Editing Helical scan (section)

{{short description|Method of recording high-frequency signals on magnetic tape}}
{{Infobox media
| image = Helical tape drive.png
| caption = Helical recording method. As the tape moves horizontally, the drum rotates and the heads in the drum create or write diagonal tracks with signals.
| type = [[magnetic tape]]
| use = recording high-frequency signals
}}
'''Helical scan''' is a method of [[Analog recording|recording]] high-frequency signals on [[magnetic tape]], used in open-reel [[video tape recorder]]s, [[video cassette recorder]]s, [[digital audio tape]] recorders, and some computer [[tape drive]]s. 

With this technique, magnetic tape heads (or head chips) are placed on a rotating head drum,<ref>{{cite web | url=https://patents.google.com/patent/US5453892A/en?q=(dynamic+tracking+vtr)&oq=dynamic+tracking+vtr | title=Rotary magnetic head drum with fluid bearing and with head chips mounted together in parallel }}</ref> which moves the chips at high speed by due to its high angular velocity. The speed of the head chips must be higher than the linear speed of the tape. The tape is wrapped tightly around the drum. The drum<ref name="Broadcast">{{Cite book|url=https://books.google.com/books?id=8YDOAwAAQBAJ&dq=helical+scan+video+recorder&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> and/or the tape is tilted at an angle that allows the head chips to read the tape diagonally. The linear speed of the tape is slower than the speed of the head chips, allowing high frequency signals to be read or recorded, such as video. As the tape moves linearly or length-wise, the head chips move across the width of the tape in a diagonal path. Due to geometry, this allows for high head chip speeds, known as writing speeds, to be achieved in spite of the low linear speed of the tape. The high writing speed allows for high frequency signals to be recorded.<ref>{{Cite book|url=https://books.google.com/books?id=NXEIVQrhKP4C&dq=helical+scan+high+frequency&pg=PA129|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=7WrCSCqMk5gC&dq=helical+scan+video+longitudinal&pg=PA149|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>{{Cite web|url=https://books.google.com/books?id=tOnyc8qyYfYC&dq=helical+scan+video+recorder&pg=PA664|title=New Scientist|date=December 1, 1983|publisher=Reed Business Information|via=Google Books}}{{dead link|fix-attempted=yes|date=August 2024}}</ref> As each head chip enters into contact with the tape, it creates or reads long and narrow areas with information recorded magnetically known as tracks. In Helical scan, these tracks are positioned diagonally, relative to the length of the tape. The diagonal tracks read or written using this method are known as helical tracks.<ref name="Broadcast" />

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