I have a setup that is now working well. The receiver dongle and small antenna are on the roof, the antenna on a 10 foot mast and the receiver just below in a waterproof box. There is a 10 meter powered USB cable that connects the roof setup to the raspberry pi.
Before the original pi succumbed to lightning I was getting some pretty good results, even a few hits at 250+ miles. That was the exception, most were within about 100 miles. I am greedy, however, and want better reception. I built a coaxial collinear antenna as described by several folks, and when I put it up (same setup with a very short cable run to the receiver) my number of aircraft tracked dropped nearly in half. The little tiny included antenna was much better!
I did check the antenna as I built it, there were no shorts.
I’m trying to figure out where things went awry. I used 75 ohm impedance coax, perhaps I needed 50 ohm? I bought some LMR-400 to use and then discovered it has a center conductor much too large for building this kind of antenna.
Any advice from someone who is seeing airplanes at great distance? I’m willing to go as tall as I can before the neighbors call the zoning board, and while not a radio person I am pretty good at building stuff. This has been a fun project.