190-01182-02
GTR 225/GNC 255 TSO Installation Manual
Rev. F
Page 6-11
6.4.3
COM Configuration Group
6.4.3.1
MIC Gain Page
The MIC GAIN page sets the MIC gains for MIC 1 and MIC 2. The MIC 1 and MIC 2 gain is adjustable
from -12 dB to +30 dB in 6 dB increments. The default is +12 dB. For MICs with low signal levels, this
can be adjusted up to increase the signal strength. For MICs with high signal levels, this can be adjusted
down to decrease the signal strength. The MIC 2 gain setting is dependent upon the MIC 1 gain setting.
Figure 6-15 MIC Gain Page
NOTE
For COM software version 2.12 or earlier, the MIC1 and MIC2 gain settings are
transposed. Change MIC1 gain setting to adjust the actual MIC2 gain. Change MIC2 gain
setting to adjust the actual MIC1 gain.
6.4.3.2
COM RX Squelch Page
The COM RX SQUELCH page configures the squelch for the COM receiver. The COM RX squelch
adjusts the signal strength required to break squelch for the COM receiver. See table 6-11 for a description
of each setting.
Garmin changed the GTR/GNC COM radio factory calibration process to allow the level when the auto
squelch opens or closes, to be set at a more sensitive level. The COM RX squelch range (0-100) was
remapped as shown in table 6-11. Installations of radios with the expanded sensitivity calibration process
may require a different COM RX squelch setting to achieve the desired RX squelch performance. Current
production units are shipped with the expanded sensitivity calibration process.
Table 6-11 contains the approximate levels when the auto squelch opens and closes for various COM RX
squelch settings. Installations of GTR/GNCs with the expanded sensitivity calibration will generally use a
COM RX squelch setting of 75 or higher. Installations of GTR/GNCs with the original sensitivity
calibration will generally use a COM RX squelch setting of zero or higher.
Figure 6-16 COM RX Squelch Page
