Sony BVU-950 - Page 24

--- ALL ABOUT FRAMING AND PHI SQUARE SERVOS ---
To Refresh Your Memory.....
An EIA/NTSC video Signal, as you are aware, consists of 525 horizontal
scanning lines per frame, and operates at 30 frams per second. To re-
duce flicker and increase resolution, each frame is broken down into
two fields of 262.5 horizntal lines each, interlaced with the 2:1 in-
terlace method. Since a field is half a frame, it lasts 1/60th of a
second. (Chart-l)
re—___
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Even
Field
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(262.5
H/60
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es
a
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(525
H/30
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TV
SCANNING
SYSTEM
NTSC/
EIA
TV_SIGNAL
Chart-1l
Now, for Helical Scan VTR's.....
Most helical scan VTR's record one field per track. For proper play-
back, a reference signal must be recorded for each revolution of the
head drum. On 2-head VTR's, such as the U-Matic and Betamax, the
head drum rotates at 30 rps, and each video head records one field
of a frame. Whereas the video tracks are recorded on a slant (the
meaning of the term, "helical,") the control signal is recorded
longitudinally, the same as the audio tracks. (Chart-2)
4-8