Northern Airborne Technology THxxx - Manual (Page 28)

Tac/Com Control Head Manual SM06 Rev. 4.10
2.3.2
Cautions
All audio installations can be severely degraded by incorrect wiring and shielding, and
may result in much higher cross-talk, hum, and ground-loop interference. This should be
considered when installing audio wiring to and from the specific radio. Both the audio Hi
and Lo wires must be connected from the radios (audio outputs are floating transformer
windings on NT-series radios), and should be grounded only at the audio panel via the
audio common.
If multiple transceivers are installed, it is very beneficial to use tri-axial cable for the
antenna feedlines, with the outer shield grounded at the radio end only. This added
electro-static shielding greatly reduces cable coupling, and eliminates many types of
interference in the final installation. Observe proper antenna spacing and good routing
practice for all RF lines to avoid cross-talk, squelch interference, and phantom sidetone
problems.
2.3.3
Cabling and Wiring
All unshielded 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. Wire types should be 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
wiring diagrams in Section 2.9 as required.
Installation cabling must allow the unit to be easily withdrawn for disconnection, switch
and pot settings (internal), and removal. Ensure an adequate service loop is allowed in
the routing of the cable. This can become a serious problem if the unit is installed with
the cables so short that the unit cannot be removed without disassembly of the
mounting console. At least 1 foot (30 cm) of free cable is recommended.
Allow 3 inches (8 cm) from the end of the wire to the shield termination to allow the
hood to be easily installed. Note that the hoods supplied by NAT in installation kits are
'clamshell' hoods, and are installed after the wiring is completed.
Generally, all wiring should be at least 22 AWG, except power and ground connections,
which should be 20 AWG - check the appropriate Interconnect drawing for the unit
under consideration. Ensure that the ground connection is clean and well secured. To
prevent inadvertent system failure, power to this system must be supplied from a
separate breaker or fuse, and not bundled to any other source. A 1A breaker is
suggested (28 Vdc source).
Notes: 1. The case is grounded electrically and should be attached to a grounded
surface for correct RFI shielding. A pin is provided for grounding the case,
and this must be connected via its own wire to a suitable ground, not
jumpered to the power ground wire connection.
Page 2-2 Jan 4, 2006
ENG-FORM: 805-0108.DOT
Amendment # 1 Oct 22, 2007
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.