LOW RF CONTROL FEEDBACK AND IQ VECTOR MODULATOR COMPENSATION FUNCTIONS.

I-Q vector modulator is key element of the gun and linac RF control circuits at Accelerator Test Facility at Brookhaven National Laboratory. I-Q modulator calibration procedure was developed to find proper compensation functions in the conversion algorithm to minimize phase-amplitude coupling and setting-reading errors: rms(Aset - Aread )= 0.03dB, rms(set - read) = 0.3 deg. Since stabilization of the RF phase and amplitude is become critical for many experiments the slow feedback was developed and applied as well to significantly compensate drifts in RF system. I-Q VECTOR MODULATOR BNL ATF use digital I-Q vector modulator (7122 series of General Microwave [1]) in low RF gun and linac control circuits. Power and phase set points cover operational range of 20 dB and 360 degree with well known accuracy. The goal of this work was upgrade I-Q modulator software control to minimize set-read error by new compensation functions. Accuracy of new control is mostly defined by temperature during calibration technique at switching power points and environmental conditions.