The AN/APN-81 Doppler Navigation System

The AN/APN-81 is a self-contained Doppler navigation system which accurately determines ground speed and drift angle independently of ground aids. This paper explains the techniques employed in the measurement of ground speed and drift angle. The beam pattern is described and major system parameters are given. In block diagram form, the functions of the transmitter and receiver, the frequency tracker, and the wind computer are explained. Accuracies of measurement and some specific applications of the equipment are given.