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Many commercial demodulator boards have an inherent problem of dc offset, due to their direct down-conversion architecture. It is necessary to measure the dc offsets and to compensate for them when the demodulators are used in a system such as a digital phased array. An automated calibration station is described, which uses a combination of commercial off-the-shelf hardware and software to generate RF signals that are used to plot the demodulator I and Q circle and to determine the offset. This automated station has improvements over a manual calibration, such as ease of use, shorter calibration time, accuracy, and repeatability.
Date of Publication: Oct. 2010