  A two channel oblique electron cyclotron emission (ECE) radiometer was
installed on the DIII-D tokamak and interfaced to 4 gyrotrons. Oblique ECE was
used to toroidally and radially localize rotating magnetic islands and so
assist their electron cyclotron current drive (ECCD) stabilization. In
particular, after manipulations operated by the interfacing analogue circuit,
the oblique ECE signals directly modulated the current drive in synch with the
island rotation and in phase with the island O-point, for a more efficient
stabilization. Apart from the different toroidal location, the diagnostic view
is identical to the ECCD launch direction,which greatly simplified the
real-time use of the signals. In fact, a simple toroidal extrapolation was
sufficient to lock the modulation to the O-point phase. This was accomplished
by a specially designed phase shifter of nearly flat response over the 1-7kHz
range. Moreover, correlation analysis of two channels slightly above and below
the ECCD frequency allowed checking the radial alignment to the island, based
on the fact that for satisfactory alignment the two signals are out of phase.
