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TO 31R2-2GRC171-2
TM 11-5820-815-14
NAVELEX 0967-LP-544-5010
front panel of the receiver-transmitter. Depending upon
the frequency displayed, each switch applies either -0.7-
servo fault circuit provides a tune-in-progress indi- cation
V dc power supply voltage or an open circuit to the
or an indication of invalid circuit conditions.
cathode of the diodes.  When connected to pullup
resistors in the d/a servo amplifier module, each
frequency select line applies either a logic 0 or logic 1
LINES.  Refer to figure FO-18.  Pullup resistors R1
voltage to the receiver-transmitter.
through R13 located in the d/a servo amplifier module
provide termination for the local and remote frequency
4-41.  The receive signal flow diagram of figure FO-16
select lines.  The resistors convert an open circuit
shows a typical (10-MHz) frequency select line for the
frequency select line into a logic 1 voltage and a
radio set. The choice between local frequency control or
grounded (actually about -0.7 V dc) frequency select line
remote  frequency  control  is  provided  by  the
into a logic 0 voltage. Diodes CR1 through CR13 isolate
REMOTE/LOCAL  switch  (A10A1S3).
When  the
the local (front panel) frequency select switches from the
REMOTE/LOCAL switch is in the REMOTE position, the
remote (C-7999/ GRC-171) frequency select switches.
-0.7-V dc power supply voltage is applied to the
Isolation diodes for the remote frequency select switches
frequency select switches of the C-7999,/GRC-171.
are  located  in  the  C-7999/GRC-171.
Refer  to
Depending upon the frequency selected, the C-7999/
paragraphs 4-40 and 4-41 for further discussion of
GRC-171 applies either a logic 0 or logic 1 voltage (note
frequency select lines.
pullup resistor in the d/a servo amplifier module) to the
frequency select lines going to the frequency synthesizer
module and to the d/a servo amplifier module. When the
figure FO-18. The d/a converter consists of four voltage
REMOTE/LOCAL switch is in the LOCAL position, the -
amplifiers (U1A, U2B, U1B, U2A) that amplify the output
0.7-V dc power voltage is applied to the local frequency
voltage from a reference voltage amplifier (U3B). The
select switches on the front panel of the receiver-
gain and, therefore. the output voltage of each voltage
transmitter. Depending upon the frequency selected, the
amplifier is varied by connecting resistors (R27 through
local frequency select applies either the -0.7-V dc power
R32 and R41) to ground through transistor switches (Q1l
supply voltage or an open circuit to the frequency select
through Q13) that are turned on by logic 1 voltage of the
lines to the d/a servo amplifier module. Isolation diodes
applied bcd frequency select information.  The output
and pullup resistors in the d/a servo amplifier module
voltage from each voltage amplifier is summed together
convert the -0.7-V dc voltage or open circuit into a logic 0
(R45) and amplified (U4B, U4A) to produce the analog
or logic I voltage. respectively, and apply the result to
voltage to the servo amplifier. The analog voltage varies
the d/a converter and to the frequency select lines to the
from about -8 V dc for a radio control frequency of 225
frequency synthesizer module.
MHz to about +8 V dc for a frequency of 400 MHz. The
following  describes  individual  circuits  of  the  d/a
4-43.  Refer to the block diagram of figure FO-4 and
4-47.  The 0.1-MHz voltage amplifier (U1A). 1.0-MHz
schematic diagram of figure FO-18 while reading the
voltage amplifier (U2B), and the 10.0-MHz voltage
following  circuit  descriptions.
Unless  otherwise
amplifier (UIB) all function identically. Therefore. only the
specified, reference designators apply to components of
0.1-MHz voltage amplifier will be discussed in detail.
the d/a servo amplifier module Al.
Resistors R27 through R30 that are connected to the
inverting input of the 0.1-MHz voltage amplifier vary the
4-44.  GENERAL.  Refer to figure FO-4.  D/a servo
amplifier gain when they are connected to ground
amplifier module Al contains the digital-to-analog (d/a)
through transistors Q1, Q2, Q3, and Q4. The transistors
converter and the servo amplifier that controls the servo
turn on in accordance with 0.1-MHz bcd frequency select
mechanism in rf filter module A7 to tune the rf filter. The
information applied to the d/a servo amplifier module.
d/a converter changes bcd frequency select information
The transistors are connected in the reverse beta mode
from the radio control into a d/a analog control signal that
so that their collector-to-emitter voltage is approximately
represents the frequency as selected on the radio
0 V dc when turned on by a logic 1 applied to their base.
control.  The servo amplifier receives the d/a analog
The reference voltage amplifier (U3B) amplifies +12-V
control signal and compares it to a position feedback
and -12-V dc power supply voltages to produce a
signal from the position feedback potentiometer in the rf
reference voltage (approximately +3.56 V de) that is
filter module that represents the tuned frequency of the rf
applied to the non-inverting input of the 0.1-MHz voltage
filter. When the two signals differ (frequencies differ), the
amplifier. As the radio control 0.1-MHz frequency digit
servo amplifier drives the servo mechanism. to position
(bcd frequency select information) varies from 0 (0000)
the rf filter to the desired frequency. The servo amplifier
to 9 (1001), the 0.1-MHz voltage amplifier amplifies the
disable circuit prevents the servo mechanism from being
reference voltage to produce an output voltage that
driven past its end stops. The
varies  from  about  3.56  to  about  7.60  volts  in
approximately 0.447-volt steps

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