Abstract: Measurement of distance is carried out by transmitting a VHF wave train crising a sinusoidal signal modulated by phase inversion in accordance with a pseudo-random sequence, at a receiver shifting a like second sequence until it coincides with the received sequence, re-transmitting a signal modulated by the second sequence, receiving the second sequence and shifting a like third sequence until it coincides with the received second sequence, and measuring the phase shift between the third sequence and a like reference sequence.

Abstract: A method of and apparatus for differential mode navigation in a sequential system of radio-navigation by phase reception. A transmitted amplitude-modulated radio-navigation carrier wave is phase or frequency modulated, this modulation being effected by a low-frequency subcarrier signal which is itself so phase modulated sequentially in accordance with phase corrections that each phase correction appears approximately simultaneously with the phase concerned. The phase corrections are derived from the difference between the phase received from each fixed station of the system and theoretical phases which should be received from that station. At a standard radionavigation receiver, the subcarrier signal modulated by the corrections is recovered, and the phase corrections are so applied to the received phases that each phase undergoes the phase correction received at the same instant.