Tests of direct-sampling coherent detection with a laboratory analog-to-digital converter

Phase accuracy and simplicity advantages of a direct-sampling coherent detection (DCD) system were demonstrated by computer simulation in earlier correspondence. This correspondence reviews the DCD approach and reports the results of experiments involving digitized samples of analog signals taken by a high-quality, off-the-shelf A/D converter. IF signals near 10, 20, and 30 MHz were sampled at 5 MHz resulting in rms DCD phase errors generally below 0.5 deg compared with errors less than 0.2 deg computed in the earlier simulations.