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• VHF 1 antenna – upper side of the fuselage
• VHF 2 antenna – underside of the fuselage
Integrated Avionics Processing System
The integrated avionics processing system (IAPS) is a card cage assembly that physically
houses some avionic line replaceable units (LRUs). The IAPS reads several avionic buses and
distributes data to those LRUs requiring the information. Most avionics data is processed by this
unit.
COMMUNICATIONS
Description
Vol. 2 06−10−5
REV 66, Feb 01/07
CL−604 Operating Manual
PSP 604−6
VHF COMMUNICATION SYSTEM (CONT'D)
VHF Communication System − Block Diagram
Figure 06−10−3
COMMUNICATIONS
Description
Vol. 2 06−10−6
REV 66, Feb 01/07
CL−604 Operating Manual
PSP 604−6
VHF COMMUNICATION SYSTEM (CONT'D)
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.
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 processing 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) long-range
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.
COMMUNICATIONS
Description
Vol. 2 06−10−7
REV 66, Feb 01/07
CL−604 Operating Manual
PSP 604−6
HF COMMUNICATION SYSTEM (CONT'D)
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.
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.
CAUTION
High voltage and current 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
　
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