Mounting, Wiring, And Power Checks; Unit Ground Checks; Tx Interlock Checkout; Antenna Check - Garmin G3X Touch Installation Manual

21.7 Mounting, Wiring, and Power Checks

Fabrication of a wiring harness is required. Sound mechanical and electrical methods and practices are
recommended for installation of the GTR 20. Refer to
Section 25.16 for pinouts.
Verify that all cables are properly secured and shields are connected to the shield block of the connectors.
Check the movement of the flight and engine controls to verify there is no interference between the cabling
and control systems. Ensure that all wiring is installed as described in
Prior to powering up the unit, the wiring harness must be checked for proper connections to the aircraft
systems and other avionics equipment. Point to point continuity must be checked to expose any faults such
as shorting to ground. Any faults or discrepancies must be corrected before proceeding.
After accomplishing a continuity check, perform power and ground checks to verify proper power
distribution to the GTR 20. Any faults or discrepancies should be corrected at this time. Remove power
from the aircraft upon completion of the harness checkout.
The GTR 20 can be installed after completion of the continuity and power checks. The GTR 20 should be
secured appropriately, as described in
and antenna.
21.7.1 Unit Ground Checks (Normal Mode)

21.7.1.1 TX Interlock Checkout

Connect pins 4 and 5 per
Pin Pin Name
4 TX INTERLOCK OUT
5 TX INTERLOCK IN

21.7.1.2 Antenna Check

If desired, the antenna VSWR can be checked using an inline wattmeter in the antenna coaxial using
frequencies near both ends of the band. The VSWR should be less than 2:1. A VSWR of 2:1 will cause a
drop in output power of approximately 12%.
21.7.1.3 Receiver/Transmitter Check
Tune the unit to a local VHF frequency and verify the receiver output produces a clear and understandable
audio output. Verify the transmitter functions properly by contacting another station and getting a report
of reliable communications.
190-01115-01
Rev. AC
Section 21.6. The GTR 20 must be connected to the wiring harness
Section 28.
Table 21-6 TX Interlock Connections
Description
Active low output that indicates the GTR 20 is transmitting.
This output is normally connected to the TX INTERLOCK IN
of other COM radios installed in the aircraft.
Active Low Input that 'desenses' (protects) the GTR 20
receiver when another communications radio is
transmitting. This input comes from another communication
radio's interlock output or MIC KEY line.
G3X/G3X Touch Installation Manual - GTR 20 Installation
Section 2.3 for wiring considerations, and to
Section 2.3.
Page 21-8