Today my ADS-B receive site here at the house has moved into position 291 on the FlightAware Leader Board! Just a few days ago it was at around 350.
There’s only so many a/c that can overfly my general coverage area – Scottsdale Arizona is not Amsterdam, London or Paris. Heck, it’s not even the greater NYC area with its multiple major airports and sheer number of flights. In other words, there’s only so much improvement to be had. The site will never even crack the top 100.
In my search for high-ranking sites in the general US west I found the one which I think will be the one to chase. The site is near to the top or atop Abajo Peak (elev 11,365′) in far southeastern Utah. In addition to being a whopping big mountain, Abajo is one of several major laccoliths in the Four Corners / Colorado Plateau region and the tallest thing for 44 miles. There’s even a live webcam atop Abajo.
From atop Abajo, the visible horizon is below 0 degrees in nearly every direction, with the 44-miles-away Mounts Mellenthin and Peale the only pieces of earth that just barely break 0° (0 degrees, or horizontal). Check out Abajo Peak at HeyWhatsThat.
From atop Abajo, a good receiver will capture a fair amount of the commercial traffic crossing over the western US. An aircraft at 40k ft can be over 200 miles from Abajo and still be above the zero-degree horizon. Since the actual horizon at Abajo averages about -0.5 degrees, this adds another 40 miles or so of crows-flight range. And that’s still not including atmospheric refraction and the occasional edge diffraction. Likely that the Abajo Peak site can hear out to 250 mi / 400 km for an a/c at 40k ft.
While a high site is a great thing, the potential number of a/c is limited by population center locations, flight routes, number of flights, number of non-commercial airports, etc. Abajo doesn’t have a major US hub airport next door. Flights headed from Denver to nearly anywhere in the West will pass through, as will flights from ORD to SoCal airports, PHX, and LAS. Flights from DFW headed west to any locations above about Los Angeles will as well, but not the great majority of flights to SoCal, which is a lot of airports. Pretty much any intercontinental from the NE US to the Southwest will intersect that area. There are a bunch of small civil airports in the footprint, as well.
Let’s compare Abajo’s stats to the Scottsdale site’s stats for the past two weeks (I know, that’s not much of a sample set, but that’s all I have).
|Abajo position reports||189,086||215,723||251,825||259,477||245,641||250,943||242,716||203,284||232,858||269,162||269,226||229,558||224,085||233,383|
|Scottsdale position reports||206,155||223,556||269,480||268,903||243,494||239,195||223,117||133,820||175,748||158,466||241,074||234,657||203,885||209,868|
|Abajo a/c count||1,910||1,939||2,211||2,218||2,021||2,103||2,100||1,762||2,013||2,277||2,240||1,928||1,843||1,964|
|Scottsdale a/c count||1,491||1,594||1,760||1,747||1,639||1,734||2,063||1,420||1,590||1,624||1,792||1,540||1,475||1,535|
What the above two weeks of data appears to show is that Scottsdale gets somewhere on the order of the same amount of position reports per day, but that Abajo sees a whole lot more a/c per day.
The Scottsdale best-case 30k ft+ range is to the ESE at just over 240 miles. (It may be just as good to the S, but there’s very few a/c flying down there due to the US/MX border.) However, I’d say the average 30k ft+ range is more like 150-160 mi due to the local hills and more distant mountains. In any case, that’s pretty amazing given that the antenna is 15′ off the ground and in a valley. A little of the performance is likely due to the desert climate and general lack of dense vegetation on exposed ridgelines.
I’ll keep working on improving the setup here at Scottsdale and see how the statistics line up with Abajo’s.