A set of extra calibration lines were turned on for a 1-week test starting 2023-07-25 (alog 71706). Part of the purpose of this test was to assess any impacts on CW data quality. Unfortunately, it looks like these lines do pollute low frequencies in a way that would be impactful to CW searches if left on.

Figure 1 shows a normalized H1:CAL-DELTAL_EXTERNAL spectrum for the week starting July 26. The gray dots indicate lines which correspond to intermodulation products of the calibration lines. For this plot, I computed a bunch of intermodulation products with up to 3 lines, and integer multiplicative factors for each line as large as +/- 3 as long as the total order was under 5. The plot intersects this list with the results of the automated linefinder.

These lines are new; their appearance corresponds to the extra lines being turned on. Spot checks of daily Fscan spectra confirm this. For comparison, I have attached an equivalent plot for the previous week (figure 2). Interactive versions of the plots can be found here: fig 1 interactive, fig 2 interactive. The product for each marked line can be seen in the hover text in those versions.