Garmin 695 Manuale Utente

190-00919-00  Rev. G

154

to the capability to both send and receive ADS-B information.  Aircraft lacking either 
ADS-In, ADS-B Out, or both ADS-B capabilities may also be referred to as ADS-B non-
participating aircraft.

Currently, rule-compliant ADS-B Out capability in the United States requires a 

TSO’ed SBAS-enabled GPS, such as a Garmin GPS 400W or similar, and one of two 
possible data links: 1090 ES transponder or a 978 MHz UAT.  Either data link system 
is capable of transmitting the aircraft’s position, velocity, identification, and other 
information every second to compatible aircraft and ground stations called Ground 
Based Transceivers (GBTs). 

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.  The GDL 39 is unique in its ADS-B In capability since 
it can receive data link information from both 1090 ES transponders and UATs.  

Thus, the GDL 39 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.  As a 978 MHz (UAT frequency) receiver, the GDL 39 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,