One or more atmospheric propagation effects are estimated by using a phase comparison between and upper sideband and a lower sideband of a modulated signal. In one embodiment, one or more propagation effects are estimated by using a phase comparison between an upper sideband and a lower sideband of a satellite navigation signal. In one embodiment, one or more ionospheric propagation effects are estimated by using a phase comparison between an upper sideband and a lower sideband of a GPS M-code signal.