> I'd set it up very near the airport but not on it
The problem is, you need to have a good height for the antenna - "height is might" in radio, particularly above VHF bands. I actually can see this with my own ADS-B receiver - I'm in a valley and precisely can see that effect when plotting received packets.
I get good distance from my ground level antenna, but while I'm in a valley, it's very wide and long. My assumption is that most airports are going to be in fairly flat areas.
The problem is, you need to have a good height for the antenna - "height is might" in radio, particularly above VHF bands. I actually can see this with my own ADS-B receiver - I'm in a valley and precisely can see that effect when plotting received packets.