CCIR System B
System B was the 625-line analog broadcast television system which at its peak was the system used in most countries. It is being replaced across Western Europe, part of Asia and Africa by digital broadcasting.
Specifications
The system was developed for VHF band Some of the most important specs are listed below.| Frame rate | Interlace | Field rate | Line/frame | Line rate | Visual b/w | Vision mod. | Preemphasis | Sound mod. | Sound offset | Channel b/w |
| 25 | 2/1 | 50 | 625 | 15625 | 5 MHz. | AC3 neg. | 50 μs | F3 | 5.5 MHz. | 7 MHz. |
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 So field rate is twice the frame rate. In each frame there are 625 lines So line rate is 625 times the frame frequency or 625•25=15625 Hz.
The video bandwidth is 5.0 MHz. The video signal modulates the carrier by Amplitude Modulation. But a portion of the lower side band is suppressed. This technique is known as vestigial side band modulation. The polarity of modulation is negative, meaning that an increase in the instantaneous brightness of the video signal results in a decrease in RF power and vice versa. Specifically, the sync pulses result in maximum power from the transmitter.
The primary audio signal is modulated by Frequency modulation with a preemphasis time constant of τ = 50 μs. The deviation for a 1.0 kHz. AF signal is 50 kHz.
The separation between the primary audio FM subcarrier and the video carrier is 5.5 MHz.
The total RF bandwidth of System B was 6.5 MHz, allowing System B to be transmitted in the 7.0 MHz wide channels specified for television in the VHF bands with an ample 500 kHz guard zone between channels.
In specs, sometimes, other parameters such as vestigial sideband characteristics and gamma correction of the display device are also given.
Colour TV
System B has variously been used with both the PAL or SECAM colour systems. It could have been used with a 625-line variant of the NTSC color system, but apart from possible technical tests in the 1950s, 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 +570 kHz. On the low-frequency side, the full 1.3 MHz sideband is radiated.
When used with SECAM, the 'R' lines' carrier is at 4.40625 MHz deviating from +350±18 kHz to -506±25 kHz. The 'B' lines' carrier is at 4.250 MHz deviating +506±25 kHz to -350±18 kHz.
Neither colour encoding system has any effect on the bandwidth of system B as a whole.
Improved audio
Enhancements have been made to the specification of System B's audio capabilities over the years. The introduction of Zweiton in the 1970s allowed for stereo sound or twin monophonic audio tracks. This was implemented by adding a second FM audio subcarrier at +5.74 MHz. Alternatively, starting in the late 1980s and early 1990s it became possible to replace the second audio FM subcarrier with a digital signal carrying NICAM sound. Either of these extensions to audio capability have eaten into the guard band between channels. Zweiton uses an extra 150 kHz. The alternative NICAM system uses an extra 500 kHz, and needs to be spaced further from the primary audio subcarrier, thus System B with NICAM has only 150 kHz guard zones between channels.Transmission channels
System B was the first internationally accepted 625-line broadcasting standard in the world. The European 41-68 MHz Band I television allocation was agreed at the 1947 ITU conference in 1947, and the first European channel plan was agreed in 1952 at the ITU conference in Stockholm. The extension to VHF Band III was also agreed in the 1950s.Since then, the System B specification has been used with slightly different broadcast frequencies in many other countries.
Western Europe (except the UK and France) plus East Germany from the 1960s
† Channel 1 was allocated, but never used.§ Not used in the former East Germany
| Channel | Channel limits | Vision carrier frequency | Main audio carrier frequency |
| E5 | 174.00 - 181.00 | 175.25 | 180.75 |
| E6 | 181.00 - 188.00 | 182.25 | 187.75 |
| E7 | 188.00 - 195.00 | 189.25 | 194.75 |
| E8 | 195.00 - 202.00 | 196.25 | 201.75 |
| E9 | 202.00 - 209.00 | 203.25 | 208.75 |
| E10 | 209.00 - 216.00 | 210.25 | 215.75 |
| E11 | 216.00 - 223.00 | 217.25 | 222.75 |
| E12 | 223.00 - 230.00 | 224.25 | 229.75 |
| Channel | Channel Limits | Vision Carrier Frequency | Main Audio Carrier Frequency |
| 1 | 58.00 - 65.00 | 59.25 | 64.75 |
| Channel | Channel Limits | Vision Carrier Frequency | Main Audio Carrier Frequency |
| 2 | 144.00 - 151.00 | 145.25 | 150.75 |
| 3 | 154.00 - 161.00 | 155.25 | 160.75 |
| E5 | 174.00 - 181.00 | 175.25 | 180.75 |
| E6 | 181.00 - 188.00 | 182.25 | 187.75 |
| E8 | 195.00 - 202.00 | 196.25 | 201.75 |
| E11 | 216.00 - 223.00 | 217.25 | 222.75 |
Transmitters were operational on the above channels in 1959. During the 1960s, channels 1 to 3 were deleted and channels E3 to E12 adopted, bringing East Germany into line with the channel allocations used in the West.
Italy
Italian channel-spacings were erratic. System B is no longer in use in Italy, the switchover to DVB-T having been completed 4 July 2012.| Channel | Channel limits | Vision carrier frequency | Audio carrier frequency |
| IA | 52.50 - 59.50 | 53.75 | 59.25 |
| IB | 61.00 - 68.00 | 62.25 | 67.75 |
| IC | 81.00 - 88.00 | 82.25 | 87.75 |
Note: Band I is no longer used for television in Italy.
| Channel | Channel limits | Vision carrier frequency | Audio carrier frequency |
| ID | 174.00 - 181.00 | 175.25 | 180.75 |
| IE | 182.50 - 189.50 | 183.75 | 189.25 |
| IF | 191.00 - 198.00 | 192.25 | 197.75 |
| IG | 200.00 - 207.00 | 201.25 | 206.75 |
| IH | 209.00 - 216.00 | 210.25 | 215.75 |
| IH1 | 216.00 - 223.00 | 217.25 | 222.75 |
Note: Unusually for Europe, Band III is used for DVB-T in Italy. At digital switchover time, Italy took the opportunity to discontinue their erratic System B frequencies, and the digital channels are regularly-spaced every 7.0 MHz from 177.5 MHz.
Australia VHF (until 1993)
Australia were unique in the world by their use of Band II for television broadcasting.| Channel | Channel Limits | Vision Carrier Frequency | Main Audio Carrier Frequency |
| D0 | 45.00 - 52.00 | 46.25 | 51.75 |
| D1 | 56.00 - 63.00 | 57.25 | 62.75 |
| D2 | 63.00 - 70.00 | 64.25 | 69.75 |
| Channel | Channel Limits | Vision Carrier Frequency | Main Audio Carrier Frequency |
| D3 | 85.00 - 92.00 | 86.25 | 91.75 |
| D4 | 94.00 - 101.00 | 95.25 | 100.75 |
| D5 | 101.00 - 108.00 | 102.25 | 107.75 |
| D5A | 137.00 - 144.00 | 138.25 | 143.75 |
| Channel | Channel Limits | Vision Carrier Frequency | Main Audio Carrier Frequency |
| D6 | 174.00 - 181.00 | 175.25 | 180.75 |
| D7 | 181.00 - 188.00 | 182.25 | 194.75 |
| D8 | 188.00 - 195.00 | 189.25 | 194.75 |
| D9 | 195.00 - 202.00 | 196.25 | 201.75 |
| D10 | 208.00 - 215.00 | 209.25 | 214.75 |
| D11 | 215.00 - 222.00 | 216.25 | 221.75 |
Australia VHF (after 1993)
| Channel | Channel Limits | Vision Carrier Frequency | Main Audio Carrier Frequency |
| D3 ‡ | 85.00 - 92.00 | 86.25 | 91.75 |
| D4 ‡ | 94.00 - 101.00 | 95.25 | 100.75 |
| D5 ‡ | 101.00 - 108.00 | 102.25 | 107.75 |
| D5A | 137.00 - 144.00 | 138.25 | 143.75 |
‡ Channels 3, 4 and 5 were scheduled to be cleared during 1993-96 to make way for FM radio stations in Band II. This clearance action took much longer than was anticipated, and as a result, many stations on channel 3 still remain, along with a few on 4 and 5.
| Channel | Channel Limits | Vision Carrier Frequency | Main Audio Carrier Frequency |
| D6 | 174.00 - 181.00 | 175.25 | 180.75 |
| D7 | 181.00 - 188.00 | 182.25 | 194.75 |
| D8 | 188.00 - 195.00 | 189.25 | 194.75 |
| D9 | 195.00 - 202.00 | 196.25 | 201.75 |
| D9A ♦ | 202.00 - 209.00 | 203.25 | 208.75 |
| D10 ‡ | 209.00 - 216.00 | 210.25 | 215.75 |
| D11 ‡ | 216.00 - 223.00 | 217.25 | 222.75 |
| D12 ♦ | 223.00 - 230.00 | 224.25 | 229.75 |
♦ New channel allocations from 1993.
‡ Channels 10 and 11 were shifted up in frequency by 1 MHz to make room for channel 9A. The frequencies of existing stations did not change; only new ones used the new allocations. Digital multiplexes on channels 10 and 11 are using the new channel boundaries.
Australia UHF
Australia are nearly unique in the world for their use of 7 MHz channel-spacing on UHF.| Channel | Channel Limits | Vision Carrier Frequency | Main Audio Carrier Frequency |
| D28 | 526.00 - 533.00 | 527.25 | 532.75 |
| D29 | 533.00 - 540.00 | 534.25 | 539.75 |
| D30 | 540.00 - 547.00 | 541.25 | 546.75 |
| D31 | 547.00 - 554.00 | 548.25 | 553.75 |
| D32 | 554.00 - 561.00 | 555.25 | 560.75 |
| D33 | 561.00 - 568.00 | 562.25 | 567.75 |
| D34 | 568.00 - 575.00 | 569.25 | 574.75 |
| D35 | 575.00 - 582.00 | 576.25 | 581.75 |
| D36 | 582.00 - 589.00 | 583.25 | 588.75 |
| D37 | 589.00 - 596.00 | 590.25 | 595.75 |
| D38 | 596.00 - 603.00 | 597.25 | 602.75 |
| D39 | 603.00 - 610.00 | 604.25 | 609.75 |
| D40 | 610.00 - 617.00 | 611.25 | 616.75 |
| D41 | 617.00 - 624.00 | 618.25 | 623.75 |
| D42 | 624.00 - 631.00 | 625.25 | 630.75 |
| D43 | 631.00 - 638.00 | 632.25 | 637.75 |
| D44 | 638.00 - 645.00 | 639.25 | 644.75 |
| D45 | 645.00 - 652.00 | 646.25 | 651.75 |
| D46 | 652.00 - 659.00 | 653.25 | 658.75 |
| D47 | 659.00 - 666.00 | 660.25 | 665.75 |
| D48 | 666.00 - 673.00 | 667.25 | 672.75 |
| D49 | 673.00 - 680.00 | 674.25 | 679.75 |
| D50 | 680.00 - 687.00 | 681.25 | 686.75 |
| D51 | 687.00 - 694.00 | 688.25 | 693.75 |
| D52 | 694.00 - 701.00 | 695.25 | 700.75 |
| D53 | 701.00 - 708.00 | 702.25 | 707.75 |
| D54 | 708.00 - 715.00 | 709.25 | 714.75 |
| D55 | 715.00 - 722.00 | 716.25 | 721.75 |
| D56 | 722.00 - 729.00 | 723.25 | 728.75 |
| D57 | 729.00 - 736.00 | 730.25 | 735.75 |
| D58 | 736.00 - 743.00 | 737.25 | 742.75 |
| D59 | 743.00 - 750.00 | 744.25 | 749.75 |
| D60 | 750.00 - 757.00 | 751.25 | 756.75 |
| D61 | 757.00 - 764.00 | 758.25 | 763.75 |
| D62 | 764.00 - 771.00 | 765.25 | 770.75 |
| D63 | 771.00 - 778.00 | 772.25 | 777.75 |
| D64 | 778.00 - 785.00 | 779.25 | 784.75 |
| D65 | 785.00 - 792.00 | 786.25 | 791.75 |
| D66 | 792.00 - 799.00 | 793.25 | 798.75 |
| D67 | 799.00 - 806.00 | 800.25 | 805.75 |
| D68 | 806.00 - 813.00 | 807.25 | 812.75 |
| D69 | 813.00 - 820.00 | 814.25 | 819.75 |
New Zealand
| Channel | Channel Limits | Vision Carrier Frequency | Main Audio Carrier Frequency |
| G4 | 174.00 - 181.00 | 175.25 | 180.75 |
| G5 | 181.00 - 188.00 | 182.25 | 187.75 |
| G6 | 188.00 - 195.00 | 189.25 | 194.75 |
| G7 | 195.00 - 202.00 | 196.25 | 201.75 |
| G8 | 202.00 - 209.00 | 203.25 | 208.75 |
| G9 | 209.00 - 216.00 | 210.25 | 215.75 |
| G10 † | 216.00 - 223.00 | 217.25 | 222.75 |
| G11 ‡ | 223.00 - 230.00 | 224.25 | 229.75 |
† Added in the 1980s
‡ Added in the 1990s
Note: the Band III frequencies are the same as Australia's.
Morocco
System G and H
When the UHF bands came into use in the early 1960s, two variants of System B began to be used on those frequencies.In most countries, the channels on the UHF bands are 8 MHz wide, but in most system B countries transmissions on the UHF channels still use system B specifications, the only difference being that the guard band between the channels is 1.0 MHz wider than for System B. That system for the UHF bands is known as System G and all RF specifications given above also apply to system G. Exceptions to this would seem to be Australia, Brunei and Tanzania where the UHF channels are 7 MHz wide, and system B is used on UHF just as it is on VHF.
A few countries use another variant of system B on UHF which is known as System H. System H is similar to system G but the lower side band is 500 kHz wider. This makes much better use of the 8.0 MHz channels of the UHF bands.