Mechanical television

From Wikinfo

Mechanical television is a television system that uses mechanical devices to capture and display images. However, images themselves are usually transmitted electronically. The mechanical part usually consists of a Nipkow disk, which has a series of holes in a spiral with a modulated light source behind. As each hole flies by, a scan line is produced. The advancement of all-electronic television and the cathode ray tube marked the beginning of the end for mechanical systems as the dominant form of television. Mechanical TV usually only produced small images. It was the main type of TV until the 1930s.

Image resolution on mechanical TV was typically very low, ranging from about one dozen lines up to 100 or so. A few systems ranging into the 200-line region were also attempted. Lines were usually oriented vertically rather than horizontally as in modern TVs, often resulting in a portrait image instead of the common landscape orientation viewers are familiar with today. By the end of the 1930s, electronic television was quickly advancing past this point, reaching 400 to more than 600 lines with fast field scan rates in the next few decades.

Since the 1970s, some amateur radio enthusiasts have experimented with mechanical systems. The early light source of a neon tube has now been replaced with super-bright LEDs. There is some interest in creating these systems for narrow-bandwidth television, which would allow a small moving image to fit into a channel less than 40 kHz wide (modern TV systems usually have a channel about 6 MHz wide, 150 times larger). Also associated with this is slow-scan TV, although that typically uses electronic systems.

There are several other technologies that can be used instead of a Nipkow disk. Other arrangements often made use of a rotating drum, either with holes or with a series of mirrors mounted on it.