طريقة فصل نبضات التزامن عن الإشارة المرئية المركبة .. كتاب التلفزيون الملون والعادي

13-3 Method of separating the synchronization pulses from the composite visual signal:

The synchronization pulses have a greater amplitude than the visual signal, as they occupy (75% to 100%) of the amplitude of the composite signal (Fig. 4-13), and thus these pulses can be separated by a diode or triode in old devices - where the voltage of the pulses operates the valve Because it is greater than the valve cutoff effort. It thus passes the synchronization pulses and prevents the negative bias voltage from passing current during the time of the picture signal and the off pulses. There is a large time constant RC resistor and capacitor circuit to form a low-pass filter that is approximately equal to the time of ten horizontal lines, in order to match the voltage generated in the RC circuit with the highest signal input voltage. No matter how large the amplitude of this signal, the valve only passes the synchronization pulses (Fig. 13-5).

Transistor synchronization circuit:

Circuit work: Figure (6-13)

When there is no visible composite signal, the transistor is in a cut-off state, because there is no potential difference between the base and the emitter. When a visible signal arrives at the base of the transistor, the voltage of the base becomes negative, and the synchronization pulses arrive. The transistor is connected and the capacitor is quickly charged. The transistor is cut off after the impulse ends, with the effect of the capacitor's polarity, which makes the base positive. The capacitor is discharged into the resistance.

The circuit is designed to determine the amplitude of the synchronization pulses from above and below, by cutting off the collector current during the absence of pulses, while it is saturated with current in the periods of effect of the pulses.

The pulses are amplified after they are separated from the composite signal, and there is a circuit in the synchronization interval to cancel the noise and suppress the disturbance pulses that may enter from the antenna or from the feeding line close to electrical devices and tools or from weather and weather factors. In Figure (7-13) a circuit Complete for sync interval and noise suppression