Northern Airborne Technology PA700 - Manual (Page 13)

PA700 Series High Power Voice Amplifier
SM44 Installation and Operation Manual
Section 2 Rev: 1.01 Issue 4 Page 2-4
ENG-FORM: 805-0117.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
2.4.6 Post Installation 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
AA21/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 AA21/AA22 and/or to the PA700
unit from the AA21/AA22.
For most RADIO and PA (voice) operations, it is suggested that the AA21/AA22 volume control be set to
maximum (fully cw). If the system is overdriving, reduce the AA21/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.
Note: Advise all nearby personnel that PA system tests are to be conducted.
Start by checking the Siren Circuit for proper operation and tone/rate adjustment. The Siren always
operates at 100% output from the AA21/AA22 and should drive the PA's to full output on audio peaks.
The Level trimpot(s) of the AA21/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 AA21/AA22. To
achieve full output capability from the AA21/AA22, a signal of 2.5 Vrms at 1 kHz must be delivered to the
AA21/AA22 radio audio input and the AA21/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 "above ground level" (AGL) of the aircraft. To achieve the
best operation, all voice commands must be spoken slowly and clearly, with extra emphasis on each
word.
Note: Remove all sound absorbing material from the speakers prior to flight.
To determine the operational capability of the system, put the aircraft in a hover and with the target
properly positioned, provide PA instruction to the target to accomplish a certain task that will give visual
cue to the flight crew that the target has understood the instructions (i.e., "touch your head", "sit down",
"turn around", etc.).
Upon satisfactory completion of all performance checks, make all required log book entries, electrical
load, weight and balance amendments and other documentation as required by your local regulatory
agency before releasing the aircraft for service.