A method of navigating a self-propelled robotic tool comprises transmitting a wireless signal (66) along a first signal path between the robotic tool (14) and a first wireless interface of a base station (16) remote from the robotic tool (14)； transmitting a wireless signal (66) along a second signal path between the robotic tool (14) and a second wireless interface of the base station (16), said second wireless interface being spatially separated from the first wireless interface by a separation distance； upon receipt, comparing the signal transmitted along the first signal path with the signal transmitted along the second signal path to obtain a propagation time difference between the signal transmitted along the first signal path and the signal transmitted along the second signal path, said propagation time difference defining a path length difference between said first and second signal paths； and calculating, based on the separation distance and the path length difference, a value representative of a bearing (φ) from the base station (16) to the robotic tool (14).
