Electronic surveying system

Claim 1

AN ELECTRONIC SURVEYING SYSTEM FOR DETERMINING THE DISTANCE BETWEEN FIRST AND SECOND POINTS, SAID SYSTEM COMPRISING: FIRST TRANSMITTING MEANS AT SAID FIRST POINT FOR TRANSMITTING A FIRST CARRIER SIGNAL; RANGE SIGNAL GENERATING MEANS SELECTIVELY OPERABLE FOR PRODUCING A SERIES OF RANGING SIGNALS HAVING A SERIES OF INCREASINGLY EFFECTIVE LONGER WAVELENGTHS, RESPECTIVELY; FIRST MODULATING MEANS ASSOCIATED WITH SAID FIRST TRANSMITTING MEANS FOR SUCCESSIVELY MODULATING SAID SERIES OF RANGING SIGNALS ON SAID FIRST CARRIER SIGNAL; RECEIVING MEANS AT SAID SECOND POINT FOR RECEIVING SAID FIRST CARRIER SIGNAL; SECOND TRANSMITTING MEANS AT SAID SECOND POINT RESPONSIVE TO SAID FIRST CARRIER SIGNAL RECEIVED BY SAID RECEIVING MEANS FOR RETRANSMITTING A SECOND CARRIER SIGNAL OF A DIFFERENT FREQUENCY FROM SAID FIRST CARRIER SIGNAL; SECOND MODULATING SIGNAL MEANS ASSOCIATED WITH SAID SECOND TRANSMITTING MEANS AND RESPONSIVE TO THE SERIES OF FREQUENCIES OF SAID SERIES OF RANGING SIGNALS AS MODULATED ON SAID FIRST CARRIER SIGNAL FOR MODULATING THE SECOND CARRIER SIGNAL PRODUCED BY SAID SECOND TRANSMITTING MEANS AT A PREDETERMINED FREQUENCY DIFFERENCE FROM EACH OF SAID SERIES OF RECEIVED RANGING SIGNALS; MEANS LOCATED AT SAID SECOND POINT FOR GENERATING A THIRD SIGNAL; MEANS LOCATED AT SAID SECOND POINT FOR MODULATING A FOURTH SIGNAL CORRESPONDING IN FREQUENCY AND PHASE TO SAID PREDETERMINED DIFFERENCE FREQUENCY ON SAID THIRD SIGNAL; MEANS LOCATED AT SAID SECOND POINT FOR MODULATING SAID MODULATED THIRD SIGNAL ON SAID SECOND CARRIER SIGNAL; AND ADDITIONAL RECEIVING MEANS AT SAID FIRST POINT AND RESPONSIVE TO THE SIGNALS TRANSMITTED BY SAID FIRST AND SECOND TRANSMITTING MEANS FOR MIXING SAID SIGNALS TO PRODUCE A SIGNAL CORRESPONDING IN FREQUENCY TO SAID PREDETERMINED DIFFERENCE FREQUENCY, THE PHASE DIFFERENCE BETWEEN THE LAST-NAMED SIGNAL AND SAID FOURTH SIGNAL RELATING TO THE DISTANCE BETWEEN SAID FIRST AND SECOND POINTS.