How does a video recorder work? — SH, Sault Ste. Marie, Ontario
A video recorder is much like a normal tape recorder, except that it records far more information each second. When you play an audiotape in a normal tape recorder, small magnetized regions of tape move past a playback head. This playback head consists of an iron ring with a narrow gap in it and there is a coil of wire wrapped around the ring. As the magnetized regions of the tape pass near the ring’s gap, they magnetize the ring. The ring’s magnetization changes as the tape moves and these changing magnetizations cause currents to flow in the coil of wire. These currents are amplified and used to reproduce sound. When you record the tape, the recorder sends currents through the wire coil, magnetizing the iron ring and causing it to magnetize the region of tape that’s near the gap in the ring.
In a video recorder, the tape moves too slowly to produce the millions of the magnetization changes needed each second to represent a video signal. So instead of moving the tape past the playback head, the video recorder moves the playback head past the tape. As the tape travels slowly through the recorder, the playback head spins past it on a smooth cylindrical support. The tape is wrapped part way around this support and two or more playback heads take turns detecting the patches of magnetization on the tape’s surface. The tape is tilted slightly with respect to the spinning heads so that the heads sweep both along the tape and across its width. That way, the entire surface of the tape is used to record the immense amount of information needed to reproduce images on a television screen. During recording, currents are sent through the heads so that they magnetize the tape rather than reading its magnetization.