A method of controlling the phases of RF output signals from a number of radio transmitters. A given radio has at least one synthesizer as a source of its RF output signal, and the synthesizer produces an output the phase offset of which relative to a reference signal is controlled by a phase offset command. A path from an antenna port of the radio obtains a fed back RF output signal and a phase difference between the reference signal and the fed back RF output signal is measured. A value of a zero degree phase offset command for the synthesizer is determined such that the phase difference between the reference signal and the fed back RF signal is nominally zero, and the value is stored. A phase offset command for providing a desired phase offset for the RF output signal is then determined based the stored value of the zero degree phase offset command.