He set up his receiver near the VOR, though. So he doesn't get any useful distance info from it. He can hear the aircraft's query and the fixed station's reply, but near the DME station, the difference will be constant, just the fixed delay.
The next step is to put the receiver far from the DME station. Then, the time delay measured will indicate the aircraft to DME station distance minus the aircraft to receiver distance. I think this lets you locate the aircraft somewhere on a hyperbola, similar to the way GPS and LORAN work off time differences. If you have two receivers at different locations, you should be able to get two hyperbolas and locate the aircraft.
This is really a 3D problem, because altitude. So you get quadric surfaces and need 3 receivers. Preferably four, because there are multiple solutions. Two is enough to get a rough aircraft location for test purposes.
This has potential as a ground backup for ADS-B. ADS-B tells you where the aircraft nav system thinks it is. This is telling you where it really is, if it's using a VOR/DME at the moment.
> The pilot will usually tune the radios to the stations that are part of the procedure that the aircraft is flying (although the pilot is free to tune to other stations as a cross check), so the kind of aircraft that we expect to see in the recording are those operating on the Madrid Barajas airport, not those flying high en route.
The article author has it right. Nowadays most aircraft are using GPS to navigate, and only use DME if on a specific approach procedure that requires it. In practice, this has far narrower scope than ADS-B.
Another commenter has it right - if instead of an experiment you actually want to locate aircraft without (or not) using ADS-B, you're far better off doing MLAT on Mode S, though you do need multiple spatially separated receivers for that. Aircraft are far more likely to have a Mode S transponder and have it switched on than they are to be using DME on the frequency you choose to monitor.
Even if an approach uses DME, depending on the aircraft or company operating procedures they still may not be using DME, because GPS is a valid substitute for DME in an approach and more convenient if you’re already otherwise using GPS RNAV.
In fact it’s quite common to shoot approaches that have DME specified fixes in an aircraft that doesn’t even have a DME transceiver.
We already do something vaguely similar with MLAT, measuring the time delay from transponder signals at different receiver sites.
MLAT data can be used for either unofficial situational awareness in non-radar facilities (to display non-ADS-B aircraft), and in some limited cases can be fed directly into official radar displays when running in sensor fusion mode.
He set up his receiver near the VOR, though. So he doesn't get any useful distance info from it. He can hear the aircraft's query and the fixed station's reply, but near the DME station, the difference will be constant, just the fixed delay.
The next step is to put the receiver far from the DME station. Then, the time delay measured will indicate the aircraft to DME station distance minus the aircraft to receiver distance. I think this lets you locate the aircraft somewhere on a hyperbola, similar to the way GPS and LORAN work off time differences. If you have two receivers at different locations, you should be able to get two hyperbolas and locate the aircraft.
This is really a 3D problem, because altitude. So you get quadric surfaces and need 3 receivers. Preferably four, because there are multiple solutions. Two is enough to get a rough aircraft location for test purposes.
This has potential as a ground backup for ADS-B. ADS-B tells you where the aircraft nav system thinks it is. This is telling you where it really is, if it's using a VOR/DME at the moment.
But not who it is. That's not in the DME poll.