Northern Airborne Technology AA22 - Manual (Page 10)

AA22 Series PA Driver/Siren Control
SM33-2 Installation and Operation Manual
Section 2 Rev: 1.00 Issue 4 Page 2-3
ENG-FORM: 805-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
2.4.4 Post Installation Checks
2.4.4.1 Voltage/Resistance Checks
Do not attach the AA22 until the following conditions are met.
Check the following:
a) Check P101, pin 1 and 2 for +28 Vdc relative to ground.
b) Check P101, pin 14, 15 and 16 for continuity to ground (less than 0.5
Ω).
c) Check P101, pin 3 for the presence of the lamp dimmer voltage.
Check the following for AA20-030 and AA20-430
d) Check P101, pin 10 for continuity to ground (less than 0.5
Ω). This ground is installation
specific and may be a 'hard' ground or supplied by a momentary switch (siren trigger).
2.4.4.2 Operational Checks
The PA system is not intended to be operated in a linear volume manner (i.e., it is not like a
stereo system). The PA is designed to provide high levels of audio power under difficult
conditions and does so by sacrificing some of the high fidelity for a higher average power output.
The volume control on the AA22 is not intended to provide linear operations from the PA system
and will result in broken and sporadic output from the PA when insufficient levels are delivered to
the AA22 and/or to the power amplifier unit from the AA22.
For most RADIO and PA (voice) operations, it is suggested that the AA22 volume control be set
to maximum (fully cw). If the system is overdriving, reduce the AA22 volume setting.
To check the system, the aircraft must be moved outside and away from as many reflective
surfaces as possible. It is not recommended to operate the PA microphone on the ground, as a
high risk exists for audio coupling and feedback. However, if the test is to be conducted on the
ground, the aircraft should be positioned on a grassy surface to help reduce the distortion
produced by sound reflected from concrete or asphalt. It is also beneficial to stuff the speaker
projectors with soft rubberized foam to reduce the risk of feedback and distortion.
Advise all nearby personnel that PA system tests are to be done.
Start by checking the Siren Circuit for proper operation and tone/rate adjustment. The Siren
always operates at 100% output from the AA22 and should drive the PA's to full output on audio
peaks. The Level trimpot of the AA22 will be set at the factory to provide rated output at full front
panel volume control adjustment.
Once the siren operation is satisfactory, you may try RADIO operations through the AA22. To
achieve full output capability from the AA22, a signal of 2.5 Vrms must be delivered to the AA22
Radio audio input and the AA22 volume must be set to maximum. Lower levels of input signal or
volume settings will result in poor output audio (very broken).
For PA (voice) tests, it is best that the aircraft is flown in an approximately 200 foot hover and
commands are given to a human ground target for visual response to the commands. Remember,
the human target should be positioned in the area that the speaker system is designed to project
the audio to. This will depend on speaker orientation and the height of the aircraft. Remove all