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CCIR System B was the 625-line analog broadcast television system which at its peak was the system used in the most countries. Currently (as of 2012) it is being replaced across Western Europe, Asia and Africa by digital broadcasting. == Specifications == Some of the important specs are listed below.〔Reference Data for Radio Engineers, ITT Howard W.Sams Co., New York, 1977, section 30〕 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 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 (AC3). 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 (being "blacker than black") 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 (as originally designed with its single FM audio subcarrier) 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.〔Nedim Ardoğa:TV Verici tekniğine giriş p.34〕 In specs, sometimes, other parameters such as vestigial sideband characteristics and gamma of display device are also given. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「CCIR System B」の詳細全文を読む スポンサード リンク
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