Helical scan

Last updated
Helical scan
Helical tape drive.png
Helical recording method
Media type magnetic tape
Usagerecording high-frequency signals

Helical scan is a method of recording high-frequency signals on magnetic tape, used in open-reel video tape recorders, video cassette recorders, digital audio tape recorders, and some computer tape drives.

Contents

With this technique, magnetic tape heads (or head chips) are placed on a rotating head drum [1] . which run the chips at high speed (or angular velocity). The tape is wrapped tightly around the drum. Either the drum [2] and/or the tape is tilted at an angle that allows the head chips to read the tape diagonally faster, so the linear speed of the tape may be slower than the speed of the head chips, which rotate at a higher speed allowing signals to be transmitted. high frequency, such as video, are recorded. [3] [4] [5] The diagonal tracks read or written using this method are known as helical tracks. [2]

The head drum of a Hi-Fi NTSC VHS VCR; three of the six heads face the reader. The helical path of the tape around the drum can clearly be seen. VHS head drum 1.jpg
The head drum of a Hi-Fi NTSC VHS VCR; three of the six heads face the reader. The helical path of the tape around the drum can clearly be seen.
The same head drum with the rotating portion elevated for clarity VHS head drum 2.jpg
The same head drum with the rotating portion elevated for clarity
The rotating portion of the head drum showing the rotary transformer and three of the six tape heads used in this particular VCR Rotary transformer 2.jpg
The rotating portion of the head drum showing the rotary transformer and three of the six tape heads used in this particular VCR

Types

There are several types of helical scan. These include:

Many helical scan cassette formats such as VHS and Betacam use a head drum with heads that use azimuth recording, in which the heads in the head drum have a gap that is tilted at an angle, and opposing heads have their gaps tilted so as to oppose each other. [20] [21] This eliminates the need for guard bands between the helical tracks allowing for a higher density of information on the tape. [22] [23] [24]

History

Earl Edgar Masterson from RCA patented the first helical scan method in 1950. [25] [26] German engineer Eduard Schüller developed a helical scan method of recording in 1953 while working at AEG. [27] [28] With the advent of television broadcasting in Japan in the early 1950s, they saw the need for magnetic television signal recording. Dr. Kenichi Sawazaki developed a prototype helical scan recorder in 1954. [29] Helical scan machines were demonstrated by Toshiba in 1959 and since they recorded one field of video per track, they were the first to allow video to be paused and played back at speeds other than real time. Helical scan type B and type C videotape began to be used in 1976. [30]

See also

Related Research Articles

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