Fraction of visible electrons with respect the frequency, the time and the distance from the center of the cluster. Top panels: Distribution of emission frequencies for the classicalRHs and megaRHs for three epochs (11.1, 12.4, and 13.3 Gyr) and γ_inj = 10² or = 10³. The vertical green areas show the frequency range covered by LOFAR LBA and HBA. Bottom left panel: Evolution of the fraction of tracers whose predicted emission frequency ν_c is larger than the central LOFAR HBA frequency, for the same models. Bottom right panel: Radial profile of the fraction of tracers whose emission frequency ν_c is larger than the central LOFAR HBA frequency, for the same epochs as those shown above.