Don,
I get this when I fly too low over the mountains around here...just can't get the ground antenna signal. Still get the GPS from above...
When this happens, I sometimes "lose" my "wingmen" who do not have ADSB-out, but somehow still get signals from those whe ARE equipped!
Have to admit, I do not always get consistent results, but the system is getting better and more reliable all the time.
HERE are the three indications I get the most (see below).
Mike N714AJ
PHOTO 1: TOWER IDLE
PHOTO 2: TOWER RECEIVING
PHOTO 3: TOWER OUT OF RANGE