CCIR System I
CCIRSystem Iis an analoguebroadcast television system.It was first used in theRepublic of Irelandstarting in December 1961 as the625-linebroadcasting standard to be used onVHFBand IandBand III,sharing Band III with405-lineSystem Asignals radiated in the north and east[1]of the country. The Republic of Ireland slowly extended its use of System I onto the UHF bands.
The UK started its own625-linetelevision service in 1964 also using System I, but onUHFonly – 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 byHong Kong,Macau,theFalkland Islands,South Africa,Angola,Botswana,Lesotho,Namibia,Tanzania,Saint Helena,Pitcairn Islands.[2]
As of late 2012, analogue television is no longer transmitted in either the UK or the Republic of Ireland. South Africa is still broadcasting in System I, but have plans to end the service at any time.
Specifications
[edit]Some of the important specs are listed below.[3]
The separation between the audio and video carriers is 5.9996 MHz.
- Frame rate:25 Hz
- Interlace:2/1
- Field rate:50 Hz[4]
- Lines/frame:625
- Line rate:15625 Hz[5]
- Visual bandwidth:5.5 MHz
- Vision modulation:AC3 negative
- Preemphasis: 50 μs
- Sound modulation: F3
- Sound offset: 5.9996 MHz
- Channel bandwidth:8 MHz
Luma carrier @ 272MHz, Chroma carrier @ 276.43361875MHz, FM audio @ 278MHz, NICAM audio @ 278.5MHz
A frame is the total picture. Theframe rateis the number of pictures displayed in one second. But each frame is actually scanned twiceinterleavingodd and even lines. Each scan is known as a field (odd and even fields.) Sofield rateis twice the frame rate. In each frame there are 625lines(or 312.5 lines in a field.) Soline rate(line frequency) is 625 times the frame frequency or 625•25=15625 Hz.
The totalRF bandwidthof 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
[edit]SystemIhas only been used with thePALcolour systems, but it would have been technically possible to useSECAMor a 625-line variant of theNTSCcolor 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 systemIas a whole.
Improved audio
[edit]Enhancements have been made to the specification of SystemI's audio capabilities over the years. Starting in the late 1980s and early 1990s it became possible to add a digital signal carryingNICAMsound. 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
[edit]
Republic of Ireland from 1962
[edit]| Channel | Channel limits (MHz) | Vision carrier frequency (MHz) | Main audio carrier frequency (MHz) |
|---|---|---|---|
| IA | 44.50 – 52.50 | 45.75 | 51.75 |
| IB | 52.50 – 60.50 | 53.75 | 59.75 |
| IC | 60.50 – 68.50 | 61.75 | 67.75 |
VHF Band 1 was already discontinued for TV broadcasting well before Ireland's digital switchover.[6]
| Channel | Channel limits (MHz) | Vision carrier frequency (MHz) | Main audio carrier frequency (MHz) |
|---|---|---|---|
| ID | 174.00 – 182.00 | 175.25 | 181.25 |
| IE | 182.00 – 190.00 | 183.25 | 189.25 |
| IF | 190.00 – 198.00 | 191.25 | 197.25 |
| IG | 198.00 – 206.00 | 199.25 | 205.25 |
| IH | 206.00 – 214.00 | 207.25 | 213.25 |
| II | 214.00 – 222.00 | 215.25 | 221.25 |
| IJ ♥ | 222.00 – 230.00 | 223.25 | 229.25 |
♥ No longer used for TV broadcasting.[6]
UHF takeup in Ireland was slower than in the UK. A written answer[7]in theDáil Éireann(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
[edit]| Channel | Channel limits (MHz) | Vision carrier frequency (MHz) | Main audio carrier frequency (MHz) |
|---|---|---|---|
| 21 | 470.0 – 478.0 | 471.25 | 477.25 |
| 22 | 478.0 – 486.0 | 479.25 | 485.25 |
| 23 | 486.0 – 494.0 | 487.25 | 493.25 |
| 24 | 494.0 – 502.0 | 495.25 | 501.25 |
| 25 | 502.0 – 510.0 | 503.25 | 509.25 |
| 26 | 510.0 – 518.0 | 511.25 | 517.25 |
| 27 | 518.0 – 526.0 | 519.25 | 525.25 |
| 28 | 526.0 – 534.0 | 527.25 | 533.25 |
| 29 | 534.0 – 542.0 | 535.25 | 541.25 |
| 30 | 542.0 – 550.0 | 543.25 | 549.25 |
| 31 | 550.0 – 558.0 | 551.25 | 557.25 |
| 32 | 558.0 – 566.0 | 559.25 | 565.25 |
| 33 | 566.0 – 574.0 | 567.25 | 573.25 |
| 34 | 574.0 – 582.0 | 575.25 | 581.25 |
| 35 † | 582.0 – 590.0 | 583.25 | 589.25 |
| 36 † | 590.0 – 598.0 | 591.25 | 597.25 |
| 37 † | 598.0 – 606.0 | 599.25 | 605.25 |
| 38 † | 606.0 – 614.0 | 607.25 | 613.25 |
| 39 | 614.0 – 622.0 | 615.25 | 621.25 |
| 40 | 622.0 – 630.0 | 623.25 | 629.25 |
| 41 | 630.0 – 638.0 | 631.25 | 637.25 |
| 42 | 638.0 – 646.0 | 639.25 | 645.25 |
| 43 | 646.0 – 654.0 | 647.25 | 653.25 |
| 44 | 654.0 – 662.0 | 655.25 | 661.25 |
| 45 | 662.0 – 670.0 | 663.25 | 669.25 |
| 46 | 670.0 – 678.0 | 671.25 | 677.25 |
| 47 | 678.0 – 686.0 | 679.25 | 685.25 |
| 48 | 686.0 – 694.0 | 687.25 | 693.25 |
| 49 | 694.0 – 702.0 | 695.25 | 701.25 |
| 50 | 702.0 – 710.0 | 703.25 | 709.25 |
| 51 | 710.0 – 718.0 | 711.25 | 717.25 |
| 52 | 718.0 – 726.0 | 719.25 | 725.25 |
| 53 | 726.0 – 734.0 | 727.25 | 733.25 |
| 54 | 734.0 – 742.0 | 735.25 | 741.25 |
| 55 | 742.0 – 750.0 | 743.25 | 749.25 |
| 56 | 750.0 – 758.0 | 751.25 | 757.25 |
| 57 | 758.0 – 766.0 | 759.25 | 765.25 |
| 58 | 766.0 – 774.0 | 767.25 | 773.25 |
| 59 | 774.0 – 782.0 | 775.25 | 781.25 |
| 60 | 782.0 – 790.0 | 783.25 | 789.25 |
| 61 | 790.0 – 798.0 | 791.25 | 797.25 |
| 62 | 798.0 – 806.0 | 799.25 | 805.25 |
| 63 | 806.0 – 814.0 | 807.25 | 813.25 |
| 64 | 814.0 – 822.0 | 815.25 | 821.25 |
| 65 | 822.0 – 830.0 | 823.25 | 829.25 |
| 66 | 830.0 – 838.0 | 831.25 | 837.25 |
| 67 | 838.0 – 846.0 | 839.25 | 845.25 |
| 68 | 846.0 – 854.0 | 847.25 | 853.25 |
| 69 § | 854.0 – 862.0 | 855.25 | 861.25 |
† Channels 35 to 37, between UHFBand IVandBand 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 ofChannel 5.
§ Channel 69 was allocated, but never used in the UK.
See also
[edit]Notes and references
[edit]- ^"405 Lines in Ireland (1961 - 1983)".Irish TV - Over forty years of Irish TV History.18 May 2007. Archived fromthe originalon 18 May 2007.Retrieved15 May2023.
- ^Amadeus Trappe, Raffael (2005)."Weltweite Fernsehsysteme (NTSC, PAL und SECAM)".paradiso-design.net.Retrieved5 June2023.[permanent dead link]
- ^Reference Data for Radio Engineers, ITT Howard W.Sams Co., New York, 1977, section 30
- ^Not an independent value: 50 Hz = 25 Hz×2
- ^Not an independent value: 15625 Hz = 25 Hz×625
- ^ab"Television frequency channels used in Ireland".Cork, Ireland - Radio & TV Information.Archived fromthe originalon 13 March 2019.Retrieved15 May2023.
- ^"Dáil Éireann - Volume 380 - 18 May, 1988 - Written Answers. - UHF System".Tithe an Oireachtas - Houses of the Oireachtas.13 November 2012. Archived fromthe originalon 13 November 2012.Retrieved15 May2023.