7.2.1 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.
Coaxial cable shall be selected in accordance with MIL-C-17 unless otherwise specified. Do not
use coax cable 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, cables losses due
to long cable runs and tight bends may reduce the ERP (Effective Radiated Power) by greater
than 50%. For optimum RF performance Cobham recommends using LMR400 low loss
coax cable or equivalent.
Allow 3" from the end of the shielded wiring to the shield termination to allow the connector
hood to be easily installed.
Maintain wire segregation and route wiring in accordance with the original aircraft
manufacturers Maintenance Instructions. Coaxial cables shall be routed separately from existing
wire bundles in the aircraft to minimize electromagnetic coupling effects.
Unless otherwise noted, signal wiring shall be a minimum of 22 AWG, except power and ground
lines to J105, which shall be a minimum of 20 AWG (RCDU) and minimum of 16 AWG (PMR &
RMR). Twisted shielded pair or triple wiring shall be a minimum of 24 AWG. 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.
7.3 ELECTRICAL INSTALLATION OF THE PMR/RMR
Figure 7-4 through Figure 7-19 define the system interconnects.
CAUTION
Do not bundle any logic, audio, or DC power lines from this unit with 400 Hz synchro wiring or AC power
lines. Do not position this unit next to any device with a strong alternating magnetic field such as an inverter
or significant interference to operation will result. In all installations, use shielded cable exactly as shown and
ground as indicated. Significant problems may result if these guidelines are not followed.
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 audio wiring to and
from the radio installation is performed.
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