FAQs from Rohde & Schwarz

RTA4004 - Power Measurements

Question

I made some power measurements using my R&S RTA4004 that lead to questionable power results. When I compare with another device I see that my power value is too high. I was using the following setup:

  • DC coupling
  • CH1 = Voltage over time
  • CH2 = Current over time
  • M1 = RMS-Cycle of the product of CH1 and CH2 (set over more than two periods)
R&S RTA4004 setup

Answer

There are several things to consider.

  • Period measurement for RMS cycle introduce an additional quantity, which can be a source of error.
  • Period measurement on a noisy signal can be affected, thus this measurement is not as accurate as wished.
  • When comparing multiple channels to each other and the starting phase of the channels in one acquisition is non-zero, then the period measurement takes place on different parts of the waveform.

So the best way to perform this measurement is to use RMS instead of RMS Cylce calculation in your measurements. It is diplayed as RMS and the following symbol in the menu:

RMS