9.1.3. Selcal в737 и а320.
Подробно рассматривается соответственно в [3] и [5] рекомендуемой литературы.
Purpose
The selective calling (SELCAL) system supplies the flight crew with indications of calls that come in from the airline ground stations. It is not necessary for the pilots to continuously monitor company communications channels.
Airline radio networks supply communication between ground stations and airplanes. For SELCAL operation each airplane has a different four-letter code. Each letter in the code equals a different audio tone. The ground stations send the applicable tones to call an airplane.
Abbreviations and Acronyms
ACP - audio control panel
comm - communication
HF - high frequency
REU - remote electronics unit
SELCAL - selective calling
VHF - very high frequency
General
Each airplane has a different SELCAL code. A ground station transmits this code to communicate with an airplane. When the airplane receives its SELCAL code, flight compartment indications come on to tell the flight crew.
System Components
The selective calling system has these components:
SELCAL decoder
SELCAL control panel
SELCAL program switch module
SELCAL aural warning relay.
The SELCAL decoder unit monitors the radio systems for audio tones. If the tones are the same as the code from the program switch module, the decoder sends a signal to the control panel to turn on the alert light. The decoder also sends a ground to
energize the SELCAL aural warning relay.
When the SELCAL decoder unit receives a call, it sends the SELCAL control panel a ground signal. The ground signal turns on the alert light for the transceiver that receives the call. Push the alert light switch to reset the decoder channel.
The SELCAL decoder unit also sends a ground to energize the aural warning relay. The energized relay sends 28V dc to the aural warning module through the REU. This tells the module to make the single high/low chime for the aural alert.
The SELCAL program switch module gives the airplane its SELCAL code. When power is applied to the airplane, the program switch module sends the SElCAL code to the SELCAL decoder.
External Interface
The selective calling system connects with these components:
VHF transceiver
HF transceiver
Remote electronics unit
Aural warning module.
The HF and VHF transceivers receive the SELCAL audio tones from the ground station. The transceivers send the received audio to the SELCAL decoder.
The SELCAL aural warning relay sends the REU 28V dc. The REU sends the 28V dc to the aural warning module. The aural warning module makes a high/low chime signal for the aural alert.
SELCAL Control Panel
The SELCAL control panel is on the P8 aft electronic panel.
SELCAL Decoder
The SELCAL decoder is on the E- 4 rack in the electronic equipment compartment.
SELCAL Program Switch Module
The SELCAL program switch module is behind the SELCAL decoder on the E-4 rack.
SELCAL AURAL WARNING Relay
The SELCAL aural warning relay is on the left side of the nose wheel well on the J22 panel.
Power
The 28v dc bus 1 supplies power to the SELCAL decoder.
SELCAL Decoder Unit
The VHF and HF transceivers send received audio to the SELCAL decoder.
The SELCAL decoder unit tries to match the audio tones sent from the transceiver with the program switch module SELCAL code. If there is a match, then the decoder sends a call set discrete to the SELCAL control panels. The call set discrete is a ground signal that turns on the call light. There is a different call set discrete for each transceiver.
The SELCAL control panel sends a ground signal to the SELCAL decoder unit to reset the decoder channel. This ground signal is a call reset discrete. There is a different call reset discrete for each transceiver.
The SELCAL decoder unit supplies a ground signal to make a high/low chime in the flight compartment. The ground signal goes to the SELCAL aural warning relay. The energized relay sends a 28v dc signal through the REU to the aural warning
module. The aural warning module makes a single high/low chime in the flight compartment.
SELCAL Program Switch Module
The SELCAL program switch module has 24 (16 active) switches. The switches are in groups of four. There are four letters in the SELCAL code. The position of the switches in each group identify one of the four SELCAL code letters. A switch in the ON position sends a ground signal to the decoder. A switch in the OFF position sends an open signal to the decoder.
Purpose
The SELCAL control panel gives visual indications and reset operation for the SELCAL system.
Controls and Indications
The control panel alert light for the active transceiver comes on when the decoder receives a call with the correct coded audio.
Push the control panel light/switch to reset the decoder channel.
Purpose
The SELCAL decoder unit does these functions:
Monitors audio from the VHF and HF communication transceivers
Identifies the SELCAL signal that is the same as its code
Causes flight compartment visual and aural indications when calls come in.
Controls
There
are no lights or switches on the SELCAL decoder front panel.
Purpose
The SELCAL program switch module sets the airplane identification code.
Each dip switch that is up is in the ON position and sends a ground to the SELCAL decoder. Each dip switch that is down is in the OFF position and sends an open to the SELCAL decoder.
Each
group of 4 dip switches sets one SELCAL letter. Four letters identify
the airplane SELCAL code.
General
The SELCAL decoder unit has these components:
Audio compressors
Filter units
Analog-to-digital converter
Microprocessor
Reset buffer
Output driver.
Power-Up
At power-up, the SELCAL program switch module sends the microprocessor the airplane SELCAL code. The microprocessor controls the SELCAL decoder.
Call Set
Each VHF and HF transceiver sends audio signals to the related audio compressor. The audio has a SELCAL tone signal. The SELCAL signal is a group of four tones. Each tone represents a letter in the SELCAL code. The audio compressor amplifies or limits the audio signal input to get a constant level. The audio compressor then sends the signal to the related filter unit.
In the filter unit, the signal goes to 16 different filters. Each filter passes only the audio signal that identifies one SELCAL tone or letter.
The filter outputs go to the analog-to-digital converter. The converter changes the analog audio signal to a digital signal and sends it to the microprocessor.
The microprocessor receives the SELCAL tone digital signals and compares them with the airplane SELCAL code from the program switch module. If the digital signals are the same as the airplane’s code, then the microprocessor sends a command to the output driver.
The output driver energizes the output relay. When the relay energizes, the control panel receives a ground signal to turn on the call light.