TM 11-5840-281-35/1
circuits. The horizontal centering and off-centering
cause the electron beam to deflect across the face of the
crt.
circuits provide reference voltages to control the
(3) The fixed coil amplifier produces vertical
horizontal position of the time-base sweep on the crt in
signals no. 1 and no. 2 and horizontal signals no. 1 and
both precision and search operation.
(a) In search operation, the horizontal
no. 2, which are applied to fixed deflection coils in the
indicator deflection yoke. During search operation, the
centering and off-centering circuits place the timebase
vertical signals place the time-base sweep origin at the
sweep origin horizontally at the center of the crt, and
vertical center of the crt and provide for operational off-
provide operational control for off-centering the sweep
centering the time-base sweep origin. During precision
origin.
During precision operation, these circuits
operation, the time-base sweep is deflected vertically in
automatically off-center the sweep origin to the left edge
synchronization with the scan action of the antennas.
of the crt, so the entire time-base sweep is presented on
During search operation, the horizontal signal places the
the display.
time-base sweep origin at the horizontal center of the crt
(b) During precision operation, a dc
and provides for operational off-centering the time-base
voltage from the precision horizontal centering control is
sweep origin. During precision operation, the time-base
applied to one input of horizontal centering amplifier
sweep is automatically off-centered to the left edge of the
transistors Q2110 and Q2112, located in the fixed coil
crt so that the entire sweep is presented on the display.
amplifier. The other input is held at a fixed level.
(4) The servo error signal, from the control
Horizontal centering amplifier transistors Q2110 and
synchro in the indicator deflection yoke, is a difference
Q2112 are differential amplifiers with the horizontal
voltage representing the difference between the motor
centering coils in series with emitter-follower transistors
drive position and the position of Antenna AS-1292/TPN-
Q2111 and Q2113. The dc voltage applied from the
8. The servo error signal is applied to the fixed coil
precision horizontal centering control causes an
amplifier and amplified. After amplification, this signal
unbalance in current through the horizontal centering
becomes the motor drive signal. The motor drive signal
coils. The unbalance causes the time-base sweep to
is connected in series with the field of the ppi deflection
originate at the left side of the crt. During search off-
coil drive motor and causes the motor to turn the ppi
centering, the operation is the same except that the dc
deflection coil so that its position will coincide with the
input to transistors Q2110 and Q2112 is derived from the
position of the azimuth antenna. The deflection coil drive
ppi horizontal centering control, and is variable. The
motor is mechanically connected to the ppi deflection
current through the coils can be adjusted to cause the
coil.
time-base sweep to originate at the right or left-side of
(5) The mixer amplifier mixes the markers
the crt. During search operation with no off-centering,
from the range marks and cursor generating subsections
the current through the coils is balanced and the time
with the video signals from the receiver section. The
sweep originates at the center of the crt.
composite video then passes through the video amplifier
(2) Vertical centering and off-centering
and is applied to the cathode of the crt. The sweep gate
circuits (fig.
7-14).
The vertical centering and
is processed by the video amplifier and becomes the
offcentering circuits provide a control current through the
intensity gate applied to the crt control grid to bias the crt
vertical centering coils which determines the vertical
on and off, and to control screen intensity. The intensity
position of the time-base sweep.
gate amplitude is dependent upon the setting of
(a) The operation of the vertical
INTENSITY control R604 on the control panel of Control-
centering and off-centering circuits during search
Indicator C-6988/TPN-18. The intensity gate is applied
operation is identical to that of the horizontal circuits.
to the control grid of the crt. The crt conducts only during
During precision operation, the function of these circuits
sweep periods.
is to deflect the time-base sweep vertically in
The indicator subsection consists of the indicator
synchronization with the scan action of the antennas.
deflection yoke, fixed coil amplifier, and a mixer
The az-el angle voltage from the range-mark section of
amplifier.
Pulse Generator 0-1333/TPN-18 is applied to emitter-
b. Fixed Coil Amplifier Circuit (fig. 7-14 and 7-
follower transistor Q2101 of the fixed coil amplifier from
60). The fixed coil amplifier consists of horizontal and
the az-el switching relay
vertical centering and off-centering circuits.
(1) Horizontal centering and off-centering
2-48
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