مكبر وفاصل إشارة اللون .. كتاب التلفزيون الملون والعادي

14-20 Amplifier and Color Signal Separator:

This unit passes the sub-carrier frequency of 4.43 MHz as well. For side frequencies it has within its width package
(2 MHz) and its characteristic curve is also in the shape of a bell, and this section contains wave traps to catch the carrier of the audio signal and the carrier of the luminance signal to prevent it from reaching the discoloration stage (Fig. 22-20).

Burst Signal Separator and Amplifier (BURST):

This circuit works to pass the burst signal (BURST) to the sub-carrier, which is sent in the back-threshold of the line synchronization signal as in Figure (20-23).

Figure (20-24) shows the flow signal amplifier diagram. It is an ordinary transistor amplifier - the coil circuit L and the stray capacitances connected to it in parallel amplify the burst signal, i.e. the sub-carrier signal * only, and this circuit is tuned to frequency
(443MHz)

The gate of the burst signal separator works to separate this signal from the rest of the signals, so the circuit stops working in the normal state, and it opens only when the burst pulses are received by order of pulses coming from the horizontal deflection section, and thus the burst signal is separated and amplified in the transistor T as in Figure (20-25 ).

Local oscillator to generate the sub-carrier of the color signal:

The resulting pulse signal is received from the pulse signal separation gate, and its page is compared with the signal of the local oscillator. If there is a difference in the page, the page difference detector produces an output signal that is applied to a capacitive diode, changing its amplitude value, which leads as a result to changing the frequency of the crystal oscillator to become equal to the frequency of the sub-carrier. In the transmitting device Figure (26-20) Thus, the purpose of these circuits and the circuits attached to them is achieved, which is to maintain the frequency and page of the local oscillator in agreement with the sub-carrier oscillator in the transmitting device - and this frequency is
(4.43 MHz) in the PAL system and others.

Sub-carrier switch and page difference combination 90 in the PAL system:

It is used in the PAL system because the two color difference signals (v) - (U) have a page difference of (90) between them - and it is known during our study of this system - in a previous chapter - that the color sub-carrier is not sent from the transmitting station, but is suppressed - and generated again in The receiver is powered by the local crystal oscillator, and the function of this switch is to reverse the sub-carrier connected to the detector (7) alternately according to the scan lines - and this switch is directed by a bistable multi oscillator. The page difference combination (90) gives the sub-carrier signal generated by the local crystal oscillator a page difference (90), so that its signal becomes the same page as the transmitted signal, as the transmitter sends the signals (V) and (U) with a page difference between them (90) as we mentioned previously.