First, I’d like to provide some context for the situation:
My main feeder is running instances of both Piaware11 and ADSBExchange. My system is located 11 meters above ground level, and we are currently experiencing a tropospheric ducting phenomenon.
I will attach a link to a screen recording so you can see it with your own eyes.
The strange thing is this: I receive messages from an aircraft on SkyAware (in the video’s case, TAP009). It displays all the standard information, except for the distance value in miles.
Meanwhile, the same aircraft appears on the ADSB Exchange global map with practically the same information shown in the SkyAware table (but in this case, the aircraft is actually plotted on the map).
Why does this happen?
I believe the default max range setting in dump1090-fa is 360 nm and any aircraft reporting a location beyond that is deemed unreliable and not plotted. Someone can correct me if I have that wrong.
I set my system to a higher value, not because I have super range or ducting, but Russian aircraft that engage in GPS spoofing now & then. I like to see all the crazy places where they pretend themselves to be.
Regarding the specific aircraft in the video: the distance between it and my station at that moment was approximately 800 km (400 NM). I had increased the maximum range in the PiAware configuration file, but that didn’t solve the issue. The same thing happened with other flights yesterday. I’m wondering why the aircraft’s location is being discarded—assuming that is indeed what’s happening—to the point where it shows up as “Other” rather than “ADS-B” in the SkyAware table. The tropospheric duct simply guided the electromagnetic waves to my antenna.
Having increased the max range value, I would have thought that would work for you. I have no further ideas except to check the running systemd service for dump1090-fa to ensure it shows the max range value you entered. Maybe the change did not get picked up for some reason and dump1090-fa needs a restart. Good luck.
I have not looked at your uploaded file, but based on your description, here’s what I think is happening.
Just because an aircraft is full ads-b (with position) does not mean that your local receiver has received enough messages of the correct type to determine lat/lon and display a position. Without that position, you also have no displayed distance. That would also explain the “other” category you mentioned, because the aircraft is still essentially mode-s for you. Your system is not discarding a known position, it just doesn’t have a position yet, or doesn’t have a position that it trusts yet.
This happens all the time, not just during tropo ducting. Ads-b aircraft at your extreme range, and lower altitudes at all ranges are usually picked up with just a few messages. Online sites will show a position, but you have not received a position yourself yet, and might not ever receive a position.
Extreme range is even trickier. Using just one single DF17 odd or even CPR message, you could get a position using local decoding. However, at extreme range, that position would almost certainly be wrong. It takes a good odd/even pair of messages being received within a reasonably short time to get a reliable position. At extreme range, that might never happen.
Don’t just wait for tropo. Take a good look at your normal traffic and you will spot many aircraft that pass right at the edge of your max range. This also happens in closer at lower altitudes, but that might not be as obvious.
Some software allows you to change the settings for local/global odd/even CPR decoding. I’m not sure if the FA view you are using allows that or not. I rarely view my traffic directly within FA.
Thanks for the comment. However, ADSB Exchange was using data from my receiver and plotting the aircraft’s position on the global map. In SkyAware, the same aircraft appears with all information populated, except for the position. That’s the strange part.
