Summary form only given, as follows. We have made a computer model of a coaxial VIRCATOR being developed at TTU. Since successful operation of a vircator is based on the highly nonlinear process of consecutive appearance and disappearance of a virtual cathode (hence the name virtual cathode oscillator), algebraic analysis of the beam/field interaction process is severely limited. Therefore, in practice, most of the information about the performance of the device can only be derived from computer modelling. We have developed a suitable computer model procedure using as our main tool the computer code MAGIC. Recently we have investigated the effect of a septum inserted in the main output waveguide immediately following the virtual cathode interaction space. The septum was introduced by the TTU group in order to improve the overall efficiency and the quality of the frequency spectrum of the vircator. In our presentation we propose to show the degree of convergence between the results obtained from computer modelling and those obtained experimentally. The comparison is based on the length and shape of the RF pulse and on the investigation of the frequency spectrum of the output. Specifically the RF pulses controlled by the duration of the power supplies are of comparable lengths; similarly the main frequency of oscillation is 1.81 GHz (experimental) against 2.09 GHz (computer model). We are currently investigating the cause of some of the discrepancies.