Computer simulation experiments of linear and nonlinear collisionless interactions between electron beams and background plasmas, for conditions relevant to active magnetospheric experiments, were carried out. Both electrostatic and electromagnetic interactions were simultaneously considered. The beam-plasma systems were infinite and homogeneous. The relative beam concentrations considered were e = nb/np = 1,0-1 and 0-01. In all cases, the background plasma (1 eV thermal energy) was penetrated by an electron beam of 1 keV streaming energy and 5 % thermal spread in the streaming direction. The paper presents a full description of the results and a brief discussion of their relevance to magnetospheric active experiments. The off-angle propagation case in unmagnetized plasmas is also briefly discussed.