Glossary of terms

A

 

Actuator 
A mechanical telescopic device for moving a motorized dish. The actuator also incorporates a sensor, so that positional information can be fed back to the positioner. 

Alignment
The process of fine tuning a dish or an electronic circuit to maximize its sensitivity and signal receiving capability. 

Amplifier
A device used to boost the strength of an electronic signal. 

Analogue
A form of transmitting information characterized by continuously variable quantities, as opposed to digital transmission, which is characterized by discrete bits of information in numerical steps. An analog signal is responsive to changes in light, sound, heat and pressure. 

Antenna
A device that collects and focuses electromagnetic waves. This process results in an energy gain, which is proportional to the surface area for a parabolic dish antenna 

Aperture
The effective area of a parabolic antenna which is exposed to the satellite signal. 

Astra
A group of satellites orbiting the earth from which the TV channels broadcast. This is one of the main satellites groups used for Europe, and in particular broadcast the Sky packages. 

Attenuation
The loss in power of electromagnetic signals between transmission and reception points. 

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. 

Azimuth/Elevation (Az/El) Mount
Antenna mount that requires two separate adjustments to move from one satellite to another: Azimuth in the horizontal plane and Elevation up from the horizon. 

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. 

 

B

 

B-Mac
A method of transmitting and scrambling television signals. In such transmissions MAC (Multiplexed Analog Component) signals are time-multiplexed with a digital burst containing digitized sound, video synchronizing, authorization, and information. 

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
Bits at unit density. A unit of transmission speed equal to the number of times the state of a line changes per second. Equal to the bit-per-second rate only if each signal element represents one bit of information. Baud rate usually refers to the number of bits transmitted each second. 

Beamwidth
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 binary digit, either a 0 or 1. Eight bits make up one byte. Bits are used in the measure of transmission capacity.

Bit Error Rate (BER)
The fraction of a sequence of message bits that are in error. A bit error rate of 10E-6 means that there is an average of one error per million bits. 

Bit Rate
The rate at which the compressed bitstream is delivered from the storage medium to the input of a decoder. 

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 Downconversion
The process of lowering the entire satellite band of frequencies in one step to some intermediate range to be processed inside the satellite receiver. 

BPSK
Binary Phase Shift Keying. 

Byte
One byte of digital video information is a packet of bits, usually but not always eight. In the digital video domain, a byte is used to represent the luminance or chrominance level. One thousand bytes is one kilobyte (kb) and one million bytes is one megabyte (MB). 

 

C

 

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. 

CATV
An abbreviation for Community Antenna Television used to describe cable TV. 

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. Television signals require an 8 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. 

Clarke Orbit (or Belt)
That circular orbit in space 35,800 km 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/N
Carrier-to-noise ratio measured either at the Radio Frequency (RF) or Intermediate Frequency (IF) 

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. 

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

Composite Video
Standard video that combines chrominance and luminance information by encoding the output of the red, green, and blue channels into the Y, I, and Q signals. composite video includes blanking and sync and is the standard for broadcast transmissions of video signals. 

Compression
Reduction of dynamic range. Used in broadcasting to achieve greater or more uniform loudness. Digital compression involves the use of algorithms to reduce the bandwidth necessary to store or transmit a digital signal.

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

 
D

 

DBS
Direct broadcast satellite. Satellites powerful enough (approximately 120 watts on the Ku-band) to transmit a signal directly to a medium to small receiving dish (antenna). DBS does not require reception and distribution by an intermediate broadcasting facility, but transmits directly to the end user. 

dBi
The dB power relative to an isotropic source. 

dBW
The ratio of the power to one Watt expressed in decibels. 

Decibel (dB)
The standard unit used to express the ratio of two power levels. It is used in communications to express either a gain or loss in power between the input and output devices. 

Declination
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. 

Decoder
A television set-top device which enables the home subscriber to convert an electronically scrambled television picture into a viewable signal. This should not be confused with a digital coder/decoder known as a CODEC which is used in conjunction with digital transmissions. 

Deemphasis
Reinstatement of a uniform baseband frequency response following demodulation. 

Demodulator
A receiver circuit which extracts or "demodulates" the "wanted "signals from the received carrier. 

Deviation
The modulation level of an FM signal determined by the amount of frequency shift from the frequency of the main carrier. 

Digital
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. Describes a system in which information is transferred by electrical pulses (1 or 0) instead of continuously varying signals as in an analogue transmission. 

Digital Composite Video
Digital video that is a digitized waveform of composite NTSC or PAL video signals, with specific values assigned to the sync, blank, and white levels. 

Dish
Jargon for a parabolic microwave antenna. 

Dolby
Dolby A, B, C, and Dolby SR are all types of electronic processing used to increase signal-to-noise ratio and reduce unwanted frequencies, specifically the tape hiss inherent in the recording process of analog signals. 

Downlink
A receiving dish. This can be a passive receiving antenna for a single household, in the case of DBS, or the antenna for the head-end of a cable system. 

DTH
Direct To Home. An industry term used to define the market for consumer satellite TV services. 

Dynamic
A term used to describe signals that are undergoing changes in amplitude or frequency. Dynamic range has to do with the range between the extremes of amplitude or frequency of an audio signal. 

 

E

 

Earth Station
The term used to describe the combination or antenna, low-noise amplifier (LNA), down-converter, and receiver electronics. used to receive a signal transmitted by a satellite. Earth Station antennas vary in size from the.2 foot to 12 foot (65 centimeters to 3.7 meters) diameter size used for TV reception to as large as 100 feet (30 meters) in diameter sometimes used for international communications. The typical antenna used for INTELSAT communication is today 13 to 18 meters or 40 to 60 feet. 

Edge of Coverage
Limit of a satellite's defined service area. In many cases, the EOC is defined as being 3 dB down from the signal level at beam center. However, reception may still be possible beyond the -3dB point. 

EIRP
Effective Isotropic Radiated Power - This term describes the strength of the signal leaving the satellite antenna or the transmitting earth station antenna, and is used in determining the C/N and S/N. The transmit power value in units of dBW is expressed by the product of the transponder output power and the gain of the satellite transmit antenna. 

Elevation
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. 

Encode/Decode
The process of converting video from its RGB components into composite video, and vice versa. 

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

Encrypt
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. 

Encryption
The science 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. 

Eutelsat
An organisation operating a group the satellites orbiting the earth from which the TV channels broadcast. This is one of the main satellite groups used for Europe. Eutelsat are operators of the Hot Bird satellites at 13 degrees EAST. 

 

F

 

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

FDMA
Frequency division multiple access. Refers to the use of multiple carriers within the same transponder where each uplink has been assigned frequency slot and bandwidth. This is usually employed in conjunction with Frequency Modulation. 

FEC
Forward Error Correction. 

Feed
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. 

Feedhorn
A satellite TV receiving antenna component that collects the signal reflected from the main surface reflector and channels this signal into the low-noise amplifier (LNA). 

Filter
A filter is used to remove spurious data from a search. Typically used when looking for a specific types of data in a list box. 

FM
Frequency Modulation - A modulation method whereby the baseband signal varies the frequency of the carrier wave. 

FM Threshold
That point at which the input signal power is just strong enough to enable the receiver demodulator circuitry successfully to detect and recover a good quality television picture from the incoming video carrier. Using threshold extension techniques, a typical satellite TV receiver will successfully provide good pictures with an incoming carrier noise ratio of 7db. Below the threshold a type of random noise called "sparkles" begins to appear in the video picture. In a digital transmission, however, signal is sudden and dramatically lost when performance drops under the threshold. 

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

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

Footprint
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. 

Forward Error Correction (FEC)
Adds unique codes to the digital signal at the source so errors can be detected and corrected at the receiver.

FPM
FEC and Phase Modulator. 

Free-to-air
Satellite TV channels designated as "Free-to-air" are broadcasted unencrypted, therefore they require no subscription or decoder to be viewed. 

Frequency
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 (Hz); 1000 cycles per second, one kilohertz (kHz); 1,000,000 cycles per second, one megahertz (MHz); and 1,000,000,000 cycles per second, one gigahertz (GHz).

 
G

 

Gain
A measure of amplification of a signal voltage or power expressed in dB. 

Geostationary
Refers to a geosynchronous satellite angle with zero inclination.So the satellite appears to hover over one spot on the earth's equator. 

Geosynchronous
The Clarke circular orbit above the equator. For a planet the size and mass of the earth, this point is 22,237 miles above the surface. 

Gigahertz (GHz)
One billion cycles per second. Signals operating above 3 Gigahertz are known as microwaves. above 30 GHz they are know as millimeter waves. As one moves above the millimeter waves signals begin to take on the characteristics of Iightwaves. 

Global Beam
An antenna down-link pattern used by the Intelsat satellites, which effectively covers one-third of the globe. Global beams are aimed at the center of the Atlantic, Pacific and Indian Oceans by the respective Intelsat satellites, enabling all nations on each side of the ocean to receive the signal. Because they transmit to such a wide area, global beam transponders have significantly lower EIRP outputs at the surface of the Earth as compared to a US domestic satellite system which covers just the continental United States. Therefore, earth stations receiving global beam signals need antennas much larger in size (typically 10 meters and above (i.e.30 feet and up). Gregorian Dual-reflector antenna systems are employing a paraboloidal main reflector and a concave ellipsoidal subreflector. 

G/T
A figure of merit of an antenna and low noise amplifier combination expressed in dB. "G" is the net gain of the system and "T" is the noise temperature of the system. The higher the number, the better the system. 

GPS
Global Positioning Satellite - a time base. 

 

H

 

Half Transponder
A method of transmitting two TV signals through a single transponder through the reduction of each TV signal's deviation and power level. Half-transponder TV carriers each operate typically 4 dB to 7 dB below single-carrier saturation power. 

HDTV
High Definition Television. 

Headend
Electronic control center - generally located at the antenna site of a CATV system - usually including antennas, preamplifiers, frequency converters, demodulators and other related equipment which amplify, filter and convert incoming broadcast TV signals to cable system channels. 

Hertz (Hz)
The name given to the basic measure of radio frequency characteristics. An electromagnetic wave completes a full oscillation from its positive to its negative pole and back again in what is known as a cycle. A single Hertz is thus equal to one cycle per second. 

 

I

 

Inclination
The angle between the orbital plane of a satellite and the equatorial plane of the earth. 

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
Integrated Receiver/Decoder. 

Isotropic Antenna
A hypothetical omnidirectional point-source antenna that serves as an engineering reference for the measurement of antenna gain. 

ITU
International Telecommunication Union 

 

K

 

Ka Band
The frequency range from 18 to 31 GHz.

Kbps
Kilobits per second. Thousands of bits per second. For example: 14.4 Kbps means 14,000 bits per second. 

Kelvin (K)
The temperature measurement scale used in the scientific community. Zero K represents absolute zero, and corresponds to minus 459 degrees Fahrenheit or minus 273 Celsius. Thermal noise characteristics of LNA are measured in Kelvins. 

Kilohertz (kHz)
KiloHertz. Kilo meaning thousand and Hertz meaning cycles so that 1KHz is equivalent to 1 thousand cycles per second. 

Ku Band
Operating in the 11 to 14 GHz range, these are medium-power satellites, requiring about 40 to 80 watts per transponder and permitting receiving dishes as small 60 cm in diameter.

 
L

 

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

Low Noise Amplifier (LNA)
This is the preamplifier between the antenna and the earth station receiver. For maximum effectiveness, it must be located as near the antenna as possible, and is usually attached directly to the antenna receive port. The LNA is especially designed to contribute the least amount of thermal noise to the received signal. 

Low Noise Block Downconverter (LNB)
An LNA which also downconverts the whole satellite bandwidth, i.e. 500 MHz for C band, at once to an intermediate frequency range. 

 

M

 

MAC (A, B, C, D2)
Multiplexed analog component color video transmission system. Subtypes refer to the various methods used to transmit audio and data signals. 

Margin
The amount of signal in dB by which the satellite system exceeds the minimum levels required for operation.

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

Mbps
Mega bits per seconds. Millions of bits per second. 

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. 

Modulator
A device which modulates a carrier. Modulators are found as components in broadcasting transmitters and in satellite transponders. Modulators are also used by CATV companies to place a baseband video television signal onto a desired VHF or UHF channel. Home video tape recorders also have built-in modulators which enable the recorded video information to be played back using a television receiver tuned to VHF channel 3 or 4. 

Mount
The structure that supports a dish antenna. Polar and Az/El mounts are the most common variety. 

MPEG
Motion Picture Experts Group. A proposed International Standards organization (IS) standard for digital video and audio compression for moving images. 

MPEG-1
1/4 broadcast quality which translates to 352 x 240 pixels. Typically compressed at 1.5 Mbps. 

MPEG-2
Similar to MPEG-1, but includes extensions to cover a wider range of applications. MPEG-2 translates to 704 x 480 pixels at 30 frames per second in North America and 704 x 576 fps at 25 fps in Europe. Typically compressed at higher than 5 Mbps. The primary application targeted during the MPEG-2 definition process was the all-digital transmission of broadcast TV quality video. 

Multiplexing
A means of transmitting two or more signals over a single wire or carrier wave. 

 

N

 

Noise
Any unwanted and unmodulated energy that is always present to some extent within any signal. 

Noise Figure (NF)
A term which is a figure of merit of a device, such as an LNA or receiver, expressed in dB, which compares the device with a perfect device. 

NTSC - National Television Standards Committee
The committee formed to determine the guidelines and technical standards for monochrome and color television. Also used to describe the 525-line, 59.95Hz color television signal used in North America and several other parts of the world. 

 

O

 

Offset dish
A dish antenna constructed by taking a section from a larger prime focus parabola. It has the advantage that the feed is still located at the focus of the larger antenna but appears to be offset from that portion of the reflective surface in use. This eliminates blockage of incoming signals by the feed/LNB assembly. 

Offset feed
A feed which is offset from the center of a reflector. This configuration does not block the antenna aperture. 

 

P

 

PAL - Phase Alternation System
The German developed TV standard based upon 50 cycles per second and 625 lines. 

Parabolic Antenna
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.

PCM
Pulse Code Modulation. Code where input signal is represented by a given number of fixed-width samples per second. 

Phase-Locked Loop (PLL)
A type of electronic circuit used to demodulate satellite signals. 

Polarization
A technique used by the satellite designer to increase the capacity of the satellite transmission channels by reusing the satellite transponder frequencies. In linear cross polarization schemes, half of the transponders beam their signals to earth in a vertically polarized mode; the other half horizontally polarize their down links. Although the two sets of frequencies overlap, they are 90 degree out of phase, and will not interfere with each other. To successfully receive and decode these signals on earth, the earth station must be outfitted with a properly polarized feedhorn to select the vertically or horizontally polarized signals as desired. 

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. 

Polarization Rotator
A device that can be manually or automatically adjusted to select one of two orthogonal polarizations. 

Polar Mount
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. 

Polar Orbit
An orbit with its plane aligned in parallel with the polar axis of the earth 

Positioner
A positioner is used to control the movement of a motorised dish, to allow access to a number of satellites, and hence more channels. The positioner can either be integrated (built into) to a receiver or as a separate unit. 

PSK
Phase Shift Keying Mode.

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.

 

Q

 

QAM
Quadrature Amplitude Modulator. 

QPSK - Quaternary Phase Shift Keying
Digital modulation technique used in digital satellite signals to provide bandwidth efficiency over PSK. 

 

R

 

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. 

 
S

 

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). 

Satellite Communications
The use of geostationary orbiting communication satellites to relay transmission from one earth sation to another or to several earth stations. It takes only three satellites to cover the whole Earth. 

Satellite receiver
The indoors electronic component of an earth station which downconverts, processes and prepares satellite signals for viewing or listening. 

SCPC
Single Channel Per Carrier. 

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. 

SCART
A specific socket and plug used to connect audio-visual equipment. A SCART socket is usually located on the rear of TVs, VCR's, satellite receivers and decoders. The SCART lead then allows these different items to be connected for signal transfer between them, allowing a much higher quality of audio and video. 

Scrambled
An encryption designation indicating that the channel is fully encrypted. Only DigiCipher decoders can receive the programming. 

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
Sequentiel Coleur A Memoire. European video standard with image format 4:3, 625 lines, 50 Hz and 6MHz video bandwidth with a total 8 MHz of video channel width. The major difference between PAL and SECAM is that the chrominance is FM modulated in SECAM. 

Sidelobe
Off-axis response of an antenna. 

Signal to Noise Ratio (S/N)
The ratio of the signal power and noise power. A video S/N of 54 to 56 dB is considered to be an excellent S/N, that is, of broadcast quality. A video S/N of 48 to 52 dB is considered to be a good S/N at the headend for Cable TV. 

Single-Channel-Per-Carrier (SCPC)
A method used to transmit a large number of signals over a single satellite transponder. 

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

Slot
That longitudinal position in the geosynchronous orbit into which a communications satellite is "parked". Above the United States, communications satellites are typically positioned in slots which are based at two to three degree intervals. 

Smart card
Usually associated with subscription services, a smart card is used in conjunction with a decoder to allow the viewing of scrambled, or encrypted channels. 

SMATV
Satellite master antenna television. A satellite broadcast service available to hotels, motels, apartment complexes, etc. 

Snow
A form of noise picked up by a television receiver caused by a weak signal. Snow is characterized by alternate dark and light dots appearing randomly on the picture tube. To eliminate snow, a more sensitive receive antenna must be used, or better amplification must be provided in the receiver (or both). 

Solar Outage
Solar outages occur when an antenna is looking at a satellite, and the sun passes behind or near the satellite and within the field of view of the antenna. This field of view is usually wider than the beamwidth. Solar outages can be exactly predicted as to the timing for each site. 

Sparklies or Sparks
Small black and/or white blips or dots in the television picture indicating a poor signal-to-noise ratio. 

Spectrum
The range of electromagnetic radio frequencies used in transmission of voice, data and television. 

Spillover
Satellite signal that falls on locations outside the beam pattern's defined edge of coverage. 

Splitter
A passive device (one with no active electronic components) which distributes a television signal carried on a cable in two or more paths and sends it to a number of receivers simultaneously. 

Spot Beam
A focused antenna pattern sent to a limited geographical area. Spot beams are used by domestic satellites to deliver certain transponder signals to geographically well defined areas such as Hawaii, Alaska and Puerto Rico. 

Spread Spectrum
The transmission of a signal using a much wider bandwidth and power than would normally be required. Spread spectrum also involves the use of narrower signals that are frequency hopped through various parts of the transponder. Both techniques produce low levels of interference Between the users. They also provide security in that the signals appear as though they were random noise to unauthorized earth stations. Both military and civil satellite applications have developed for spread spectrum transmissions.

Stationkeeping
Minor orbital adjustments that are conducted to maintain the satellite's orbital assignment within the allocated "box" within the geostationary arc. 

Stream
A continuous receipt of packets that have an identical packet ID. 

Subcarrier
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. 

Synchronous
The instantaneous alignment of two or more events in time. Events may occur at irregular intervals, though at the same instant and still be synchronous. 

 

T

 

Telecommunications
Any process which enables a telecommunications entity to relay and receive voice, data, electronic messages, written or printed matter, fixed or moving pictures, words, music or visible or audible signals or any control signals of design, and for any purpose by wire, radio or other electromagnetic, spectral optical or technological means. 

Threshold
A measurement of the sensitivity of the satellite receiver. Most satellite receivers have a threshold rating of around 6dB to 8dB. Receivers stating 'Low threshold' as a feature usually have a rating of less than 4dB. Low threshold receivers are capable of translating normally unviewable pictures, due to a weak signal, to a viewable image. Another option is to increase the dish size used to capture more of the signal. 

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

Transceiver
Transmitter-receiver. The physical device that connects a host interface to a local area network, such as Ethernet. Ethernet transceivers contain electronics that apply signals to the cable and sense collisions. 

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. 

Transponder
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. 

TVRO
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. 

Tweeking
The process of adjusting an electronic receiver circuit to optimize its performance. 

 

U

 

UHF
Ultra High Frequency. Band in the 500-900 MHz range, including TV channels 14 through 83. 

Unscrambled
An encryption mode designation indicating that the channel is being processed into the DigiCipher waveform but is not encrypted. 

Uplink
A sending dish. A transmitter sends its signal to a large parabolic dish antenna that is aimed at the intended relay satellite. 

 

V

 

VHF
Very High Frequency - Refers to Electromagnetic waves between approximately 54 MHz and 300 MHz. 

VHS
Video Home System - The more popular of the two types of videocassette recorders 

VSAT
Very Small Aperture Terminal - Small earth stations, usually 1.2 meter to 1.8 meter in diameter (antenna dish sizes from 0.6 meter to 3.8 meter in diameter can also be used as Very Small Aperture Terminals). Means of transmission of video, voice, and data by SCPC, TDM/TDMA, or DAMA to a satellite. Used in business applications. Small aperture terminals under 0.5 meters are sometimes called Ultra Small Aperture Terminals (USATs). 

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)

 

W

 

Waveguide
A metallic microwave conductor, typically rectangular in shape, used to carry microwave signals