(b)
In RADIO configuration, use the rectangular PA pushbutton switch located on each ACP to make the passenger address announcements. This pushbutton switch is unstable, i.e. hold it pushed to make the announcements: this avoids unwanted transmissions. The electronic processing of this channel is identical to that of the other transmission channels. The operation of this pushbutton switch can be made identical to that of the other transmission channels (stable operation) : to achieve this, modify the AMU pin-program (Ref. Para. Operation -Pin Program).
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Hand Microphone - Circuit Block Diagram
Figure 019
R 1EFF : 001-049, 051-099, 101-105, 151-199, 1 23-51-00Page 56 1201-220, 1May 01/05 1 1 1CES 1 (7) Muting circuit
(a)
Purpose (Ref. Fig. 020) The feedback produced by the loud speaker-microphone acoustic coupling when the microphones are used (acoustic feedback) is eliminated by a muting circuit. To achieve this, the muting circuit reduces the gain and/or the frequency range of the loud speakers. This attenuating circuit is controlled by the PTT switch of any of the radio communication microphones. The attenuating circuit is an integral part of the loud speakers.
(b)
Operation (Ref. Fig. 021) The logic processing channel receives PTT switch type information. From this information it activates the muting module. A ground is sent to the loud speaker units which set the direct muting function into service.
**ON A/C 001-049, 051-099, 101-105, 151-199, 201-220,
B. Reception Function
(1) General The reception circuit selects and adjusts the volume on the reception channels. The operator selects and adjusts these channels on the ACP. Each user of the audio integrating system has a separate associated reception-channel. It ensures the various supplementary functions of the circuit:
-VOR/DME/ILS/MLS switching
-VOICE/ON function
-Emergency function (for reception section).
R **ON A/C 106-149, 221-299, 301-399, 401-499,
B. Reception Function
(1) General The reception circuit selects and adjusts the volume on the reception channels. The operator selects and adjusts these channels on the ACP. Each user of the audio integrating system has a separate associated reception-channel. It ensures the various supplementary functions of the circuit:
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R Muting Circuit - Block Diagram Figure 020
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R Direct Muting - Block Diagram Figure 021
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-VOR/DME/LS switching
-VOICE/ON function
R **ON A/C 001-049, 051-099, 101-105, 151-199, 201-220,
(2)
Composition of the circuit
(Ref. Fig. 022)
The audio circuit comprises:
-An interface card common to all the audio cards
-
A volume control module assembly
-
A stop-band filter
-
An adder amplifier
-
An emergency switching circuit
-
An output transformer.
(3)
Reception mode operation The audio signals delivered by the various communication and navigation units are connected to the interface card. This card ensures the adaptation and the connection of the receivers. This card is a common point to the system and no active components are used (it is mainly comprised of resistors). The input impedance of a channel is 600 ohms. The maximum input level is 50 mW/600 ohms (The nominal value is 10 mW/600 ohms). At the output of the interface card, the signals are applied to the volume control modules. An analog switch is installed at the input of each volume control. This switch disconnects the audio inputs when :
-
their reception is not selected (information from ACP)
-
their reception level selected on the ACP is at minimum (this condition does not apply to VHF and HF communication channels. A minimum reception level is ensured on the channels even when the potentiometers on the ACP are set to minimum).
When the levels are adjusted in accordance with the information from the logic processing function, the analog signals are sent to an amplifier, then to an output transformer. The audio signals are available on the secondary of the output transformer. Separate windings send these signals either to the boomset, the loud speaker or the CVR circuit. Output signal characteristics: 50 mW/600 ohms (the nomimal value is 10 mW/600 ohms).
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