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REL
COMMUNICATIONS
For Training Purposes Only
May 03
6-7
P I LOT T R A I N I N G GU I D E
Controls and Indicators
The VHF communication system controls and indicators are described in the
following sections of this chapter:
• Audio control panel is described in the Audio Integrating System
• RTU and reversionary / inhibit panel are described in Radio Tuning System
The VHF transceiver is normally tuned by the on-side RTU. The VHF transceiver may
also be tuned by the cross-side RTU or by the FMS. The VHF transceiver supplies an
audio output to the audio system and a digital bus output to the IAPS. The data output
contains the communication frequency which is echoed back to the RTUs.
COMMUNICATIONS
6-8 For Training Purposes Only
Jan 04
P I LOT T R A I N I N G GU I D E
HF Communication System
Description
The HF communication system consists of two high-frequency (HF) transceivers
(HF 1 and HF 2) which operate independently.
Communication range on HF frequencies is longer (potentially global), but less
reliable than on conventional VHF and UHF frequencies, and varies substantially with
factors such as operating frequency, season, time of day, atmospheric noise, and solar
activity.
Components and Operation
The HF communication system consists of the following components:
• two transceivers
• two couplers
• one antenna
Associated components:
• two radio tuning units (RTUs)
• two audio control panels
• one reversionary / inhibit panel
• one SELCAL decoder
• Integrated Avionics Processor System (IAPS)
Transceivers
The transceivers provide signal processing for transmission and reception. The unit
consists of a control module, RF/IF module, frequency synthesizer, frequency
standard, power supply/audio module and a power amplifier.
The transceivers provide amplitude modulated (AM) and single sideband (SSB) longrange
voice communications in the frequency range of 2 to 30 MHz, selectable in
increments of 100 Hz. Limited preset channel selection is also available and a
SELCAL (selective calling) feature is incorporated.
The two HF transceivers are identical and independent. They may be operated
simultaneously in receive mode but only one transceiver at a time can operate in
transmit mode. In a dual HF system configuration, antenna coupler No. 1 and antenna
coupler No. 2 exchange status (interlock) data to ensure that only one transceiver is
connected to the antenna for the transmit mode. When one transceiver is keyed to
transmit, the other transceiver is disconnected from the antenna and is unable to
receive or transmit. Frequency and mode selection is covered in the RTU section.
COMMUNICATIONS
For Training Purposes Only
May 03
6-9
P I LOT T R A I N I N G GU I D E
Antenna Coupler
The antenna coupler matches the impedance of the transceivers to the antenna as
different frequencies are selected and keyed.
Antenna
The antenna is an integral part of the leading edge of the vertical stabilizer. The
antenna is connected to the antenna coupler units via an RF strap.
High voltages and currents are present in this area during
transmissions.
Selective Calling (SELCAL)
Both HF transceivers are coupled to a SELCAL system, which monitors the selected
HF frequencies for the airplane’s unique SELCAL code without requiring the crew to
continuously monitor the HF audio. If the code is detected, an EICAS message and an
audio alert are triggered to advise the flight crew that a ground station is calling. The
EICAS message is reset when the appropriate HF transceiver is keyed to transmit.
Controls and Indicators
The HF communication system controls and indicators are described in the following
sections of this chapter:
• Audio control panel is described in Audio Integrating System
• RTU and reversionary / inhibit panel are described in Radio Tuning System
CAUTION
COMMUNICATIONS
6-10 For Training Purposes Only
May 03
P I LOT T R A I N I N G GU I D E
HF Communication System - Block Diagram
Figure 6-4
AUDIO SYSTEM
SELCAL
IAPS
ANTENNA
COUPLER
#1
ANTENNA
COUPLER
#2
A
B
A
B
HF COMM
NO.1
XCVR
HF COMM
NO.2
XCVR
COPILOT'S RTU
REVERSIONARY /
INHIBIT PANEL
DC
UTILITY
BUS 2
DC
UTILITY
BUS 2
PILOT'S RTU
P604_06_004
DC
BUS 1
DC
BUS 1
INHIBIT PUSH
1-RTU-2 FMS TUNE
1 2
AFCS
　
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