Glossary of Terms

A circuit which automatically controls the frequency of a signal.

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

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

with digital satellite reception, the sound is transmitted in packages and is selected either in a special audio mode or pre-selected by using the installation set-up.  This makes it possible to select between several different languages in a channel.  The number of choices is dependent on what is available in the signal. 

Antenna mount that requires two separate adjustments to move from one satellite to another.

The angle of rotation (horizontal) that a ground based parabolic antenna must be rotated through to point to a specific satellite in a geosynchronous orbit. The azimuth angle for any particular satellite can be determined for any point on the surface of the earth giver the latitude and longitude of that point. It is defined with respect to due north as a matter of easy convenience.

The basic direct output signal in an intermediate frequency based obtained directly from a television camera, satellite television receiver, or video tape recorder. Baseband signals can be viewed only on studio monitors. To display the baseband signal on a conventional television set a "modulator" is required to convert the baseband signal to one of the VHF or UHF television channels which the television set can be tuned to receive.

The rate of data transmission based on the number of signal elements or symbols transmitted per second. Today most digital signals are characterized in bits per second.

The angle or conical shape of the beam the antenna projects. Large antennas have narrower beamwidths and can pinpoint satellites in space or dense traffic areas on the earth more precisely. Tighter beamwidths thus deliver higher levels of power and thus greater communications performance.

Slang for a communications satellite located in geosynchronous orbit.

A single digital unit of information

The fraction of a sequence of message bits that are in error. A bit error rate of 10-6 means that there is an average of one error per million bits.

The speed of a digital transmission, measured in bits per second.

The ratio of the received carrier power and the noise power in a given bandwidth, expressed in dB. This figure is directly related to G/T and S/N; and in a video signal the higher the C/N, the better the received picture.

That circular orbit in space 22,237 miles from the surface of the earth at which geosynchronous satellites are placed. This orbit was first postulated by the science fiction writer Arthur C. Clarke in Wireless World magazine in 1945. Satellites placed in these orbits, although traveling around the earth at thousands of miles an hour, appear to be stationary when viewed from a point on the earth, since the earth is rotating upon its axis at the same angular rate that the satellite is traveling around the earth.

Direct broadcast satellite. Refers to service that uses satellites to broadcast multiple channels of television programming directly to home mounted small-dish antennas.

The offset angle of an antenna from the axis of its polar mount as measured in the meridian plane between the equatorial plane and the antenna main beam.

Conversion of information into bits of data for transmission through wire, fiber optic cable, satellite, or over air techniques. Method allows simultaneous transmission of voice, data or video.

The Digital Video Broadcast group was created to establish a technical framework for the introduction of digital video broadcasting systems.

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.

Electronic Program Guide.  A software that enables viewers to navigate easily among a large number of channels provided by digital technology, in order to select a program or service.

Ratio of antenna focal length to antenna diameter. A higher ratio means a shallower dish.

This term has at least two key meanings within the field of satellite communications. It is used to describe the transmission of video programming from a distribution center. It is also used to describe the feed system of an antenna. The feed system may consist of a subreflector plus a feedhorn or a feedhorn only.

Distance from the center feed to the center of the dish.

The area toward which the primary reflector directs and concentrates the signal received.

A map of the signal strength showing the EIRP contours of equal signal strengths as they cover the earth's surface. Different satellite transponders on the same satellite will often have different footprints of the signal strength. The accuracy of EIRP footprints or contour data can improve with the operational age of the satellite. The actual EIRP levels of the satellite, however, tends to decrease slowly as the spacecraft ages.

Adds unique codes to the digital signal at the source so errors can be detected and corrected at the receiver.

The number of times that an alternating current goes through its complete cycle in one second of time. One cycle per second is also referred to as one hertz; 1000 cycles per second, one kilohertz; 1,000,000 cycles per second, one megahertz: and 1,000,000,000 cycles per second, one gigahertz.

A measure of amplification expressed in dB.

The prefix Giga means billion, and Hertz means cycles per second.  Signals in the GHz range are often referred to as microwave.

The frequency range from 18 to 31 GHz.

The frequency range from 10.9 to 17 GHz.

The frequency range from 0.5 to 1.5 GHz. Also used to refer to the 950 to 1450MHz used for mobile communications.

An electronic unit mounted on the satellite dish used for receiving satellite signals and converting them to signals that can be used by the receiver.

Local oscillator part of the LNB/F.  Converts the satellite frequency down to a frequency usable by the receiver.

The prefix Mega means million, and Hertz means cycles per second.

Moving Picture Experts Group.  Body established by the International Standards Organization to provide the basis for a picture coding and compression system.

The agreed standard covering the compression of data (coding and encoding) for digital television.

Main Provile at High Level - The agreed much higher bit-rate system adopted to provide high definition television in wide screen format.

A number of digital channels transmitted from one source.  Grouped under separate headings in a channel list.

A video standard established by the United States (RCA/NBC} and adopted by numerous other countries. This is a 525-line video with 3.58-MHz chroma subcarrier and 60 cycles per second.

The German developed TV standard based upon 50 cycles.per second and 625 lines.

The most frequently found satellite TV antenna, it takes its name from the shape of the dish described mathematically as a parabola. The function of the parabolic shape is to focus the weak microwave signal hitting the surface of the dish into a single focal point in front of the dish. It is at this point that the feedhorn is usually located.

A feature that allows parents to "Lock" programs that they consider unsuitable for children.  A "Locked" channel or program can only b "unlocked" with the special parental access code.

Program Clock Reference

In some installations, the feedhorn has the capability of receiving the vertical and horizontal transponder signals simultaneously, and routing them into separate LNAs for delivery to two or more satellite television receivers. Unlike most domestic satellites, the Intelsat series use a technique known as left-hand and right-hand circular polarization.

Antenna mechanism permitting steering in both elevation and azimuth through rotation about a single axis. While an astronomer's polar mount has its axis parallel to that of the earth, satellite earth stations utilize a modified polar mount geometry that incorporates a declination offset.

System of modulating a satellite signal.

Loss of signal at Ku or Ka Band frequencies due to absorption and increased sky-noise temperature caused by heavy rainfall.

Radio Frequency

A serial communication standard data port found on most receivers.

Short for Sony/Philips Digital Interface, a standard audio file transfer format. Developed jointly by the Sony and Phillips corporations, S/PDIF allows the transfer of digital audio signals from one device to another without having to be converted first to an analog. format. Maintaining the viability of a digital signal prevents the quality of the signal from degrading when it is converted to analog.

A dish shaped antenna with the ability to reflect satellite signals to a LNB/F.

A company that distributes a program or programs to the end user.

A method used to transmit a large number of signals over a single satellite transponder.

An adjustment that compensates for slight variance in angle between identical senses of polarity generated by two or more satellites.

Signal to Noise Ratio.  Signal quality measurement.

A second signal "piggybacked" onto a main signal to carry additional information. In satellite television transmission, the video picture is transmitted over the main carrier. The corresponding audio is sent via an FM subcarrier. Some satellite transponders carry as many as four special audio or data subcarriers whose signals may or may not be related to the main programming.

Size of the digital package transmission.

A combination receiver, frequency converter, and transmitter package, physically part of a communications satellite. Transponders have a typical output of five to ten watts, operate over a frequency band with a 36 to 72 megahertz bandwidth in the L, C, Ku, and sometimes Ka Bands or in effect typically in the microwave spectrum, except for mobile satellite communications. Communications satellites typically have between 12 and 24 onboard transponders although the INTELSAT VI at the extreme end has 50.

Transport Stream.

Television Receive Only terminals that use antenna reflectors and associated electronic equipment to receive and process television and audio communications via satellite. Typically small home systems.

Very small aperture terminal. Refers to small earth stations, usually in the 1.2 to 2.4 meter range. Small aperture terminals under 0.5 meters are sometimes referred to Ultra Small Aperture Terminals (USAT's)

A metallic microwave conductor, typically rectangular in shape, used to carry microwave signals into and out of microwave antennas.