FlightAware Discussions

Mystery contact -thoughts and opinions?


Throwing this out to the learned and more experienced operators out here…

So I have been seeing this Mode S contact periodically and have found it puzzling- I have thought at times that it was a decoding error or bad transponder, etc. However It comes up consistently enough though that those possibilities are not very likely.

Each time it is received it is apparently only one transmission and each transmission contains a new squawk code- invariably it displays an extreme indicated altitude. At times it may adopt a new “identity” within seconds, with constant altitude and varying but somewhat consistent RSSI, other times there are no broadcasts for a minute then reappears again as a new identity. Additionally, the displayed squawk code is not in use by any other aircraft in the vicinity, so it is not random.

I would not expect an aircraft to need to switch squawk codes 264 times !

Here’s a few screen grabs


Best guess: testing of some ADS-B receiver?


@wiedehopf I suppose its possible- given the nearly constant altitude- but RSSI values do change within a range consistent with movement of some type. If I compare the RSSI to other similar signals the range would be ~60 to ~150nm or so from my receiver. Broadcasts are far too brief for any MLAT, so even if others near me were picking this up, we wouldn’t get a location fix.

I’m hoping that someone else out there sees this and checks for it as well.


Since you do a good job following this, I gave you access to my receiver webpage, so you can cross-reference. Let me know if it works.
I will be traveling next two weeks, so no access to the Pi.

Just don’t post here a screen-shoot of my house :smiley:


@SoNic67 Sent you a pm