Digitrac display system for air-traffic control. I. Digital azimuth and sweep generation

The most frequently used way to send azimuth information from the aerial to the plan-position indicator is to use a synchro transmission system. At the receiver end a sine-cosine generator or resolver transforms data to Cartesian coordinates. Analogue data processing is used. By careful synchronization of the rotary components of the system, a relatively high degree of accuracy is obtained. Digitrac uses a digital computer and digital display unit which makes digital processing of azimuth data the logic choice. The azimuth and range data not only control the display but also provide a continuous flow of information in binary form to the computer. The only two places where the azimuth information appears in analogue form are at the aerial shaft and at the input to the deflection coils of the indicator. Significant features of the azimuth processing are the use of a digital azimuth transducer and of an electronic flywheel principle, which makes use of the inertia of the aerial and gives a high degree of noise suppression and azimuth resolution.