RECEIVER OPERATION.

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

voltage.

(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

voltage.

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

4-22.

RECEIVER OPERATION.

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

4-3