otographic hobbyist. He conceived of a novel experimental program using photo- graphic techniques for storing a noise-like signal and for building a nearly ideal cross correlator. Supported by ITT funds and doing some work in a makeshift home lab, Rogoff prepared a 4 in. X 5 in. sheet of film whose transmissivity varied linearly in both directions, thus creating a mask whose transmission characteristic at every point (X, Y) was proportional to the product XY. Two signals then were correlated by using them as the X and Y inputs to the oscilloscope, reading the light emitted from the Early Spread-Spectrum Systems masked oscilloscope face with a photomultiplier, and low-pass filtering the resultant output. Rogoff's noise-like carrier came straight from the Manhattan telephone directory. Selecting at random 1440 numbers not ending in 00, he radially plotted the middle two of the last four digits SO that the radius every fourth of a degree represented a new random number (see Figure 2.15). This draw- ing was transferred to film which, in turn, when rotated past a slit of light, intensity-modulated a light beam, providing a stored noise-like signal to be sensed by a photocell. In initial experiments, Rogoff mounted two identical noise wheels on a single axle driven by a Diehl 900 rpm synchronous motor (see Figure 2.16). Designed and assembled by Rogoff and his colleague, Robert Whittle, sep- arate photocell pickups were placed on each wheel, one stationary and one on an alidade, SO that the relative phase between the two signals could be varied for test purposes. Using time-shift keying (an extra pickup required) to generate MARK or SPACE, one noise wheel's signal was modulated and then combined with interference to provide one correlator input, while the other input came directly from the second noise wheel. These baseband experiments, with data rates on the order of a bit per second and, hence, a multiplicity factor of well over 40 dB, indicated that a noise-like signal hid- den in ambient thermal noise could still a