helical scan


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helical scan

A tape recording method that uses a spinning read/write head and diagonal tracks. Although it uses a rather complex transport mechanism, it is very gentle on the tape. After the cassette is inserted into the drive, the tape is pulled out and wrapped around the read/write head. While the head rotates as much as 30 meters per second, the tape travels as little as 1 inch per second (ips), compared to linear technologies where the tape travels at more than 100 ips.

Helical scan was invented by Ampex in 1956. It was the only method that provided fast-enough transfer rate and sufficient storage capacity to record video on tape so that TV programs could be recorded. Using two-inch tape and running at 15 ips, the going rate for tape recorders of the time, the rotating head created an effective rate of 1500 ips. The helical scan method is used in many different tape technologies, including VHS videotape, DV/MiniDV (camcorders), 4mm DAT, Exabyte's 8mm and Mammoth lines, Sony's AIT and StorageTek's Redwood.


Helical Scan
The helical scan method uses a rotating head and diagonal tracks, which allows a slow-traveling tape to provide a very fast transfer rate. The tape is pulled out of the cartridge and wrapped around the read/write head.


Helical Scan
The helical scan method uses a rotating head and diagonal tracks, which allows a slow-traveling tape to provide a very fast transfer rate. The tape is pulled out of the cartridge and wrapped around the read/write head.







Helical Scan Formats
As you can see from this illustration, there are numerous helical scan formats used for digital storage. The predecessors to VHS tape (top) were the reason for helical scan in the first place. Although mostly used for analog recording, there have been digital applications of VHS tape as well.


Helical Scan Formats
As you can see from this illustration, there are numerous helical scan formats used for digital storage. The predecessors to VHS tape (top) were the reason for helical scan in the first place. Although mostly used for analog recording, there have been digital applications of VHS tape as well.







The Real Thing
Notice the slant on this helical scan head from a VHS video recorder. This precise angle of the head is used to record and play back all helical scan formats.

helical scan

helical scanclick for a larger image
In radar scanning, varying the azimuth and elevation of the antenna continuously to generate a spiral pattern of the beam. This scan pattern is used in fire-control and GCI (ground-controlled interception) radars. Also called spiral scanning.
References in periodicals archive ?
Oakland, NJ) is typical of helical scan recorders in airborne applications.
Information is recorded on these tapes in a variety of fashions, such as linear tracks, multiple linear tracks, helical scans and rotary transverse scans.
In order to overcome problems of modulation noise and signal dropout at the very high head-to-tape speeds of helical scan recording, it is essential that the tape's magnetic base film be exceptionally smooth.
Limitations come in to play related to relative head to tape speed with helical scan drives where both the tape and the head are moving.
As another high-capacity format seeking to take market share from the industry leader DLT, Exabyte's Mammoth 2 is currently the highest-capacity helical scan format available with a native capacity of 60GB and a native transfer rate of 12MB/sec.
It uses a helical scan recording mechanism, which records at a slight angle instead of linearly for higher capacity rates.
Multiple choices in both linear and helical scan formats offer users more freedom to choose the tape option that best meets their requirements, from small offices to departmental and workgroup environments to multi-terabyte enterprise applications.
SLR is based on proven linear recording technology, which provides significant reliability advantages over traditional helical scan drives and media.
Intravenously, 125 mL of 68% iodinated contrast material was administered as a sustained bolus at 4 mL/sec, after which dynamic helical scans (LightSpeed, GE Healthcare, Chalfont St.
The underlying technical concept behind Helical Shuttle was to break through the old paradigm that helical scans must be performed at a constant table speed or pitch, relative to the slice thickness," said Brian Duchinsky, General Manager of Global CT at GE Healthcare.
Toshiba has developed a unique, helical cone-beam reconstruction technique based on the Feldkamp method for axial image reconstruction from helical scans.
Toshiba has developed a unique, helical cone-beam reconstruction technique for the Aquilion 16 based on the Feldkamp method for axial image reconstruction from helical scans.