Dynamic spectrum differences of τ Boo in Stokes-V () in the ON-beam in L570725 with the OFF beams in L569131 (panel a), L569127 (panel c), L569123 (panel e), L569119 (panel g), L570729 (panel i), and L581807 (panel k). Dynamic spectrum differences of the two OFF beams for each date can be found in the right column (panels b, d, f, h, j, and l). The data from the range 21–29 MHz is shown. The x-axis for all plots is the UT time of the observation subtracted by the transit time of the meridian. Moving to this reference frame ensures that even though the observations were taken at different dates, the characteristics of the beams (elevation, main beam pattern, and side lobes) at each time step are exactly the same. Thus, ionospheric variations, differential instrumental effects, and any remaining low-level RFI are the only difference between beams. The structured differences between the ON and OFF beams suggest that the signal in L570725 does not have the same time-frequency characteristics as the features seen in OFF beams of all the other dates. We do not see any obvious structure in the OFF beam difference plots. This suggests that for each observation the OFF beams are similar in their time-frequency emission structures. We find a consistent conclusion with what we find when comparing Q1b (integrated spectrum) for the two OFF beams for each individual observation (Fig. D.1).