Re: Are they saying the transmitter can be fingerprinted?
"And the fingerprint is unique to a single transmitter - somehow. Components in the radio set itself? Combination with aerial tuning?"
All of the above, presumably. The idea doesn't sound particularly surprising really. Nothing is perfect, so every transmitter is going to have slightly different characteristics in terms of noise and so on. The only question is how practical it is to distinguish them in a real world with weak signals and all kinds of other noise around.
"You'd still need a history database of squawks vs fingerprints"
This seems to be the main problem with the idea. Assuming you can get a good enough signal for the fingerprinting to work, it doesn't actually tell you what is transmitting, it only allows you to identify unique transmitters. So unless you've previously identified what the transmitter is attached to and suddenly it starts claiming to be something else, you don't gain anything much of use.
It also ties in to the above point. Since the fingerprint is characteristic of the whole transmitting system, it would be trivial to change it. You don't need to do things like swapping transponders between different planes as others have suggested, simply changing the length of a single wire would likely be enough to produce a completely new fingerprint. Swap a card, alter a voltage slightly, knock the antenna with a hammer... almost anything is going to change how noise and other factors vary.
So it's kind of a neat idea, and relatively impressive if it can actually be made to work at all in the real world. But it seems to be of fairly little use in pratical terms, and likely trivial to work around if it actually did start being used.
Biting the hand that feeds IT
