Table 6-1 Summary Of Com Rx Squelch Settings And Auto Squelch Levels; Com Rx Squelch Check (Gtn 635/650/750 Only) - Garmin GTN 6 Series Maintenance Manual

6.3.5

COM RX Squelch Check (GTN 635/650/750 Only)

NOTE
COM RX Squelch was referred to as COM RF Squelch in software versions prior to v6.50.
The COM RX Squelch settings allow adjustment of the noise signal strength required to
break squelch for the COM receiver.
In late 2013, Garmin changed the GTN COM radio factory calibration process to allow the level at which
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 6-1. Installations of radios with the expanded sensitivity calibration
process may require a different COM RX Squelch setting to achieve the desired RX squelch performance.
All current production units are shipped with the expanded sensitivity calibration process.
Approximate levels when the auto squelch opens and closes for various COM RX squelch settings is
provided in Table 6-1. Installations of GTNs with the expanded sensitivity calibration will generally use a
COM RX Squelch setting of 75 or higher. Installations of GTNs with the original sensitivity calibration
will generally use a COM RX squelch setting of 0 or higher.

Table 6-1 Summary of COM RX Squelch Settings and Auto Squelch Levels

COM RX Squelch Setting
0
75
100
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 Carrier Squelch Check (GTN Main Software v6.50 or Later, COM v2.30 or Later)
COM carrier squelch settings allow adjustment of the carrier signal strength required to break squelch for
the COM receiver.
The COM carrier squelch level adjustment reduces the sensitivity of the COM receiver. Elevated, ambient
RF interference levels in certain flight environments, such as aircraft operating busy airport environments
or aircraft with equipment installed that interferes with the COM radio, may require adjustment of the
COM carrier squelch to reduce undesired squelch breaks.
190-01007-B1
Rev. 4
Auto Squelch open
Auto Squelch close
Auto Squelch open
Auto Squelch close
Auto Squelch open
Auto Squelch close
GTN 6XX/7XX Part 27 AML STC Maintenance Manual
Original
Expanded Calibration
Calibration
Approximation
-99 dBm
-101 dBm
-97 dBm
-99 dBm
-93 dBm
-95 dBm
Approximation
-105 dBm
-107 dBm
-99 dBm
-101 dBm
-93 dBm
-95 dBm
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