190-01182-02 GTR 225/GNC 255 TSO Installation Manual
Rev. F Page 4-5
4.7.2 GTR/GNC Unit Insertion and Removal
Prior to placing the unit in the rack, in order to ensure correct position of the retention
mechanism, it may be necessary to insert the hex drive tool into the access hole and turn
the drive tool counterclockwise until it completely stops.
The application of hex drive tool torque exceeding 15 in-lbs can damage the locking
mechanism.
Insertion
1. The GTR/GNC unit is installed in the rack by sliding it straight in until it stops, approximately 3/8
inch short of the final position.
2. Insert a 3/32" hex drive tool into the access hole at the bottom of the unit face.
3. Turn the hex tool clockwise while pressing on the left side of the bezel until the unit is seated in the
rack.
Removal
1. Insert the hex drive tool into the access hole on the unit face.
2. Turn hex drive tool counterclockwise until the hex drive tool stops.
3. Pull the unit from the rack.
4.7.3 Unit Replacement
Whenever the GTR/GNC unit is removed or reinstalled, verify that the unit powers up successfully.
4.8 COM Antenna Installation and Connections
The GTR/GNC unit requires a standard 50 vertically polarized antenna. Follow the antenna
manufacturer’s installation 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 by 18 inches. See section 3.2.1 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 voltage standing wave ratio (VSWR). 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 should be inserted as close to the transceiver as possible. When rack and harness
buildup is performed in the shop, the coax termination may be provisioned by using a 6" in-line 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.
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