(b)
The RF center conductor of the antenna coupler mount to the auxiliary spar. 1) Make sure the resistance is 10 milliohms or less.
(3)
Install the HF antenna coupler(s) (AMM 23-11-01/401).
S 426-005
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A
757 MAINTENANCE MANUAL
322BL HF COMMUNICATION
AUXILIARY SPAR ANTENNA COUPLER BAY
(REF)
SEE A CONNECTION FEEDLINE LEFT HF
(REF) ANTENNA COUPLER, COMMUNICATION
SEE B M241
ANTENNA (REF)
FWD
VERTICAL STABILIZER
VERTICAL STABILIZER AUXILLARY SPAR LEADING EDGE (REF) ACCESS OPENINGBONDING CHECK: (322BL)RF CENTER CONDUCTOR
RIGHT HF TO AUXILLARY SPAR
COMMUNICATION (2 LOCATIONS) CRAWL SPACE
ANTENNA COUPLER, (REF)
M242
1
INSULATOR DISK
HF COMMUNICATION ANTENNA COUPLER BAY
RF CENTER
A
CONDUCTOR
MOUNT
BONDING CHECK:
RF CENTER CONDUCTOR TO MOUNT
(2 LOCATIONS)
NOTE: THE HF ANTENNA COUPLER(S) ARE REMOVED.
FWD
HF ANTENNA COUPLER MOUNT(S)
B
1 IF INSTALLED
HF Communications Antenna Electrical Bond Check Figure 601
E26316
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A
757 MAINTENANCE MANUAL
VHF COMMUNICATION SYSTEM - DESCRIPTION AND OPERATION
____________________________________________________
1. General_______
A. Two VHF (Very High Frequency) communications systems (referred to as the VHF systems) are installed on the airplane.
B. The VHF systems provide short-range line-of-sight voice communications with ground stations or other airplanes. The VHF systems can operate in the 118.00-megahertz (MHz) to 136.975-MHz frequency range, in either 25-khz or 8.33-khz increments.
C. All of the VHF systems use 28v dc power. The left VHF system uses power from from the dc standby bus, the right VHF system from the right dc bus, and the center VHF system (if installed) from the left dc bus. Each VHF system has a circuit breaker on the overhead circuit breaker panel, P11.
D. The VHF system major components are: a VHF communication control panel, a VHF communication transceiver, and a VHF communication antenna.
2. Component Details (Fig. 1)_________________
A. VHF Communication Control Panel
_______________________________
(1)
The VHF communication control panel (referred to as the control panel) provides frequency tuning data to the VHF communication transceiver. Each control panel contains a dual set of frequency control knobs, two frequency displays, two frequency-in-use lights, and a TFR (transfer) switch.
(2)
The frequency selector knobs are two concentric knobs used to dial a desired frequency. The outer knob varies the ones, tens, and hundreds of MHz; the inner knob varies the tenths and hundredths of MHz.
(3)
The TFR (transfer) switch allows selection of either displayed frequency. When set, the selected frequency display is illuminated, and the frequency-in-use light above the display is on.
(4)
The left, right, and center, (if installed), control panels are installed on the pilots' P8 panel.
B. VHF Communication Transceiver
_____________________________
(1)
The VHF communication transceiver (referred to as the transceiver) processes audio inputs for radio frequency (rf) transmission, and processes rf signals for audio reception.
(2)
GUN 051; The front panel of the transceiver contains two jacks, a SQ/TEST switch, and three test result lights. The two jacks (MIC and PHN) enable testing of the transceiver without going through interphone circuits. The SQ/TEST switch disables the squelch circuits, and enables a self-test of the critical circuitry in the system. The two COMM lights indicate transceiver health (green) or failure (red), and the red DATA IN light indicates frequency tuning data input failure.
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