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A
757 MAINTENANCE MANUAL
LEFT VHF COMMUNICATION ANTENNA STA 753
RIGHT VHF COMMUNICATION ANTENNA (STA 730)
VHF COMMUNICATION ANTENNA LOCATION
P5 PANEL P11 PANEL
P8 PANEL
LEFT VHF COMMUNICATION CONTROL PANEL RIGHT VHF COMMUNICATION CONTROL PANEL SEE A
FLIGHT COMPARTMENT FREQUENCY-IN-USE FREQUENCY-IN-USE
FREQUENCY-IN-USE
LIGHT LIGHT
TRANSFER LIGHT
FREQUENCY-IN-USE TRANSFER FREQUENCY(TFR) SWITCH
LIGHT FREQUENCY
(TFR) SWITCH DISPLAY DISPLAY VHF COMM TFR TFR
CV
FREQ SEL
OH MF M
COMM TEST
FREQUENCY FREQUENCY FREQUENCY COMMUNICATIONFREQUENCYFREQUENCY DISPLAYS SELECTOR SELECTOR TEST SWITCH SELECTORSELECTOR
KNOBS KNOBS
KNOBS VHF COMMUNICATION CONTROL PANEL
KNOBS
VHF COMMUNICATION CONTROL PANEL
A2
A1
1 GUN 051
2 GUN 001-050,052-999
VHF Communications System - Component Location
Figure 1 (Sheet 1)
D04748
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757 MAINTENANCE MANUAL
RIGHT VHF COMMUNICATION TRANSCEIVER
LEFT VHF E4-3
HAND
JACK
VSWR/POWER DISPLAY
POWER TEST (RFL/OFF/FWD) SWITCH
TEST RESULT LIGHTS
HAND MICROPHONE (MIC) JACK
VHF Communications System - Component Location
Figure 1 (Sheet 2)
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757
MAINTENANCE MANUAL
(3)
GUN 001-050,052-999; The front panel of the transceiver contains two jacks, two test switches, a three-position switch, two test result lights, and a digital display. The two jacks (MIC and PHONE) enable testing of the transceiver without going through interphone circuits. The SQL/LAMP TEST switch disables the squelch circuits, and tests all front panel lights. The TEST switch enables a self-test of the critical circuitry in the system. The two test result lights indicate LRU PASS and frequency CONTROL INPUT FAIL. The RFL/OFF/FWD (reflected, off, forward) switch, checks rf power to the antenna, and shows the result in watts on the display.
(4)
The left, right and center (if installed) transceivers are located in the main equipment center on rack E4.
C. VHF Communication Antenna
_________________________
(1) The VHF communication antenna (referred to as the antenna) is a blade type antenna, mounted on the centerline of the airplane fuselage. Each antenna is impedance-matched to its transmission line. A coaxial cable connector on the antenna provides interconnection between the antenna and transceiver.
3. Operation (Fig. 2)
_________
A. Functional Description
______________________
(1)
The left, right and center (if installed) VHF systems are identical for voice communications.
(2)
Voice communications:
(a)
The reception and transmission of the audio are accomplished on the same frequency. The selected frequency is set on the control panel, and the applicable VHF MIC SELECTOR switch is pushed on the crewmember's audio selector panel of the flight interphone system (AMM 23-51-00/001).
(b)
The SELCAL system (AMM 23-21-00/001) alerts crewmembers when a ground station desires contact with them. The appropriate VHF switch light, on the pilots' call panel (P5), comes on and a chime sounds.
(c)
To receive, the volume control on the crewmember's audio selector panel is adjusted to obtain a comfortable listening level for the applicable VHF system. The crewmember may then listen to any messages received over the selected frequency.
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