Impulse cross

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Not all parts of the video signal are displayed on the screen.
Other areas are made visible through a time shift.

A pulse Cross (Engl. Pulse-cross) is the representation of usually not visible components of an analog video signal on a studio monitor for fault analysis.

Only part of the video signal contains picture information: With an analog 625-line video signal, each field lasts 20 ms. Of this, only 18.4 ms (287.5 lines) are provided for image information; the remaining 1.6 ms (25 lines) form the vertical blanking interval, a time that is reserved for the image return of the electron beam. Likewise, of the 64 µs of each line, only 52 µs are available for image information; the remaining 12 µs form the horizontal blanking interval for the line return. These blanking gaps are therefore outside the picture.

A pulse cross circuit delays the synchronization in the monitor, which shifts the image to the left or upwards. This reveals areas of the video signal that are normally outside the picture. In addition, the circuit lowers the contrast of the image so that the synchronization pulses are also mapped, the voltage of which is below the black level.

In a standardized video signal, the vertical synchronization signal consists of five long pulses of 59.3 µs duration and is framed by five 2.35 µs short pulses before and after, the so-called satellites. Home computers, game consoles, etc. often do not provide a standard-compliant signal: the synchronous signal contains no interruptions and no satellites. This can be easily recognized by means of pulse cross switching.

With PAL color coding, the burst signal can be recognized in the form of an orange bar. The burst is absent in a pure black and white signal.

The timing error of a video recorder can also be seen on the signal cross . When switching the video heads, a single line in the picture is either too long or too short. This error can be corrected with a Time Base Corrector .

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