Garmin GNS 480 Installation Manaul

Also see for Apollo CNX80: User Newsletter User Newsletter Supplemental Flight manual Pilot's guide Data list

Contents

Installation ProceduresGNS 480 (CNX80) Installation Manual 560-0982-01 Rev L 2-433b. The GPS antenna should be mounted no closer than two feet from any antennas emittingmore than 25 watts of power. An aircraft EMC check can verify the degradation of GPS inthe presence of interference signals.3c. To minimize the effects of shadowing at 5° elevation angles, the GPS antenna should bemounted no closer than 6 inches (edge to edge) from other antennas, including passiveantennas such as another GPS antenna or XM antenna.4. To maintain a constant gain pattern and limit degradation by the windscreen, avoidmounting the antenna closer than 3 inches from the windscreen.5. For multiple GPS installations, the antennas should not be mounted in a straight line fromthe front to the rear of the fuselage. Also varying the mounting location will help minimizeany aircraft shading by the wings or tail section (in a particular azimuth, when one antennais blocked the other antenna may have a clear view).Figure 2-11 shows the recommended placement of antennas.NOTEThe internal GNS 480 COM does not interfere with its own GPS receiver. However,placement of the GNS 480 GPS antenna relative to other COM transceivers and antennas(including the GNS 480 COM antenna) may be critical.The connectors are included in the installation kit, and are intended for use with RG-142B or RG-400 size coaxcable. If using a different diameter coax, alternative connectors may be required. Assembly instructions for theconnectors are included in Figure 2-12. RG-142B or RG-400 cable can be used as long as the length is lessthan 35 feet. For longer lengths, use low-loss 50Ω coax.Suggestion: Temporarily locate the GPS antenna with coax connected to the GNS 480 and check the GPSperformance as described in the GPS Operation and Position test in the Post Installation Checkout insection 3.3.2.1.2. Once a suitable location has been verified, then permanently mount the antenna.NOTEIf using a GPS antenna that was already on the aircraft, or if mounting the antenna closerthan two feet from a COM antenna, conduct the GPS Operation and Position test in thePost Installation Checkout on page 3-32. If the GNS 480 passes the test, then furthermeasures are not necessary.Once the antenna mounting position has been prepared, route the coax cable from the antenna to the GNS480. Proper selection of coax cable and assembly of connectors is critical to GPS signal performance. Thecable loss from the GPS antenna (excluding antennas in Table 1-2) shall be between 1.5 dB and 6.5 dB inorder to maintain proper rejection to interference signals.NOTEGPS antenna in Table 1-2 require a cable loss between 3 dB and 7 dB.The coaxial connectors and adapters, such as TNC to BNC, add additional loss to the cable and should beconsidered when computing the cable loss. A typical loss of 0.2 dB can be used for each connection. Tomaintain integrity of the WAAS signal, the GPS antenna coaxial cable must have a minimum of twoshields (e.g. RG-400 or RG-142B). The typical cable loss for 20 feet of RG-142B or RG-400 coax with aconnector on each end is 4 dB. For very short runs, where the loss is less than 3dB, additional cable shouldbe used to increase the loss to within 3 dB to 7 dB. This additional cable may be coiled, taking intoaccount the minimum bend radius of the cable.During the post-installation checkout, susceptibility to harmonics of VHF COM transmitters will beevaluated. If problems arise, then better isolation, or distance, may be required between the GPS and COMantennas, or a 1575.42 MHz notch filter may be installed in series with the antenna coax of the VHF COMtransceiver to reduce or eliminate the harmonic interference. A notch filter for this use (part #162-1059) isavailable from Garmin AT.