r band-spreading probably was employed, since 1950s technology could not reliably support higher-speed m-sequence generators. CORREL ATION SIGNAL MIXER DETECTOR AMPLIFIER AND OUTPUT PULSED AMPLITUDE AMPLIFIER DETECTOR OSCILLATOR BALANCED 0.2usec MODULATOR DETECTOR PULSE DISPERSAL GENERATOR PATTERN GENERATOR OSCILLATOR Dr t 0.1 usec (30°) f<lmc (Imc-Ikc) DISABLE CLOCK REACTANCE I m c MODULATOR Figure 2.13(b). The receiver's T-dither tracker is built around a correlator which compares a locally generated replica of the transmitted car- rier to the received signal. Superimposed on the 1 MHz clock driving the carrier dispersal pattern generator is a sinusoidal phase variation con- trolled by the oscillator, which in turn produces a corresponding oscillation of the correlator's output amplitude. The phase of this amplitude oscillation, relative to that of the oscillator, provides an error signal for clock correction. (Both digrams are abstracted from [119].) The Historical Origins of Spread-Spectrum Communications be abandoned in favor of an FH-SS system. In 1957, a demonstration of the breadboard system, operating between Buffalo, NY, and Mountain View, CA, was given to a multiservice group of communications users. Vincent Oxley was system engineer on this development, as well as for the follow-on effort in 1958 to produce a packaged prototype. The original breadboard contained only an FH-SS/FSK anti-jam mode. The system achieved its protection ratio (Sylvania's then current name for processing gain) by using the code generator to select two new frequencies for each baud, the final choice of frequency being dictated by the data bit to be transmitted. To be effective, a jammer would have to place its power on the other (unused) frequency, or as an alternative, to place its power uni- formly over all potentially usable frequencies. Because of the possibility that a jammer might put significant power at the unused frequency, or that the selected channel frequency might be in a fade, a (15,5) error-correcting code was de