Methods and apparatus for testing a broadcast channel in which information is transmitted within a synchronous area of an electric power grid are described. A characteristic relating to a frequency of power flowing in the electric power grid is measured at a testing device and a signal based on a frequency modulation of the grid frequency is extracted from the electric power grid. Data indicative of a characteristic of the signal is then sent for receipt at a control node via a second channel different to the broadcast channel. This enables testing of the broadcast channel.
