FAQs from Rohde & Schwarz

Voltage Noise Measurement


I tried to measure the Voltage Noise of my power supply unit which is specified to the following values:

My results have been much higher and I sent in the device for alignment/calibration. After getting it back I still gather the same results. Can you explain how to perform such a measurement?


We set up an example measurement with the following setup (ref. to IEEE Std 1515-2000):

  • HMP4040 (which is specified as mentioned before)
  • Load= 10 Ohm (Hi Power R, 50 W)
  • Connection via RG58CU / BNC-T to HMP4040, CH1
  • Connection from HMP4040 to MXO4 via RG58 CU
  • Termination on MXO4 with BNC-T / 50 Ohm in a row with 680nF ceramic
  • MXO: Coupling = AC, 20 MHz BW limit, automated RMS measurement for CH1

Measurement 1: PSU Mains OFF

Measurement 2: PSU Mains ON, Output CH1 OFF:

Measurement 3: PSU Mains ON, CH1 Output ON:

The RMS value for CH1 is in specs.

Remarks for voltage mode:

Following the standard, the specified value (datasheet) has been captured at 90% load (current). In this case, the basis is a specific application running with about 1 A at a 10 Ohm load. We recommend performing the measurement only with a total ohmic load as electronical loads can cause additional noise!