Doppler frequency tracker

Claim 1

A FREQUENCY TRACKER SUITABLE FOR USE IN A PAIRED DUAL MULTIPLE BEAM DOPPLER RADIO NAVIGATION SYSTEM COMPRISING, A VARIABLE OSCILLATOR FOR SUPPLYING TWO FREQUENCIES EQUALLY SPACED ABOVE AND BELOW A BASE REFERENCE FREQUENCY, SAID SPACING BEING PROPORTIONAL TO AN ERROR VOLTAGE, AND A THIRD FREQUENCY EQUAL TO ONEHALF THE FREQUENCY DIFFERENCE OF SAID TWO FREQUENCIES EQUALLY SPACED ABOVE AND BELOW THE SAID BASE FREQUENCY, IDENTICAL UPPER AND LOWER SIGNAL PROCESSING CHANNELS EACH OF WHICH INCLUDE, A MIXER FOR RECEIVING AND MIXING A DOPPLER SHIFTED REFERENCE FREQUENCY SUPERPOSED ON BROADBAND NOISE AND IN EACH OF SAID MIXERS A DIFFERENT ONE OF THE EQUALLY SPACED FREQUENCIES SUPPLIED BY THE ABOVE SAID OSCILLATOR, FIRST MEANS INCLUDING A VARIABLE FILTER RESPONSIVE TO THE THIRD FREQUENCY FROM SAID OSCILLATOR FOR PROVIDING A NARROW BAND OUTPUT ABOUT A POINT DETERMINED BY THE SAID THIRD FREQUENCY FROM SAID OSCILLATOR, AND SECOND MEANS RESPONSIVE TO THE NARROW BAND OUTPUT FROM THE FIRST MEANS IN EACH OF SAID CHANNELS FOR DERIVING AN ERROR SIGNAL, AND THIRD MEANS FOR PROCESSING THE UPPER AND LOWER CHANNEL ERROR SIGNALS TO DERIVE ERROR SIGNALS FOR INDICATING INSTANTANEOUS CHANGES IN THE SYSTEM FLIGHT PARAMETERS.