Helical scan
As helical scanning, helical scanning or helical scan an invented by Eduard Schüller method for recording signals is referred to a VCR or tape drive. In contrast to the linear recording, the track is recorded at an angle to the tape.
Construction
A tape running on a head drum over, it is arranged obliquely to the belt and rotates in the same direction as the belt. This allows the band to be better utilized. Due to the higher relative velocity between the magnetic heads and the higher frequency band can be recorded. However, this also increases the mechanical stress on the belt.
- Vk: peripheral speed of the video heads
- Va: scanning speed of the strip
- DK: diameter of the head drum. In this VHS is 62 mm.
- Nk: The speed of the video head wheel at 25 frames per second ( PAL standard ) 1500 revolutions per minute.
- BB: When VHS tape speed is 0.0234 m / s
When VHS so is the relative velocity about 4.85 m / s It would be used instead of the helical scan method, the longitudinal recording ( sampling rate = belt speed ), you would consume per second 4.85 m band when high frequencies, VHS up to 3 MHz records. In helical scanning system is this in VHS only 0.0234 m / s
The method enabled by the compact video tape cassettes. The so-called hi-fi soundtrack, which was subsequently introduced to improve the quality of conventionally along the recorded audio signal at different video systems will be recorded along with the image information according to a frequency modulation angle.
Following the same principle, digital data can be recorded in high density. While classical streamer to record the data on parallel longitudinal tracks, grab devices with helical scanning partly on formats from the consumer sector back (DDS: DAT, Exabyte: Video 8).
Swell
- Table book of radio and television technology / radio electronics - Frankfurt publishing house
- Electrical shedding Kommunikationstelektronik 2 Radio-/Fernseh-/Funktechnik - Westermann