-Ensures the CAA recording function.
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There is an independent transmission channel for each user of the audio integrating system.
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(2)
Composition of circuit
A transmission channel comprises :
-The various microphone inputs with their power supplies
-A unit gain amplifier
-An output transformer
-
A transmitter selection system
-
A module for CAA recording
-
A switching system for emergency function
-
A switching system for use of hand microphone.
(3)
Transmission with boomset (Ref. Fig. 017) The analog signals of the boomset microphone are connected to the OdB gain amplifier, then sent to the output transformer. At the transformer output, the switching module switches these signals to the transmitter selected by the ACP in accordance with information received from the logic processing function.
(4)
Transmission with oxygen mask microphone (Ref. Fig. 018) In normal flight configuration, the oxygen mask microphone is not connected to the microphone circuit. Operation is as follows in flight configuration with use of oxygen mask. This system sets a control switch contained in the stowage box of the oxygen mask to the ground. This activates the relay which sets the oxygen mask into service. The pressurization of the oxygen circuit when masks fall out automatically activates this control switch.
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Audio Management Unit - Block Diagram of Transmitter Circuit
Figure 017
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Audio Management Unit - Simplified Schematic of Transmission Circuit
Figure 017A
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Oxygen Mask Microphone - Circuit Block Diagram
Figure 018
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(3) Transmission with various microphones (Ref. Fig. 017A) For transmission, each crew member can use either a hand microphone, a boomset or an oxygen mask. The analog signals of these three microphones are adapted and filtered on the adaptation board of the AMU, which also receives the hand microphone PTT and oxygen mask control discretes. The microphone selection is done by a dedicated circuit according to the following logic:
-----------------------------------------------------| OXYGEN MASK CONTROL DISCRETE | |---------------------------------------------------| | 0 | 1 |
---------------------|------------------------|--------------------------| | | 0 | Boomset signal valid | Boomset and oxygen mask | | HANDMIKE | | | signals valid | | PTT |-------|---------------------------------------------------| | | 1 | Handmike signal valid | --------------------------------------------------------------------------
NOTE : Input 6 microphone is valid when PTT6 is activated.
____ Ground Mech microphone is valid when air/ground discrete is set to GND.
The selected microphone signal is then sent to an output transformer.
At the transformer output, this signal is switched to the transmitter
selected by the operator on the ACP, in accordance with information
received from the DSP.
This discrete information is consolidated with both hardware and
software processings, to avoid permanent transmission.
(4) Not Applicable
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(5) Transmission with hand microphone
(Ref. Fig. 019)
The hand microphone can be used in two ways:
-1st case: Radio transmission The logic processing card associated with relay K1 delivers a command. This command supplies relay K1 (AND function between the PTT switch of the hand microphone and the selected radio transmission, except for INT). Relay K1 directly connects the hand microphone to the tranmission selection circuit. The station selected in transmission mode then supplies the hand microphone.
-2nd case: Flight Interphone transmission When INT transmission is selected, relay K1 is not supplied; the logic processing card associated with relay K2 delivers a command. This command supplies relay K2 (AND function between the PTT switch of the hand microphone and the INT transmission selection). Relay K2 connects the power supply of the boomset microphone to the hand microphone. This system applies the analog signals of the hand microphone to the OdB amplifier, then to the INT channel via the transmission line. This removes the microphone power supply from the interphone amplifier.
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