Unexpected Attenuation When Using PXIe-5668 Under 16kHz

Updated Jan 6, 2020

Reported In


  • PXIe-5668

Issue Details

We are using PXIe-5668 under 16kHz frequency and get unexpected attenuation about 40dB everytime. The signal source is proved to be correct and the PXIe-5668 has passed self calibration. I don't know what causes the problem.


  • Refer to the PXIe-5668 specification document. The specifications for amplitude accuracy are not specified below 10MHz. Also, there's a note in Table 8 and Table 10 that says "RF attenuation is 20dB for frequencies < 10MHz and is 10dB for frequencies > 10MHz."
  1. PXIe-5624 digiliter
  2. PXIe-5606 RF signal downconverter
  3. PXIe-5653 synthesizer/LO source
The PXIe-5606 has no internal DC block but ships with a 2.92 mm DC block attached to the RF IN connector to prevent damage to the device when a DC input signal is present. You cannot accurately measure signals below 16kHz with the DC block attached to the RF input. In order to make a measurement below 16kHz, you must remove the DC block because series capacity reactance of the device increases as the RF input frequency drops from 16kHz to 20Hz. Removing the DC block leaves the RF front end susceptible to damage with voltage levels greater than 0V DC. NI recommends that you keep the DC block attached to the RF IN connector for all measurements at frequencies greater than or equal to 16kHz to maximize the accuracy of the device, and is not responsible for damage resulting from improper signal connections.