Northern Airborne Technology NTX - Manual (Page 22)

NTX VHF-FM Series Remote Mount Transceivers Manual SM28 Rev. 4.10
2.3.2
Cautions
Severe degradation of audio installations may result from incorrect wiring and shielding.
This could cause much higher cross-talk, hum, and ground-loop interference.
2.3.3
Notes
For maximum resistance to low frequency interference, electrically ground the case of
the transceiver.
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.
To provide easy installation of the hood, allow 3 inches from the end of the wire to the
shield termination. Note: Install the hood after the wiring is complete.
Installation cabling must allow the transceiver to be easily withdrawn for disconnection and
field service adjustments. Ensure an adequate service loop in the routing of the cables.
All wiring should be 22 AWG, except power and ground connections, which must be
18 AWG or larger, as indicated on the installation drawings. Ensure that the ground
connection is clean and well secured. To prevent inadvertent system failure, supply
power to this system from a separate breaker or fuse not connected to any other
device. NAT recommends a 5 A fuse or breaker (28 Vdc Source).
Coaxial cable should be in accordance with MIL-C-17 unless otherwise specified. Do
not use coax with PVC insulation. NAT recommends Teflon dielectric cable 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 (Effective
Radiated Power) to less than 50% of specification.
To prevent RF interference between similar systems, NAT recommends that VHF FM
coax runs be widely separated, or be made using triaxial cable. Bond the outer shield to
the airframe at the transceiver end only.
In communication intensive applications, bad cable routing and shielding may drastically
compromise over-all system performance. Symptoms will be spurious squelch opening,
RFI (Radio-Frequency Interference), and garbled reception.
Neatly terminate RF cables (solder or crimp) and test for shorts prior to system check-
out (not while connected to the radio!!). Keep cable bends to a minimum at the antenna.
Page 2-2 Jun 1, 2004
ENG-FORM: 805-0108.DOT
Amendment # 3 Jan 14, 2008
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