I have a pretty good location between LAX and SAN (with lots of other airports too) and the traffic from the north dominates my receiver with omni antenna. I took note of the positions from my receiver that make it into Flightaware.com and they tend to be out in the desert to the east and south where there are no FA receivers.
I put up two new receivers with directional antennas, one pointing east and one pointing south. Sure enough, suppressing the interfering signals from the north gets better range and turns dotted tracks into solid lines.
Right now the three receivers are running as separate sites even though they are collocated.
I would like to combine the feeds and filter the duplicates. The ultimate would be to have all three receivers plugged into a single pi3, but that’s just a nice-to-have.
I realize that having antennas physically separated would impact MLAT, so the sector antennas must be close together. Mine are mounted on the same mast.
I found a dump1090 discussion where the messages from a secondary pi were read by a primary pi and netcat used to send as a combined stream, but no mention was made of filtering duplicates.