Left: resulting global spectrum of an M 51-like galaxy from our 3D model as seen face-on (red solid line) with the synchrotron component without absorption (orange dotted line) and thermal free-free emission (black dashed line). Black solid circles denote literature data used during the modelling and the interpolated flux density at 150 MHz from MSSS survey. For the sake of completeness, data from the individual MSSS sub-bands (blue circles) are also shown. Middle: global spectra for different inclination angles of 0, 30, 60, and 90 degrees, respectively. Right: local spectrum of an area surrounding the galaxy centre for different inclination angles.