UBC Theses and Dissertations
A multi-level digital correlation spectrometer Whyte, Don Andrew
The design of a 256-channel cross-correlation spectrometer is described, which is to be used in the study of line-spectra in radio astronomy at the Dominion Radio Astrophysical Observatory, near Penticton, British Columbia. The correlator is a dual instrument, providing 128 channels for the determination of each of the Co- and Quadrature-spectra of the signals from two paraboloidal antennas, over a bandwidth ranging from 1/4 MHz to 8 MHz. Digital circuitry is used, for the long-range stability and freedom from drifts that it provides. The instrument employs a unique design of a simple digital multiplication and accumulation circuit, which minimizes the cost of implementing multi-level digitizing. One signal is quantized in three-levels, the other in five levels. This produces a degradation in the signal-to-noise of the cross-correlation coefficients, over that obtained in an analog correlator, by a factor of 1.16. Previous digital correlators of wide bandwidth have employed one-bit quantization, with a degradation factor of 1.57. The cross-correlation products in each channel are accumulated in fourteen-stage counters. Extended accumulation is provided by a 4,096-bit circulating glass memory. The coefficients are periodically transferred to a PDP-9 computer, where a fast Fourier transform is performed to yield the complex cross-spectrum. The design of the analog-to-digital, arithmetic, timing, pulse distribution, and control circuitry is described in this thesis.
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