مرشح نوتش (notch Filter) .. كتاب التلفزيون الملون والعادي

9-2 notch filter:

This filter (Fig. Color killer.

It is a serial resonant circuit consisting of a file and a capacitor C-L, and its impedance is equal to zero at the frequency (4.43 MHz), so it suppresses this frequency, and the voltage (11 volts) comes from the color killer circuit to the diode D, which makes it in a state of forward connection, canceling the sub-carrier frequency and leaving the signal do not pass

3-9 Requirements for the picture signal in color TV:
The stage of amplifying the visual signal is similar in monochrome and color television, and it has an important function, which is to raise the level of the image signal to enter it into the screen valve, and to give the best contrast. Certain - and two signals are applied to these launchers, namely - the luminance signal, which carries all the information of the black and white image. And the appropriate color reference - each launcher has its own color reference. The sum of the two signals on each launcher produces a good color image. Figure (9-5).

Control the contrast in the visual amplifier (Contrast-Control) manually:

Contrast is the ratio of the intensity of illumination of the whitest points to the blackest points in the image - and the intensity of the contrast is similar - the strength of the audio signal in the radio and the contrast ratio is due to the amount of voltage applied between the image valve network and its cathode - and with the amplitude of the visual signal, the amount of contrast increases - and the control is done In contrast with an external special key that can be set according to the desire of the viewer. It is preferable to increase the contrast when the place is more lit
We control the contrast by controlling the signal connected to the base of the visual signal amplifier (Fig. Depending on the device design and code.

Brightness control manually:

It is an external switch that the viewer deals with exactly according to his desire with the rest of the other control keys and its symbol * and it adjusts the bias of the screen (i.e. the voltage of the screen’s ruling network), and thus controls its lighting according to the illumination of the location of the device and the image displayed on the screen. The effect of the lighting switch and the contrast switch is linked, as changing the settings of one may require a reset of the other. The voltage connected to the screen valve network varies from zero to approximately 120 volts, and this voltage is often mentioned on the diagram