190-01007-C1
GTN Xi Part 23 AML STC Maintenance Manual
Rev. 1
Page 7-5
7.1.2.2 Signal Acquisition Check
NOTE
All other avionics should be turned off at the start of this test and the GTN Xi should be
powered on in Normal mode. After re-installation, the initial acquisition of position can
take up to 20 minutes. Subsequent acquisitions will not take as long.
NOTE
For best results, this check should be performed outdoors away from large buildings or
objects that could obstruct the GPS antenna.
Ensure the GTN Xi is able to acquire sufficient satellites to compute a GPS position. From the home page,
touch the
System
key and then touch the
GPS Status
key. Under GPS Solution, ensure that a “3D Fix” or
“3D Diff Fix” is obtained. If the unit is unable to acquire satellites, move the aircraft away from
obstructions that might be shading GPS reception. If the GPS solution does not improve, check the GPS
antenna installation.
Once GPS position information is available, verify that the LAT/LON agree with a known reference
position.
7.1.2.3 Receiver/Transmitter Operation (GTN 635Xi/650Xi/750Xi Only)
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.
7.1.2.4 COM RX Squelch Check (GTN 635Xi/650Xi/750Xi Only)
The COM RX Squelch settings allow adjustment of the noise signal strength required to break squelch for
the COM receiver.
Approximate levels when the auto squelch opens and closes for various COM RX squelch settings is
provided in Table 7-2. The GTN Xi will generally use a COM RX Squelch setting of 57 or higher.
Table 7-2 Summary of COM RX Squelch Settings and Auto Squelch Levels
To set the COM Squelch setting, tune the COM to a local COM frequency. Verify squelch breaks when the
pilot begins talking. If the squelch breaks too early, increase the value. If it does not open when the pilot
begins speaking over the radio, decrease the value.
COM RX
Squelch Setting
Calibration
Approximation
0
-107.0 dBm
25
-103.5 dBm
50
-99.0 dBm
75
-96.5 dBm
100
-93.0 dBm
