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DIDS-402-2AMI3
The Y -deflection voltage include sal. 3-MHz minor vertical sweep sine
wave, and a dc analog voltage that results from the conversion of a 3-bit digital
word •. The amplitude of this digital word is such that the beam is positioned on
the Y-axis over one of the horizontal rows on the target anode.
The 1. 3-MHz
sine wave component causes the beam to move up and down on the Y-axis at a
s~nusoidal
rate.
With the X- and Y -deflection voltages simultaneously positioning the beam,
the beam scans over the entire selected target character.
When the beam strikes
the deposited carbon portion of the character, the ratio of primary beam current
to secondary emission is approx:mately 1: 1.
When, however, the beam strike s
the aluminum oxide of the target anode, there is a high ratio of secondary
emission to primary electrons.
This ratio causes current to flow through a load
re sistance that is connected between the target anode and the collector.
As the
beam moves from carbon to aluminum oxide areas of the target, the current
flowing through the load resistance varies at a rate that is determined by the
character in the selected location on the target.
Current flowing through the
load resistance is connected to the input of the video preamplifier circuit.
4-27 VIDEO PREAMPLIFIER A 7
Video Preamplifier A7 (shown in Raytheon Drawing No. 425105) amplifies
the monoscope target video by a factor of 100 before coupling the amplified video
to Video Amplifier A8.
When the monoscope scan is directed to a character
symbol on the target element, secondary emis sion develops a low-level current
of 1 to 3 iJ.A.
This current flows through a video compensation network formed
by Ll and R4 and develops approximately 1 mv of video across input load
resistor R5.
The amplified and inverted output of differential amplifier lCl is
coupled through capacitor C3 and resistor RIO to the input circuit of video
amplifie r A8.
4-28 VIDEO AMPLIFIER A8
Video Amplifier A8 (shown in Raytheon Drawing No. 425102) consists of
circuits that perform the following functions:
a.
Amplify monoscope or cursor video levels to a level sufficient
for driving the CRT cathode element (AI, Ql, and Q2)
b.
Disable the video to the CRT when a blanking signal is present
(Blanking)
c.
Disable video to the CRT when either the vertical or horizontal
deflection amplifier fails (CRT protect)
d.
Adjust the screen brightness of the CRT
4-28. 1 Video Amplification
Input video signals are coupled from Monoscope Video Preamplifier A 7
or from Timing and Discrete Board A14.
From the video preamplifier, video
signals are applied to Wideband Video Amplifier Al and developed across input
load re sistor R4.
4-159
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