An interesting thing from reading about practical experiments in EM eavesdropping is that it's not just the obvious emanations that you have to worry about. Your sidechannels have sidechannels. In that paper, for example, the actual communication radiates and can be received in the shortwave band, but also a frequency-modulated version of it appears in the FM radio band. Presumably a bit of power-supply droop is modulating a local oscillator causing it to transmit a clear signal.
An interesting thing from reading about practical experiments in EM eavesdropping is that it's not just the obvious emanations that you have to worry about. Your sidechannels have sidechannels. In that paper, for example, the actual communication radiates and can be received in the shortwave band, but also a frequency-modulated version of it appears in the FM radio band. Presumably a bit of power-supply droop is modulating a local oscillator causing it to transmit a clear signal.