en the RF oscillator and the code chip clock, these two signals were generated independently in the transmitter. The receiver's PLL bandwidth was constrained by the fact that no frequency search was scheduled in the synchronization procedure; the assumption being that the pull-in range of the PLL was adequate to overcome both The Historical Origins of Spread-Spectrum Communications oscillator drifts and Doppler effects. Being a push-to-talk voice system which could operate either as a conventional AM radio or in an SS mode, a 5 S sync delay was encountered each time the SS modem was activated. Ranging up to 300 miles was possible with the measurement time taking about 40 S. To retain LPI capability in this AJ system, transmitter power was adjustable from minute fractions of a watt up to 100 W. Testing of the Magnavox ARC-50 began in 1959. Bob Dixon, joined by John G. Smith and Larry Murphy of Fort Wayne, put the ARC-50 through preliminary trials at WPAFB, and later moved on to the Verona site at RADC. One radio was installed in a C131 aircraft and the other end of the link resided in a ground station along with a 10 kW, CW jammer (the FRT- 49). Testing consisted of flying the aircraft in the beam of the jammer's 18 dB antenna while operating the ARC-50. Limited results in this partially con- trolled environment indicated that the receiver could synchronize at jam- mer-to-noise ratios near those predicted by theory. Shortly after these flight tests, an upgraded version of the ARC-50 was developed with significantly improved characteristics. To alleviate SS-code correlation problems, a new design was adopted, including an m-sequence combining procedure developed by Bob Gold [189], [190] which guaranteed low SS-code cross correlations for CDMA operation. The SS sync delay was Figure 2.28(a). Examples of early- and mid-1960s technoogy. (a) SS code genera- tor portion of a TH system developed by Brown, Boveri, and Company for surface- to-air missile guidance. (Photo courtesy of I. Wigdorovits of Brown, Boveri, and Co.