CCIR System G is an analog broadcast television system used in many countries. There are several systems in use and letter G is assigned for the European UHF system which is also used in the majority of Asian and African countries. (However some countries in Europe use different systems.)
Some of the 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.||8 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 (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 RF parameters of the transmitted signal are exactly the same as those for System B which is used on the 7.0 MHz wide channels of the VHF bands. The only difference is the width of the guard band between the channels, which on System G is 1.0 MHz wider than for System B: in other words 1.15 MHz (assuming the worst case which is when NICAM sound is in use).
A few countries (Belgium, Luxembourg and Netherlands) use a variant of system G which is known as System H. System H is similar to system G but the lower (vestigial) side band is 500 kHz wider. This makes much better use of the 8.0 MHz channels of the UHF bands by reducing the width of the guard-band by 500 kHz to the still perfectly generous value of 650 kHz.
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CCIR 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.
CCIR System H is an analog broadcast television system primarily used in Belgium, the Balkans and Malta on the UHF bands.
CCIR System A was the 405-line analog broadcast television system broadcast in the UK and Ireland. CCIR service was discontinued in 1985.
CCIR System I is an analog broadcast television system. It was first used in the Republic of Ireland starting in 1962 as the 625-line broadcasting standard to be used on VHF Band I and Band III, sharing Band III with 405-line System A signals radiated in the north of the country. 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.