A method for detecting a preamble in a received radio signal comprises demodulating a received radio signal based on a carrier derived from a local timing source to provide a digital signal comprising a sequence of bits oscillating at approximately a modulated data rate. A bit width of each successive bit of the digital signal is determined. If a pair of consecutive bit widths have a combined width within a threshold value, the bit pair is indicated as potentially belonging to a preamble. If a threshold number of potential preamble bit pairs in a sequence of bit pairs within a given window is detected, the sequence of bit pairs is indicated as potentially comprising a preamble. A measure of bit widths of at least some bits within a sequence of preamble bit pairs can be provided and a frequency of the local timing source can be adjusted according to said measure.