A framework, EwSim, for electronic warfare duel simulations, in the visual/infrared wavelength range has been developed and is described in the report. EwSim is based on the commercial product, Vega, with the plug-in for infrared imagery, SensorVision (the plug-in SensorWorks can also be used for sensor performance). Several in-house modules have been adapted to this framework in order to get EW-simulation capabilities. EwSim has real time (or close to real time) simulation capacity which means that it is possible to extend the use of the framework to include EW training of military personnel. This document gives a technical description of EwSim.