In high-end professional video cameras a triax system is used for transferring various signals back and forth over a single coaxial cable between the camera and a base unit using frequency multiplexing. In low-cost camera systems the analogue camera CVBS video output signal is replaced by a standard serial SDI signal from the camera to a base unit, having a maximum data rate of e.g. 270 Mbit/s for standard definition TV signals. According to the invention, the camera/base unit system is locked via SDI channels whereby the base unit video output is synchronised to the base unit Genlock signal. The camera unit and the base unit each use a local oscillator and H and V counters, whereby in the camera unit only a frequency locking is carried out.