Analysis of energy-release history with |$\mathcal {Q}(z)=5 \times 10^{-8}$| in the redshift interval 10³ < z < 5 × 10⁶ using signal eigenmode, |${{\bf S}}^{(1)}$| (Fig. 4). We assumed {ν_min, ν_max, Δν_s} = {30, 1000, 15} GHz and channel sensitivity ΔI_c = 5 × 10⁻²⁶ W m⁻² Hz⁻¹ sr⁻¹. The dashed blue lines and red crosses indicate the expected recovered values. Contours are for 68 per cent and 95 per cent confidence levels. All errors and recovered values agree with the Fisher estimates. We shifted Δ_T by Δ_i = Δ_f + Δ_prim with Δ_f = 1.2 × 10⁻⁴ and Δ_prim ≃ −8.46 × 10⁻⁹, where Δ_prim is the primordial contribution.