Integrated spectrum (Q1b) for the OFF beams on τ Boo (observation L570725) and the pulsar B0809+74 (observation L570723, taken 15 min before observation L570725). For observation L570725 only the first 15 min of data were used to calculate Q1b to allow for a more consistent comparison with the pular observation. The two observations have similar features in Q1b and above 30 MHz are consistent with each other assuming Gaussian error bars. We performed a K-S test on the two curves above 30 MHz and find that the probability that the two curves are drawn from the same parent distribution (the null hypothesis) is 97%. The fact that the two beams are pointed at completely different parts of the sky and still have similar overall flux levels suggests that the majority of the signal in the beams is instrumental. The 20–30 MHz feature in the OFF beam of τ Boo observation L570725 is the faint signal replicated from the ON-beam (Sect. 5.1.2; Fig. 6).