ng, the gate array connec- tions were controlled by changeable punched cards and this served the role of a key for the system. At the time, there were discussions concerning the possibility of making the SS signal provide cryptographic security as well, but this idea was eventually dropped in favor of conventional data encryp- tion before modulation. Both the SS signal generator and data modulation technique were later modified to improve spectral and correlation characteristics and change the SS signal period, thereby increasing AJ and privacy capabilities [142]. (For a discussion of the effects encountered in combining sequences of different periods, see [143]-[145].) Also, in a 1955 secret report [226], Price proposed improving DS-SS by resorting to error correction coding in combination with soft or hard decisions against CW or pulse jammers. this first conceptual- ization of error correction in an AJ strategy was not implemented in the F9C system. At the suggestion of Signal Corps Capt. John Wozencraft, the bandpass filter in Basore's bandpass correlator was replaced by an active filter [146] employing a diode-quenched high-Q L-C tank circuit, thereby attaining true IF integrate-and-dump correlation operation. A different circuit achieving the same matched-filter-type improvement on sinusoids was developed independently by M. L. Doelz for the Collins Radio Company [147]. Synchronization of the SS signal was accomplished initially by sending a tone burst at a preagreed frequency to start the four 7-stage counters in near synchronism. A fine search then began to bring the receiver's SS modula- tion clock into precise alignment with the received modulation. When syn- chronism was achieved, a tracking loop was closed to maintain sync. The fine search was conducted at a rate of 1000 S for each second of relative delay being swept. The frequency standards used in the system were stable enough that even with propagation variations, a disablement of the tracking loop for a day would cause a desynchronization of at m