Editing Helical scan (section)

== Types ==
There are several types of helical scan. These include:
* Alpha wrap (α), in which the tape is wrapped around the drum in a full, [[Degree (angle)|360 degree]] fashion.<ref>{{Cite book|url=https://books.google.com/books?id=TOMOmmrvwCcC&dq=alpha+wrap+helical+scan&pg=PA120|title=The History of Television, 1942 to 2000|first=Albert|last=Abramson|date=September 15, 2007|publisher=McFarland|isbn=9780786432431 |via=Google Books}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=kmBQDwAAQBAJ&dq=helical+scan+alpha+wrap&pg=PA248|title=Television Fundamentals|first=John|last=Watkinson|date=April 17, 1996|publisher=Taylor & Francis|isbn=9781136027543 |via=Google Books}}</ref> 
* Omega wrap (Ω), in which the tape is wrapped almost fully around the drum similar to the Greek letter Omega. Used in [[Type C videotape|Type-C videotape]] recorders. The tape is wrapped 346 degrees around the drum with 270 degrees used for recording. Because of this, the vertical blanking interval of the video signal is lost and to prevent this a secondary head in a "1 1/2 head" configuration must record the interval when the video head is not reading the tape. A full frame of video with two fields can be recorded in a single revolution of the drum with a single head creating a single diagonal track on the tape.<ref>{{Cite book |last=Gulati |first=R. R. |url=https://books.google.com/books?id=u-3oFBzrQ0sC&dq=quadruplex+playback&pg=PA195 |title=Monochrome and Colour Television |date= December 2005|publisher=New Age International |isbn=978-81-224-1776-0 |language=en}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=7WrCSCqMk5gC&dq=helical+scan+video+recorder&pg=PA170|title=Magnetic Recording: The First 100 Years|first1=Eric D.|last1=Daniel|first2=C. Denis|last2=Mee|first3=Mark H.|last3=Clark|date=August 31, 1998|publisher=John Wiley & Sons|isbn=9780780347090 |via=Google Books}}</ref><ref name="auto">{{Cite book|url=https://books.google.com/books?id=8YDOAwAAQBAJ&dq=omega+wrap+helical&pg=PA468|title=Broadcast Engineer's Reference Book|first=E. P. J.|last=Tozer|date=November 12, 2012|publisher=CRC Press|isbn=9781136024184 |via=Google Books}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=PdruCAAAQBAJ&dq=omega+wrap+helical&pg=PA465|title=Magnetic Recording Handbook|date=December 6, 2012|publisher=Springer Science & Business Media|isbn=9789401094689 |via=Google Books}}</ref> 
*C wrap, where the tape is wrapped around the head drum in the shape of a backwards C, used in the [[Betacam]] format, uses a wrap of 200 to 300 degrees where 180 to 270 degrees are active or used for recording, similar to the U wrap which is reminiscent of an U laid on its side and is used in the [[U-matic]] format. Because the tape is not wrapped around the drum as much as with the omega wrap, two heads creating two diagonal tracks must be used to record a video frame, one field for every track and head.<ref>{{Cite book|url=https://books.google.com/books?id=-cEdAAAAQBAJ&dq=helical+scan+180+degree+two+head&pg=PA24|title=Sound Person's Guide to Video|first=David|last=Mellor|date=July 18, 2013|publisher=Taylor & Francis|isbn=9781136120787 |via=Google Books}}</Ref><ref>{{Cite book|url=https://books.google.com/books?id=BHfNCgAAQBAJ&dq=helical+scan+180+degree+two+head&pg=PA134|title=VCR Troubleshooting and Repair|first1=Robert|last1=Brenner|first2=Gregory|last2=Capelo|date=August 26, 1998|publisher=Elsevier|isbn=9780080520476 |via=Google Books}}</Ref><ref name="auto"/><ref>{{Cite book |last1=Jackson |first1=K. G. |url=https://books.google.com/books?id=OJqjBQAAQBAJ |title=TV & Video Engineer's Reference Book |last2=Townsend |first2=G. B. |date=2014-05-15 |publisher=Elsevier |isbn=978-1-4831-9375-5 |language=en}}</ref>
*M wrap, used in [[VHS]] and the [[D-1 (Sony)]] and [[D-2 (video)]] digital videotape formats, wraps the tape around the head drum in a pattern or in a tape path reminiscent of the letter M, around the left and right side of the head drum, 250 to 300 degrees around it where 180 to 270 degrees are active or used for recording, with two heads if 180 degrees are used.<ref>{{Cite book|url=https://books.google.com/books?id=BHfNCgAAQBAJ&dq=vhs+180+degree&pg=PA149|title=VCR Troubleshooting and Repair|first1=Robert|last1=Brenner|first2=Gregory|last2=Capelo|date=August 26, 1998|publisher=Elsevier|isbn=9780080520476 |via=Google Books}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=BHfNCgAAQBAJ&dq=vhs+two+heads+180+degrees&pg=PA134|title=VCR Troubleshooting and Repair|first1=Robert|last1=Brenner|first2=Gregory|last2=Capelo|date=August 26, 1998|publisher=Elsevier|isbn=9780080520476 |via=Google Books}}</ref><ref name="auto" /><ref>{{Cite book|url=https://books.google.com/books?id=QmaQTIdoWmYC&dq=m+wrap+tape&pg=PA386|title=Newnes Guide to Television and Video Technology|first=Eugene|last=Trundle|date=June 11, 2001|publisher=Newnes|isbn=9780750648103 |via=Google Books}}</ref>
* Half wrap, used to denominate any type of wrap where the tape covers approximately 180 degrees, or half of the circumference of the drum. To record a full frame of video it requires at least two video heads, each recording a video field, of which two are necessary to record a video frame.<ref>{{Cite web|url=https://books.google.com/books?id=BH8GEAAAQBAJ&dq=helical+half+wrap&pg=PA393|title=Audio Video Systems|first=S. P. Bali, Rajeev|last=Bali|publisher=Khanna Publishing House|via=Google Books}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=-cEdAAAAQBAJ&dq=helical+tape+half+wrap&pg=PA22|title=Sound Person's Guide to Video|first=David|last=Mellor|page=24|date=July 18, 2013|publisher=Taylor & Francis|isbn=9781136120787 |via=Google Books}}</ref>

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.<ref name="poptronics">{{Cite magazine |last=Goldwasser |first=Sam |date=January 2000 |title=VCRs |url=https://search.ebscohost.com/login.aspx?direct=true&db=f6h&AN=2782584&site=eds-live&scope=site |magazine=[[Poptronics]] |volume=1 |issue=1 |pages=77–79 |issn=1526-3681}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=8YDOAwAAQBAJ&dq=dv+9000+rpm&pg=PA473|title=Broadcast Engineer's Reference Book|first=E. P. J.|last=Tozer|date=November 12, 2012|publisher=CRC Press|isbn=9781136024184 |via=Google Books}}</ref> This eliminates the need for guard bands between the helical tracks allowing for a higher density of information on the tape.<ref>{{Cite book|url=https://books.google.com/books?id=8YDOAwAAQBAJ&dq=azimuth+guard+band&pg=PA465|title=Broadcast Engineer's Reference Book|first=E. P. J.|last=Tozer|date=November 12, 2012|publisher=CRC Press|isbn=9781136024184 |via=Google Books}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=NXEIVQrhKP4C&dq=azimuth+guard+band&pg=PA137|title=VCR Troubleshooting and Repair|first1=Gregory|last1=Capelo|first2=Robert C.|last2=Brenner|date=June 26, 1998|publisher=Newnes|isbn=9780750699402 |via=Google Books}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=pY2jBQAAQBAJ&dq=azimuth+guard+band&pg=PA234|title=Newnes Guide to TV and Video Technology|first=Eugene|last=Trundle|date=May 12, 2014|publisher=Elsevier|isbn=9781483183169 |via=Google Books}}</ref>