I regularly seem to have on my dump1090 output a large number of aircraft without positions after MLAT.
Right now i’m seeing 218 aircraft, with 154 positions.
I know there will be a few that won’t mlat. I see a TEST1234 at various altitudes, and traffic on the ground at dulles which there may not be other receivers for. But 50+ seems like there might be something i can do to make that smaller?
Looking at your stats page to see where you are, then looking at the map page showing all feeders worldwide and zooming into your area shows that there are not many Pi-Aware feeders to the South West of your location - there are flocks of them in other directions. Those of us who took part in Objs initial trial in the UK will have noticed that there is quite a rapid fall off in detection of MLAT flights in a direction where there are few effective feeders (as little as 40 - 50 miles)
This why it is important to get an antenna in the best position to collect lots of signal, above roof level is best so the signal is not attenuated by whatever covers the roof - not so much to increase cover in the immediate area, but so that MLAT planes are detected by the 4 minimum required receivers where receivers are sparse.