A Novel automatic level control for gain stabilization in a radio interferometry

An automatic level control (ALC) procedure is designed to stabilize the gain drift in the Array for Microwave Background Anisotropy (AMiBA) caused by the diurnal temperature change. We make use of a feedback proportional-integral-derivative (PID) control approach to maintain the optimal sensitivity in the AMiBA radio telescope for detecting the extremely faint variations in the cosmic microwave background. A typical ALC commonly used in radio telescope works by injecting a known noise source into the receiver periodically. From there, observers can tune a variable device to match the desired level. This approach requires a lot of hardware, resulting in higher costs and making the system more complicated. Our proposed ALC procedure will make use of a mathematic model to derive the signal level of each receiver channel. The 7-elements AMiBA interferometric array generates a total of twenty-one sets of correlated data during any instance of observation. Utilizing this set of overly constrained data, we have devised two online conversion formulae to derive the signal levels from each individual receiver element. Subsequently, the derived data set is fed back into the PID control program embedded in a Linux computer, after which the output from the PID will be fed to the variable gain amplifiers(VGA) for the second stage of gain control. This report will expound on the details of the work and the methodology employed, also preliminary result of one of the methods is presented.