High resolution frequency modulated tracker

Claim 1

A TRACKER COMPRISING IN COMBINATION AND IN OPTICAL ALIGNMENT, (A) A MOVING DRUM SHAPED RETICAL PROVIDED WITH UNIFORM RADIATION INTERRUPTING PATTERN ON THE DRUM PERIPHERY AND A RADIATION DETECTOR, (B) COLLECTING AND IMAGING OPTICS PRODUCING A CONVERGING BEAM TO IMAGE THE FIELD OF VIEW OF THE INSTRUMENT IN THE PLANE OF THE RETICLE, (C) MEANS FOR ROTATING THE IMAGE ABOUT AN AXIS AT RIGHT ANGLES TO THE MOVEMENT OF THE RETICLE BEAM PATTERN AND TO THE RETICLE PLANE, SAID MEANS COMPRISING A PAIR OF REFLECTING SURFACES INCLUDING A RIGHT ANGLE, THE ANGLE BEING CENTERED ON THE AXIS OF THE CONVERGING BEAM FROM THE COLLECTING OPTICS WHEREBY SAID BEAM IS RETROFLECTED FROM THE PAIR OF REFLECTING SURFACES BACK ALONG THE AXIS OF THE BEAM AND MEANS FOR ROTATING SAID REFLECTING SURFACES ABOUT THE BEAM AXIS AT A FREQUENCY LOWER THAN THE RADIATION INTERRUPTION FREQUENCY FROM THE PATTERN ON THE RETICLE, WHEREBY A FREQUENCY MODULATED SIGNAL IS PRODUCED FROM THE RADIATION DETECTOR, (D) MEANS FOR AMPLIFYING AND DEMODULATING THE SIGNAL FROM THE RADIATION DETECTOR TO PRODUCE AN AMPLITUDE MODULATED OUTPUT PROPORTIONAL TO FREQUENCY MODULATION, (E) PHASE REFERENCE GENERATING MEANS AT 90* OUT OF PHASE WITH THE ROTATION OF THE IMAGE, MEANS FOR ACTUATING THE REFERENCE SIGNAL GENERATING MEANS IN SYNCHRONISM WITH BEAM ROTATION, AND (F) PHASE DETECTING MEANS HAVING INPUTS CONNECTED TO THE DEMODULATED SIGNAL AND THE PHASE REFERENCE SIGNALS IN OPPOSITE PHASE WHEREBY SAID DETECTING MEANS PRODUCES OUTPUTS IN PROPORTION TO THE RELATIVE PHASES OF THE DEMODULATED FM SIGNAL.