Abstract Wave and plasma observations were made in a close vicinity of a xenon gun, carried at altitudes near 500 km in the APEX-experiment. Wideband noise associated with neutral gas releases and steady beam currents were detected. In modulation regime even and odd harmonics of the beam modulation frequency were observed. A delay in wave emissions after modulated beam injection was terminated was also detected. This effect was accompanied by electron temperature and density disturbances as measured by a plasma density and temperature device.