Advancetech

Glossary

ANIK
The Canadian domestic satellite system that transmits Canadian Broadcasting Corporation's (CSC) network feeds throughout the country. This system also carries long distance voice and data services throughout Canada as well as some trans border service to the U.S. and Mexico.

Antenna
A device for transmitting and receiving radio waves. Depending on their use and operating frequency, antennas can take the form of a single piece of wire, a di-pole a grid such as a yagi array, a horn, a helix, a sophisticated parabolic-shaped dish, or a phase array of active electronic elements of virtually any flat or convoluted surface.

Audio Subcarrier
The carrier between 5 MHz and 8 MHz containing audio (or voice) information inside of a video carrier.

Automatic Frequency Control (AFC)
A circuit which automatically controls the frequency of a signal.

Automatic Gain Control (AGC)
A circuit which automatically controls the gain of an amplifier so that the output signal level is virtually constant for varying input signal levels.

AZ/EL Mount
Antenna mount that requires two separate adjustments to move from one satellite to another;

Azimuth
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.

Backhaul
A terrestrial communications channel linking an earth station to a local switching network or population center.

Backoff
The process of reducing the input and output power levels of a traveling wave tube to obtain more linear operation.

Band Pass Filter
An active or passive circuit which allows signals within the desired frequency band to pass through but impedes signals outside this pass band from getting through.

Bandwidth
A measure of spectrum (frequency) use or capacity. For instance, a voice transmission by telephone requires a bandwidth of about 3000 cycles per second (3KHz). A TV channel occupies a bandwidth of 6 million cycles per second (6 MHz) in terrestrial Systems. In satellite based systems a larger bandwidth of 17.5 to 72 MHz is used to spread or "dither" the television signal in order to prevent interference.

Baseband
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.

Baud
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.

Beacon
Low-power carrier transmitted by a satellite which supplies the controlling engineers on the ground with a means of monitoring telemetry data, tracking the satellite, or conducting propagation experiments. This tracking beacon is usually a horn or omni antenna.

Beam width
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.

Bird
Slang for a communications satellite located in geosynchronous orbit.

Bit
A single digital unit of information

Bit Error Rate
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.

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

Blanking
An ordinary television signal consists of 30 separate still pictures or frames sent every second. They occur so rapidly, the human eye blurs them together to form an illusion of moving pictures. This is the basis for television and motion picture systems. The blanking interval is that portion of the television signal which occurs after one picture frame is sent and before the next one is transmitted. During this period of time special data signals can be sent which will not be picked up on an ordinary television receiver.

Block Down Converter
A device used to convert the 3.7 to 4.2 KHz signal down to UHF or lower frequencies (1 GHz and lower).

Broad beam
A single large circular beam that covers a large geographic area

Broadcast
The sending of one transmission to multiple users in a defined group (compare to unicast).

Business Television
Corporate communications tool involving video transmissions of information via satellite. Common uses of business television are for meetings, product introductions and training.

C Band
This is the band between 4 and 8 GHz with the 6 and 4 GHz band being used for satellite communications. Specifically, the 3.7 to 4.2 GHz satellite communication band is used as the down link frequencies in tandem with the 5.925 to 6,425 GHz band that serves as the uplink.

Carrier to Noise Ratio (C/N)
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.

Carrier
The basic radio, television, or telephony center of frequency transmit signal. The 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 Frequency
The main frequency on which a voice, data, or video signal is sent. Microwave and satellite communications transmitters operate in the band from 1 to 14 GHz (a GHz is one billion cycles per second).

Cassegrain Antenna
The antenna principle that utilizes a subreflector at the focal point which reflects energy to or from a feed located at the apex of the main reflector.

CDMA
Code division multiple access. Refers to a multiple-access scheme where stations use spread-spectrum modulations and orthogonal codes to avoid interfering with one another.

Channel
A frequency band in which a specific broadcast signal is transmitted. Channel frequencies are specified in the United States by the Federal Communications Commission. Television signals require a 6 MHz frequency band to carry all the necessary picture detail.

Circular Polarization
Unlike many domestic satellites which utilize vertical or horizontal polarization, the international Intelsat satellites transmit their signals in a rotating corkscrew-like pattern as they are down-linked to earth. On some satellites, both right-hand rotating and left-hand rotating signals can be transmitted simultaneously on the same frequency; thereby doubling the capacity of the satellite to carry communications channels.

Clamp
A video processing circuit that removes the energy dispersal signal component from the video waveform.

Clarke Orbit
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.

C/No
Carrier-to-noise ratio measured either at the Radio Frequency (RF) or Intermediate Frequency (IF)

Codec
Coder/decoder system for digital transmission.

Co-Location
Ability of multiple satellites to share the same approximate geostationary orbital assignment frequently due to the fact that different frequency bands are used.

Color Subcarrler
A subcarrier that is added to the main video signal to convey the color information. In NTSC systems, the color subcarrier is centered on a frequency of 3.579545 MHz, referenced to the main video carrier.

Common Carrier
Any organization which operates communications circuits used by other people. Common carriers include the telephone companies as well as the owners of the communications satellites, RCA, Comsat, Direct Net Telecommunications, AT&T and others. Common carriers are required to file fixed tariffs for specific services.

Companding
A noise-reduction technique that applies single compression at the transmitter and complementary expansion at the receiver.

Composite Baseband
The unclamped and unfiltered output of the satellite receiver's demodulator circuit, containg the video information as well as all transmitted subcarriers.

Conus
Contiguous United States. In short, all the states in the U.S. except Hawaii and Alaska.

Cross Modulation
A form of signal distortion in which modulation from one or more RF carrier(s) is imposed on another carrier.

EOL
End of Life of a satellite.

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

INMARSAT
The International Maritime Satellite Organization operates a network of satellites for international transmissions for all types of international mobile services including maritime, aeronautical, and land mobile.

INTELSAT
The International Telecommunications Satellite Organization operates a network of satellites for international transmissions.

Interference
Energy which tends to interfere with the reception of the desired signals, such as fading from airline flights, RF interference from adjacent channels, or ghosting from reflecting objects such as mountains and buildings.

IRD
An integrated receiver and decoder for reception of a transmission of voice, video and data.

ISDN - Integrated Services Digital Network.
A CCITT standard for integrated transmission of voice, video and data. Bandwidths include: Basic Rate Interface - BR (144 Kbps - 2 B & 1 D channel) and Primary Rate - PRI (1.544 and 2.048 Mbps).

Master Antenna Television (MATV)
An antenna system that serves a concentration of television sets such as in apartment buildings, hotels or motels.

Megahertz (MHz)
Refers to a frequency equal to one million Hertz, or cycles per second.

Microwave
Line-of sight, point-to-point transmission of signals at high frequency. Many CATV systems receive some television signals from a distant antenna location with the antenna and the system connected by microwave relay. Microwaves are also used for data, voice, and indeed all types of information transmission. The growth of fiber optic networks have tended to curtail the growth and use of microwave relays.

Microwave Interference
Interference which occurs when an earth station aimed at a distant satellite picks up a second, often stronger signal, from a local telephone terrestrial microwave relay transmitter. Microwave interference can also be produced by nearby radar transmitters as well as the sun itself. Relocating the antenna by only several feet will often completely eliminate the microwave interference.

Modulation
The process of manipulating the frequency or amplitude of a carrier in relation to an incoming video, voice or data signal.

PTT - Post Telephone and Telegraph Administration
Refers to operating agencies directly or indirectly controlled by governments in charge of telecommunications services in most countries of the world.

Pulse Code Modulation
A time division modulation technique in which analog signals are sampled and quantized at periodic intervals into digital signals. The values observed are typically represented by a coded arrangement of 8 bits of which one may be for parity.

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

Receiver (Rx)
An electronic device which enables a particular satellite signal to be separated from all others being received by an earth station, and converts the signal format into a format for video, voice or data.

Receiver Sensitivity
Expressed in dBm this tells how much power the detector must receive to achieve a specific baseband performance, such as a specified bit error rate or signal to noise ratio.

Router
Network layer device that determines the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information.

Satellite
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).

Scalar Feed
A type of horn antenna feed which uses a series of concentric rings to capture signals that have been reflected toward the focal point of a parabolic antenna.

Scrambler
A device used to electronically alter a signal so that it can only be viewed or heard on a receiver equipped with a special decoder.

Secam
A color television. system developed by the French and used in the USSR. Secam operates with 625 lines per picture frame and 50 cycles per second, but is incompatible in operation with the European PAL system or the U.S. NTSC system.

SFD - Stauration Flux Density
The power required to achieve saturation of a single repeater channel on the satellite.

Sidelobe
Off-axis response of an antenna.

T1
The transmission bit rate of 1.544 millions bits per second. This is also equivalent to the ISDN Primary Rate Interface for the U.S. The European T1 or E1 transmission rate is 2.048 million bits per second.

T3 Channel (DS-3)
In North America, a digital channel which communicates at 45.304 Mbps.

TDMA
Time division multiple access. Refers to a form of multiple access where a single carrier is the shared by many users. Signals from earth stations reaching the satellite consecutively are processed in time segments without overlapping.

TI - Terrestrial Interference
Interference to satellite reception caused by ground based microwave transmitting stations.

Transmitter
An electronic device consisting of oscillator, modulator and other circuits which produce a radio or television electromagnetic wave signal for radiation into the atmosphere by an antenna.

VSWR
Voltage Standing Wave Ratio. A measurement of mismatch in a cable, waveguide, or antenna system.

VSAT
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)