Range determining system

A method for finding the distance between an interrogation means and a transponder means comprising the steps of:

• generating and transmitting an interrogation signal comprising a carrier signal modulated by a signal which is a concurrent function of a first two-level tone of frequency f.sub.T and a first iterative two-level pseudo random sequence whose level transitions are coincident with level transitions of said first tone;
• responding to said interrogation signal at said transponder means to generate a first tracking signal which identifies the times of occurrence of the propagation delayed phases of said first tone and said first pseudo random sequence;
• generating and transmitting a responsive signal comprising a carrier signal modulated by a signal which is a concurrent function of a second two-level signal of frequency f.sub.T and a second iterative pseudo random sequence whose phases are the same as the propagation delayed phases of said first tone and said first pseudo random sequence;
• receiving said responsive signal at said interrogation means;
• generating a second tracking signal at said interrogation means which identifies the times of occurrence of the propagation delayed phases of said second tone and said second pseudo random sequence;
• determining the phase difference of said first pseudo random sequence before transmission thereof and the propagation delayed second pseudo random sequence;
• and
• computing the distance between said interrogation means and said transponder means from said phase difference.

A method for finding the distance between an interrogation means and a transponder means comprising the steps of:

• generating and transmitting an interrogation signal of at least two successive portions;
• first and second portions comprising a carrier signal amplitude modulated by a first iterative two-level pseudo random sequence whose level transitions are coincident with level transitions of a first two-level tone of frequency f.sub.T ;
• said second portion being further phase shift modulated by said first two-level tone;
• said third portion being phase shift modulated by the product of said first tone and said first pseudo random sequence;
• responding to said interrogation signal at a transponder to generate a first tracking signal having first and second signal components;
• phase locking the phases of said first and second signal components with the propagation delayed phases of said first tone and said first pseudo random sequence;
• generating and transmitting a responsive signal comprised of two successive responsive portions;
• the first responsive portion being a carrier signal amplitude modulated by a second iterative pseudo random sequence and phase shift modulated by a second two-level tone of frequency f.sub.T ;
• the second portion being phase shift modulated by the product of said second two-level tone and said second pseudo random sequence;
• phase locking said second two-level tone and said second pseudo random sequence with the propagation delayed phases of said first tone and said first pseudo random sequence;
• receiving said responsive signal at said interrogation means;
• generating a second tracking signal at said interrogation means;
• phase locking a first and second signal component of said second tracking signal with the propagation delayed phases of said second two-level tone and said second pseudo random sequence;
• determining the phase difference of said first pseudo random sequence before transmission thereof and the propagation delayed second pseudo random sequence;
• and
• computing the distance between said interrogation and said transponder means from said phase difference.

A radio for use in a system of the type in which a first radio station transmits a first carrier modulated by a first code sequence to a second radio station, said first code sequence including a plurality of successive cycles of a given pseudo random code which occur in time synchronism with a time reference at said first station;

• in which said second station receives said modulated first carrier after a certain propagation time delay which is short relative to a cycle period of said given pseudo random code sequence;
• in which said second station transmits a second carrier modulated by a second code sequence to said first station, said second code sequence including a plurality of successive cycles of said given pseudo random code which are phase locked with said pseudo random code of said first code sequence received by said second station;
• and in which said first station receives said modulated second carrier after a certain propagation time delay and then determines said range between said stations in accordance with the phase delay between said pseudo random code received by said first station and said pseudo random code transmitted from said first station;
• the improvement wherein a radio station for use in said ranging system comprises:
• a tone source generating a tone at a given frequency which is low relative to the frequency of the carrier of that station;
• a pseudo random code generating means responsive to said tone for repetitively deriving a pseudo random code consisting of a predetermined number of successive binary code chips with the code chip period of said pseudo random code being equal to a period of said tone;
• and
• modulation means for modulating the carrier of that station during at least one certain portion of said code sequence of that station with a modulating signal that is a preselected concurrent function of both said tone and said pseudo random code.