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Uhf Test Generator Module 1A5 - TM-11-6625-564-450018
TM-11-6625-564-45 Maintenance Kits Electronic Equipment MK-731/ARC-51X Manual
Readout Mechanism
C2, TM 11-6625-564-45
a. The 300-mc signal from uhf test gener-
1-19. Audio Amplifier Module 1A1
ator module 1A5 is applied to antenna jack J3
through DC1.  The directional coupler con-
verts this 300-mc power to dc and applies it
The output of Handset H-101A/U is con-
to terminal 8 of TEST SELECT switch S1.
nected through HEADSET H-101A/U jack J4
to input transformer T1 of audio amplifier
When TEST SELECT switch S1 is set to
VSWR CAL, this voltage is applied to meter
module 1A1 and through coupling capacitor
Ml. This voltage is varied by VSWR CAL
C6 to the base of audio amplifier transistor
potentiometer R2 until meter M1 indicates
Q1. The signal is amplified and coupled suc-
cessively to succeeding stages Q1, Q2, and Q3
b. The reflected power from the antenna
for increased amplification. Final voltage am-
plification stage Q 4 develops the audio output
applied to the coupler is also converted to dc
by the directional coupler. It is applied to ter-
across the primary of transformer T2. The
minal 9 of TEST SELECT switch S1. When
output of T2 is applied to both bases of
TEST SELECT switch S1 is set to VSWR
prower o u t p u t t r a n s i s t o r s Q 5 a n d Q 6 .  T h i s
TEST, this voltage is applied to meter Ml
power output is developed on the primary of
for an indication of standing wave ratio (swr).
transformer T3 and supplied to the radio set
control for volume control and output
1-18. Audio Amplifier Module 1A2
through pins U and R of connector J2. Re-
(fig. 4-8)
sistors R5 and R14, R7 and R15, R9 and
R17, and R11 and R18 are used as voltage di-
An audio signal is supplied from the pilot's
viders to provide base bins for transistors Q1,
microphone (mike) output through pins E
Q3, QX and Q4, respectively. Resistors R24
and V of connector J2 of the radio set simula-
and R25 feed back avc voltages. which are
tor to terminals El and E2 of audio amplifier
tapped from the voltage-dividing networks
module 1A2.
This signal is then applied
formed by resistors R24 and R26, and R25
through input transformer T1 to AUDIO
and R27, to the emitters of amplifier transis-
GAIN potentiometer R23. AUDIO GAIN po-
tors Q1 and Q3.  Feedback capacitor C5, con-
tentiometer R23 controls the volume by vary-
nected from the collector to the base of tran-
ing the amplitude of the input signal.  This
sistor Q4, suppresses any high-frequrncy
controlled input signal is coupled through
noise applied to the base of Q.1. Resistor R30,
capacitor C1 to the base of audio amplifier
connected across the primary of transformer
transistor Q1.
The amplified output of Q1
T2. protects transistor Q4 from transient
is applied to the primary of transformer T2
voltages caused by the collapsing field around
and coupled by transformer T2 to the bases
transformer T2 when power is removed. Ca-
of power amplifier transistors Q2 and Q3. The
pacitors C1, C2, C3, and C4 are decoupling
power output of these two transistors is ap-
capacitors used with series resistors R1, R2,
plied to the primary of output transformer
and  R3  to  keep  the  audio  stages  from  re-
T3 and coupled by T3 to HEADSET H-101
acting  with  each  other.  R e s i s t o r s R 1 2 a n d
A 17 jack J-4. The audio can be listened to
R13 feed back signals to the base of transistors
with a headset at this jack. Transient blanker
Q5 and Q6 that are 180 out of phase. This
module  1A4  supplies  the  +20  volts  dc  (para
feedback keeps the output constant.
1-14) for B+. Resistors R1 and R8 form a
voltage divider to provide base bias for tran-
1-20. Readout Mechanism
sistor Q1.
Resistors R3 and R11 are feed-
back resistors which reduce the effect of noise
in the power output circuit. Capacitor C3 in a
a. The readout mechanism indicates the fre-
high-frequency noise present. Resistor R4 and
quency selection made by a radio set control.
capacitor C3 form a negative feedback path to
The readout mechanism contains four Auto-
improve current stability.
positioners, each of which is attached to a dial

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