Garmin AERA 660 Pilot's Manual page 119

Because 1090 ES transponders and UATs operate on different frequencies, aircraft
not similarly equipped cannot transmit/receive data link information directly to/from
each other. Instead, operation within range of a GBT is required to receive data link
information on both frequencies.
Thus, the weather/traffic device receives traffic information directly from any ADS-B
Out aircraft within range as well as the rebroadcast of ADS-B information from any
nearby GBT. This rebroadcast is called Automatic Dependent Surveillance-Rebroadcast
(ADS-R) and is automatically triggered by the detection of an ADS-B participating
aircraft within the service volume of the GBT. The weather/traffic can receive both the
Traffic Information Service-Broadcast (TIS-B) and Flight Information Service-Broadcast
(FIS-B) provided in conjunction with ADS-R services when in range of a GBT.
FIS-B service is provided continuously, but ADS-R including TIS-B will only be
broadcast by a GBT when an ADS-B participating aircraft is within the GBT's defined
service volume. In this case, a GBT will only rebroadcast TIS-B information relative
to the ADS-B participating aircraft. Only traffic that is within 15 nm lateral
and 3,500' vertical of the ADS-B participating aircraft is provided in the
broadcast. Non-participating traffic aircraft located farther than 15 nm laterally and
3,500' vertically from the participating aircraft is are excluded from the information
transmitted by the GBT.
TIS-B traffic information includes non-participating aircraft detected by ATC
surveillance radar. As TIS-B data is derived from ATC surveillance radar data, TIS-B
traffic position updates typically occur every three to thirteen seconds. Therefore,
TIS-B traffic may be displayed with degraded positional accuracy. Aircraft
without operating transponders are invisible to TIS-B. Aircraft operating
outside of the ATC radar coverage area are also not displayed.
Since weather/traffic devices are receive-only devices, even when used onboard an
aircraft equipped with a qualifying GPS and 1090 ES transponder, a GBT may not
identify it as an ADS-B participating aircraft. The squitter of some 1090 ES transponders,
including the Garmin GTX 23ES, must be configured to communicate that the aircraft
has 978 MHz receive capability in order to be identified as an ADS-B participating
aircraft.
190-02017-20 Rev. A Garmin aera 660 Pilot's Guide
Hazard Avoidance
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