I just got a new AirSpy SDR, and wanted an improved antenna for receiving 1090 MHz ADS-B aircraft transponder signals. Previously I used a regular VHF/UHF discone antenna, which is mounted on the roof of the house. It worked OK, but not great. I built various specialized ADS-B antennas, such as small ground plane and colinear antennas, but none produced great results. They were all mounted inside the shack, and that was the problem, a lack of height.
I considered putting up a mast, but that was going to be a lot of work and expense. I've got a lot of trees in the yard that I use for HF antennas, certainly I could find a way to make one work for this application. All my HF antennas are hung via ropes shot over tree limbs. This works fine for dipoles, etc, but with a VHF/UHF antenna you want height, as well as being in the clear, away from branches and leaves that can cause significant attenuation at 1090 MHz.
I then hit upon the idea of finding a way to pivot the antenna up above the branch that the rope is over. I attached the antenna to the end of 20 ft of plastic conduit. The coax runs down the center of the conduit. The rope is attached about one third from what will be the top end of the conduit when it is hanging from the tree. The weight of the lower 2/3 of the conduit, plus the coax, pivots the conduit so it is nearly vertical. This allows it to mostly clear the tree limb. It's not completely above the entire tree, but it is over most of it. And it is about twice as high as the existing discone. The result is significantly further range and a higher decode rate. Before I was lucky to get 100 nautical miles, now I get 200 nautical miles. I am getting a peak decode rate of about 1000 frames per second, not bad for a Saturday afternoon. Can't wait to try it on a weekday.
Some photos, the red arrow points to the antenna, which is a small ground plane antenna I threw together in about ten minutes. Just a 2.75" wire mounted on an F connector, which is on a paint can lid as the ground plane. Next I will try making an improved antenna. I also have a discone antenna on order. I have a pre-amp mounted right at the antenna, to amplify the signal before the 100 ft coax run. None of this is weather proof right now, it is more of an experiment.