Systematic measurements of the frequency and damping rate of stable n=0-2 modes in the Alfvén frequency range are obtained on the JET tokamak in various plasma operating regimes. The JET saddle coils are used as external antennas to drive and detect stable AEs. The diagnostic technique uses repetitive sweeps of the driving frequency in a pre-defined range [1,2], controlled in real-time. The plasma response is extracted from background noise using synchronous detection, and is used to identify in real-time the resonance corresponding to a global mode. When a resonance is found, the real-time controller locks to that frequency and tracks the mode.