A number between 21 and 68 corresponding to the frequency of the transmission. Each channel is 8MHz wide and contains one analogue TV programme or one digital MUX. Channel 21 covers 470 to 478MHz and so on up to Channel 68 which covers 846 to 854MHz
Coded Orthogonal Frequency Division Multiplexing is a modulation scheme that uses multiple closely spaced orthogonal sub carriers, forming one MUX. Each sub-carrier is then modulated using QAM at a relatively low data rate for digital TV transmission.
"Chroma, Video, Burst and Sync". This is the combination of the various elements required for a TV picture in a single connection. This gives a lower quality picture than HDTV, RGB or S-video. CVBS format is used by e.g. VCRs, and is often referred to as "composite video".
Digibox is a generic name given to either a Freeview box or a satellite receiver, and is the unit that receives the incoming digital signal and sends out a TV picture (usually on a SCART connector).
Digital Switchover is the process initiated by the government which started in Oct 2007 (Whitehaven) that replaces analogue TV transmission in the UK with digital TV. The process is intended to provide better quality TV and a wider viewing choice to almost all of the UK population.
Digital Terrestrial Television is a generic name for the digital signal processing technology that compresses video signals, allowing a number of TV programmes to be viewed on a single MUX. Different countries use different technology to achieve this, but all variants can still be termed DTT.
Digital Video Broadcasting is the global consortium that defines the standards for digital television and data services. This enables different manufacturers to provide compatible equipment for e.g. digiboxes. The DVB standards apply not just to terrestrial TV (DVB-T), but to satellite (DVB-S), and internet based services also.
Digital Video Disc is an optical storage technology that uses a laser to read or write data from a reflective surface in a plastic disc. A standard DVD can store 4.7GB of data or file, sufficient for over 2 hours of MPEG2 video.
A Digital Video Recorder or alternatively (Personal Video Recorder - PVR) is a device that records digital video to a computer hard disc typically. Using a hard drive enables a large storage capacity (similar to a DVD - 1 hour per 2GB) and removes the need for tapes or discs for short term storage and rescheduling of programmes. These devices can output either CVBS or RGB video, to give a recorded picture quality that is indistinguishable from the original programmme.
The Fast Fourier Transform is an essential part of the COFDM modulation format that is used to reduce intersymbol interference in sub-carriers used with QAM modulation. The transmit side uses an inverse fourier transform, and the receive side (digibox) uses the fast fourier transform to recover the signal.
Freesat is the service due to be launched in March 2008 by the combination of the BBC, ITV and Channel 4 and using the Astra 2D satellite (as used by Sky). The serivce appears to be a satellite equivalent of the terrestrial Freeview service. Sky also offer "Freesat from Sky" - which enables non-encrypted (FTA) Sky services to be viewed using a Sky box and FTV programmes to be viewed using a £20 (one off payment) viewing card.
Freeview is the name of the service provided by DTV Services Ltd (formed by the BBC, BSkyB, Channel 4, ITV and National Grid Wireless). Freeview provides non-subscription TV and radio programmes, received via a TV aerial and a set-top box (digibox).
Frequency is the measurement of "cycles per second" of a wave. For FM radio, the frequency range is 88MHz to 108MHz. For UHF television, the frequency range is 470MHz to 860MHz.
Free to Air is the term given to satellite programmes that are not encrypted. These do not require a Sky viewing card.
Free to View is the term given to satellite programmes that are encrypted, but which can be viewed using a £20 card (one off payment) from Sky. These programmes currently include Five, Sky Three, Channel 4+1, Five US, Five Life.
High Definition Multimedia Interface is a small 19 pin connector provided on TVs and some digiboxes to allow high data rate digital signals (for both video and audio) to be interconnected.
High Definition Television provides higher resolution images on the TV, giving sharper, clearer images with improved colour (HDTV has more pixels). HDTV is only available on some satellite channels and some cable broadcasts at present, and requires a compatible receiver and TV (with HDMI interfaces) and an HDMI cable to connect them. Some HDTV services are only available on subscription channels.
A Liquid Crystal Display uses a very thin layer of a special liquid between glass plates that can have its optical polarisation altered by an electrical signal. A colour display is made up using three sub-pixels (red, green & blue) for each "white" pixel. The electrical signal is applied to the liquid crystal material from a transparent (thin) layer of transistors printed on the inside of the glass.
The Moving Pictures Expert Group have defined the software encoding standards for use with both video and audio. DVB-T uses the MPEG2 compression format.
MUX is an abbreviation for "multiplex" - a comination of several different programmes into the same bandwidth as occupied by a single analogue programme or channel. This is achieved by software compression (see MPEG) above.
Phase Alternating Line is the colour encoding system that is used for analogue TV in most of Europe. Alternative systems are used in France (SECAM) and the US (NTSC). PAL-I is used in the UK. The PAL system combines the chrominance (colour) with the luminance (brightness) signal to form a composite video signal (CVBS).
Personal Video Recorder is an alternative name for a DVR (see above), loosely based on the association of a personal computer (with a hard drive) and a video recorder (with a hard drive).
Quadrature Amplitude Modulation is the format of the modulation applied to the sub-carriers within a MUX. Prior to the digital switchover, both QAM16 and QAM64 are being transmitted, but this is expected to become just QAM64 post switchover. QAM16 enables up to four TV programmes to be combined into one MUX, whereas QAM 64 has double the capacity of QAM16.
Red, Green & Blue are the three primary colours used to make a TV picture. SCART leads have separate connections for the red, green and blue video signals, in addition to the composite (CVBS) signal. Using the RGB connection can result in significantly better picture quality, and most digiboxes, DVDs and DVRs have a menu option to select either RGB or CVBS. N.B. using the RGB connections still requires the CVBS signal as well as the RGB signals (since they don't carry the necessary sync signals).
S-Video stands for "separate video" as distinct from composite video. S-video (also known as Y/C) keeps the brighness and colour content of the video separate (i.e. has two wires for these), using a 4 pin mini-DIN connector. Stereo sound is carried separately using a lead with two phono plugs at each end. S-video provides a better picture quality than CVBS, but is not as good as RGB.
SCART stands for "Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs" and is the term used for the 21 pin connectors on the back of most TV and video equipment. The SCART interface provides both RGB and CVBS connections, stereo sound, auto switching control and a couple of additional data comms lines. N.B. not all equipment has all of these pins connected!
Set Top Box is an alternative name for a digibox, and is often used for a standard Freeview box.
Thin-Film Transisitors are printed onto glass sheets and used inside LCD monitors to control the brightness of each sub-pixel. The red, green and blue pixel colours then combine to produce the full colour and intensity range.
Television - a common abbreviation. Televisions with an analogue tuner only will require a digibox after the digital switchover.
Ultra High Frequency is the term for electromagnetic frequencies used for TV transmission (470MHz to 860MHz).
Video Cassette Recorder - although an obsolete means of recording TV programmes, VCRs are still widely used. They contain an analogue TV tuner, so can only be used with a SCART connection to record a digital TV programme. A separate digital tuner is required to record a different digital programme to the one being watched. VCRs are being superseded by DVRs / PVRs - some of which are available with dual digital tuners.