. طريقة إرسال إشارتي النصوع والالوانC-y .. كتاب التلفزيون الملون والعادي

. 3-3 Method of transmitting luminance and color signals -C: It is necessary to separate the luminance and color signals in the transmitter - because each of them carries its own information. They have different properties and features. So an additional frequency is used that carries the color signal. In addition to the original frequency that carries the luminance signal, the luminance signal must cover a wide frequency range. Figure (3-5). It is the entire frequency range of the TV channel (6-7 megahertz), while it is sufficient for the color signal to have a frequency range of (15 megahertz) without this narrow frequency range affecting the image quality. Because as we mentioned that the human eye distinguishes the brightness of the image details are greater. From its ability to distinguish or identify the change of colors and the degree of their saturation.
The bandwidth of the luminance signal for the color difference signals. The bandwidth of a signal does not take up the entire bandwidth and the bandwidth of the color difference signals is (1.5MHz) only .
. If we check the power distribution diagram of the vision signal in Figure (3-6), we see that most of this energy gathers at the low frequencies of the signal. And that high frequencies do not consume only a small part of the energy, and therefore the additional color-carrying frequency is placed in the upper part of the TV channel - i.e. in the upper part of the frequency range of the Y-luminance signal that carries black and white information and its range is the entire frequency range of the channel, Figure (3-6) But within the frequency range of the channel, the carrier frequency of the color difference is called the subcarrier frequency (fp) and its value is chosen in the region (4-5 MHz), where the luminance signal is very small and its changes curve is parallel to the frequency axis.

The sub-frequency (3.58) or 4.53 MHz in the two difference signals carries the appropriate selection of the additional carrier amplitude and modulation properties (which is AM capacitive modulation in the PAL and NTSC systems and the FM frequency in the SECAM system. This ensures the possibility of transmitting the color signal separately from the signal Color brightness with

The adjustment takes place, as for the two signals of the luteal difference (0.1), and they are separated from each other when transmitting, by passing in a phase shift circuit at an angle of (990). There is no interference between the two signals when modulating, and they can be transmitted instantaneously without losing the color information of the two signals, and the color sub-carrier (1) is modified at a balanced rate (Balanced Modulator), and it performs its work at the transmitting station - by deleting or suppressing the carrier signal after it has been replaced, except for the signals The side band does not appear on the output of the rectifier except for the side bands after modification, and their frequency is (4.43) MHz. The goal is to reduce color overlap with the subcarrier. And it is recovered in the receiver for the purpose of detecting the coloring signal. This explains the necessity of having a local oscillator with the same frequency in the color receiver - when the color signal loaded within the side beams of the color sub-carrier frequency part reaches the color circles via the beam amplifier: a pair of synchronous detectors is used to separate the color signals from the carrier part of the side beam signals . Thus, the two signals can be used in their original form by means of the face angle detector in the receiver. Figure (3) - (7) and (3) - (8) show the box diagram for the formation of the color difference and luminance signals and their composition in the transmitter.
It is the output of both rates (Q1) added to each other and the result is . Loaded coloring signal (C). It is transmitted with (Y) by capacitive modulation (AM) in PAL and (NTSC) systems. And by frequency modulation (FM) in the SECAM system. When there is no color signal, the output of each of the two rectifiers will be zero (zero). The picture appears in black and white thanks to the luminance indication
Added to the previous signals are color synchronization signals or a burst: colors (Burst) so that the colors are matched in place so that the image appears on the screen as it was sent from the station. All of these signals are called the visible (combined) signal, Figure (3) - (9). The process of converting colored visual signals into a composite visual signal in the transmission stages and within electronic units and circuits is called the (TERMIN) or encoding process (ENCODER).
As for the process of restoring all the color information transmitted in the color receiver
It is called the decoder process.