Canadian domestic satellite system which is used primarily by CSC, the Canadian Broadcasting Corporation. This network of satellites transmits a variety of network signals throughout Canada.  There is also some transponder service to the United States and Mexico.  This system carries both analog and digital services which provide video, audio, long distance voice and data services.   Some of the broadcasts are in French.

Antenna

A device used to transmit and/or receive radio waves.   Depending on their use and frequency range, antennas can be vastly different in shape and appearance.
They may range from items as simple as a single piece of wire, a di-pole (a simple antenna using two polarities, (-) and (+)), a grid such as a yagi array (this is the one that you see on top of most homes and is used primarily for local television reception), a horn, a helix, a parabolic-shaped dish, or a phase array of active electronic elements on virtually any flat or convoluted surface.

Anti-taping

The process by which a video signal is altered to prevent high quality reproduction by VCR or VTR machines which have not been modified to overcome the alterations in the signal.

Aperture

A cross sectional area of the antenna which is actually exposed to the satellite signal.

Apogee

The point in an elliptical orbit in which an object is farthest from the object it is orbiting.  Geosynchronous satellites are first launched into an elliptical orbit with apogees of 22,237 miles.  When the satellites reach this apogee, a rocket motor is fired to place the satellite into a permanent circular orbit at this distance.

Apogee Kick Motor (AKM)

The rocket motor that is fired when a geosynchronous satellite reaches it's proper apogee.  This motor causes the satellite orbit to change from elliptical to circular.

Aspect Ratio

The ratio of the width of a display screen to it's height.   For standard television sets this ratio is 4:3.  For HDTV the ratio is 16:9.   The aspect ratio and the number of vertical scan lines in an image are what determine the sample rate to be used when digitizing a video signal.

Attenuation

The loss in power of electromagnetic signals between the transmission and reception sites.  Many variables contribute to the value of this type of loss.  Two of the most common natural causes of satellite signal attenuation are atmospheric changes, (such as clouds, rain, and snow) and solar activity (such as sunspots and sun outages).  Attenuators are devices that allow this signal loss to be varied on purpose either to a fixed value or through a variable range.

Attitude

The attitude of a satellite refers to it's orientation in relationship to the earth and the sun.  Geosynchronous satellites must maintain the proper attitude in order to allow consistent reception of the signals over targeted areas.

Attitude Control

Attitude control is maintained by periodic use of small rocket motors which allow ground control facilities to maintain a satellite's proper orientation in relation to the earth.  This process is also referred to as "station keeping".

Audio Subcarrier

A subcarrier inserted into the main carrier in order to transmit additional information discretely.  The audio (or voice) subcarriers in a typical satellite video carrier are inserted between 5 MHz and 8 MHz from the main carrier center frequency.

Automatic Frequency Control (AFC)

A circuit which automatically controls the frequency of a signal.  Most transmitters and receivers contain this type of circuit in order to compensate for slight variations which may occur in the modulated frequency.

Automatic Gain Control (AGC)

A circuit which automatically controls the gain of an amplifier so that the output signal is virtually constant for varying input signal levels.

AZ/EL Mount

Antenna mounts which require separate adjustments of azimuth and elevation in order to move from one satellite to another.

Azimuth

The azimuth refers to the magnetic heading for ground based parabolic antennas from a given latitude and longitude to a specific satellite in geosynchronous orbit.  This heading is in a horizontal plane from horizon to horizon.   The azimuth is defined with respect to due north as a matter of convenience. 

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