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What is SECAM, Parameters, Principle, Features
The luminance signal is transmitted in each line when the SECAM standard in the process of signal transmission. But two color difference signals are transmitted in chronological sequence line by line. That is to say, use this method of stagger transmission time to avoid the cross-color and color distortion in the process of transmission.
SEC AM Features
Advantage: Strong anti-jamming capability; good color effects
Disadvantage: Poor compatibility
SECAM frame rate: 25 frames per second and 625 lines per frame
Screen ratio: 4:3
Resolution: 720* 576, about 400 000 pixels
Brightness bandwidth: 6.0MHz
Color amplitude carrier: 4.25MHz
Chroma bandwidth: 1.0MHz (U) 1.0MHz (V)
Sound carrier: 6.5MHz
SECAM is the abbreviation of the French, that is Sequential Couleur a Memoire (sequentially transmit color and storage). It is a new color television system to overcome the disadvantage of tonal distortion in NTSC system. SECAM system's main characteristic is transmitting color signal R-Y and B-Y sequentially line by line. At the same time one transmission channel only transmit one color signals, therefore it fundamentally avoids the mutual interference of two difference color amount. The luminance signal Y must be sent in each line, so SECAM system is a sequence of at the same time.
Receiver must have Y, R-Y and B-Y three signals to demodulate three basic color signal R, G and B, so in SECAM silks also uses the ultrasound delay line. Last line color information has been stored for time of a line, and was transmitted with this line color information; this line information also is stored, and the information will be sent with the next line once. In this way, the color information of each line sent twice to put the two sequential color difference signals are transmitted into the color difference signals appear. The two color difference signal and Y signal will be put into the matrix circuit, and then solved the R, G and B signals.
In the SECAM system, each line just sends a color signal, and thus the transmission of the chrominance signal does not have orthogonal balanced AM but FM. Thus, introducing differential phase distortion has less impact on a large area of color in the transmission, so that the differential phases distortion tolerance of ± 40 °. FM signal can be amplitude limiting before detect, the chrominance signal is almost free from the effects of amplitude distortion that make the differential gain distortion tolerance of 65%.
Meantime, it can be detected directly on the color difference signal FM demodulation, without having to restore the color subcarrier for the receivers. However, due to the FM signal spectrum is more complex, cannot exchange with the spectrum of the luminance signal, thus there are strong interference of the color subcarrier brightness. Taken some measures, such as, let subcarrier three lines of the phase invert one time to make in each sub-carrier interference points of light staggered with each other; each phase also invert one time to make two adjacent sub-carrier interference spot each other offset.
From the implementation point of view, the NTSC system has been used for more than 30 years, and SECAM system and PAL system uses more than 20 years. Therefore, the three standard color broadcast television standard is effective accumulated considerable experience. In terms of technical performance alone, cannot come to fully confirm or deny the conclusions of a particular standard. In fact, countries in the selected format are often constrained by various factors, not only technical considerations.
Inconvenience in view of the different standards to the international program exchange, equipment manufacturing, etc. with the continuous development and progress of science and technology, scientist have begun to research a new standard for satellite television broadcasting. In addition, research on next-generation high-definition television HDTV (High Definition Television) and Hi-FiTV (the High-Fidelity Television) standard, high-fidelity television work are also in progress.
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