Smudge, with "the blue signal becoming unstable" i mean that the signal gets weak (low amplitude) and thus noisy so the scope has problems to accuratly calculate data like amplitude, frequency and phase. Setting up the measurement as proposed by you made the "exceeding 90°" dissappear Below 1st screenshot shows the same 2.6MHz frequency as yesterday, but now only having 86° phase shift. Yellow is the FG input voltage (for reference). Red is the math: yellow minus blue for input voltage. blue is voltage across csr thus current (10 Ohm) There is a slight(er) above 90° range, but more down in frequency, see screenhot 2 Here we are at 70Khz but the blue (and yellow) signal is low in amplitude (still 20Vpp input from the FG, but the impedance seems low). This low in amplitude again has an effect on the math calculations as the sigs become noisy and thus inaccurate, so the shown 96° phase shift here is doubtfull. Is this shown data OK (V rms, frequency and phase shift) or do you need different data and/or more range? Itsu
