دارة التوليف الدقيق الاتوماتيكي (aft) .. كتاب التلفزيون الملون والعادي

19-12 Automatic Fine Tuning (AFT) Circuit:

When synthetic frequency is used, there is no need for an AFT tuning circuit. However, many types of TV sets do not use synthetic frequency - and in most cases, the AFT circuit is useful in obtaining an image with far specifications and correct colors, and it contains most of the devices with synthetic frequency On the AFT circuit because this circuit can correct inaccurate frequencies and compensate for the frequency of channels.

The fine tuner in the television set tunes the frequency of the local oscillator in the voter. In the monochromatic device, the adjustment defect in the (FTC) can be tolerated, but in the color devices, some deviation of the frequency of the oscillator from its correct position can lead to distortion or complete loss of colors.

Even if the fine tuner is initially set. , the frequency of the oscillator can shift from its nominal frequency, and cause color distortions - and the deviation of the oscillator frequency is mainly caused by changing some of the specifications of the oscillator circuit elements when the correct temperature changes.

AFT circuits are designed so that tuning the FTC circuit within the tuning range will make the tuning of the oscillator correct, and a tuning indicator can be used to manually tune the fine tuning adjuster to the required range. In the simplest form, the tuning indicators are light indicators that light up as long as the fine tuning is not correct.

Functions of Automatic Fine Tuning (AFT) Systems:

The local oscillator of the voter tunes at a frequency higher than the carrier frequencies in the range of VHF and UHF channels by an amount equal to the intermediate frequency IF and the AFT circuit allows the oscillator of the voter to have a correct frequency. The voter has to be set to the correct value and this will make the IF intermediate frequencies of sound and image appear from the voter output at the appropriate points in the response curve of the IF amplifier.

It has passed with us that the stability of the frequency of the local oscillator in the color device is more important than the monochromatic device. So in fact, special efforts are made in the design so that when the channel is changed, the oscillator is precisely at the correct frequency.

13-19 Functions and types of remote controls:

The complexity of the circuits and the number of elements in a remote control increases with the multiplicity of functions it performs. The most important basic function is to change the channel, and because of it, the viewer is forced to leave his place repeatedly and go to the TV panel, and the other important function is to control the volume gradually, as well as or the station, the operation of turning on and off ON OFF.

Other functions include controlling lighting, contrast and colors, and each function added to the device carries a new cost.

There are two types used in the remote control signal system:


1- Ultrasonic waves, which range from 34-54 kilohertz, and are generated mechanically or electronically.

2- Infrared waves in the transmitter and receiver. Infrared transmission is used by light emitting diodes (LED). Sensitive future.


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