Development
The earliest mechanical television systems used spinning disks with patterns of holes punched into the disc to "scan" an image. A similar disk reconstructed the image at the receiver. Synchronization of the receiver disc rotation was handled through sync pulses broadcast with the image information. However these mechanical systems were slow, the images were dim and flickered severely, and the image resolution very low. Camera systems used similar spinning discs and required intensely bright illumination of the subject for the light detector to work.
Analog television did not really begin as an industry until the development of the cathode-ray tube (CRT), which uses a steered electron beam to "write" lines of electrons across a phosphor coated surface. The electron beam could be swept across the screen much faster than any mechanical disc system, allowing for more closely spaced scan lines and much higher image resolution, while slow-fade phosphors removed image flicker effects. Also far less maintenance was required of an all-electronic system compared to a spinning disc system.
Read more about this topic: Analogue Television Synchronization
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