Northern Airborne Technology NPX138 - Manual (Page 19)

NPX138 Panel Mount Radio Manual SM41 Rev. 4.00
2.3.3
Notes
The case of the NPX138 must be electrically grounded for maximum resistance to low
frequency interference. A pin on the connector (Chassis ground) is provided and must
be connected by a short wire to a clean ground, not jumpered to the power ground wire
connection.
Refer to the aircraft structural repair manual and maintenance manual for instructions
and information pertinent to this installation.
2.3.4 Cable 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 2.5 as required.
Allow 3 inches from the end of the wire to the shield termination to allow the hood to be
easily installed. Note that the hood is installed after the wiring is complete.
Installation cabling must allow the NPX138 to be easily withdrawn for disconnection and
field service adjustments. Ensure an adequate service loop in the routing of the cables.
It can be a serious issue if the unit is installed with the cables so short that the unit
cannot be removed without disassembly of the surrounding structures. At least 30 cm
(1 foot) of free cable is recommended.
All wiring should be 22 AWG minimum, except power and ground connections, which
must be 20 AWG or larger, as indicated on the installation drawings. 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
connected to any other device. A 5 A fuse or breaker is recommended (28 Vdc).
Coaxial cable should be in accordance with MIL-C-17 unless otherwise specified. Do
not use coax with PVC insulation. Teflon dielectric cable is encouraged at or above VHF
frequencies or where cable runs exceed 8 feet. Note that at VHF frequencies, cable losses
due to long cable runs and tight bends may cut the ERP (Equivalent Radiated Power) to
less than 50% of spec.
To prevent RF interference between similar systems, it is recommended that VHF FM
coax runs be widely separated, or be made using triaxial cable, with the outer shield
bonded to the airframe at one end only (transceiver end).
In communication intensive applications, poor cable routing and shielding may
drastically compromise over-all system performance. Symptoms may be spurious
squelch opening, RFI (Radio-Frequency Interference), and garbled reception.
Page 2-2 Nov 10, 2003
ENG-FORM: 805-0104.DOT
Amendment # 5 Jan 14, 2008
PROPRIETARY AND CONFIDENTIAL TO NORTHERN AIRBORNE TECHNOLOGY LTD.