AbstractThe principles of plasma electron cyclotron (EC) radiometry are reviewed. The aim is to lay the groundwork for discussion of new high performance electron cyclotron emission (ECE) detectors. One example is that of heterodyne arrays. Preliminary results are presented of data obtained with a novel ECE imaging system on TEXT-U based on such an array. A variety of preliminary experiments have already been performed with this system where the ultimate space and time resolutions of ECE are attained. As examples we cite average electron temperature profile measurements with 1 cm resolution, high frequency fluctuations and their vertical chord correlation, magnetohydro-dynamic mode reconstruction and magnetic island detection.