This study demonstrates the frequency coupling in pulse width modulated (PWM) single-phase converters and inverters. As current state of the art, the harmonic frequency range, e.g. from fundamental frequency up to 2 kHz, is typically assessed separately from the so-called supraharmonic frequency range, i.e. above 2 kHz up to 150 kHz. The frequency coupling between the harmonic and supraharmonic frequency range has not been thoroughly studied and is currently often neglected in the design process as well as for the analysis of the emission of power electronic devices. The aim of this study is to analyse the behaviour of the frequency coupling between the harmonic and the supraharmonic range. In addition, laboratory measurements of a commercially available single-phase inverter for photovoltaic applications are shown to verify the findings.