Hello G3X Users,
G3X V9.00 is now available
and contains some changes in support of improving TIS-B performance.
The GDL 39/39R is a dual frequency (978 Mhz, 1090 Mhz) ADS-B receiver that receives ADS-B traffic air-to-air whether the traffic has a UAT and is transmitting on 978 Mhz, or has a mode S 1090ES transponder transmitting on 1090 Mhz. The GDL 39/39R also receives free FIS-B weather on 978 Mhz from ADS-B ground stations.
Additionally, the GDL 39/39R receives notification from ground stations of nearby Mode C aircraft using the TIS-B datalink.
Ok, you probably knew all of that. Here is where the changes in V9.00 get significant. All G3X and G3X Touch systems today using a GTX 23ES tranponder and a GDL 39/39R ADS-B receiver are automatically configured by the system to report to the ground stations in the 1090ES squitter that they are capable of listening on both
978 Mhz and 1090 Mhz (because they can).
Because of this dual frequency listening capability, the ADS-B ground stations have to decide whether they will use 978 Mhz or 1090 Mhz to uplink TIS-B/ADS-R data (including service status messages) to your G3X aircraft. Our friends who operate the ground stations tell us that the stations might be sometimes having difficulty making this decision, and it would be better if we report that we can only receive on 978 Mhz so the ground stations don't have to make this decision and will always use the 978 Mhz datalink to provide this data.
We made a change in V9.00 (for GDU 37X based systems) to allow you to configure the system to tell the ground stations that you can only listen on 978 Mhz, and this is done by telling the ground station you don't support listening on 1090 Mhz. A similar change is coming soon for G3X Touch systems in V2.80.
To implement this configuration change, simply enter configuration mode on the PFD, select the transponder page, and set ADS-B 1090ES IN to ?NOT SUPPORTED?. Those of you using a GTX 330ES transponder can make the same configuration change through the front panel.
This change DOES NOT in any way disable the ability for your GDL 39/39R to receive traffic on both 1090 Mhz and 978 Mhz, it just simplifies things for the ground station and forces it to always use 978 Mhz for the TIS-B/ADS-R datalink.
One last thing. This not a silver bullet that will magically always make your TIS-B Uplink icon show green. There will still be times when the ground stations are not providing the TIS-B/ADS-R uplink service, most often because of a lack of radar coverage or aircraft movement between radar service areas. Remember, you must be in radar coverage and one or more ground stations must be hearing your ADS-B Out before you will receive TIS-B/ADS-R datalink services.
Several of us have been flying with this change for several months and believe it does improve TIS-B services, and hope you see the same.
Let us know if you have questions.
: The FAA has communicated that this ground station issue has been corrected, so it is no longer necessary to set the "ADS-B 1090ES IN" field to NOT SUPPORTED. G3X and G3X Touch systems may now set both fields to "SUPPORTED" to correctly indicate that the GDL 39/39R is able to directly receive the signals from both types of ADS-B Out aircraft with no help from the ground stations.