ombining tech- niques [152], and Turin's multipath studies [153], the Rake receiver could in turn be viewed as a predecessor of adaptive equalizers [154]. The Rake processor [155]-[157] (patented at Davenport's prompting) is adaptive in the sense that the weight on each MARK-SPACE tap pair is determined by the outputs of that MARK-SPACE tap pair, averaged over a multipath stabil- ity time constant. (See Figure 2.24.) In its ultimate form, the magnetostric- tive tapped delay line (patented by Nicholson [158]), around which the processor was built, contained fifty taps spanning 4.9 ms, the spacing being the reciprocal of the NOMAC signal bandwidth. In addition to solving the multipath dilemma and thereby securing the full 23 dB of potential processing gain, Rake also allowed the sync search rate to be increased SO that only 25 S were necessary to view one second of delay IDENTICAL NOISE - LIKE Early SIGNALS CONVERTER SUPER- AND POWER METERODYNE AMPLIFIER RECEIVER Signatures BANDPASS BANDPASS BALANCED SIDEBAND NOISE MIXER NOISE MIXER FILTER CIRCUITS SOURCE SOURCE fc=150 kcps fc 130 kcps fc=150 kcps W = 12.7 kcps W = 10 kcps W = 10 kcps AVERAGING AVERAGING OSCILLATOR OSCILLATOR FILTER FILTER 19,908 cps 20,092 cps 19,908 cps 20,092 cps TELETYPE COMPARISON TELETYPE DISTRIBUTOR DEVICE PRINTER Figure 2.23(a). Original F9C block diagram with FSK data modulation. (Redrawn from [141], [142].) DIGITAL CONVERTER SUPER- NOISE AND POWER HETERODYNE CIRCUITS AMPLIFIER RECEIVER SPACE FILTER AND BALANCED SIDEBAND FILTER AND MIXER MIXER COMPLEMENT LIMITER MIXER FILTER LIMITER SPACE FILTER AND DIGITAL COMPLEMENT NOISE LIMITER CIRCUITS TELETYPE OSCILLATOR INPUT CIRCUITS SPACE AVERAGING AVERAGING FILTER FILTER COMPARISON TELETYPE SAMPLE DEVICE PRINTER Figure 2.23(b). Revised F9C block diagram with alternate chip inversion for the creation of orthogonal MARK and SPACE signals. (Redrawn from [142].) Early Spread-Spectrum Systems DELAY LINE SIGNAL INTEGRATING MARK BUS FILTER DECISION RECEIVER CIRCUIT BINARY OUTPUT SPACE BUS SPACE INTEGRAT