TM 11-5840-281-35/1
CR2304. With diode CR2304 disconnected, the base of
applied to diode CR2303.
d. Range-Mark Generator Circuit (fig. 7-10 and
transistor Q2308 is allowed to rise in a negative direction
towards the potential appearing across Zener diode
7-54).
The first signal applied to the range-mark
CR2305, and the rangemark multivibrator begins to
generator is the delayed pretrigger (called the A-trigger
oscillate.
at this point) from the trigger delay generator
(2) Characteristically, the initial cycle of a
subassembly.
free-running multivibrator is nonlinear with respect to the
(1) The negative A-trigger occurs several
period of its normal oscillations. Since the first oscillation
microseconds before the range-mark trigger, and sets
(corresponding to the first range-mark trigger) is later
flip-flop transistors Q2509 and Q2510 so that Q2509 is
deleted, and the independently-produced touchdown
conducting and Q2510 is cut off. In this state, the
marker is inserted in its place, a means is provided to
collector of transistor Q2508 will virtually be grounded
accurately control the starting time of the second
and the A-trigger will have no effect. If transistor Q2509
oscillation so that it will have the proper time relationship
is cut off and transistor Q2510 is conducting, the rising
with the touchdown marker; clamp circuit transistor
voltage on the collector of Q2509, due to the negative
Q2306 and RM POS control R2319 provide this control.
input at transistor Q2508, will drive the base of transistor
(3) A portion of the negative range-mark
Q2510 in a positive direction, causing Q2510 to cut off.
gate appearing at the emitter of transistor Q2304 is
The negative voltage at the collector of Q2510 will make
tapped off by the wiper arm of control R2319,
the base of Q2509 negative, causing Q2509 to conduct.
differentiated, and applied to the base of transistor
The collector of transistor Q259 will rise to zero volt.
Q2306. Transistor Q2306 acts as an emitter follower in
Capacitors C2512 and C2514 pass high-frequency
this case, and couples the negative pulse through diode
components of the switching signals to speed up the
CR2307 to capacitor C2310.
The negative pulse
change of state. Once the change of state has been
appears as an additional current to the normal charging
accomplished, the flip-flop will remain at that state until a
current of capacitor C2310; thus, the charging time of
new signal resets it by changing to the opposite state.
capacitor C2310 is modified proportionally to the
(2) The first negative range-mark trigger
amplitude of the pulse delivered by transistor Q2306.
from the range-mark oscillator subassembly arrives at
RM POS control R2319 is adjusted to make the second
the base of blocking oscillator transistor Q2501
range mark occur exactly 12.36 sec after the
simultaneously with the positive-going range mark cancel
pulse; consequently, the two cancel each other. When
touchdown marker.
The range-mark multivibrator
the first negative rangemark trigger is applied to the base
frequency is set by RM FREQ control R2323 to 80.916
kHz, which corresponds to a period of 12.36 ,sec (or
of transistor Q2501 through capacitor C2502, the range-
mark cancel pulse will keep the base of transistor Q2501
one cycle every nautical mile of radar range). The
clamped at zero volt so the trigger will have no effect.
range-mark multivibrator output is amplified by transistor
(3) The first negative range-mark trigger is
Q2307, differentiated by capacitor C2309, resistor
also applied to the 5:1 countdown circuit consisting of
R2328, and applied as negative range-mark triggers to
transistors Q2502 through Q2506. Applied to the base
the range-mark generator.
of clamp transistor Q2502, transistor Q2502 conducts
(4) The range-mark gate, in addition to
with its collector rising toward zero volts. Capacitor
starting the range-mark triggers, is also used to initiate
C2506 starts to charge through Q2502, 5 MILE CDN
the touchdown marker. The range-mark gate appearing
ADJ control R2511, and resistor R2512, driving the base
at the collector of transistor Q2302 is differentiated by
of transistor Q2505 in a positive direction toward cutoff.
capacitor C2304 and resistor R2308, and the negative
The collector of transistor Q2505 will start going toward -
spike coincident with its leading edge is applied to the
12 volts, causing transistor Q2506 to conduct harder.
base of blocking oscillator transistor Q2303 as a trigger.
The emitter of transistor Q2506 will become more
The positive pulse developed by transistor Q2303 is
negative, making the base of transistor Q2504 negative.
coupled through diode CR2303 directly to the indicator
Transistor Q2502 will start conducting, providing a path
section circuits as the touchdown marker. TD MARKER
for capacitor
INTENS control R2310 adjusts the amplitude of the
touchdown marker by controlling the amount of back bias
2-37
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