The 21-cm distortion as a function of redshift for various values of f_PBH. The fiducial parameters are f_{BH, X} = λ = 0.1 and f_duty = 0.01. We have ignored any modification to thermal history of Universe such as changes in electron fraction and matter temperature. We also show the case where we fix f_PBH to 10⁻⁴ but tune f_{BH, X}, λ, and f_duty such that radio luminosity is boosted by a factor of 20. With a further boost of a factor 2–3, the parameters could help explain the ARCADE excess.