190-01115-01 G3X/G3X Touch Installation Manual - GTR 20 InstallationRev. AC Page 21-721.6 Mounting ConsiderationsThe GTR 20 is designed to mount remotely.21.6.1 Bracket InstallationThe GTR 20 is shipped with the brackets positioned on the ends of the unit. The brackets can be removedfrom the bottom of the GTR 20 and repositioned by the installer. The GTR 20 mounting brackets can bepositioned on the sides or the ends of the GTR 20. The installer determines the orientation and position ofthe brackets that best suits the installation. See Figure 21-2 and Figure 21-3 for bracket positions.21.6.2 Unit MountingSecure the GTR 20 to the airframe in a suitable mounting location using a minimum of four #10 fasteners(not provided). Hardware is intended to be located in the 4 outermost mounting locations. The centerlocations in each bracket are additional locations provided for the installer’s convenience.Do not mount the GTR 20 on the “hot” side (engine side) of the firewall. To reduce interference, route theGTR 20 wiring harness separately from any COM radio or transponder antenna coax.No cooling air is required for the GTR 20/200, however, as with all electronic equipment, lower operatingtemperatures extends equipment life. Reducing the operating temperature by 15° to 20°C (27° to 36°F)reduces the mean time between failures (MTBF).For final installation and assembly, see Figure 21-2, Figure 21-3, and Figure 21-4.21.6.3 Antenna Installation and ConnectionsThe GTR 20 requires a standard 50 vertically polarized antenna. Follow the antenna manufacturer’sinstallation instructions for mounting the antenna.The antenna should be mounted on a metal surface or a ground plane with a minimum area of 18 inches x18 inches. Refer to Section 21.5.1 for installation location considerations.21.6.4 Antenna Coaxial Cable InstallationThe antenna coax cable should be made of RG-142B, RG-400 or a comparable quality 50 coax. SeeSection 2.4 or follow the BNC connector manufacturer’s instructions for cable preparation/connectorinstallation.Check that there is ample space for the cabling and mating connectors. Avoid sharp bends in the antennacable, and routing near aircraft control cables. Route the COM antenna cable as far as possible away fromany GPS antenna cables.Check for insertion loss and Voltage Standing Wave Ratio (VSWR). VSWR should be checked with anin-line type VSWR/wattmeter inserted in the coaxial transmission line between the transceiver and theantenna. The VSWR meter should be inserted as close to the transceiver as possible. When rack andharness buildup is performed in the shop, the coax termination may be provisioned by using a 6-inch in-line BNC connection. This would be an acceptable place to insert the VSWR meter. Any problem withthe antenna installation is most likely seen as high reflected power. A VSWR of 3:1 may result in up to a50% loss in transmit power. VSWR at the low, mid and high end of the tuning range should be less than3:1, for best performance VSWR should be less than 2:1. A high VSWR decreases the amount of powerradiated by the antenna and increases power supply current and heat dissipated by the radio when the radiois transmitting.
