by Zach Grant L1011jock » Fri Sep 26, 2014 8:51 pm
Just a couple of things about ADS-B. When it comes to the weather broadcast, it is a blanket broadcast that anyone with a 978 receiver and appropriate means of display, who is listening in range of an ADS-B tower,will get. Traffic on the other hand is a different animal. Traffic can come in in several different ways. If you are in the vicinity of an ADS-B equipped aircraft, you will see the direct broadcast from the aircraft, IF you have or someone in your area have an ADS-B system that interrogates it on the 978 frequency, or an ATC radar or TCAS interrogates on the 1090 frequency. This can come from either 978 or 1090ES equipped aircraft, but not Mode C or S only equipped aircraft. If the ADS-B in/out equipped aircraft is in range of an ADS-B tower, then any traffic that the ATC radar sees in the area of that aircraft will be up linked. This includes any traffic that has a transponder regardless of type. Those using the "listen only" receivers without having an ADSB out source in the aircraft will not trip the uplink and thus will not see the tower transmitted traffic unless there is an out equipped aircraft within plus or minus 1800' and within 15 miles. The GDL88 hears both frequencies, but only tea mitts on 978 so it does not qualify for the high altitude mandate that piggy backs on the TCAS technology of aircraft to aircraft datalink with no ground station.
Zach
"Keep it above 5 feet and don't do nuthin dumb!"