daptive spectral nulling against nonwhite jamming was at least implicitly available in this system. Lockheed Transmitted Reference System: Of the several TR-SS systems patented, this one designed by Jim Spilker (see Figure 2.32) made it into pro- duction in time to meet a crisis in Berlin, despite the inherent weaknesses of TR systems [202]. The interesting question here is, "What circumstances could cause someone to use a TR system?" Evidently, extremely high chip rates are part of the answer. For an earlier TR patent that spent almost a quarter-century under secrecy order, see [203]. NOMAC Encrypted-Voice Communications: In 1952, Bob Fano and Bennett Basore, with the help of Bob Berg and Bob Price, constructed and briefly tested an IF model of a NOMAC-TR-FM voice system. At first sur- prised by the clarity of communication and lack of the self-noise which typ- ifies NOMAC-AM systems, Basore soon realized that SS-carrier phase noise was eliminated in the heterodyne correlation process and that SS- carrier amplitude noise was removed by the limiting frequency-discrimina- tor. Little more was done until years later when, in 1959, John Craig of Lincoln Laboratory designed an experimental SR-SS system based on low- deviation phase modulation of a voice signal onto an F9C-like noise carrier. The system provided fair quality voice with negligible distortion and an out- put SNR of about 15 dB, the ever-present noise deriving from system flaws. Simulated multipath caused problems in this low-processing-gain system, and it was postulated that Rake technology might alleviate the problem [204], [205], but the work was abandoned. NOMAC Matched Filter System: In approximately October 1951, Robert Fano performed a remarkable acoustic pulse experiment involving high time-bandwidth-product matched filters (see Figure 2.33). At that time he disclosed a multiple matched-filter communication system to his colleagues [206]. Based on Fano's research, an MF-SS teletype communication system was suggested in 1952 [207]. Research at Lin