Demonstration of the temporal modulation of P_det as recorded during an HPA measurement. All P_det were measured with the scanning plane centred on the beam from the ISS. (a) Raw time-stream data for P_det of MKID 171 at 205.07 GHz. We normalised to the time-averaged power < P_det > entering the MKID. We plot the data for a time range of 50 ms. The modulation at n∆f is visible as the rapid oscillation of the time-stream data, which has a period of about 3.9 ms. (b) Raw time-stream of MKID 96 at 214.84 GHz. (c) Raw time-stream of MKID 47 at 224.61 GHz. (d) Magnitude of the Fourier transforms of the signals in panels a, b, and c. The abscissa represents the frequencies present in the time-modulation of P_det and is denoted by ƒ_mod. The dashed vertical cyan line represents the n∆f for nf₀ = 205.07 GHz. Given the value of ƒ₀, this corresponds to n = 21 and thus n∆f = 254.31 Hz, which is where we would expect the peak. The dashed pink line corresponds to n = 22 for nf₀ = 214.84 GHz, and the dashed violet line shows n = 23, nf₀ = 224.61 GHz.