استرجاع مركبة التيار المستمر dc .. كتاب التلفزيون الملون والعادي

9-4 DC vehicle retrieval:


The composite visual signal contains, in addition to the variable image signal - synchronization pulses, extinguishing and equalization, Figure (9) - (8) - and all signals pass through the capacitor connecting the visual signal, but the direct current cannot pass, and its loss results in the following:

1- The lack of lighting in the image, so its details appear blacker.

2- The extinguishing pulses are weakened and traces of the reflected beam appear on the screen.

Many methods are used to re-compound the direct current, including the diode crystal in modern devices, and the diode was used in the old valve devices. These circuits may be dispensed with in modern devices - to reduce the costs of designing the circuit and the cost of the price of the device - and replace them by increasing the brightness of the screen by manually controlling the intensity of the illumination - and to see the effect of the beam returning on the screen, a negative pulse is delivered to the picture diode network - or a positive pulse to its cathode, during a period Ray bounce. This is done through the horizontal and vertical synchronization circuit. As for the contrast of the image, which is weakened by the loss of the DC vehicle, it was possible to overcome it by developing the phosphorescent layer of the screen - so that it has greater sensitivity and a wider contrast.

Automated Gain Governor AGC in Image Enlarger:

We mean that its function is to maintain the level of the image signal at the output of the visual detector - regardless of the level of the received signal in the antenna - it increases or decreases the amplification - so the image remains stable, and the synchronization pulses maintain their voltage, especially in the case of receiving weak signals and the presence of noise. The level of the synchronization pulses is used As a reference level of the AGC automated gain ruler because the continuous composite of the visual signal cannot be used for this purpose, because it
It changes depending on the lighting of the scene - a well-lit image makes the continuous component of the detector's output small. As for the existing form, its continuous component is large. As for the voltage of the automatic gain governor, it comes through a diode in the visual amplifier or the stage of the visual detector - and the connection of the diode generating the AGC voltage is proportional to the type of transistors. If it is an NPN type, its positivity must decrease with the increase in the signal voltage. The AGC voltage value depends on the pulse level, which in turn is proportional to the signal strength. The AGC voltage must be cleared of the variable compounds and filtered by a large filter capacitor, so that only direct current (DC) passes through. In modern devices, a transistor is used in the circuit of the automatic gain governor AGC or performs its work as part of an integrated circuit - IC, for example in the Seronix device (270LS) integrated circuit (TDA440 IC). Intermediate Frequency IF and its faults and circuits in a previous chapter, including the type AGC reserved for canceling interference and jamming and others - circuit (TDA440) enters the image signal from the visual amplifier and enters the pulses of horizontal deviation from the horizontal output, and does not open the transistor integrated within this integrated circuit only when the presence of the two signals together. Thus, the reserved automatic gain governor is not affected by interference or jamming when the planes pass, because his work is limited to a very short period, which is the back threshold of the extinguishing pulses.