TM 11-5840-28135/1
angle, and indicate to the operator the position of the
taken at the collector and delivered to the range mark
azimuth antenna beam with respect to the target in
generator subassembly where it is used to cancel the
elevation. By tilting the azimuth antenna until the
first range mark trigger. The second output, a negative
blanked sector of the range marks bracket the target, the
pulse (B-trigger), is delivered to the range mark oscillator
operator is assured of maximum return signal to the
subassembly.
azimuth antenna. The blanked area in the azimuth
(2) When switch S2201 on the trigger delay
display range marks indicates the bearing of the
generator subassembly is placed in the INTERNAL
elevation antenna (antenna AS-1291/TPN-8) with
position, Control-Indicator C-6988/TPN-18 can be
respect to the target. By servoing the elevation antenna
operated without Radar Receiver-Transmitter RT-
until the blanked area of the range marks bracket the
818/TPN-18 for test purposes. One pole of switch
target, maximum target return to the elevation antenna is
S2201 on the trigger delay generator subassembly
obtained. The range mark cancel pulse is delivered to
opens a circuit which allows relay K1108 on the Pulse
the 1-mile blocking oscillator in the range mark generator
Generator 0-1333/ TPN-18 chassis to be restored and
subassembly, where it is used to delete the first range
connect certain of the 35-volt circuits to the internal
mark. The range mark circuits are located in the trigger
power supplies of Control-Indicator C-6988/TPN-18. The
delay generator, range mark oscillator, range mark
other pole of switch S2201 disconnects the base of
generator, and az-el blanking pulse generator.
blocking oscillator transistor Q2201 from the pretrigger
b. Trigger Delay Generator Circuit (fig. 7-10
and connects the base to a bias circuit which establishes
and 7-51). The input to the range mark circuits is the
an operating point which allows the blocking oscillator to
pretrigger pulse from the transmitting section through the
free-run.
c. Range-Mark Oscillator Circuit (fig. 7-10 and
sweep generating section.
7-52). The B-trigger from the trigger delay generator is
(1) Blocking oscillator transistor Q2201
applied to the base of transistor Q2301 of monostable
shapes the pretrigger into a sharp negative spike which
multivibrator transistors Q2301 and Q2302.
is applied to delay multivibrator transistors Q2205 and
The B-trigger causes transistor Q2301 to conduct, which
Q2206. Since the trailing edge of the first half-cycle
in turn cuts off transistor Q2302. The duration of
output of transistor Q2205 is used to initiate the range
transistor Q2302 cutoff is determined by the setting of
marks, the delay gate width is made variable. Delay
RM GATE WIDTH control R2306. RM GATE WIDTH
control is achieved by varying the resistance in the
control R2306 is adjusted to keep transistor Q2302 cut
discharge path of capacitor C2210. In the search mode,
off for 500sec, at which time the multivibrator reverts to
capacitor C2210 is returned to -12 volts through resistor
R2219, the operated contacts of relay K1102, and PPI
its original state. When RANGE MILES switch S10iB is
DELAY control R1105 on Pulse Generator O-1333/TPN-
in the 80 MILES position, capacitor C2312 is placed in
18 top deck. PPI DELAY control R1105 is adjusted to
parallel with capacitor C2303, causing transistors Q2301
initiate the range marks at the start of the sweep as
and Q2302 to produce a negative gate of approximately
1200sec. In the other switch positions, the negative
observed on the crt. In precision operation, the contacts
of restored relay K1102 connect either PREC DELAY 1
500-sec gate (called the range mark gate) appearing at
control R1120 or PREC DELAY 2 control R1119 into the
the collector of transistor Q2302 is coupled through
discharge path, depending upon the setting of CURSOR
inverter transistor Q2304 to switching transistor Q2305.
SELECT switch S1104. PREC DELAY controls R1119
Prior to the arrival of the range mark gate, transistor
and R1120 are adjusted to place the touchdown marker
Q2305 is conducting, which makes the junction of diode
at the point on the time base sweep corresponding to
CR2304 and resistor R2316 slightly positive. This
touchdown. The positive-going variable width gate taken
positive voltage also appears at the base of transistor
at the collector of transistor Q2205 is differentiated by
Q2308 and keeps Q2308 cut off, preventing the free-
capacitor C2212 and resistor R2229. The negative spike
running rangemark multivibrator from oscillating. The
produced by the trailing edge is coupled through diode
positive range-mark gate appearing at the base of
CR2208 to the base of blocking oscillator stage transistor
transistor Q2305 cuts off Q2305, which, in turn, allows
Q2207.
Blocking oscillator stage transistor Q2207
the junction of diode CR2304 and resistor R2316 to go
provides two pulses at its output. The first output, a
negative, effectively disconnecting diode
positive pulse (range mark cancel pulse), is
2-36
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