Expected LS I +61 303 pulsed flux density along the orbit at different frequencies for α  = − 1.0 assuming that the intrinsic pulsed flux density at 1.3 GHz is S₀ and considering free-free absorption effects. Periastron and apastron are indicated by the vertical black lines at phases 0.23 and 0.73, respectively. The highest observable flux density is expected to occur at 0.6 GHz at orbital phase ~0.6−0.7, three days before apastron. The observation phase range of this work is indicated by the vertical green stripe centred at 0.54.