Garmin GDL 88 User Guide - Page 14

2.2 Automatic Dependent Surveillance - Rebroadcast (ADS-R) Because it is not required that ADS-B In capable aircraft be able to receive ADS-B data on both the 1090 MHz and 978 MHz data links, a means to get data from one data link to the other is required. ADS-R is the rebroadcast of ADS-B data by FAA ground stations and provides this service by taking data from one link and rebroadcasting it on the other. For example, two aircraft are in the service volume for a ground station, and one transmitting on 1090 MHz and the other 978 MHz, the ground station will retransmit the data from each aircraft on the other link to ensure the two aircraft can "hear" each other. Figure 2-4 ADS-R Operation - FAA Illustration The GDL 88(D) is capable of receiving ADS-B traffic reports directly on a 1090 MHz data link in addition to traffic reports and FIS-B weather uplinks on the 978 MHz data link. This allows the GDL 88 to directly receive all ADS-B position reports from aircraft in the vicinity guaranteeing the most complete traffic picture is available to the flight crew without relying on being within ground station coverage and ADS-R to provide this complete picture. 2-4 GDL 88 ADS-B Transceiver Pilot's Guide 190-01122-03 Rev. A