@fk9 My experience agrees with your suggestion - I have a cell tower about 1000 feet directly east in line of sight. Without a filter, my aircraft and position numbers were very poor and short distance (less than 75nm) looking east. I replaced the dongle with a FlightAware ProPlus stick (the blue one with the filter) and all the counts and distance improved dramatically, getting consistent numerous contacts out to 200nm. The Raspberry Pi, software, cable, antenna remained the same. See maps in my update at QUICK SPIDER - No Soldering, No Connector - #9 by AhrBee
