Details are provided of a new fast data acquisition system that records RF data for a complete four-strap JET ICRH antenna array with sampling rates up to 250kHz, triggered by the rapid increase in plasma Da emission intensity during an ELM. The coupling properties are deduced from the transmission line voltage amplitude and phase measured using 80dB directional couplers installed close to the antenna. Resistive and reactive components of antenna loading perturbation are reported during different types of ELMs and discharge magnetic configurations.