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Block Diagrams
Mono TV Camera Tutorial


The scene to be converted to a video signal is focused onto the face of the camera tube by a lens. 

The tube has an electron gun which shoots a beam of electrons at the tube face.

The scene focussed on the face of the tube is "scanned" by the beam.

This is like reading a book.

The eye scans the first line then flies back rapidly and then scans the next line and so on.

When it reaches the bottom of the page it flies back to the top left.

This scanning process is done by the line (horizontal) and frame (vertical) time bases.

Both of these generate a saw tooth waveform which are applied to scan coils mounted on the tube.

These cause the beam to scan and fly back.

Have a look at the web pages on the CRT and the oscilloscope.

As the tube scans the scene it gives an output voltage which is proportional to the brightness at each part of the scene.

The scanning of the camera and the TV receivers in peoples houses must be in step (synchronised).

Therefore at the end of each line a synchronizing pulse is sent to the receivers telling them to fly back to start a new line.

At the end of each frame a wider pulse is sent to tell the receiver to fly back to the top left ready to start a new frame.

The mixture of video and sync pulses is called "composite video".


The scene is actually scanned twice to obtain the complete picture.

The scene is scanned once and the next time it is scanned the lines fall between the first set of scan lines.

This is called "interlaced scanning" and reduces flicker.

In the diagram the red lines show the first scan and the blue ones the second.

The sync pulses and the frequency of the time bases are controlled by the sync pulse generator.

The composite video signal is amplitude modulated on a carrier in the UHF band.

The associated audio signal is frequency modulated on a carrier spaced 6 MHz from the vision carrier.

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