LESSON 2
FUNDAMENTALS OF HELICAL SCAN VIDEO RECORDERS
TASK
Describe the principles of helical scan recording.
CONDITIONS
Given information on the fundamentals of helical scan recorders and tape construction.
STANDARDS
Demonstrate competency of the task skills and knowledge by correctly responding to 80 percent of the
multiple-choice test questions covering fundamentals of helical scan video recorders.
REFERENCES
None
Learning Event 1:
IDENTIFY AND DEFINE THE PRINCIPLES OF HELICAL SCAN RECORDING
1.
Helical scan means "in a spiral formation," a line around a cylinder at an angle other than parallel
with the axis. This should give you a mental picture of the tape path around the head drum assembly.
2.
The basic design features for helical scan magnetic recorders must satisfy the requirements of a
very wide market. They must have a frequency response wide enough to handle the standard television
signals, specialized closed circuit video, high-bit-rate digital, radar type signals, and high frequency
PCM. They must be portable to provide easy handling. They must also be simple to operate with a
minimum of maintenance.
3.
Dual head recorders (fig 2-1) use two rotating heads spaced 180 degrees apart, each sweeping the
same arc repetitively. In this case, the tape need not be wrapped in a complete loop around the head
drum assembly. It should be noted that one head will be in contact with the tape at all times. The heads
are electrically switched so the head that is in contact with the tape is continuously active during its pass.
The long signal dropout that was present in the previous example is eliminated. This type of scanning is
referred to as the half-helical or two-head helix method of video recording. When the two heads are
used, extreme care must be taken to place the heads accurately with respect to each other. Mechanical
tolerances are critical, and placement errors are easily introduced.
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