I’ve been using FlightAware for about 3 weeks now (user name Weiliwen), using their cheapo little antenna attached to my Raspberry Pi 4. It works great. I live near both O’Hare and Chicago Executive Airport, so get a good number of hits. It’s a lot of fun to see where planes are coming from and going to, and especially cool to see planes with unusual features - going very fast, or no flight plan noted, etc.
I do occasionally see something strange and wonder if the collective wisdom on this site can help explain. Occasionally, I actually pick up signals from airplanes that are still taxiing on the runways of both of these airports. It’s not common, but I have seen it happen twice this week. Again, I’m using the cheapest of antennas perched on a windowsill outside of my home.
Does Anybody else see this? Does anybody else have an explanation? Thanks!
Depending on where you are located in regards to the airports that is something that is quite common.
I live 7.5 NM from EHAM and I have ground traffic all the time, 2-3 aircraft and even sometimes more depending on the traffic.
As soon as the aircraft switches the transponder on I will recieve it.
This will remain until the aicraft is out of sight or when the transponder is shut down.
If you have some good line of sight or maybe some favourable transmission condtions in the atmosphere this can be something common.
Both O’Hare and Chicago Exec have ground mounted towers that also rebroadcast some traffic on 1090 MHz, so it is entirely possibly that you might be seeing some of that also.
If you are using a local web based SkyAware, just go to “Select Columns” and enable the Data Source option. Rebroadcast traffic (from the towers, not the planes) will appear as either TIS-B or ADS-R. You can do an online search for those two terms for good info if you are curious.
Your normal traffic direct from the planes will be ADS-B (broadcasting position), MODE-S (without position) and MLAT, which uses multiple receivers to determine position. Mode-a/c only is a completely different story.
Those rebroadcast towers are scattered around the country. Some are at airports, but many are not. They receive data that is fed in to the FAA networks, and also rebroadcast data on both 1090 MHz and 978 MHz. The 978 broadcast even includes weather and other info, but other software is needed to decode that.
The link below might have dated info, but it is the best source I know of for these towers. It shows the Chicago Exec tower nicely. The O’Hare location actually plots on the control tower. My local one here looks like the typical communications tower next to the very typical cell tower. You would never expect it is FAA related.
I live about 6nm from KMKC, and about 200ft above it. Even though there is a hill between me and the airport, I nearly have a line-of-sight to it that, under the right conditions, gives me an excellent view of the airport. This is especially the case in the fall and winter after the leaves have fallen (like now).
The other day I was picking up three aircraft on the ground simultaneously (taxi speeds of 12, 16, and 17kts when I looked at them). So it’s not uncommon.
From the map @MC130E provided, it looks like there’s one at KCMI, but I don’t pick up those signals even though the airport is about 8nm away – although from that map it looks to be north of Dearborn, so .
The 1090 rebroadcast is not constant. It only happens when an aircraft reports that it is equipped to receive it. Then the traffic usually appears in clusters near that supported traffic.
The ADS-R traffic will appear with a real mode-s code hex.
The TIS-B will appear with a pseudo hex. From a very old 2015 document here, the code for Kansas City used to identify those TIS-B traffic with a hex starting with 294xxx, but that might have changed. That old document shows my local Jacksonville TIS-B starting with 290xxx, but I now see multiple codes starting with 29xxxx. The TIS-B pseudo hex can be things like a mode-a/c only aircraft with radar position, and the occasional otherwise blocked mode-s aircraft with either radar or FAA mlat position.
The towers are designed for aircraft reception, so their ground range is fairly limited. Mine is about 3 nm away.
It just occurred to me that you can check HeyWhat’sThat for your visible horizon, not just the “up in the air” stuff. That means you can see if you have visibility at or near one of your local airports.
Although I’m sure trees and buildings obscure the actual line of sight, I really do have partial visibility from my antenna directly onto the KMCK ramp. So as I improve my system performance and eventually raise the antenna another 8-10 feet, I should see even more ramp traffic at that airport.
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