Top: schematic drawing of the distributivity pattern across a radio beam (looking down the magnetic axis). The annulus represents a cross-section of the emission beam, while the two dashed curves represent the telescope’s paths traversing this cross-section. The yellow and light-green shaded ellipses represent the peaks and troughs of the beating pattern formed from two counter-circulating current density waves, and physically correspond to the sub-pulses (note they are indeed observed to be almost evenly spaced, see e.g. Boriakoff et al. 1981), with yellow corresponding to δΦ > 0. They rotate slowly around the magnetic axis as indicated by the red arrow, while at the same time rapidly switch colour. Bottom: simulated signal using Eq. (29) overladen with an envelop (red dashed line) representing the effect ofmaking a B passage (see top panel) periodically. The parameters used are slightly adjusted as compared to the values given in the main text to make the signals wider and their features more visible in the figure. The jaggedness is due to the limited number of sampling points used by the plotting software, and conveniently simulate the limitedsampling rate of a telescope. The drifting of the sub-pulses is visible as the tip of the red envelop starting off coincident with a sub-pulse, but shifting to between two sub-pulses at the end of the sequence. Only δΦ > 0 segments areshown, as in real signals the dim δΦ < 0 segments are usually overwhelmed by noise.