A positioning device (4) is disclosed comprising at least one antenna (14, 16) for receiving ranging signals, such as GNSS signals. The device comprises a local oscillator (18) for providing a local frequency or phase reference and an inertial sensor (22) for measuring a movement of the device. A processor (36) is provided for performing calculations. The device can receive a first reference signal at a known or predictable frequency or phase. A local oscillator offset determination module (26) is provided to calculate an offset to the received frequency or the received phase based on the movement of the receiver in the direction of the first reference source. A local signal generator (28) can then use the local frequency or phase reference from the local oscillator (18), and the offset calculated by the local oscillator offset determination module (26), to provide a local signal using a local signal generator (28). The local signal can be correlated against a received ranging signal for use in positioning calculations performed by a positioning calculator (34).