A digital correlation spectrometer employing multiple-level quantization

The correlation of quantized signals yields a lower signal-to-noise ratio than analog correlation by a factor D. The dependence of D on number and spacing of quantization levels, and on quantization rate is shown. A digital cross correlator is described which multiplies the signals from two antennas of a synthesis telescope. One signal is quantized into 5 levels and the other into 3 levels. D = 1.16, a significant improvement over a 2-level correlator where D = 1.57, with little increase in complexity. The complex cross-correlation function of the input signals is generated for 125 delay values, with overall bandwidths of 0.25-8 MHz. Special channels of the correlator monitor signal power and quantizer performance.