VIDEO HIGH DENSITY (JVC/THORN-EMJ)

Technically and price wise, VHD falls between laservision and selectavision. The JVC system resembles the RCA approach in its use of capacitance pick-up from an electrically conductive disc with a spiral of pits on its surface. But the 25cm (10 inch) JVC disc has a smooth surface with no groove. The stylus electrode is constrained to follow the spiral pits by a servo system. The spiral of program pits (which the electrode stylus tracks to produce pictures on TV screen) is interlaced with a spiral of tracking pits which are sensed to control the servo system to guide the electrode.

Fig. 34.10 illustrates the method of controlling the stylus. The stylus is mounted at the end of a cantilever pick-up arm opposite ...

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