NR were predicted [111]. Early Spread-Spectrum Systems 2.2.2 A Note on CYTAC WHYN was one of the competitors in the development of LORAN (LOng RAnge Navigation), a competition which was eventually won by Sperry Gyroscope Company's CYTAC [112]. Developed in the early 1950s, the CYTAC system and its CYCLAN predecessor had many of the attributes of WHYN, but signal-wise, CYTAC was different in two regards. First, pulse modulation was used SO that earliest arriving skywaves could be rejected by gating, and second, phase coding of the pulses was inno- vated to reject multihop skywaves. These same properties, designed into the system and later patented by Robert Frank and Solomon Zadoff [113], were also used to discriminate between signals from different LORAN stations. The polyphase codes originally designed for CYTAC's pulse modulation were patented separately by Frank [114], but were eventually replaced in LORAN-C by biphase codes to reduce complexity [115]. A certain degree of receiver mismatching also was employed for enhancing time resolution, a similar strategem having been used for the WHYN sys- tem [109]. Since narrow-band interference was a potential problem in LORAN, the anti-interference capabilities of this pulse-compression type of signaling were appreciated and reported in 1951 [116]. To further improve performance against in-band CW interference, manually tuned notch filters were added to CYTAC in 1955, and automatic anti-CW notch filters [117], [118] were added to LORAN-C in 1964. To indicate progress, Frank notes that LORAN receivers with four automatically tunable notch filters are now on the mar- ket, some for under $1600. 2.2.3 Hush-Up In the summer of 1951, Madison Nicholson (see Figure 2.12) of Sylvania Buffalo headed a proposal effort for the study of a communication system which he called "Hush-Up." Undoubtedly, the SS ideas therein were distilled versions of those brought to Colonial radio from the WHYN project by Norman Harvey shortly before that subsidiary lost its identity and was absorbed 