TM 11-5840-281-35/1
centering control is used. When the ppi display is off-
(7) For the purpose of this discussion,
centered to the edge of the tube face, the 5mile range is
assume initially that Radar Set AN/TPN-18 is in the
extended to 10 miles, the 10-mile range is extended to
search mode (relay K4501 operated) and RANGE MILES
20 miles, and the 20-mile range is extended to 40 miles.
switch S1101 is in the 40-mile position. In the quiescent
(4) When Radar Set AN/TPN-18 is used in
state, emitter-follower transistor Q4504 is cut off and
precision operation, the entire time base sweep is used;
sweep clamp transistor Q4505 is conducting. The
consequently, the sweep gate length is needed to display
conduction of transistor Q4505 clamps the voltage at the
the selected range.
junction of capacitor C4509 and resistor R4523 to
(5) The sweep gate shutoff state uses a
ground (P4501-F is connected to P4501-M in this mode).
unijunction transistor to develop the shutoff pulse.
The negative sweep gate makes transistor Q4504
The two-terminal base of transistor Q4501 can be
conduct and allows the base of transistor Q4505 to go
considered a center-tapped 10k ohm resistor in series
negative. The negative voltage cuts off transistor Q4505
with resistors R4505 and R4506, forming a voltage
and allows capacitor C4509 to charge towards +35 volts
divider. The transistor Q4501 emitter junction can be
through resistor R4523, PPI SWEEP EXP control R4522,
considered a diode connected to the center-tap of the
the contacts of operated relay K4501, and diode CR4506
base resistance. In the quiescent condition, the voltage
In the 40-mile range, the time constant of the charging
at the center-tap of the base resistance is more positive
circuit is such that capacitor charges to approximately 20
than the voltage applied to the emitter. The emitter
volts before the sweep gate is terminated. Resistor
junction is back-biased and for all practical purposes, no
R4526 produces a small step on the sawtooth waveform.
emitter current flows.
When the positive sweep
When conducting, switch transistor Q4507 clamps the
feedback sawtooth is applied, at some point the emitter
junction of resistor R4526 and capacitor C4509 to
will become forward-biased and current will flow through
ground, eliminating the step effect produced by resistor
the base region between the emitter junction and resistor
R4526. Transistor Q4507 is cut off in the search mode
R4506.
The current flow effectively reduces the
and conducts in the precision mode..
resistance of that section of the base to around 20 ohms,
(8) To improve sawtooth linearity, the
allowing capacitor C4505 to discharge rapidly through
positive sweep feedback sawtooth is added to the
resistor R4506 and transistor Q4501. The positive pulse
capacitor C4509 integrating circuit as a bootstrap
developed across resistor R4506 as a result of the
voltage. The feedback path is through capacitor C4503
discharge of capacitor C4505 is coupled by capacitor
and relay K4501 (connector P4501-A is connected to
C4506 and diode CR4502 to the base of transistor
connector P4501-T in the 40-mile range). RANGE
Q4502, where it terminates the sweep gate. The time it
MILES switch S1101 connects capacitor C4510 and
takes the emitter of transistor Q4501 to rise to firing
resistor R4528 into the circuit in the 20-mile range;
potential is a function of the amount of sweep feedback
capacitor C4511 and resistor R4529 in the 10-mile
attenuation introduced by SWEEP GATE LENGTH
range; capacitor C4512 and resistor R4530 in the 5-mile
control R4503.
range; and capacitors C1103, C1104, and resistor
The configuration of the sawtooth generator circuit is
R1144 in the 80-mile range. In each case, a linear step
determined by relay K4501 and the setting of RANGE
sawtooth is produced. The slope of the sawtooth
MILES switch S1101 on the front panel of Pulse
generated is determined by the value of the integrating
Generator O-1333/TPN-18. The chart below provides a
capacitor in the circuit while the duration and amplitude is
list of the various sweep generator subassembly plug
dependent on the setting of SWEEP GATE LENGTH
terminal interconnections made by RANGE MILES
control R4503.
switch S1101 in the different positions:
(9) During precision operation in the 40and
20-mile ranges, the same two integrating capacitors are
5 mile
10 mile
20 mile
40 mile
80 mile
used that were used during search operation; however, a
X to R
X to R
X to P
X to P
X to P
lower value series resistance is inserted in the circuit by
T-open
T-open
T to A
T to A
T to A
means of relay K4501, and the two step-producing
Y to A
Y to A
Y-open
Y-open
Y-open
resistors are shunted by the conduction of switch
F to H
F to N
F to V
F to M
F to C1103
transistors Q4507 and Q4508. The charging path of the
and C1104
integrating capacitor now becomes diode CR4506, the
contacts
2-41
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