radio communications. The production version ofNOMAC, named the F9C, generated a pseudonoise (PN) sequence at the receiving terminal in synchronism with the PN modulation ofthe transmitted signal. The F9C achieved as much as 17 dB ofjamming protection. Obtaining an additional 6 dB ofprotection (the original NOMAC design had promised 23 dB) required addressing the effects ofmultipath propagation. Lincoln Laboratory solved the multipath problem by adding a Rake receiver to the NOMAC system. The Rake receiver synthesized an adaptive matched filter corresponding to the collection oflinear propagation paths that produced the actual received signal. The insights that led to Rake ultimately found application to sonar problems, the analysis ofseismic signals, the radar mapping ofthe moon and nearby planets, and the radar imaging oforbiting satellites. T HE YEAR 1991 marked the 40th anniversary of the formal organization ofMIT Lincoln Laboratory
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