The planetary radio astronomy (PRA) experiment on the Voyager 2 spacecraft reveals strong radiation in the form of arcs when the data are displayed in time-frequency coordinates. The vertex frequencies of these arcs, i.e., the central frequencies at which the arcs are first or last observed, are correlated with the magnetic field strength at the foot of the L = 6 shell magnetic flux tubes that emitted the arcs, provided that the emission is conical with a cone angle that varies slightly in a prescribed way. This interpretation further supports the association of the left circulary polarized arcs with the southern hemisphere, where the relation between vertex frequency and magnetic field strength is preserved. One way to produce a frequency dependent cone angle is described; it is relevant to processes where the cyclotron emission originates directly from streaming electrons with apparent cyclotron frequencies that are both relativistically depressed and Doppler shifted. This process is qualitatively consistent with the cone angles inferred from the PRA data.