Garmin GPS 155XL Installation Manual

Also see for GNC 300XL: Pilot's guide and reference Installation manual

Garmin GPS 155XL Installation Manual Manual pdf 15 page image

GPS 155XL/GNC 300XL Installation Manual Page 2-3190-00067-22 Revision F2.3 RACK CONSIDERATIONS2.3.1 AccessibilityPlan a location that gives the pilot comfortable access to the keypad and provides good visibility from thepilot's perspective. Check that there is adequate depth for the rack in the instrument panel. A locationaway from heating vents or other sources of heat generation is optimal. Figure 2-1 illustrates a typicalaviation rack installation.2.4 CABLING AND WIRINGThe 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 with50 ohms nominal impedance and longer lengths can be used for the GPS antenna, provided the installerinsures that the attenuation does not exceed 10 dB 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 GNC 300XL COMM antenna cable, and routing near aircraft control cables. Cabling forthe GPS 155XL/GNC 300XL should not be routed near components or cabling which are sources ofelectrical noise. Do not route the GNC 300XL 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.2.5 COOLING AIRThe GPS 155XL/GNC 300XL units meet all TSO requirements without external cooling. However, aswith all electronic equipment, lower operating temperatures extend equipment life. On the average,reducing the operating temperature by 15-20 °C (25 to 35 °F) doubles the mean time between failure(MTBF). Recommended airflow rating is 1 CFM (cubic foot per minute) at a pressure equivalent to 0.1inches of water.Units tightly packed in the avionics stack heat each other through radiation, convection, and sometimesby direct conduction. Even a single unit operates at a much higher temperature in still air than in movingair. Fans or some other means of moving the air around electronic equipment are usually a worthwhileinvestment. A 5/8” diameter air fitting is provided on the rear of the mounting rack for the purpose ofadmitting cooling air under such conditions. If a form of forced air cooling is installed, make certain thatrainwater cannot enter and be sprayed on the equipment.