نظام سيكام ( SECAM) الفرنسي ٢_a .. كتاب التلفزيون الملون والعادي

And the degree of stability is good if the signal is transmitted over a long distance. In particular, each color difference has a sub-carrier frequency, which is modulated (4406 MHz for the - signal) (4,250 MHz for the R-Y signal).

Coding in the SICAM system: It means, as in all color systems, the conversion of the three color signals (RGB) - whose values ​​were taken from analyzing the color image into red, green and blue colors - into a color TV signal transmitted by the station's antenna and received by the receiver's antenna.

The encoding unit includes the circuits shown in the box diagram in Figure (3- (29) and there is no need to explain the coding process in detail. Rather, we must know that there are special pulses for synchronizing the swap page and they are called Line identifi (cation) signals - these signals are sent through nine lines Horizontal during the extinguishing time, lines from (7) to (15) in the single-line field, and lines from (320) to (328) in the double-line field, and the exchanger rectifies the line assignment signals and then gives them to the matrix unit, Figure (3) (33). The frequency of the electronic transducer is half the frequency of the horizontal scan, i.e. 15625 7812.2 Hz, which is approximately 7.8 kHz. ) its height differs between the two signals: D Di - resulting from (R-Y) (Y) after the necessary correction.
The amplitudes of the line-setting signals were chosen so that the frequency shift they cause is equal to (350 kHz for the (D) signal and equal to (350 kHz) for the (D) signal. These signals, like the rest of the differential signals, pass through the correction operations in the frequency correction units and the frequency modulation operations, and are accompanied by Composite visual signal.

Finally, the SECAM system is used in France, most of the Eastern European countries, and in some Arab countries such as Algeria, Lebanon, and Egypt.
As a result of operating the switch and the delay line, we get two color difference signals always at the same moment. (a) 2 signals: R, DB' (delayed) (b) 2 signals: B, DR' (delayed)

Keys Synchronization: Know that each visual signal passes sequentially into the receiver for one horizontal line period. The signal that was received, the signal that was received, or the signal that came before it, and it is repeated by memory.

The advantages of the SICAM system are due to the method of frequency modulation of the color sub-carrier. And sending each signal one color difference at the same time, and the second signal at the other time and sequentially while the delay line in the receiver stores the line information and then gives it through the line that follows it, this provides the following features: Scan period

1- The transmission is stable and is less susceptible to distortion, noise and interference. 2- It is not affected as a result of the change in width.
3- It is not exposed to the page difference error due to the change in width, as in the PAL system. And NTSC
4 - if the signal is weak or the station is far away, the image will be better than other systems and its stability will be better.
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e - In the event of distortion, noise, or interference, what is affected is the color saturation, not the purity of the color, as in the PAL and NTSC systems. Figure (3)-(33) shows the main differences between the global systems. Comparison of differences between transmission systems (SECAM- PAL- NTSC).