Master/slave synchronisation method in a bluetooth system

A transmitter (2) for transmitting in a low power frequency hopping network, the low power frequency hopping network comprising the transmitter (2) and at least one receiver (6) wherein the transmitter (2) is arranged to synchronise to a common time reference having distinguishable instances, the transmitter comprising: means (160) for obtaining a clock value at an identified instance of the common time reference; and means (144) for transmitting an identification of a first instance of the common time reference and an identification of a clock value that is valid at the first instance of the common reference.