How did "Mehikon"
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- As you know, in Israel in the late 70s artificially removed color from television signals when broadcasting (this system was called “Mehikon” - “eraser”), so that the owners of expensive color TVs would not be conceited before the owners of black and white. But few know how it worked.
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So, the television signal consists of lines (the screen consists of approximately 576 visible lines, there are 625 frames per frame, some of which are used for vertical synchronization,
15625 lines are transmitted per second - 25 frames per second.
At the beginning of the image line, there is a low-voltage pulse, called a sync pulse. So the TV knows when the line starts on the screen. Behind him comes a part of the color signal.
The device cut the color signal at the beginning of the line (as we remember, it included the display), but left it in the picture!
This was noticed by some engineers, and a device was invented called the “Anti-Mechanic”, which was sold for one-tenth of the cost of a color TV at the time.
It inserted a color signal after the sync pulse, and the TV started to show color. The only problem was that the chrominance signal, as described above, was used for automatic adjustment, respectively, the signal could not be completely restored. Those who use the device often had to turn the adjustment knob on it (once every 15-20 minutes), since the color began to “float” due to a frequency failure.
- As you know, in Israel in the late 70s artificially removed color from television signals when broadcasting (this system was called “Mehikon” - “eraser”), so that the owners of expensive color TVs would not be conceited before the owners of black and white. But few know how it worked.
')
So, the television signal consists of lines (the screen consists of approximately 576 visible lines, there are 625 frames per frame, some of which are used for vertical synchronization,
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and should not be displayed).Synchronization is needed in order to be able to understand the beginning of the frame (the topmost line on the screen, the scan goes from top to bottom from left to right) and the beginning of each of the lines,
15625 lines are transmitted per second - 25 frames per second.
At the beginning of the image line, there is a low-voltage pulse, called a sync pulse. So the TV knows when the line starts on the screen. Behind him comes a part of the color signal.
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This signal is used as a reference (which you can navigate when receiving), and also as an indicator of color transmission (if the program is black and white and the TV is color, then it can confuse parts of the picture with color, showing it where it is not necessary , and so he just turn it off). After the color signal is the visible part of the line image. Voltage is brightness, and the color signal itself is mixed into it. And now - how the Mekhikon itself worked.The color signal is part of the luminance signal, and on black and white TVs looked like groups of small dots in bright places, and the color ones separated it.
The device cut the color signal at the beginning of the line (as we remember, it included the display), but left it in the picture!
This was noticed by some engineers, and a device was invented called the “Anti-Mechanic”, which was sold for one-tenth of the cost of a color TV at the time.
It inserted a color signal after the sync pulse, and the TV started to show color. The only problem was that the chrominance signal, as described above, was used for automatic adjustment, respectively, the signal could not be completely restored. Those who use the device often had to turn the adjustment knob on it (once every 15-20 minutes), since the color began to “float” due to a frequency failure.
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The frequency of the signal changes slowly due to the heating of parts, etc. Over time, the change becomes significant.
Source: https://habr.com/ru/post/393761/
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