CCIR System I is an analogue broadcast television system. It was first used in

Ireland Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...

starting in December 1961 as the 625-line broadcasting standard to be used on VHF

Band I Band I is a range of radio frequencies within the very high frequency (VHF) part of the electromagnetic spectrum. The first time there was defined "for simplicity" in Annex 1 of "Final acts of the European Broadcasting Conference in the VHF and ...

and

Band III Band III is the name of the range of radio frequencies within the very high frequency (VHF) part of the electromagnetic spectrum from 174 to 240 megahertz (MHz). It is primarily used for radio and television broadcasting. It is also called h ...

, sharing Band III with 405-line System A signals radiated in the north and east of the country. Ireland slowly extended its use of System I onto the UHF bands. The UK started its own 625-line television service in 1964 also using System I, but on UHF only – the UK has never used VHF for 625-line television except for some cable relay distribution systems. Since then, System I has been adopted for use by

Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...

Macau Macau or Macao is a special administrative regions of China, special administrative region of the People's Republic of China (PRC). With a population of about people and a land area of , it is the most List of countries and dependencies by p ...

, the

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South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

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Namibia Namibia, officially the Republic of Namibia, is a country on the west coast of Southern Africa. Its borders include the Atlantic Ocean to the west, Angola and Zambia to the north, Botswana to the east and South Africa to the south; in the no ...

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Saint Helena Saint Helena (, ) is one of the three constituent parts of Saint Helena, Ascension and Tristan da Cunha, a remote British overseas territory. Saint Helena is a volcanic and tropical island, located in the South Atlantic Ocean, some 1,874 km ...

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. As of late 2012, analogue television is no longer transmitted in either the UK or Ireland. South Africa is still broadcasting in System I, but have plans to end the service at any time.

Specifications

Some of the important specs are listed below: *

Frame rate Frame rate, most commonly expressed in frame/s, or FPS, is typically the frequency (rate) at which consecutive images (Film frame, frames) are captured or displayed. This definition applies to film and video cameras, computer animation, and moti ...

: 25 Hz * Interlace: 2/1 *

Field rate Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an airport * Battlefield * Lawn, an area of mowed grass * Meadow, a gras ...

: 50 Hz * Lines/frame: 625 *

Line rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...

: 15.625 kHz * Visual bandwidth: 5.5 MHz * Vision modulation: AC3 negative * Preemphasis: 50 μs * Sound modulation: F3 * Sound offset: 5.9996 MHz * Channel bandwidth: 8 MHz PAL-I

A frame is the total picture. The frame rate is the number of pictures displayed in one second. But each frame is actually scanned twice interleaving odd and even lines. Each scan is known as a field (odd and even fields.) So field rate is twice the frame rate. In each frame there are 625 lines (or 312.5 lines in a field.) So line rate (line frequency) is 625 times the frame frequency or 625×25=15625 Hz. The total RF bandwidth of System I (as originally designed with its single FM audio subcarrier) was about 7.4 MHz, allowing System I signals to be transmitted in 8.0 MHz wide channels with an ample 600 kHz guard zone between channels. In specs, sometimes, other parameters such as vestigial sideband characteristics and gamma of display device are also given.

Colour TV

System I has only been used with the

PAL Phase Alternating Line (PAL) is a color encoding system for analog television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...

colour systems, but it would have been technically possible to use

SECAM SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''sequential colour memory''), is an analog color television system that was used in France, Russia and some other countries or territories of Europe and Africa. ...

or a 625-line variant of the

NTSC NTSC (from National Television System Committee) is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170. In 1953, a second ...

color system. However, apart from possible technical tests in the 1960s, this has never been done officially. When used with PAL, the colour subcarrier is 4.43361875 MHz and the sidebands of the PAL signal have to be truncated on the high-frequency side at +1.066 MHz (matching the rolloff of the luminance signal at +5.5 MHz). On the low-frequency side, the full 1.3 MHz sideband width is radiated. (This behaviour would cause some U/V crosstalk in the NTSC system, but delay-line PAL hides such artefacts.) Additionally, to minimise beat-patterns between the chrominance subcarrier and the sound subcarrier, when PAL is used with System I, the sound subcarrier is moved slightly off the originally-specified 6.0 MHz to 5.9996 MHz. This is such a slight frequency shift that no alterations needed to be made to existing System I television sets when the change was made. No colour encoding system has any effect on the bandwidth of system I as a whole.

Improved audio

Enhancements have been made to the specification of System I's audio capabilities over the years. Starting in the late 1980s and early 1990s it became possible to add a digital signal carrying

NICAM Near Instantaneous Companded Audio Multiplex (NICAM) is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks.Croll, M.G., Osborne, D.W. and Spi ...

sound. This extension to audio capability has completely eaten the guard band between channels, indeed there would be a small amount of analogue-digital crosstalk between the NICAM signal of a transmitter on channel N and the vestigial sideband of a transmission on channel N+1. Good channel planning means that under normal situations no ill effects are seen or heard. The NICAM system used with System I adds a 700–kHz-wide digital signal, and needs to be placed at least 552 kHz from the audio subcarrier.

Transmission channels

Ireland from 1962

VHF Band 1 was already discontinued for TV broadcasting well before Ireland's digital switchover. ♥ No longer used for TV broadcasting.

UHF takeup in Ireland was slower than in the UK. A written answer in the

Dáil Éireann Dáil Éireann ( ; , ) is the lower house and principal chamber of the Oireachtas, which also includes the president of Ireland and a senate called Seanad Éireann.Article 15.1.2° of the Constitution of Ireland reads: "The Oireachtas shall co ...

(Irish parliament) shows that even by mid-1988 Ireland was transmitting on UHF from only four main transmitters and 11 relays.

United Kingdom from 1964

† Channels 35 to 37, between UHF Band IV and Band V, were originally reserved for radio astronomy. However, from 1997 until the finish of analogue TV in the UK in 2012, the UK used these channels for analogue broadcasts of Channel 5.

§ Channel 69 was allocated, but never used in the UK.

Notes and references

External links

World Analogue Television Standards and Waveforms

{{Analogue TV transmitter topics ITU-R recommendations Television technology Video formats Broadcast engineering CCIR System