Learning Event 2:
DESCRIBE SINGLE OR MULTIPLE TACHOMETER OUTPUTS OF VIDEO TAPE RECORDERS
1. Comparison. To compare the recording of a field, or 262 1/2 lines of picture
information, with a frame which is two fields on the quadruplex and helical
recorders, we will examine the number of lines on the tape involved.
a. The quadruplex recorder requires 16 transverse tracks to record one field
or 32 transverse tracks to record one frame which is a complete television picture.
b. The helical recorder uses one diagonal track to record one field or two
tracks to record a complete frame.
c. Where the quadruplex recorder uses a track of less than 2 inches in
length, the helical scan recorder uses a track which is approximately 19 inches
long.
d. With the helical recorder putting the entire television frame on two
diagonal lines, you can see how even a slight misalignment or improper spacing of
tracks at the various points on the tape could cause a pronounced effect on the
picture when it is displayed on a monitor.
2.
Location. Below the top deck of the transport is the location of the motor
or motors which drive the wheels and pulleys necessary to turn the tape spools and
capstan, the necessary tape guide mounting assemblies, the head supports, and other
mounting castings. All of these components are a part of the tape transport.
3.
Single or multiple motors.
The number of
motors
used
to
operate
the
transport mechanism may be one, two, three, or four.
a. In the single motor applications, belts and drive wheels are used to
obtain the proper drive speeds on capstan and reels.
b. Some recorders/reproducers use two motors, one motor for the capstan drive
and the other providing reel torque.
c. Other models use four motors, one for set feed reel (provides hold-back
torque and rewind power), and one set for take-up reel torque.
d. The most common motor is the standard wire-wound synchronous motor.
Recently, a new type of motor has been developed. It is the printed circuit motor
illustrated in Figures 2-3 and 2-4.
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