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Laboratory Experiments to Investigate Effects and Causes of Doppler Spreading in Heterodyne Correlators.
NAVY ELECTRONICS LAB SAN DIEGO CA
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It was found that there was a 6 db correlation loss at the lower sample rate 200 Hz compared with the two higher sample rates 400 Hz and 800 Hz when processing a zero doppler 100 Hz bandwidth PN signal. An investigation showed that at the 200 Hz sample rate, the correlator output was divided nearly equally between two comb-filter teeth which were located a distance of two teeth on either side of the zero doppler tooth. This frequency splitting was not observed at the higher sample rates. The cause of this problem was traced to slight frequency errors in the correlators heterodyne oscillators. When the oscillators were replaced with precise frequency sources, the problem disappeared.
APPROVED FOR PUBLIC RELEASE