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Nuclear Fundamentals


TO 31R2-2GRC171-2
TM 11-5820-815-14
NAVELEX 0967-LP-544-5010
high-level modulated rf amplifiers in power amplifier
comparator is amplified by the servo amplifier to develop
module A8 where the rf signal is amplitude modulated by
the servo motor drive voltage. To tune the rf filter, the
the output of the modulator. The modulated rf signal is
servo motor runs until the position feedback signal nulls
then applied to the rf predriver/ALC attenuator where it is
the output of the d/a servo potentiometer comparator.
attenuated by an ALC control voltage to provide a
The center frequency of the rf filter is aligned so that the
Constant carrier power output to the antenna.  The
position feedback signal for each of the 7000 frequency
attenuated rf signal is then amplified by rf power
channels tracks the d/a analog voltage. Thus, when the
amplifiers and applied through the reflecto-meter to rf
output of the d/a servo potentiometer comparator nulls,
filter module A7. The forward and reflected powers of
the rf filter is tuned to the selected transmit frequency.
the transmit rf signal from the power amplifier are
detected by the reflecto-meter and fed back to the ALC
4-20.  A READY lamp is located on the front panel of
circuit where they are used to develop ALC control
the receiver-transmitter and on the C-7999/GRC-171
(figure FO-16, sheet 1). The REMOTE/'LOCAL switch
selects the C-7999/GRC-171 READY lamp for remote
4-17.  The transmit rf signal from power amplifier
operation and the front panel READY lamp for local
module A8 is applied through the transmit/receive switch
operation. The selected READY lamp is turned on and
(actually a diode switch) of rf filter module A7 to the rf
off by the output of the fault switch of audio module A4.
filter. The transmit/receive switch is closed by the fast
The pll fault signal from the phase-locked loop of
attack-slow release transmitter key line (key 1) whenever
frequency synthesizer A2 and the rf filter fault signal from
the transmitter is keyed.  Harmonic content of the
the servo fault amplifier of d/a servo amplifier module Al
transmit rf signal is filtered out by the rf filter which
are applied to the fault switch.  The selected READY
consists of four capacity- tuned resonators that provide a
lamp is turned on by the fault switch whenever the
2-dB bandwidth of about 1.5 MHz from center
phase-locked loop is locked and the rf filter is tuned to a
frequency and greater than 40 dB of attenuation beyond
frequency between 225.000 and 399.975 MHz. The pll
7 MHz. The output of the rf filter is applied through the
fault signal causes the selected READY lamp to turn off
directional coupler to the antenna.  The forward and
if the phase-locked loop is in the process of tuning or if
reflected power of the transmit rf signal applied to the
the phase-locked loop malfunctions.  The rf filter fault
antenna are detected by the directional coupler.  The
signal causes the selected READY lamp to turn off if the
detected power signals are amplified and fed back to the
rf filter is in the process of tuning, or if the frequency
ALC circuit where they are used to develop ALC control
select control is set to a frequency below 220 MHz, or if
the servo amplifier malfunctions. In addition to turning
off the selected READY lamp, the fault switch inhibits the
4-18.  Although not shown in figure FO-16, the pa and
key 2 key line to prevent the power amplifier from being
antenna forward and reflected power signals are
keyed on.
monitored by a voltage standing-wave ratio (vswr)
comparator and a pa/antenna power ratio comparator in
4-21.  The power amplifier is turned off by the key 2
the ALC circuit of power amplifier module A8. Also, the
key line whenever the receiver-transmitter is un-keyed or
heat-sink temperature of the power amplifier module is
when the READY lamp is turned off by the fault switch as
monitored. If the antenna vswr exceeds 3 to 1, or if the
described above. The key 2 key line is applied to the
pa power output exceeds the power to the antenna by
ALC circuit of power amplifier module A8.  When un-
more than about 2 dB, or if the heat- sink temperature
keyed, the ALC circuit develops ALC control voltage that
exceeds 100 degrees Celsius, the ALC circuit develops
causes maximum attenuation to the rf transmit signal. At
ALC voltage that reduces the rf power output by about 7
the same time, the transmit rf signal is removed from the
dB to approximately 4 watts.
input  to  the  power  amplifier  module  by  the
transmit/receive switch of the frequency synthesizer
4-19.  The servo motor that positions the rf filter is
module. This turns off the power amplifier. The fast
controlled by servo motor drive voltage supplied from d/a
release of key 2 assures that the power amplifier is
servo amplifier module A1.  The servo motor drive
turned off before the transmit/receive switch of the rf filter
voltage is developed as follows: Bcd frequency select
module is switched to receive by the slow release of key
information from either the local frequency select control
or the C-7999/GRC-171 frequency select control is
applied to the d/a con- verter of d/a servo amplifier
module A1.  For each frequency between 225 and
399.975 MHz, the d/a converter develops a unique d/a
4-23.  Refer to the receive signal flow diagram of figure
analog voltage that represents 1 of the 7000 frequency
FO-15. The receive section of the receiver- transmitter
channels. The d/a analog voltage is applied to the d/a
consists of receiver rf module A3, receive audio circuits
servo potentiometer comparator where it is compared to
of audio module A4, and the common rf signal path
the position feedback signal from the position feedback
through rf filter module A7. Receive squelch is contained
potentiometer of rf filter module A7. The resulting error
in audio module A4.
voltage from the d/a servo potentiometer

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