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C3 and C6 Control Assembly 2A5 Detailed Functional Operation
Up
TM-11-5820-873-34 Radio Set AN/URC-92 (NSN
Next
Chapter 3. DIRECT SUPPORT


TM 11-5820-873-34
A drive signal is received at either 2XA6-4 or 2XA6-5 for
phase correction. The drive signal is a ground supplied
CAUTION
by Control Logic Board 2A1. When no ground is present
If a drive signal (ground) is placed on
at either 2XA6-4 or 2XA6-5, both are at + 28 VDC. Thus
2XA6-4 and 2XA6-5 simultaneously,
the servo amp is cutoff from driving in either direction.
the transistors will be destroyed A
A drive signal (ground) at 2XA6-4 causes 2A6Q1 to
positive brake signal at 2XA6-12
conduct.  Transistor 2A6Q1 then triggers 2A6Q2 and
anytime the motor is being driven
2A6Q4 on. When 2A6Q2 conducts, +28 VDC is applied
will also destroy transistors.
to 2M1-1. When 2A6Q4 conducts, a ground is provided
to 2M1-2. This causes 2M1 to rotate in one direction.
2-21. 3 dB Attenuator Detailed Functional Operation
Removing the ground level drive signal from 2XA6-4
(Fig FO-32)
cuts off 2A6Q1. The DC excitation to 2M1 is removed
The 3 dB Attenuator consists of 2K4, 2CR1, and a 3 dB
and rotation stops. A drive signal (ground) at 2XA6-5
pad containing 2C4, 2R3, 2R4, 2R5, 2R6, 2R7 and 2R8
causes 2A6Q6 to conduct.  Transistor 2A6Q6 then
The 3 dB circuitry is used to prevent transmitting into a
triggers 2A6Q5 and 2A6Q3 on. When 2A6Q5 conducts,
possible open or short circuit. The accomplish this, a 3
+ 28 VDC is supplied to 2M1-2 When 2A6Q3 is
dB pad is switched in series with the transmission line.
conducting, ground is present at 2M1-1 The motor then
Switching is accomplished thru 2K4 Control Logic Board
rotates In the opposite direction Again, removing the
2A1 operates 2K4. The pad is switched in when coupler
ground level drive signal at 2XA6-5 this time, cuts off
tuning is initiated. When reflected power drops below
2A6Q6 Motor 2M1 stops rotating.  A positive braking
threshold, the 3 dB pad is taken out of the RF path If
signal is applied at 2XA6-12 to prevent overshoot and
reflected power goes above threshold the pad will be
oscillation of 2M1.  The positive brake signal causes
switched in series in the RF path again.
both 2A6Q3 and 2A6Q4 to conduct and place a ground
at 2M1-1 and 2M1-2.
Section IV. NONCONVENTIONAL CIRCUITS
2-22. Key Line
(Fig. FO-8)
amplifier bias circuit. Also, low voltage transmit (+ 12T)
Keying the radio set to transmit mode is accomplished
is switched in, low voltage receive (+ 12R) is grounded
by grounding the key line.  For normal operation a
through 1A5R9 and the front panel meter is switched to
ground from the mic key, the cw key, or AUDIO
output monitor If the band channeling motor 1A5Bl is
connector 1A8J2-G will establish transmit mode. During
running, 1A5K1 is energized opening contacts 12 and 4
tuning, the Antenna Coupler Unit grounds the key line at
to prevent transmit operation.
1A8J4-P to switch the radio set to transmit mode for
tuning purposes.
b. CW Keying. For CW transmission the key line is
NOTE
ground in the following manner The mode switch must
The Antenna Coupler Unit must be
be set to CW When the CW key is depressed a ground
connected
to
ACCESSORY
is applied to the base of 1A3A3Q12 thru 1A1S13B
connector 1A8J4 or 1A8J4-p and
contacts 2 and 6. Transistor 1A3A3Q12 is turned on
1A8J4-n  jumpered  for  keying  to
and applies ground to terminal 1A3E26 through
occur.
1A3A3Q14. The key line then functions as described in
a. LSB, USB and AM Keying. In these modes the
paragraph 41a. above.
key line is grounded when the handset press to talk
switch is depressed. This ground is applied to terminal
c.  Tuning Cycle Keying. When the mode switch is
1A3E26 on the key line. From there the key line routing
set to CPLR TUNE KW, a ground is to the key line
is to the Antenna Coupler Unit and through relay 2K1
through 1A1S13A-8 and 10.  But in this case 2K1 is
closed contacts 11 and 3. Diode 1A8CR6 prevents the
energized by the ground and 2K1-11 and 3 open The
grounded key line from energizing 2K1 at this time. The
key line ground is then controlled by the Control Logic
key line then returns to the transceiver and goes through
Board (2A1) output on pin 7. From this point on, key
closed contacts 12 and 4 of lA5Kl to energize 1A5K2.
line operation is as described in paragraph 2-22a.
Energizing 1A5K2 also energizes 1A8K1 through 1A5K2
above Refer to Chapter III Section III for Control Logic
now closed contacts 1 and 5. With 1A5K2 and 1A8K1
Board 2A1 operation.
energized, all switching is complete for LSB, USB and
AM transmit. The RF power amplifier is switched to the
low pass filter and + 28 VDC is applied to the power
2-22


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