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DIDS-402-2AM13
The four MSB
IS
arriving from the character readout register are applied
to a D/ A converter to produce an X-axis deflection voltage.
This voltage is
amplified and applied to the monoscope X-axis deflection plates to position the
scan on the appropriate column of the monoscope target font.
The three LSB
IS
arriving from the character readout register are also
D/
A converted to develop a Y-axis deflection voltage.
This voltage is combined
with the minor vertical expansion voltage and amplified before being applied to
the Y -axis deflection plate s.
The purpose of the Y - deflection voltage is to posi-
tion the scan to the appropriate row of the monoscope target font.
Each of the
96
character images etched into themonoscope target can be accessed in this manner.
An intercharacter blanking signal is applied to the X -deflection amplifier
between each character time.
This signal, developed by the timing circuitry.
produces a sawtooth ramp signal which sweeps the scan across each character,
then cuts off the amplifier when the monos cope beam is repositioned to the next
character po sition.
The minor vertical expansion voltage (mentioned in previous text) is a sine
wave signal that occurs at a rate of
1.
2288 MHz.
This signal amplitude modulates.
the Y -deflection voltage producing a composite voltage that varies at the minor
vertical expansion rate.
Although the monoscope scan is positioned to only one
of
96
character positions, the beam cannot be entirely stable because of the
modulating voltage.
This modulating voltage causes the scan to alternately sweep
up and down in a vertical direction several times before the scan is repositioned
to another character.
This painting motion provides a high degree of character
resolution by enabling several scans of the character symbol.
4-15.1.5 Monoscope,Amplifiers, and CRT
The monoscope, amplifiers, and CRT are respectively used to develop,
amplify, and display actual visual characters.
The preceding text has described
the method employed to position the monos cope scan to a specific position on the
target; the following explanation describes what occurs when the beam is properly
positioned.
The monoscope tube is a vacuum tube device designed to function similarly
to a conventional electron gun.
An electron beam is formed within the tube by
placing a high negative potential on the cathode element and operating the collector
at or near ground potential.
The resulting accelerated electron beam is electro-
statically deflected to bombard one position on the target element.
The target
element consists of an etched aluminum disk with a character font identical to
that shown in figure 4-3.
As the beam is directed to a particular character of
the font, secondary emission produces a low current video output peculiar to the
particular character being scanned.
This video signal is amplified twice by
video preamplifier A
7
and video amplifier A8 before being applied to the CR T
cathode.
4-31
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