It’s been over two weeks since I installed my ADS-B setup, and it’s been a real performer and seems to be very reliable. As I’ve pointed out, I’ve continued to tweak the setup, first with a better antenna, then by raising the antenna a bit, then with a cheap satellite preamp.
An important thing I still don’t know is the absolute amount of air traffic on any one day. ADS-B transmitters are only on a limited number of civil a/c, so it doesn’t see all the non-equipped a/c that might be flying on that particular day. I’ve never looked in any detail at commercial traffic repeatability, so I can’t say for sure if flight XYZ123 between airport A and airport B flies every day of the week. I don’t know if Monday is a busier flight day locally than is Tuesday. And with so many non-commercial airports within hearing range (KSDL, KDVT, KGEU, KFFZ, KCHD, KPAN, etc.) the number of small a/c equipped with ADS-B could change dramatically on any given day. KDVT has an especially large number of ADS-B-equipped a/c and they’re constantly flying loops around KDVT, so they provide a good number of position reports.
With all that said, when I saw the precipitous drop (34%) in location reports on the rainy day here on the 30th, I was concerned that my setup might have some issues that needed resolution. After doing a few checks, it appeared that things were nominal, so the next thing was to compare my station’s statistics with those of other stations near me. There aren’t any stations within 7 miles, but that was good enough to start as the rain was a southern-AZ-wide event, a good soaking, steady winter rain, which was over a very large area.
I took the best performing stations and a couple of typical stations for comparison. I also marked when I changed something in my setup to see if what I did actually mattered or if everyone else reflected some change that day which might indicate that my equipment changes had no particular effect.
The above graph (done in Excel) compares the JonAdams ADS-B receive site against two other solid performers (SN and DR) and two others down in the typical performance range (LY and PE). Raising the antenna (just noticed I drew it one day later than it should be) improved the performance from about 130k reports to about 150k reports. Adding the preamp was the real improvement, improving sensitivity and increasing the number of reports between 25 and 35%. I also noticed that my ultimate range improved as well. At least the preamp change to my station’s setup doesn’t correspond with significant changes in the other stations, so I’d say that the preamp was a big deal.
Another important thing, and why I started this article, was my concern over the rain having a specific deleterious effect on my station. But, it appears that the other high performers suffered very similar degradation. In my case, the drop was 34%. Comparing that to station SN, the drop there was also 34%. For station DR, the drop was 63%. For the other two typical stations, there was no particularly significant change in performance.
So, for now I will conclude that my ADS-B station has no unique problems not faced by other high performing stations. I remain interested in the cause of the drop, but have never had so much data at this particular frequency range that it’s going to take a little more Googling to figure out why and to what extent the rain should have an impact.