The invention permits a user to derive his pseudo range from earth-orbiting, signal-transmitting satellites without knowledge of the code sequence of modulation carried by the signal, if any. A modulated radio frequency signal having a component at a given frequency, which is transmitted from a satellite is intercepted at a user position. The component is recovered from the intercepted signal. The phase and frequency of the component are measured. From these measurements and similar measurements from other such satellites, the pseudo range of the satellite can be derived. Specifically, a fractional phase is derived from the measured phase and frequency of the intercepted signal. A Doppler range value is also derived from the measured frequencies of the satellites. The Doppler range value is divided by the wavelength of the given frequency to produce an integer and a remainder. The integer is added to the fractional phase to produce a value proportional to the pseudo range.