But the direction is just calculated by the phase shift between an omnidirectional and a directional signal. So it can be implemented very cheaply on every plane.
It truly is 60s level wizardry.
There are some convincing reasons for being cautious on general on that front. Accidents have happened because some beacons have been substituted for the wrong location or even things like slant range being different from true range. In general ADF is so inaccurate that its protected areas are massive.
That's the last thing you want to do. Here in Europe, we're dealing with serious issues because the Russians are jamming GPS from somewhere in Kaliningrad, but unfortunately we can't respond adequately without legitimately risking WW3.
Great for listening to LW & MW(AM) radio stations in the cockpit though. Rumour has it some pilots would patch big sports games into the in-flight entertainment channels so you wouldn't miss them just because you're in the air.
When a rotating, say one turn in 10 seconds, green light is pointing north, a red light flashes.
If you see a green flash 1 second before a red flash, you're on the 36 degree radial.
The mechanical differences are quite obvious when you look at a VOR, a TACAN, and a VORTAC, but the engineering behind them is interesting.
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.
This is the crucial thing. The article says
> 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.
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.
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.
