Polarisation ratio (L_obs/L_int) of the linear polarisation as a function of RM for a frequency channel of width ∼0.976 MHz at three reference frequencies ν of 4, 5 and 6 GHz shown in blue, orange and green, respectively. L_obs is the observed linear polarisation and L_int is the intrinsic linear polarisation of the signal. The polarisation ratio is computed following Schnitzeler & Lee (2015) and starts to show significant depolarisation across our channel bandwidth at 4 GHz with RM ≳500 000 rad m⁻². The RM polarisation ratio curve is symmetric around RM zero.