My guess ....
.... would be that this technique relies on the fact that the components within the transponder sub-system for each aircraft are unique in that the components will always have tiny variances to other 'identical' components, and that the technique is identifying the tiny variations that these components generate.
My first thought would be that any change of any component in the transponder sub-system would cause the 'signature' to change.
The next thought would be that the variance in components in your 'detector' might be enough that the signatures learnt on one system might not transfer to other 'duplicate' sytems. So it might just be necessary to teach each detector separately.
Biting the hand that feeds IT
