Absolute value of the Faraday spectrum (FDF; solid blue line) and the real (Q; solid green line) and imaginary (U; solid yellow line) components of the FDF, for two example polarised source components. The Q,U plots have a restricted range on the y-axis to better visualise the noise. The ‘real’ peak, i.e. the highest signal-to-noise polarised component outside the leakage range, is marked with a red cross. The leakage peak is noticeable in both cases at ϕ ∼ 0 rad m⁻². The rms noise (σ_QU) level is shown as a dashed line. After inspection, the top source at S/N ∼ 8 is excluded, while the bottom source, at S/N ∼ 40 is accepted.