(b)
The received RF signal enters the antenna coupler via the antenna feedlines and thru a relay to an isolation amplifier. The relay protects the isolation amplifier whenever the right HF system is transmitting (if installed). The RF signal is routed thru transmit/receive relays, the discriminator circuits, and on to the transceiver via the coaxial cable.
(c)
The received RF signal enters the transceiver thru a transmit/receive relay into the RF amplifier controlled by internal AGC and the RF SENS on the control panel. The tuning circuits perform the frequency conversions and the IF detectors provide the AM or USB audio portions of the signal. The audio is output to the headphone jack and to the flight interphone system (AMM 23-51-00/001) . The AM audio is also output to the SELCAL system (AMM 23-21-00/001).
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MAINTENANCE MANUAL
(3) Transmit Mode
(a)
The microphone and PTT inputs for the HF system are provided by the flight interphone system via the audio selector panels (AMM 23-51-00/001). After the frequency is selected and the antenna coupler has been tuned, pushing the PTT switch will cause the transceiver to transmit. The microphone input is modulated as AM or USB onto the RF and the power amplifiers output the signal from the transceiver thru a directional coupler and transmit/receive relay. The audio sidetone is detected and output, provided the power output is greater than 40 watts.
(b)
The transmitted signal enters the front of the antenna coupler via the coaxial cable. The PTT input from the transceiver is also provided to the antenna coupler. The RF signal inputs to the discriminator circuits, thru transmit/receive relays, the tuning network and thru another transmit/receive relay. In dual HF systems, an inhibit signal goes to the other system.
(c)
The RF signal output is fed to the antenna on the feedline from the antenna coupler mounting rack. The transceiver and antenna coupler will be inhibited by the key interlock signal if any antenna coupler faults exist or if the other HF system is transmitting (dual HF installations only).
B. Test
____
(1)
Listen and make sure the transceiver internal blower fan is on.
(2)
Do these steps at the front panel of the transceiver:
(a)
Push and hold the SQL/LAMP TEST switch.
1) Make sure the LRU FAIL, KEY INTERLOCK, and CONTROL INPUT FAIL lights come on and remain on. Make sure the receiver squelch is disabled.
(b)
Release the SQL/LAMP TEST switch. Make sure the LRU FAIL, KEY INTERLOCK and CONTROL INPUT FAIL lights go out.
C. Control
_______
WARNING: DO NOT OPERATE THE HF COMMUNICATION SYSTEM WHILE PERSONS REFUEL
_______ OR DEFUEL THE AIRPLANE. AN EXPLOSION CAN CAUSE INJURIES TO PERSONS AND DAMAGE TO THE AIRPLANE.
WARNING: MAKE SURE PERSONNEL STAY A MINIMUM OF 6 FEET AWAY FROM THE
_______ VERTICAL STABILIZER WHEN THE HF SYSTEM TRANSMITS. RF ENERGY FROM THE HF COMMUNICATION ANTENNA CAN CAUSE INJURIES TO PERSONNEL.
(1) Turn on procedure.
(a)
Provide electrical power (AMM 24-22-00/201).
(b)
Make sure the HF COMM LEFT and HF COMM RIGHT (if installed) circuit breakers on the overhead circuit breaker panel, P11, are closed.
(c)
Set the mode selector switch on the HF communication control panel (P5) to either the AM or USB position.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
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ALL ú ú 04 Page 10 ú May 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757
FAULT ISOLATION/MAINT MANUAL
HF COMMUNICATIONS SYSTEM
* SEE THE WDM EQUIPMENT LIST GUN 051 GUN 001-050,052-999 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 COMMUNICATIONS 通讯(9)
