Installation Instructions

190-01007-A3 GTN 6XX/7XX AML STC Installation Manual
Rev. 4 Page 3-7
3.3.2 COM Antenna Cable Considerations
The GTN requires a standard 50Ω vertically polarized antenna. Follow the antenna manufacturer’s
installation instructions for mounting the antenna, and gain other FAA approval.
For optimum performance the antenna should be mounted on a metal surface or a ground plane with a
minimum area of 18 x 18 inches. Refer to Section 2.4.4.2 for installation location considerations.
The antenna coaxial cable must be made of RG-142B, RG-400 or a comparable quality 50Ω coaxial.
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 the
antenna. The VSWR/ wattmeter should be inserted as close to the transceiver as possible. When rack and
harness buildup is performed in the shop, the coaxial termination may be provisioned by using a 6 inch
inline BNC connection. This would be an acceptable place to insert the VSWR. Any problem with the
antenna installation is most likely seen as high reflected power. A VSWR of 3:1 may result in up to a
50% loss in transmit power.