Normalised radio flux density measurement as a function of frequency for 9 SNR spectra presented in Castelletti et al. (2021) plus 3 new spectra for the SNRs G189.1+3.0, G290.1−0.8, and G316.3+0.0, constructed for this work (coloured filled circles), along with data from Kovalenko et al. (1994b) (black filled squares) and Kassim (1989) (black filled triangles). In order to highlight the drop-off behavior, the data are normalised to the power-law emission E(x) = x^α, where x = ν/ν_*. The curved solid line is the normalised absorption A(x) = exp(−x^−2.1). The total root mean square (rms) of the coloured circles is less than 11%. At ν ~ 2.75ν, approximately 50% of the emission is absorbed.