figuration, which spanned the 1953-1959 time frame, was carried out in cooperation with the Coles Signal Laboratory at Ft. Monmouth, in particu- lar with the aid of Harold F. Meyer, Chief of the Long Range Radio Branch, and Bernard Goldberg, Chief of the Advanced Development Section, and also Lloyd Manamon and Capt. H. A. ("Judd") Schulke, all of that labora- tory. This effect had the whole-hearted support of Lt. Genl. James D. O'Connell, then Chief Signal Officer of the U.S. Army. Paul Green remained at Lincoln Lab after completing his thesis, and was placed in charge of building and testing F9C equipment. Included in the group of engineers contributing to the development of the F9C were Bob Berg, Bill Bergman, John Craig, Ben Eisenstadt, Phil Fleck, Bill McLaughlin, Bob Price, Bill Smith, George Turin, and Charles Wagner (originator of the Wagner "code," the simplest version of the Viterbi algorithm). The F9C system [141] occupied 10 kHz of bandwidth and originally employed frequency-shift data modulation at a rate of approximately 22 Early Spread-Spectrum Systems 200 kc CRYSTAL OSCILLATOR DRIVER UNIT SCALE- SCALE- SCALE- OF -129 OF-128 OF-127 COMMUTATOR COMMUTATOR COMMUTATOR 12345 12345 $2345 RESONATORS OUTPUT Figure 2.21. The boxes in the above diagram of Paul Green's SS signal generator are located SO that they correspond to the physical layout in the equipment racks of Figure 2.20. An SS signal generator similar to the one shown here, combining waveforms of relatively prime periods, was chosen for the F9C system. (Redrawn from [139].) The Historical Origins of Spread-Spectrum Communications ms/bit. This resulted in a multiplicity factor greater than 200. The F9C radioteletype system was intended for long-range fixed-plant usage over HF channels. Initially, SS signal generation was accomplished by combining the 28 outputs of four 7-stage counters (fixed to have periods 117, 121, 125, and 128) using an array of AND gates, and driving a bandpass filter with the resultant pulse train. For security against jammi