The Janson Directive - By Robert Ludlum Page 0,224
security system was useless if it regularly issued false alarms. Outdoor microwave systems always used signal processing to distinguish human intruders from the thousand other things that could cause anomalies in the signal - a branch tumbling in the wind, a scampering animal.
Still, he was taking a stomach-plunging gamble. In less exigent circumstances, he would have field-tested his hypothesis before staking his life on it.
One more time, he studied the configuration of the stanchions. The bistatic sensors could be placed as far as seven hundred feet away from each other. These were merely a hundred feet away - a spare-no-expenses approach that must have gladdened whoever had been paid to install the system. And yet the proximity of the sensors was another factor in Janson's favor. The farther apart they were, the broader the coverage pattern between them. At 250 yards, the coverage pattern would swell to an oval that reached, at the midpoint between the two sensors, a width of forty feet. At thirty yards, the coverage pattern would be tighter and more narrowly focused, no wider than seven feet. That was one of the things that Janson was counting on.
As he had expected, the poles along the second, staggered tier beamed to the alternating pole in the tier closer to him, and vice versa. The point where the two beams intersected, accordingly, was the narrowest possible area of coverage. One stanchion was three feet to the left and two feet behind the other pole; thirty yards to either side, the pattern was repeated. In his head, he drew an imaginary line connecting the pair of adjacent stanchions, then the imaginary line connecting the next pair. Midway between those two parallel lines would be the point where the area of coverage was at its minimum. Janson moved toward that point, or where he intuitively estimated it to be. Holding the steel rod, he moved the Phantom II toward that spot. The system would have instantly detected the appearance of an object, but it would also immediately determine that the waveform patterns did not correspond to that of any human intrusion. It would remain quiet and undisturbed - until Janson himself tried to cross. And that would be the moment of truth.
Would the radar scrambler confuse the signal receivers, preventing them from registering the presence of the very human intruder that was Paul Janson?
He couldn't even be sure that the Phantom II was working. As a precaution, Janson had disabled its displays; there would be no reassuring red light indicating that it was mirroring the signals it received. He would have to proceed on faith. He kept the Phantom II steadily in position, moving himself down the pole, hand over hand, keeping it aloft without shifting its position. Then he rotated the rod and continued to back away from the microwave barrier.
And ... he was through.
He was through.
He was a safe distance on the other side. Which was not a safe place to be at all.
As Janson walked toward the gently sloping fairway toward the mansion, he felt the hairs on the back of his neck bristling, conscious on some animal level that the greatest risks lay ahead.
He looked at the dimly illuminated LCD display of his black Teltek voltmeter, holding it in cupped hands. It wasn't field-caliber equipment, but it would do.
Nothing. No activity.
He traveled another ten feet. The digits began to climb; he took another step, and they surged.
He was approaching the subterranean pressure sensors. Though the voltmeter indicated that the buried cable itself was still a ways off, he knew that the electromagnetic flux of TriStar's buried-cable sensors created a detection field that was more than six feet wide.
The rate of increase in the voltmeter's display suggested that he was nearing the active field. Nine inches beneath the sod, the "leaky" coaxial cable was designed to have gaps in the outer conductor, allowing an electromagnetic flux to escape and be detected by a parallel receiving cable that ran in the same jacket. The result was a volumetric detection field around the coaxial cable, about one foot high and six feet wide. Still, as with other outdoor intrusion-detection systems, microprocessors were tasked with distinguishing one kind of disturbance from another. A twenty-pound animal would not trigger an alarm; an eighty-pound boy would. Intruder speeds, too, could be detected and interpreted. Snow, hail, gusting leaves, temperature changes - all could alter the flux. But the brains of the system would filter out such noise.