GNS 400W Series Installation Manual Page 3-9190-00356-08 Rev. G3.10.2 COM AntennaThe 400W Series unit requires a standard 50 vertically polarized antenna. Follow the antennamanufacturer‘s installation instructions for mounting the antenna.The antenna should be mounted on a metal surface or a ground plane with a minimum area of18 x 18 inches. Refer to Section 2.4.2 for installation location considerations.The antenna coax cable should be made of RG-142B, RG-400 or a comparable quality 50 coax.Check for insertion loss and VSWR (voltage standing wave ratio). VSWR should be checked with an in-line type VSWR/wattmeter inserted in the coaxial transmission line between the transceiver and theantenna. The VSWR should be inserted as close to the transceiver as possible. When rack and harnessbuildup is performed in the shop, the coax termination may be provisioned by using a 6 inches inline BNCconnection. This would be an acceptable place to insert the VSWR. Any problem with the antennainstallation is most likely seen as high reflected power. A VSWR of 3:1 may result in up to a 50% loss intransmit power.3.10.3 NAV AntennaThe NAV antenna is a standard 50Ω horizontally polarized NAV/VOR/Localizer/Glideslope antenna (theglideslope may be a separate antenna in some aircraft) that receives VOR frequencies between 108 and117.95 MHz, and localizer frequencies between 108 and 112 MHz, and glideslope information between328.6 and 335.4 MHz. Follow the antenna manufacturer‘s installation instructions for mounting antennas.It is recommended that the installer use RG-142B, RG-400 or equivalent 50Ω coax for the NAVantenna(s).The GNS 430W has a separate VOR/LOC and Glideslope inputs requiring some installations to use astandard external diplexer or triplexer.
