A method and a device for generating a modulated navigation signal which is intended to be used to position a downlink receiver. Four pseudorandom navigation codes of chip rhythms greater than 0.5 MHz are modulated onto a carrier of frequency greater than 500 MHz according to an 8-PSK modulation of constant amplitude with a modulation frequency fM such that: 8fc.ltoreq.fM where fc=Max(fci), and fci designates the chip rhythms.