If a COMM antenna is found to be the problem, a 1.57542 GHz notch filter (GPN 330- 00067-00) may be installed in the VHF COMM coax, as close to the COMM as possible. This filter (GPN 330-00067-00) is required for the GNC 300 transmitter).

If a COMM is found to be radiating, the following can be done:

1)Replace or clean VHF COMM rack connector to assure good coax ground.

2)Place a grounding brace between the GNC 300, VHF COMM, and ground.

3)Shield the VHF COMM wiring harness.

2.1.6COMM ANTENNA INSTALLATION INSTRUCTIONS

The COMM antenna should be installed according to the manufacturer's recommendations.

2.2RACK CONSIDERATIONS 2.2.1 ACCESSIBILITY

Plan a location which gives the pilot complete and comfortable access to the entire keypad and which is plainly visible from the pilot’s perspective. Check that there is adequate depth for the rack in the instrument panel. A location away from heating vents or other sources of heat generation is optimal. Figure 2-2 illustrates a typical aviation rack installation.

2.3CABLING AND WIRING

The recommended antenna cable type for both antennas is M17/155-0001 (RG-58A/

U)per MIL-C-17. Maximum allowable length for the GPS antenna using this cable type is 40 feet. Other cable types with 50 ohms nominal impedance and longer lengths can be used for the GPS antenna, provided the installer insures that the attenuation does not exceed 10dB at 1.5 GHz for the specific installation. Check that there is ample space for the cabling and mating connectors. Avoid sharp bends in cabling, particularly the COMM antenna cable, and routing near aircraft control cables.

Cabling for the GNC 300 should not be routed near components or cabling which are sources of electrical noise.

Do not route the COMM antenna cable near any ADF antenna cables.

Route the GPS antenna cable as far as possible away from all COMMs and COMM antenna cable.

2.4COOLING AIR

Cooling air is not required for the GNC 300 but is highly recommended because, as with any electronic equipment, reduced operating temperature can contribute to increased reliability. Additionally, location of the GNC 300 in a stack of other power

Av. Kit Install. Manual

190-00067-02 Rev. J

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