Index and Glossary of Terms

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

22KHz tone The signal generated by a satellite receiver and relayed to an LNB to select the “high” local oscillator.
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A

Amplifier A circuit that increases the power or voltage of a signal.
Amplitude The strength or magnitude of a signal
Amplitude modulation A transmission system in which the modulating waveform is made to vary the carrier amplitude.
Analogue A mode of transmission of information. An analogue waveform has a physical similarity with the quantity it represents.
Antenna (aerial) A device used to transmit or receive radio waves.
Aspect ratio The ratio of width to height for a TV screen.
Astra The “trade” name for satellites operated by SES (“Societe Europeenne des Satellites”).
Attenuator A passive device that decreases signal power.
Azimuth A compass bearing east or west of true south
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B

Balun A balance-to-unbalance transformer (sometimes an integral part of an aerial) used to match an unbalanced coaxial cable to a balanced device such as an aerial dipole or receiver input.
Bandpass filter A circuit that passes a restricted band of frequencies. Unwanted lower and upper frequencies are attenuated.
Bandwidth The total range of frequencies occupied by a signal. It is normally measured between half-power points.
Baseband The band of frequencies containing information after demodulation.
Beamwidth An aerial acceptance angle measured between half- power points.
Bit A binary digit (a “1” or “0”).
Bit error ratio (BER) A ratio of the number of errors in a data stream to the total number of data bits.
Bit rate The number of digital bits transmitted per second.
Boltzmann’s constant The relationship between the energy of a particle and its motion is related to its absolute temperature multiplied by Boltzmann’s constant, which has the value of -228.6dB. This very small factor exerts a powerful influence on the effects of noise and thus on quality.
Boresight The principle centre axis of an aerial or dish antenna.
Bouquet A number of programmes grouped within a multiplex.
BSkyB British Sky Broadcasting.
BSS (Bus. Satellite Services) The band of frequencies 11.7-12.5GHz
Byte A group of 8 digital “bits”.
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C

C120 flange A standard mating flange for circular Ku band waveguides.
CAM “Conditional Access Module”. Normally fits into the PCMCIA socket of a satellite receiver, to hold a viewing card.
Capacitance A energy storage device that is formed wherever an insulator separates two conductors between which a voltage difference exists. Capacitance is measured in “Farads”.
Carrier-to-noise (C/N) ratio A ratio of the received carrier power to the noise power in a given bandwidth, in dBs.
Cascade amplifier A line-powered amplifier that also passes the powering voltage to its input terminals.
Cassegrain A dish with a paraboloid prime focus main reflector and a convex sub-reflector.
Catenary wire A supporting wire for an overhead coaxial cable between buildings or structures.
Cathode ray tube (CRT) An evacuated glass vessel in which an electron beam produces a luminous image on a fluorescent screen.
CATV Community (Cable) Antenna Television.
C band The band of frequencies 3.6-4.2GHz.
CCIR “International Radio Consultative Committee”.
CCIR impairment scale A 5 point scale of subjective analogue picture quality.
CCTV “Closed Circuit TeleVision”
CDM (construction/design/maint) Regulations concerning activities on a building site that must be complied with in certain circumstances.
Ceefax The teletext service of the BBC.
Channel The frequency band over which information (data, audio TV) is relayed.
Characteristic impedance The impedance in ohms of a device in the path of a communications signal
Circuit protective conductor A cable used to earth a mains power socket.
Circular polarity Electromagnetic waves whose electric field uniformly rotates along the signal path. Facing an incoming wave, clockwise rotation is called Right-Hand Circular (RHCP) and anti-clockwise rotation is called Left-Hand Circular Polarisation (LHCP).
Chrominance The hue and saturation of a colour. A chrominance signal carries the colour information.
Cinemascope A widescreen TV picture format, usually 16:9.
Cladding The outer coating of a glass fibre which provides a reflective surface.
Clarke belt The circular orbital belt 35 786Km above the equator, at which all satellites appear to be stationary.
Cliff effect The effect of a digital picture suddenly blocking or freezing when the signal parameters degrade below a certain level.
Cluster amplifiers A series of filters/channel amplifiers tuned to amplify and pass a single cluster of analogue and/or digital terrestrial TV channels.
Cluster filter A series of filters, each tuned to attenuate a single cluster of analogue and/or digital terrestrial TV channels.
Coaxial cable An internal conductor surrounded by an insulating dielectric and one or two outer conducting screens..
Co-channel interference Interference on a single terrestrial TV channel resulting from signals on the same TV channel.
COFDM “Coded Orthogonal Frequency Division Multiplex”. The method of modulation used for digital terrestrial broadcasts in Britain.
Composite baseband The raw demodulator analogue output before filtering, clamping and decoding.
Composite video A complete video signal, including luminance, sync. and colour information but not audio or data sub-carriers.
Constellation diagram A representation of the amplitude and phase of each bit of information in a digital symbol.
Cross colour A TV picture defect that results in swirling coloured patterns.
Cross luminance A TV picture defect that results in brightness variations and colour changes.
Cross modulation A form of interference caused by the modulation of one or more carriers affecting that of another signal. It can be caused by non-linearity or the overloading of an amplifier, or signal imbalances.
Cross-polarisation Signals of the opposite polarity to those being received.
Cross-polar discrimination The ratio of the amplitude of the wanted polarity to the unwanted one.
Cross talk Interference between two or more video or audio baseband signals.
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D

D2MAC A satellite analogue encryption technique whereby the luminance and chrominance components of a video signal are transmitted seqentially. Used by European broadcasters.
DAB “Digital Audio Broadcasting”.
dBi The gain of an aerial relative to an isotropic source. This is normally 2.15dB more than the gain relative to that of a half-wave dipole.
dBm dB power relative to a 1 milliwatt standard.
DBS (Direct Broadcast Satellite) The band of frequencies 11.7-12.5GHz
dBw dB power relative to 1 watt.
DC pass The ability of a circuit element (usually a splitter, diplexer or outlet plate) to pass dc voltages – this is necessary to power a masthead amplifier or LNB, or to pass remote control signals.
DCT (Discrete Cosine Transform) An MPEG technique that converts pixel values from the time domain to the frequency domain and “quantises” the values to compress the data bandwidth.
Decibel (dB) The logarithmic ratio of voltage or power levels, used to indicate the gains or losses of signals.
Declination offset The adjustment angle of a polar mount between the polar axis and the plane of a satellite dish used to aim at the geosynchronous arc. Increases from zero with latitude away from the equator.
De-emphasis A reduction of the higher frequency parts of a signal to neutralise the effect of pre-emphasis.
Demodulator A device that extracts the baseband signal from a transmitted carrier wave.
Depolarisation The twisting of the polarisation of a radio wave as it travels through the atmosphere.
Deviation The maximum amount the carrier frequency is shifted by the modulating signal.
Dielectric Insulating material used to separate the conductors of a coaxial cable or the conducting circuits of a capacitor.
Dielectric plate A device for insertion into a feedhorn to convert circularly polarised signals to a linear polarity.
Digibox A generic name for a satellite or terrestrial digital receiver.
Diplexer A frequency-conscious device for combining or splitting signals in different frequency bands. A diplexer has a lower insertion loss than the equivalent splitter.
Dipole Normally a single aerial element half a wavelength long with cable connections at its centre point.
Director element An element mounted on an aerial boom in front of the dipole that modifies the aerial characteristics.
Discriminator A type of circuit used to demodulate an FM signal.
DiSEqC “Digital Satellite Equipment Control”. An extension of the 22KHz concept to provide control of multiple devices.
Down conductor A conductive link to an earth termination to provide lightning protection.
Down-conversion A reduction of a band of high frequencies to a lower band.
Downlink The transmission path from an orbiting satellite to a receiving dish.
Drip loop A loop formed in a coaxial cable so that water will drip off instead of penetrating apparatus or a structure.
Drop-in cable A coaxial cable linking each dwelling unit to the signal distribution network.
DSB (Double SideBand) A form of amplitude modulation where both the upper and lower sidebands (which result from modulation of the carrier by the signal) are transmitted.
DTH (Direct-to-home) Satellite transmissions intended for reception in homes.
DTT Digital Terrestrial Television.
DVB (Digital Video Broadcast) Definitions of the methods of digital signal modulation.
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E

Earth bonding The connection of a system to an earth point
Earth station A ground-based transmitting or receiving satellite installation.
EBU European Broadcasting Union.
EIRP The power of a transmitter with reference to that of a point (isotropic) source.
EIT (Event Information Table) Programme data relating to events occurring within a digital multiplex.
Electromagnetic wave The technical name for a radio wave, so called because it comprises electric and magnetic fields moving in unison.
Elevation The vertical angle measured from the horizon up to a target satellite.
Encoding Converting a message to code eg when characters are stored in binary code. Often used to describe a process in which the form of an electronic signal is changed.
Encryption The process of hiding information or keys needed to unlock scrambled signals.
Energy dispersal A low frequency signal added to the baseband signal before modulation. Used to reduce the peak power per unit of bandwidth of an FM signal to reduce its interference potential.
EPG (Electronic Prog. Guide) A compilation of all the programmes available.
ESA European Space Agency.
Eutelsat European Telecommunications Satellite Organisation.
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F

F/D ratio A ratio of the focal length to the diameter of a dish.
FEC (Forward Error Correction) A10 A technique for improving the accuracy of data transmission. Excess bits are included in the outgoing data stream so that error correction can be applied by the receiver,
Feeder cable The main coaxial cable emanating from the head end equipment and connected to one or more spur distribution cables.
Feedhorn A device that collects microwave signals from the surface of a dish (located at the focal point).
Fibre optics The relay of signals on glass fibres using light waves.
Field One half of a complete TV picture or frame. There are 50 fields per second in a PAL system.
Filter A device used to pass or reject a specified range of frequencies. This normally comprises one or more tuned circuits.
Filter/leveller A series of filters with adjustable attenuation, each tuned to a single analogue terrestrial TV channel.
Flat screen display A TV screen using LCD or plasma display techniques instead of a cathode ray tube.
Flylead A plug-in lead to link together two domestic satellite or TV products.
FOB (Flush Outlet Box) A TV or satellite outlet designed for flush mounting on to a flush conduit or surface pattress box.
Focal length The distance from the reflective surface of a parabola to its focal point.
Focal point A point in front of a satellite dish to which all the reflected energy is focussed.
Folded dipole Two half-wave dipoles connected in parallel in order to modify the centre impedance.
Footprint The geographical area towards which a satellite downlink signal is directed. The contours indicate lines of equal signal strength.
Frame One complete TV picture, composed of two fields.
Frequency The number of oscillations per second of an electrical or electromagnetic signal, expressed in cycles/sec or Hertz
Frequency modulation (FM) A transmission system in which the modulating waveform is made to vary the carrier frequency.
Freznel zones Circular regions of an electromagnetic wave where the signals are in the same phase
Front-to-back ratio The ratio of the gain of an aerial in the forward direction to that in the reverse direction.
FSS (Fixed Satellite Service) The band of frequencies 10.7-11.7GHz
Fused spur A mains electrical power supply outlet comprising a fuse and captive mains cable (but not including a power socket).
Fusion splice The low-loss glass fibre jointing technique using heat to join two fibres together.
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G

Gain The amplification of input to output power in dBs.
Geostationary orbit The circular orbital belt 35 786Km above the equator.
Galvanic isolator An in-line device to improve lightning protection and electrical safety by providing dc isolation between different parts of a cable network. Satellites in this belt appear to be stationary.
Ghosting Multiple TV images usually caused by the reception of a signal via two different paths.
Gregorian A dish with a parabolic offset main reflector and a concave sub-reflector.
Grid aerial A series of stacked “X” arrays with a grid reflector, to give a high front-to-back ratio.
G/T (Gain/noise Temperature) The figure of merit of a dish and LNB. The higher the G/T ratio, the better its reception capabilities.
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H

Half power beamwidth The beamwidth angle of a transmitting antenna that produces a beam footprint contour on which the signal power is 3dB lower than the maximum value.
Half transponder A compromise method of broadcasting two signals through one transponder.
Harmonic A component of a wave having a frequency an integral number of times that of the basic (fundamental) frequency eg if the fundamental frequency is fHz, then the harmonics are 2f,3f,4f etc.
HDTV (High Definition TV) A TV format with 1250 scanning lines to improve picture resolution and viewing quality.
Head-end equipment The portion of an MATV system where all the signals are received and processed prior to distribution.
Hertz (Hz) An abbreviation for the frequency measurement of one cycle per second.
High-pass filter Circuit that passes signals above a designated frequency.
Home gateway An STB interface between the delivery platform and appliances or systems throughout the home.
Horizontal polarisation A radio wave where the electrical field is horizontal and the magnetic field is vertical.
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I

Impedance The resistance to alternating current flow in an electrical circuit.
Impulse noise External interference from terrestrial sources such as thermostats, fridges etc, that can cause a DTT receiver to block or freeze.
Inclinometer An instrument used to measure the angle of elevation to a satellite from the surface of the earth.
Inductance The effect of a magnetic flux created by a current flowing in an electrical circuit. An inductor is normally a coil of wire mounted on a former. Inductance is measured in “Henries”.
Insertion loss or through loss The signal loss in dB caused by inserting a splitter or insert into a communications line.
Interframe (temporal) compression An MPEG compression technique transmitting only changes between frames.
Interlaced scanning A technique to minimise picture flicker whilst conserving channel bandwidth. Even and odd-numbered lines are scanned in separate fields to make one complete frame.
Intermediate frequency (IF) A middle frequency range generated after down- conversion in an LNB or receiver.
Intermodulation A form of interference caused by the modulation of one carrier affecting that of another signal in the same frequency band. It can be caused by non-linearity or the overloading of an amplifier.
Intraframe (spatial) compression An MPEG compression technique eliminating repitition.
Ionosphere A layer of the atmosphere that refracts or reflects electromagnetic radio waves,
IRD “Integrated Receiver-Decoder”.
IRS “Integrated Reception System”.
Isotropic Ideally, a point source that transmits signals of equal power in all directions.
ITU International Telecommunications Union.
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K

Ka band A band of frequencies 20-30GHz.
Kelvin A degree of temperature in degrees Celcius or Centigrade. The Kelvin scale starts at absolute zero so Oo Celsius is equivalent to 273o Kelvin.
Krone tool A specialist tool for connecting telephone wires to phone sockets using the insulation displacement technique.
Ka band The band of frequencies 20-30GHz.
Ku band The band of frequencies 10.7-18GHz.
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L

Ladder styles The vertical part of a ladder to which the rungs are attached.
LAN (Local Area Network) A system to link computer terminals together.
Laser diode A device used in an fibre-optic transmitter that emits light waves at a single frequency.
Latitude The measurement of a position on the surface of the earth north or south of the equator, in degrees of angle.
L band A band of frequencies at 1.7GHz
Letterbox A format for viewing widescreen pictures on a 4 x 3 TV screen.
Lightning protection A system to minimise the effects of a lightning strike.
Link budget An overall calculation of power gains and losses from transmission to reception.
Linear polarisation Horizontally or vertically polarisation (as opposed to circular polarisation).
LNB “Low Noise Block downconverter”. A low noise microwave amplifier and converter that downconverts a block or range of frequencies to an IF range.
Local oscillator A device used to supply a stable frequency to a down- converter. The local oscillator signal is mixed with the carrier wave to change its frequency.
Loft box A unit containing all the devices commonly needed for the reception and distribution of terrestrial and satellite services within the home.
Log-periodic aerial A wideband TV aerial with elements of different lengths.
Longitude A distance in degrees east or west of the Greenwich meridian
Loop-wired network An MATV network (no longer recommended) where the cable loops from room to room between padded outlet plates
Low pass filter A circuit that only passes signals lower than a designated frequency.
LSOH (Low smoke/zero halogen) A type of cable specified for use in public buildings to minimise the fire risk.
Luminance The part of a TV waveform that contains the brightness information.
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M

Macro block A defined group of pixels used in MPEG compression.
Magnetic north The earth can be considered as a huge magnet having north and south magnetic poles. The line joining these poles is inclined slightly to the axis of rotation, hence true north and magnetic north do not coincide. A compass points to magnetic north.
Magnetic variation (or deviation) The difference between true north and the north indication on a compass.
MATV Master Antenna Television System
Method statement A statement of the method to be used to carry out tasks.
Microwave The frequency range from 1-30GHz and above.
Mini DiSEqC A simple version of DiSEqC with only two states.
Mixer A device used to combine signals together.
Modem (modulator/demodulator) A telephone interface used in computers and digital TV receivers
Modulation A process by which information is added or encoded on to a carrier wave
Modulation error ratio (MER) A form of S/N ratio measurement, the noise being measured within the active channel.
Modulation index The ratio of peak deviation to the highest modulating frequency.
Modulator A device that modulates a video signal or MPEG2 transport stream onto a radio frequency carrier.
Monochrome A black and white TV picture
Motor feedback Information fed back to a motorised satellite receiver concerning the orientation of the dish
MPEG “Moving Picture Experts Group”.
MPEG2 A set of digital TV compression standards.
MPEG4 A new compression standard that is “object-based”.
Multicrypt A digital scrambling system that uses a common PCMCIA interface. Several CAMs can be daisy-chained in a single receiver.
Multimode A low-bandwidth mode of fibre-optic transmission using more than one light frequency. Used predominantly for telecommunication applications.
Multiplex (mux) The simultaneous transmission of several signals or programmes over a single communication channel.
Multiple dwelling unit (MDU) A group of homes, sometimes within the same building.
Multiswitch An IF switching unit to enable any satellite receiver to access either polarity or band using voltage and 22KHz tone commands. Some versions relay terrestrial signals and allow access to multiple satellites using DiSEqC control signals.
Mutual isolation The isolation in dBs between drop-in cables connected to the same network tee insert.
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N

NICAM “Near Instantaneous Companded Audio Multiplex. Terrestrial transmitters broadcast sound channels using NICAM for improved sound quality in stereo.
NIT (Network Information Table) A table that describes the transport medium for services on the currently demodulated and other multiplexes.
Noise An unwanted signal that interferes with reception of the desired information. It is usually expressed in oK or dB.
Noise figure A ratio of the actual noise power generated at the input of an amplifier to that which would be generated in an ideal resistor. The lower the noise figure, the better the performance.
Noise temperature A measure of the amount of thermal noise present in a system or device. The lower the noise temperature, the better the performance. Expressed in (degrees) Kelvin.
NTSC The National Television Standards Committee. The system standard for TV broadcasts in the USA and Japan.
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O

Offset angle The adjustment angle of a polar mount between the polar axis and the plane of a satellite dish used to aim at the geosynchronous arc. Increases from zero with latitude away from the equator.
Offset dish A dish with a reflector that forms only part of a paraboloid of revolution, usually excluding the pole or apex,such that a front feed causes no aperture blockage.
Offset feed A feed that is offset from the centre of a dish antenna. This configuration does not block the dish aperture.
Ohms law The most fundamental relationship in the theory of electrical circuits is that relating potential difference, current and resistance, known as Ohm’s Law (V=IxR).
OMT (OrthoMode Transducer) A waveguide splitter. The input port is a circular C120 waveguide. The two output ports can be either circular or rectangular (WR75).
Orthogonal At right angles to each other.
Output derating The action of reducing the maximum output level of each of several amplifiers in cascade or of a single amplifier relaying several TV channels, to compensate for the overall increase in distortion levels.
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P

PAL (Phase Alternate Line) The TV broadcasting format used in some parts of Europe.
PAL G The UHF TV broadcasting standard used in Germany. The vision/sound carrier spacing is 5.5MHz
PAL I The TV broadcasting standard used in Britain and South Africa. The vision/sound carrier spacing is 6MHz
Panel or grid aerial A series of stacked “X” arrays with a grid reflector, to give a high front-to-back ratio.
Parabola A geometric shape that has the property of reflecting all signals parallel to its axis to a single focal point.
Parity bit (check sum) Error correction data that is added to a data stream to make the bit values total either an odd or even number.
Path loss The attenuation of a signal when travelling over a path between two points. Path loss varies inversely as the square of the distance travelled.
Pattress (pattra) box An adaptor used to surface-mount a flush outlet plate.
Phase A measure of the relative position of a signal relative to a reference, in degrees.
Phase modulation A transmission system in which the modulating signal is made to vary the carrier phase.
Phase shift keying (PSK) A transmission system in which the modulating signal is made to vary the carrier phase.
PID (Programme Ident. Data) A series of 4 character hexidecimal video and audio codes to distinguish between digital SCPC signals that are close together.
Pixel An element of a digital picture.
Plasma display A flat TV screen using light modulators or emitters to reproduce a TV picture.
PLL (Phase-Locked Loop) A technique used to accurately lock oscillator frequencies.
PME (Primary Multiple Earth) The main earth in a building, to which a cable distribution system must be bonded.
Polar diagram A plot of the relative gain of an aerial or dish in various directions.
Polar mount A dish mount that allows all satellites in geostationary orbit to be received with the movement of only one axis.
Polarisation The plane of propagation of an electromagnetic wave. There are 4 states – horizontal, vertical, left-hand circular and right-hand circular.
Polarotor A polarity-selection device with “skew” adjustment.
Polykit A kit of all the parts needed to fix a lashing bracket to a chimney.
Polythene (polyethylene) A waterproof material used as the outer sheath for outdoor cables.
Pre-emphasis A technique to increase the higher frequency components of a signal before transmission to compensate for the greater cable loss, thereby improving the signal-to-noise ratio.
Prime focus dish A parabolic dish with its focal point on its centre axis directly in front of the dish.
PSK (Phase-Shift Keying) A type of digital modulation.
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Q

PVC (PolyVinyl Chloride) A material used for the outer sheath of coaxial cables.
QAM “Quadrature Amplitude Modulation”.
QPSK “Quadrature Phase Shift Keying”. A modulation technique used on satellite transmissions that uses phase shifts of a carrier wave to relay 4 symbols per cycle.
Quantising Rounding up or down to the nearest whole number.
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R

Radian The angle at the centre of a circle subtended by an arc equal in length to its radius. It is equivalent to 57.3o.
Rain degradation A reduction in C/N ratio due to rainfall.
Rain outage Loss of a Ku band signal due to absorption and thermal noise accompanying heavy rainfall.
Raster A pattern of scanning lines on a TV screen.
RCD (Residual Current Device) An electrical safety device designed to disconnect mains power in the event of an earth current.
Reed Solomon An MPEG error correction technique using “outer coding” to minimise burst errors.
Reed switch A mechanical switch operated by a rotating magnet to count the revolutions of a motor-actuator.
Refraction The deflection of a radio wave or light wave as it passes between two mediums of different densities.
Reflection The rebounding of a radio or light wave from a surface or junction of two different materials with different densities.
Reflector plate or element The rear element of an aerial mounted behind the dipole that modifies the aerial characteristics.
REN(ringer equivalence number) The loading factor of a unit connected to a phone line.
RF Radio Frequency.
RGB (red/green/blue) The three primary colours used in colour television.
RHCP Right-Hand Circular Polarisation.
Risk assessment An assessment of the risks involved in carrying out a task, and how they will be minimised.
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S

Satellite IF The band of frequencies eminating from an LNB that are relayed via a coaxial cable to the IF input of an amplifier, multiswitch or satellite receiver.
S band A band of frequencies at 2.5GHz
Scalar feed A wide-flare corrugated dish feed.
Scalar rings A corrugated concentric surround to a prime focus feed to improve its impedance-matching characteristics.
Scanning A moving electron beam to reproduce an entire picture as a sequence of horizontal lines.
SCART “Syndicat des Constructeurs d’Appareils Radio recepteurs et Televisieurs”. A European 20 pin standard connector used to interlink video/audio circuits between domestic audio and TV products.
SCPC (Single Carrier per Chan.) A satellite transmission system that uses a separate carrier for each channel (compared with frequency division multiplexing which combines several channels on to a single carrier).
SDT (Service Description Table) Data relating to the services contained within a digital multiplex.
SECAM “SEquential Couleur A Memoire”. The French TV Standard.
SES “Societe Europeenne des Satellites”. Astra is the Trademark of SES.
Shadowmask tube A CRT employing 3 electron guns to reproduce the red, green and blue components of a colour TV picture.
Side lobe A parameter used to describe the ability of an aerial or dish to receive off-axis signals. The larger the side lobes, the more noise and interference that is received.
Side loss The signal loss in dB of a network tee insert, between the input coaxial cable and the drop-in cable
Signal level meter A frequency selective heterodyne receiver capable of tuning to the frequency band of interest, with an indicating meter showing the magnitude of the input voltage at a specific frequency.
Signal to noise (S/N) ratio A ratio in dBs of the peak voltage of the signal of interest to the root-mean-square (rms) voltage of the noise in that signal.
Simulcrypt A digital scrambling system where some of the functionality is built into the receiver itself.
Single mode A high-bandwidth mode of fibre-optic transmission using a single light frequency.
Skew Adjustment of an LNB to minimise reception of the unwanted polarity.
Slices A group of digital macro blocks.
Slope The uneven attenuation of a broadband signal across its frequency band as it travels along a coaxial cable
SMATV “Satellite Master Antenna Television”. A system intended to receive and distribute radio, TV and satellite programmes to multi-dwelling units.
Snow Video noise caused by a insufficient S/N ratio.
SOB (surface outlet box) A TV or satellite outlet designed for surface mounting on a window frame or skirting board.
Software download The action of upgrading the software operating system in a digital satellite receiver.
Source switching The use of 12V on pin 8 of a SCART connector to switch between the aerial socket and SCART inputs of a TV receiver.
Sparklies Small black and/or white horizontal dashes in an analogue TV picture caused by an insufficient S/N ratio.
Spatial (intraframe) compression An MPEG compression technique eliminating repitition.
Spectrum analyser A scanning receiver with a display that shows a plot of frequency versus amplitude of the signals being measured.
Splitter A device used to split radio signals on a coaxial cable.
Spot beam A circular or eliptical beam covering some defined region of the earth’s surface.
Spur cable A coaxial cable feeding drop-in cables via tee inserts.
Spur insert A device that transfers a specific amount of energy from a main feeder cable to one or more spur cables.
Stacking combiner A matching device to combine the outputs of several identical aerials on to one coaxial downlead.
Standing wave Peaks and troughs of signal on a cable due to forward and reflected signals being either in-phase or out-of- phase.
Star-wired network An MATV network with separate drop-in cables linking each dwelling to a multiswitch at a central “node”.
STB “Set-Top Box”.
Sub carrier An information-carrying wave that in turn modulates the main carrier in a communications system.
S-VHS A method of video/audio interconnection that relays the brightness, colour and audio information separately.
Synchronising (sync.) pulses Pulses imposed on a video signal to keep the TV picture scanning synchronised with that of the picture source.
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T

Tap loss The signal loss in dB of a network tee insert, between the input coaxial cable and the drop-in cable.
TDT (Time and Date Table) Digital data received to synchronise the IRD clock.
Tee insert (tap) A device that transfers a specific amount of energy from the main distribution system to a secondary outlet.
Telecom band The band of frequencies 12.5-12.75GHz
Telephone connection The connection of an interactive digital receiver modem to a telephone line.
Teletext Separate information transmitted with a TV picture signal that can be displayed on the screen in place of the normal picture. This service is called CEEFAX by the BBC and ORACLE by the ITV companies
Temporal (interframe)compression An MPEG compression technique transmitting only changes between frames.
Terminating resistor A 75ohm matching resistor fitted across the end of an unterminated coaxial cable to prevent the creation of standing waves.
Threshold The minimum S/N input required to allow a satellite receiver to produce a picture.
Through loss or insertion loss The signal loss in dB caused by inserting a splitter or insert into a communications line
Tilt The uneven attenuation of a broadband signal across its frequency band as it travels along a coaxial cable.
Triad A group of three dots representing the red, green and blue content of a single picture element on a TV screen.
Transformer A device to link two rf circuits together, comprising two or more coils of wire. Used to provide voltage and impedance matching and/or galvanic isolation.
Transponder One circuit on a satellite that receives and retransmits an uplinked signal.
Transport stream An MPEG2 multiplex with short, fixed-length packets carrying programmes intended for general broadcast.
Tree-and-branch network An MATV network with spur cables connected to individual “drop-in” cables using tee inserts.
Tree-and-bush network An extension of the “tree-and-branch” MATV network concept where the with spur cables are connected via “nodes” to individual drop-in cables feeding each viewing location.
Tuned circuit (filter) A device used to pass or reject a specified range of frequencies.
TV plug or Belling plug A standard UK TV connector to specification IEC95.
TVRO A TV Receive-Only earth station designed to receive (but not transmit) satellite communications.
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U

UHF (ultra-high frequency) The frequency spectrum 300MHz-3GHz. Terrestrial UHF broadcast TV occupies the band 470-860MHz.
Universal LNB A Ku band LNB with 9.75/10.6GHz local oscillators, that uses voltage and tone switching to select polarity and band respectively.
Uplink The earth station electronics and aerial that transmit information to a communications satellite.
USB An external computer interface.
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V

Vector A voltage that varies with time in a sinusoidal manner.
Videocrypt A satellite analogue encryption technique using the cut-and-rotate principle, formerly used by BSkyB.
Viterbi An MPEG error correction technique using a variable amount of “inner coding”, known as FEC. This is also called “convolutional error correction”.
VSB “Vestigial Sideband” transmission. Used for TV broadcasting. Double sideband transmission is used for low video frequencies, and single sideband transmission for higher video frequencies.
VSWR The Voltage Standing wave Ratio. The ratio between the minimum and maximum voltage on a coaxial cable. The ideal VSWR is 1.0. Ghosting can result as the VSWR increases. It is also a measure of the reflected power to the total power at any point on the system.
WARC “World Administrative Radio Conference”.
Waveguide Usually a hollow copper tube of such rectangular or circular dimensions that it will propagate electromagnetic waves of a given frequency. Used for relaying super high frequency waves, or microwaves.
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W

Wavelength The length of one complete cycle of an electromagnetic wave. Wavelength decreases as the signal frequency increases.
Wegener A proprietary system for subcarrier stereo transmission. It uses discrete low level companded subcarriers.
Weighting The correction of S/N ratio measurements to take into account such factors as bandwidth and annoyance value.
White noise Noise having a constant energy per unit bandwidth over a particular frequency band.
Widescreen A “cinemascope” TV picture format, usually 16:9.
Window of operation A range of minimum and maximum parameters required for the satisfactory performance of a system.
WR75 flange A standard mating flange for rectangular Ku band waveguides.
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X

X band The frequency band 7-8GHz.
X-type aerial A type of high gain TV aerial design with several elements connected at each point on the support boom, to give increased overall gain whilst minimising the overall length of the aerial.
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Y

Yagi A common type of aerial design comprising a dipole with a rear reflector and several front director elements.
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Z

Zone beam A beam pattern (usually a shaped beam) intermediate between hemispheric and spot beams.

 

With thanks to Bob Calez of Race Communications for the extensive glossary of terms.

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