توضيح عمل نظام التحكم عن بعد نوع( Quasar کوازر) .. كتاب التلفزيون الملون والعادي

7-19 Clarifying the operation of the Quasar remote control system:

Quasar's electronic tuning system relies on a selector with capacitive diodes (fractors), linked to a PLL circuit that maintains the precision of the crystal oscillator and the stability of the desired channel - and the microcomputer handles information processing, appropriate decision-making and system monitoring. The simplified box diagram of the operation of this system is shown in the figure.

This is done as its PLL (phase-locking loop) circuit checks and stabilizes the frequency of the crystal oscillator. The frequency splitters lock the page comparator reference signal. The voter oscillator signal is also split and applied to the page comparator. The division factor of the oscillator must give the same frequency as the reference signal. When the channel is tuned to its exact nominal frequency and when there is a difference between the two input signals, the page comparator generates a voltage that automatically corrects the frequency of the voter oscillator, until the two signals are fully compatible. As a result, the voter guarantees the accuracy and stability of the reference oscillator.

tuning effort:

We obtain the tuning voltage of UHF and VHF by stabilizing the voltage (+130V) to (+33V). The output pulses of the page comparator control the connection of the transistor which gives the correct tuning voltage to each channel.

Direct channel switching:

Press the keyboard buttons to enter the desired channel number. It always consists of two numbers, such as 09-21-35 05, and then it performs several operations:

1 - The microcomputer gives the appropriate signal to the LEDs in the digital screen to show the required channel number.

2- The microcomputer provides the appropriate and correct division factor for the frequency divider in the voter oscillator, and as a result, the frequency entered into the page comparator is adjusted.

3- When the frequency entered into the page comparator is not equal, it will produce a signal at the output that adjusts the tuning voltage to the correct value suitable for the required channel.

4 - The microcomputer selects the desired channel. Is it in the VHF field or in the UHF field and applies the correct output B to the appropriate field switch VHF low or high.

e- The output of the microcomputer turns on the audio mute switch when the station signal is absent.

8-19 Sensitivity circuits:

The sensitivity circuits receive several signals, including (389) MHz, 33.4 MHz, vertical synchronization pulses - the composite visual signal - a circuit voltage for automatic fine tuning (AFT), which directs the logical functions that control the work of a computer. The incoming signals tell the computer whether the station signal is present or not. - What is the accuracy of the required tuning? If it is in (Seekon) mode, the voter searches for the next channel, if there is no signal in the requested channel station, and when a device is in (Seekoff) mode, the microcomputer ignores the signals of the sensitivity signals. Thus, it is possible to tune in to a channel that is not used to invest the TV set in showing recorded video movies or video games.

Circuit (PLL) to adjust and filter the tuning voltage:

Returning to the diagram, we find that the input voltage, De V130, is reduced and stabilized to about De V33 by means of a diode Zys D32 and resistance R80, and this forms the voltage. If there is a frequency difference between the two input signals of the phase comparator, the comparator will produce De pulses at its output. It enters into the bias voltage of the Q58 transistor base via C45-R75 and C47, and transistor 58 and 59 are connected so that the connection of 058 secures the operation of the 059 base. Voltage changes between +2 and + DC (V30)

When there is a difference in phase between the two inputs of the comparator and the frequency is equal, a small base current is formed for the transistor 058, which maintains the desired tuning voltage.