Glossary of Terms N-Z

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

 

 
 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.
Back to Index

 


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.
Back to Index

 


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.
Back to Index

 


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.
Back to Index

 


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.
Back to Index

 


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 12 V on pin 8 of a SCART connector to switch between the aerial socket and SCART inputs of a TV receiver.
S/PDIF or SPDIF  Sony/Philips Digital Interface Format is a type of digital audio interconnect cable used in consumer audio equipment to output audio over reasonably short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fibre optic cable with TOSLINK connectors.
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.
sRGB

sRGB is a standard RGB color space created cooperatively by HP and Microsoft in 1996 for use on monitors, printers, and the Internet.
sRGB uses the ITU-R BT.709 primaries, the same as are used in studio monitors and HDTV and a transfer function (gamma curve) typical of CRTs.

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.
Super Audio CD Super Audio CD (SACD) is a read-only optical disc for audio storage, introduced in 1999 and was intended to be the successor to their Compact Disc format. While the SACD format can offer more channels (e.g. surround sound), and a longer playing time than CD, research published in 2007 found no significant difference in audio quality between SACD and standard CD
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.
Back to Index

 


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 12.5-12.75 GHz
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.
Back to Index

 


U

UHF (ultra-high frequency) The frequency spectrum 300 MHz - 3 GHz. Terrestrial UHF broadcast TV occupies the band 470 - 860 MHz.
Universal LNB A Ku band LNB with 9.75 / 10.6 GHz 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.
Back to Index

 


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.
Back to Index

 


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.
Back to Index

 


X

X band The frequency band 7-8 GHz.
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.
xvYCC xvYCC or Extended-gamut YCC (also x.v.Color) is a color space that can be used in the video electronics of television sets to support a gamut 1.8 times as large as that of the sRGB color space.
Back to Index

 


Y

Yagi A common type of aerial design comprising a dipole with a rear reflector and several front director elements.
YCbCr Is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the luma component and CB and CR are the blue-difference and red-difference chroma components. 
Back to Index

 


Z

Zone beam

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