Earth Station

The term used to describe a satellite communication facility which includes the combination of an antenna, with an LNA or LNB, the down-converter, and the satellite receiver electronics used to receive a signal transmitted by a satellite.  Satellite dish sizes vary from as small as .2 feet to as much as 100 feet.  If you receive a satellite signal at your home via a satellite dish located on your premises you are considered an Earth Station in the broadest interpretation of the term.  The actual designation of an Earth Station is usually reserved for sites that are capable of both transmitting and receiving satellite signals.  Transmit/Receive sites are sometimes referred to as "Teleports".

Echo Canceller

An electronic circuit which attenuates or eliminates the echo effect on satellite telephony circuits.  Echo cancellers are largely replacing archaic echo suppressor circuitry.

Echo Effect

A time-delayed electronic reflection of a speaker's voice.

Edge of Coverage

The limit of a satellite broadcast's defined service area.  This is roughly the area in which the signal level of a satellite generated signal drops below acceptable levels for reception.  A loss of 3 dB in signal level when compared to the signal level at the beam center is usually the demarcation point for edge of coverage although reception may still be possible beyond this -3 dB point.

EIRP (Effective Isotropic Radiated Power)

This term describes the strength of the signal leaving the satellite antenna or the transmitting earth station antenna.  It is used in determining the C/N (carrier to noise) and the S/N (signal to noise) ratios.  The transmit power value in units of dBW (decibel Watts) is expressed by the product of the transponder output power and the gain of the satellite transmit antenna.


The angle in degrees at which an antenna is tilted above the horizon to acquire the signal for a given satellite.  Antennas pointed at the horizon from a level surface have an elevation of 0.  Antennas pointed directly overhead from a level surface have an elevation of 90.  Equatorial antennas use an angle of 90 and this angle will decrease towards 0 as you move north or south from the equator.  The highest evelation value in degrees will usually be for the satellite directly due south* of the antennas position and will fall off slightly to the east and west depending on the satellite's position in the portion of the equatorial arc visible from the antennas position.

* Some satellites are positioned in what are referred to as inclined orbits.   These satellites are positioned slightly north or south of the true equatorial plane.  These satellites will have elevation values that will differ in correspondence with the number of degrees of inclination from the true equatorial plane.


A device used to electronically alter a signal so that it can only be viewed by a receiver equipped with the proper decoder protocols and authorizations.

EOL (End of Life)

The date at which the usable life of a satellite is expected to end.

Entitlement Control Message Stream (ECM)

These messages define a program's access requirements, specifying the tiers required for subscription, and the cost associated with impulse purchase of the program. Encrypted program keys are delivered in the ECM stream.

Entitlement Management Message Stream (EMM)

Entitlement Management Messages define access rights for each individual decoder. The EMM stream is processed with the access control device, but the user processor is responsible for buffering EMMs and feeding them via an interface to the access control device.


To scramble the contents of a file or message in such a way as to make it unreadable to everyone except those with a key or code. The code makes it possible to unscramble the encrypted file or message.


The process of encoding data so that it cannot be interpreted by anybody or any machine that does not have the key or code. This process is also called "scrambling".

Equatorial Orbit

An orbit with a plane parallel to the earth's equator.

ESC (Engineering Service Circuit)

The 300 - 3400 Hz voice plus teletype (S+DX) channel that is used for earth station-to-earth station and earth station-to-operations center communications for the purpose of system maintenance, coordination and general system information dissemination.   In analog (FDM/FM) systems there are two S+DX channels available for this purpose in the 4,000-12,000 Hz portion of the baseband signal.  In digital systems there are one or two channels available which are usually confined to a 32 or 64 Kbps digital signal and combined with the earth station traffic digital bit stream.  Modern ESC equipment interfaces with any mix of analog and digital satellite carriers, also with backhaul terrestrial links to local switching centers.


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