Northern Airborne Technology AA9x - Manual (Page 11)

AA9x Series Single Channel Audio Controller
SM56 Installation and Operation Manual
Section 2 Rev: 1.00 Issue 4 Page 2-3
There are numerous manufacturers of in-line PTT cordsets, offering many 'electrical' variations to
accomplish different functions. To meet the operational requirements for headset stations supported by
the AA9x series, NAT recommend the dual switch type: a 3-position (momentary/center-off/locking) slider
switch for the ICS functions and a momentary push-button switch for the Transmit functions. Both
switches provide a ‘mic interrupt’ function. The 3-position ICS switch will allow the user to change the
switch settings to match the operational intercom mode that has been selected at the AA9x series
(e.g., LIVE, KEYED or VOX). The cable should have 6 conductors with the MIC and PHONE pairs
shielded (MIC wires must be shielded as a minimum). To ensure proper shielding, the shield(s) should be
terminated to the MIC LO connection at the airframe connector of the PTT cordset. See Figure 1 below
for details.
Figure 1: PTT Cord for Use with NAT Audio Controllers (XMIT and ICS)
To avoid complications in the aircraft, it is recommended that the same type of PTT cordsets be used for
all headset locations in the aircraft. It is not good practice to create a situation where a specific cordset is
needed for the copilot, which might cause operational errors if moved to a passenger location.
Although in-line PTT cordsets can be used to conveniently address a number of requirements for
microphone and PTT control, they can also be a source of trouble if incorrectly configured, or improperly
shielded.
Many in-line PTT cordsets use the PHONE LO connection as the ground reference for the ICS and TX
PTT keylines. The PHONE LO connection in the AA9x series is floating, which will lead to incorrect keying
of the intercom and radio systems if this type of cordset is used.
ENG-FORM: 805-0115.DOT
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