I think I can answer my own question - I get a bunch of planes with NO Lat/Long data ... only planes with Lat/Long data actually display. So my question is - why wouldn't these other planes be broadcasting Lat/Long ?
I think the answer is that you are getting Mode-C transponder packets and not ADS-B packets from those airplanes. Almost all of my airplanes without Lat/Long do have an altitude and a squawk code that is being reported which looks like what a Mode-C transpoder would be sending out. I have noticed that all of the international flights in my area seem to have ADS-B. It is just a guess...
Watching Planes on Windows
in SDR - Software Defined Radio
Posted
I think the answer is that you are getting Mode-C transponder packets and not ADS-B packets from those airplanes. Almost all of my airplanes without Lat/Long do have an altitude and a squawk code that is being reported which looks like what a Mode-C transpoder would be sending out. I have noticed that all of the international flights in my area seem to have ADS-B. It is just a guess...