I was in the lab and measured the analogue voltage at the output of an RC filter VF4 (top circuit). I now want to do simulations with these measurements to see how loading this voltage affects it. I can not use a source with zero output impedance, since this would not be realistic. If I apply Thevenins equivalent voltage source, I get the lower circuit with the measured voltage VF4 as a voltage source and parallel R4/C4 as source impedance. Does this conversion hold true for all frequencies? It should, but my intuition tells me something is wrong.

TLDR; does Thevenin apply to AC circuits as in the circuits below?

thank you very much

I was in the lab and measured the analogue voltage at the output of an RC filter VF4 (top circuit). I now want to do simulations with these measurements to see how loading this voltage affects it. I can not use a source with zero output impedance, since this would not be realistic. If I apply Thevenins equivalent voltage source, I get the lower circuit with the measured voltage VF4 as a voltage source and parallel R4/C4 as source impedance. Does this conversion hold true for all frequencies? It should, but my intuition tells me something is wrong.

TLDR; does Thevenin apply to AC circuits as in the circuits below?

thank you very much

Edit: Maybe rephrasing my question helps: Lets say I have measured a voltage VF4 in the EMC lab (the output of an RC filter as shown in the top circuit, measured with very high impedance so it's an unloaded "impedance divider"). I now would like to know the difference a second RC filter would make to that signal (with different time constant). For this I create a voltage source in tina with the measured voltage as .csv-input. If I now connect the second RC filter directly to that voltage source, my simulation results will be wrong, since the voltage source has zero internal resistance / impedance. I would like to know which internal impedance I should use for this voltage source to achieve accurate simulation results.