نظام بال pal الألماني .. كتاب التلفزيون الملون والعادي

: - 8 German PAL system

The page switching system is called Phase Alternation Line, from which the name PAL was derived, and it is a development of the American NTSC system - and it was developed by the scientist (Bruch) in West Germany between (1962) - (1966) by the Telefenken Company in West Germany. He addressed the defects and disadvantages of distortions that appear in the encoding analyzer - and developed a solution to that that is summarized in turning the signal axis (R-Y) at an angle of 180 per second from every two lines. Figure (3) - (21) and from which the name is taken (Page Alter System Line (PAL). The page-turning circuit is located in the transmitter - and a page-reflecting switch for the (R-Y) signal in the receiver turns the page completely synchronously. It requires a delay line that plays the role of memory, so that every two consecutive lines are collected, so that is existence
Page errors have opposite signs and cancel each other out
. This principle was based on the (France) law, which explained and proved that the color information for each two consecutive scan lines is almost identical. This system is used in Germany, England, and many Western countries, and in some Arab countries such as Jordan, Kuwait, and the Arab Gulf states, and in Syria as well. The color information is more reliable and of better quality, because any error in the page difference changes the color saturation and not the color purity and formula. This does not affect the viewer.

The PAL system specification is the number of scan lines 625 lines. The number of photos is 25 photos/minute. Vertical frequency Sub-carrier frequency 4.43 MHz. 50 Hz.

The two signals (U-V) are used, which correspond to (R-Y) and (B-Y). The modulation of the color sub-carrier is a capacitive modulation (AM) and Figure (3-22) is between the box diagram of the transmitter. In the future, the two color differential signals are treated as in the NTSC system, except for the polarity of the sub-carrier of signal (7), i.e. (R-Y), because it It reflects on the scan lines of the images alternately, i.e. a fluctuation of (180) degrees per second, the scan line of Figure (3) - (23) - and the carrier (U) ie (BY) remains unchanged, and this process occurs simultaneously in the transmitter and receiver.

This system is called (PAL-D) because it has a time delay line. As for the simple PAL system, it is completely similar to the NTSC system and differs from it only in some specifications such as the number of lines and the carrier frequency. It has the same disadvantages, if not. more .
It shares with him the color saturation, not the hue - and we have mentioned that the laminar distortions (on the page) of the two consecutive lines are one and therefore some of them cancel out the others. 2 - No errors occur in field width, because signal 1 is transmitted in two opposite pages in a row according to scan lines and makes the side bars in the spectrum of signal I symmetrical. Thus, there is a switch between the upper and lower side beam. The page difference between 1 and changes from () to (9) in each scan line. The result is to get rid of the error in (B). It is worth noting that the color information is lost, and it is several times less than the luminance statement. But this does not affect as long as the human eye does not sense the colors of very small parts

Advantages and disadvantages of the PAL system This system has avoided many of the disadvantages of the previous system (NTSC).

several specifications. Its features are as follows: 1 - In the case of visual recording, moving the recording heads causes errors in degree
And the existence of the delay line, its stability and accuracy are very necessary to obtain the exact match on the page between the immediate and the delayed Q (64 microseconds). In any case, the PAL system
It has the following features
1- Greater image quality at the expense of increasing the complexity of the receiver circuit 2- Ease of external adjustment of the receiver by the viewer- Ease of dealing with magnetic recording-
3- despite the presence of errors on the page
It has no obvious bad effect