Select an SMA attenuator that complies with the following specifications.

  • The VST’s LO input power range is -4 dBm to 0 dBm. NI recommends using an LO power target of -1 dBm when performing an acquisition LO calibration.
  • To achieve the desired power level at the LO input of each instrument, the LO amplifier needs to operate above its minimum gain, in the linear region, and below its maximum gain.
  • The path loss of cables and splitters due to the system's frequency of operation can affect the transmitted power. Ensure the path loss does not affect the minimum required power for operation.

Example of what NI measured for our 4-channel test system:

  • A 6 dB attenuator between the LO source and amplifier using the splitter and recommended cables from the four channel LO star configuration.
  • The LO source produced an LO signal at -1 dBm.
  • The ZC4PD-5R263-S+ splitter has an approximate insertion loss of 6.5 dB to 7.5 dB in the RF frequency range of the VST.
  • The requested gain values of the LO amplifier in NI’s test system ranged from 17 dB to 20 dB.
  • The resulting power at LO input was approximately -1 dBm for all frequencies within the range of the VST.