نظام ( National Television System Committee NTSC) الأمريكي ٢_a .

Width of frequency bands required for both luminance and chrominance signals:

a - luminance signal no

b - visual cue

C - the coloration signal Q is loaded with the color subcarrier.

d - sign | visible.

e - coloration signal 1 .

F - total chrominance signal (0.1)

g - the overall composite and colored visual signal and contains (Q,1,Y)

h - side band of the TV color signal for channel 4 (American system) Figure (3-15) Bandwidth of the signal luminance and coloration

Signal 1:

Signal 1 can transmit smaller details in the image than a signal transmits, and therefore it must occupy a wider frequency range and its side band extends up to (1.5 MHz), but the upper side band cannot exceed (42 MHz) allocated to the visual signal, and this requires suppressing the upper side band So that it does not extend more than (06 MHz), while the lower side band extends up to (1.5 MHz), meaning that the side band extends from (3.58 MHz) to (3.58 - 1.5 = 2008 MHz).
As for the upper side band, it extends from (3.58 MHz) to 180.63 MHz). Figure (3) - (16) shows the distribution of the entire signal.

colored.

The main reason why signal 1 occupies a wider frequency range than it does is because it carries more colors in nature and images, which the eye senses more than others - and that a ray! It is located in the field of orange color. At the positive maximum value of 1, it reaches the red belt, and at the negative maximum value, 1 appears at the belt

Turquoise is bluish green.

The loss or absence of a signal of 1 in the color image will cause it to lose many colors and distort it greatly, so it is not acceptable for viewing. That is, its effect is greater and greater than the signal).
Delay line: Since the Q signal is transmitted within a bandwidth narrower than 1, it is subjected to a certain time delay - and to make the two signals 1 and compatible on the page, it is necessary to delay the signal 1 for a certain time so that the two signals together reach the rates (AM) - Figure (3) - ( 17).
The color synchronization signal (Burst (colors) in the (NTSC) system: The color burst (Burst) is the process of tightening and adjusting the frequency and page difference of the oscillator signal located inside the receiver - and this burst or burst consists of 11 oscillations with the same frequency as Oscillator i.e. 3.58 MHz (3.579545 MHz) It comes after each horizontal sync pulse and is located on the rear sill of the horizontal off pulse

There is no interference between the color splash and the horizontal synchronization pulses, because the average value of the splash is equivalent to the image signal, as it is less amplitude and length, so neither one affects the other, nor does any error occur between them. a fourth

For the operation, the presence of the local oscillator in the receiver is necessary because the two signals 0,1 are modulated capacitively in the transmission, and the sub-carrier is written and the side beams are left. The detection must restore the carrier frequency signal, and the oscillator must be identical in its frequency and page with the frequency and page of the sub-carrier.
NTSC Receiving and Decoder System: The (I-O-Y) signals reach the receiver, Figure (3) - (18). The (chromatic) sub-carrier signal is separated from the luminance signal using packet filters. This signal, after being separated, synchronizes the sub-carrier generator within the receiver required for the detection process and the crystal oscillator. The page of the color synchronization signal is compared within the page discriminator circuit, and the difference voltage of the two signals (error signal) resulting from the comparison process is taken, filtered and amplified, and then taken to adjust the crystal oscillator in terms of frequency and page, until the matching process is completed with the frequency and page of the color synchronization signal.
The generated signal is taken in two ways, with an angle shift of (990), one from the other. and directed to harmonic reagents. As a result of the detection process, we get the two signals 1 and Q, so each of them passes to its own filter - and the signal 1 is delayed to equalize the difference in the passage time of each of them - and mathematical operations are carried out in the color matrix circuit on the two incoming signals 1, and we get in the output of the matrix the color signals BY

G-Y, R-Y)

As for the no signal, it is separated from the sub-carrier frequency by a down-pass filter. It is passed through an appropriate delay line to cause the Q-I-Y signals to coincide in time.

The matrix performs mathematical operations to give:

R = (R-Y) + Y

G = (B-Y) + Y

B = (G-Y) + Y = G

Which is applied to the three launchers in the colored screen, so that each signal reaches the launcher designated for the same color, and the beam of each launcher is directed to hit the phosphorescent points that radiate the same color only.

Advantages and disadvantages of the NTSC system: This system was the first colored system to be designed and implemented in the world. Scientists have benefited from studying its defects and disadvantages to develop other systems such as PAL and SECAM. Its disadvantages were as follows:
1- Existence. Errors and distortions. Including the distortion of non-linearity when increasing the power. It is called differential gain distortion - and differential page distortion - every non-linear distortion affects the color purity and the degree of saturation, or both - because the first is related to the page, and the second is related to amplitude as well as bandwidth errors (orthogonal error) - which require that the distinction analyzer be well thought out and designed accurately. 2 - The need to use additional adjustment keys in the receiver - to adjust the color and saturation in addition to the brightness and contrast controls - which necessitates a complex and lengthy process to adjust the image.

- The emergence of some disadvantages and difficulties in the visual recording process of recording programs and retrieving them at the transmitting station - and this is manifested by changing the page and length when recording on devices that contain four rotating heads - and this is what confuses the work of the crystal oscillator in the receiver - so horizontal bands of different colors and degrees appear on the color image saturation. This is what called for the introduction of additional correction units on the recording devices called the (color) correction unit - the problems of visual recording appeared late when using it, i. These errors from

The advantages of the NTSC system are:

. 2- Low price of the receiver 3- Ease of mixing images and special effects in the transmission studio 4- Not using a delay line in the receiver (64 microseconds).

1- The simplicity of the system compared to the PAL and SECAM system.