A 1D model of an RF driven ion source is presented and is based on the ionisation of thermal electrons. The RF source differs from traditional filament and arc ion sources because there are no primary electrons present, and is simply composed of an antenna region (driver) and a main plasma discharge region. However the model does still make use of the classical plasma transport equations for particle energy and flow, as seen previously in DC source models where they have worked well. The model currently uses the geometry and other source parameters of the Small Negative Ion Facility (SNIF) ion source at CCFE and only considers the hydrogen ion species, but may be easily adapted to model other RF sources. The model provides a detailed description of the plasma parameters along the source axis, i.e. plasma temperature, density and potential, as well as current densities and species fluxes, but does not consider the RF matching unit or the accelerator. The inputs to the model are the RF power, the magnetic filter field, the source gas pressure and the plasma grid insert bias. Results from the model are presented and where possible compared to existing experimental data from SNIF, with varying RF power, source pressure and insert bias.