Global radio continuum spectrum of M 51. We show integrated flux densities calculated from our data and compare them with literature data compiled by Mulcahy et al. (2014). Power-law fits correspond to radio spectral indices of −0.80 ± 0.05 for our data (blue data points and solid line) and −0.79 ± 0.02 for the literature data (red data points and dotted line). The flux density at 619 MHz is only given as a lower limit and was not included in the fit.