Northern Airborne Technology AA39 - Manual (Page 9)

AA39 Series Headset Adapter
SM43 Installation and Operation Manual
Section 2 Rev: 1.00 Issue 4 Page 2-2
ENG-FORM: 805-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
2.4.2 Cautions
CAUTION:
In all installations, use shielded cable exactly as shown, and ground as indicated.
Significant problems may result from not following these guidelines.
All audio installations can be seriously degraded by incorrect wiring and shielding, and
may result in abnormal crosstalk, hum and ground-loop noise. Be especially careful
with all microphone wiring and tie line wiring, as these lines carry the lowest level
signals in the aircraft.
CAUTION:
Do not bundle any lines from this unit with transmitter coax lines. Do not
bundle any audio or DC power lines from this unit with 400 Hz synchro wiring
or AC power lines. Do not position this unit or wiring from this unit next to any
device with a strong alternating magnetic field such as an inverter, or
significant audio interference will result.
2.4.3 Cabling and Wiring
All wire shall be selected in accordance with the original aircraft manufacturer's Maintenance Instructions
or AC43.13-1B Change 1, Paragraphs 11-76 through 11-78. Unshielded wire types shall qualify to
MIL-W-22759 as specified in AC43.13-1B Change 1, Paragraphs 11-85, 11-86, and listed in Table 11-11.
For shielded wire applications, use Tefzel MIL-C-27500 shielded wire with solder sleeves (for shield
terminations) to make the most compact and easily terminated interconnect. Follow the connector map in
Section 2.7 as required.
Allow 3" from the end of the shielded wiring to the shield termination to allow the connector hood to be
easily installed. Reference the interconnect drawing in Section 2.7 for shield termination details. Note that
the hood is a "clamshell" hood, and is installed after the wiring is complete. Aircraft harnessing shall
permit the unit to be lowered from the panel for easy access to all side adjustments. Do NOT mount the
unit until all adjustments have been performed.
Maintain wire segregation and route wiring in accordance with the original aircraft manufacturers
Maintenance Instructions.
Unless otherwise noted, all wiring shall be a minimum of 24 AWG, except power and ground lines, which
shall be a minimum of 22 AWG. Reference the Interconnect drawing for additional specifications. Check
that the ground connection is clean and well secured, and that it shares no path with any electrically noisy
aircraft accessories such as blowers, turn and bank instruments or similar loads. Power to this unit must
be supplied from a separate circuit breaker or fuse (fast blow), and not attached to any other circuit
breaker without additional protection. Verify that the selected circuit breaker size and wire gauge are
adequate for the installation using the techniques specified in AC43.13-1B Change 1, Paragraphs 11-47
through 11-51 and 11-66 through 11-69.
2.3.4.1 Microphone Wiring
In all installations that use Dynamic microphones, extreme care must be taken with the shielding and
routing of the microphone wiring. This is especially true of the 5-ohm Dynamic mic input, where typical
signals are in the range of 100-250 μVrms. Special wire with Mumetal shielding should be considered if
there are any concerns about installation-related noise. Do not bundle the microphone wiring with high-
level lines (headphone, radio audio, coaxial cables, etc.).