Radio lightcurve at 5 GHz showing the separate contributions to the emission: free-free emission from the colliding winds region (ff-cwr), free-free emission from the un-shocked winds (ff-wnd), and synchrotron emission from the colliding winds region (syn). The calculation was performed using ζ_rel = 0.15, ζ_B = 5 × 10^-5, p = 1.6, i = 60^°, and θ = 280^°. Non-thermal emission clearly dominates at radio wavelengths for Cyg OB2#9.