Northern Airborne Technology AA39 - Manual (Page 10)

AA39 Series Headset Adapter
SM43 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.
Headset and/or helmet wiring may also need to be reviewed if using Dynamic microphones. Many of the
headsets and helmets on the market have minimal shielding for the wiring associated with the mic and
phone circuits. Those with shielded wiring often use the Phone Lo connection for the shield ground. In
the AA39, the Phone Lo connection is not ground referenced, so the shielding has no effect. This will
result in substantial coupling of the Phone signal onto the Microphone wires, leading to high levels of
crosstalk in the intercom system. These shielding considerations also apply to in-line PTT cordsets. If a
review of the headset wiring indicates there will be a problem with the shield termination, it is acceptable
to ground the Phone Lo connection to a local ground at the headset jack/connector.
2.4.4 Post-Installation Checks
2.4.4.1 Voltage/Resistance Checks
Do not attach the AA39 until the following conditions are met.
Check the following:
AA39-075 and AA39-087
Check J101, pin <9> for continuity to ground (less than 0.5 Ω).
AA39-187 and AA39-287
Check J1, pin <4> for continuity to ground (less than 0.5 Ω).
2.4.4.2 Power On Checks
Power up the aircraft’s systems and confirm normal operation of all functions of the AA39.
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.
2.5 Adjustments and Connections
The AA39-075 and AA39-087 have a MIC LEVEL adjustment trimpot, accessible through a hole in the
rear of the unit. Rotating the trimpot cw will increase the mic level, and ccw will decrease it.
There are no adjustments for the AA39-187 or AA39-287.