LO Sharing Between NI-RFSA and NI-RFSG

To reduce phase noise for some measurements, the PXIe-5841 allows for sharing the same internal LO or using the PXIe-5655 during NI-RFSA and NI-RFSG sessions.

To share the same LO between an NI-RFSA and NI-RFSG session, you must initiate both sessions and ensure both sessions use the same shared setting.

PXIe-5841 without Using the PXIe-5655

To share an LO between NI-RFSA and NI-RFSG without using the PXIe-5655, complete the following steps:

  1. Connect RF OUT LO OUT to RF IN LO IN on the PXIe-5841.
  2. In NI-RFSG, set the LO Out Enabled property. In NI-RFSA, set the LO Source property to LO In.

You can also share an LO in the opposite direction by completing the following steps:

  1. Connect RF IN LO OUT to RF OUT LO IN on the PXIe-5841.
  2. In NI-RFSA, set the LO Out Enabled property. In NI-RFSG, set the LO Source property to LO In.

PXIe-5841 with the PXIe-5655

The following high-level block diagrams show the difference between an independent and shared LO configuration within the PXIe-5655 LO0 and LO1 paths.



In the shared configuration, the shared LO must use the same frequency or the second driver session will return an error when committing the settings to hardware.

To share the same LO signal between NI-RFSA and NI-RFSG sessions, configure the NI-RFSA or NI-RFSGLO Source property as appropriate for your hardware configuration, as shown in the following table.

Table 15. LO Source Configurations
PXIe-5841 with PXIe-5655 Hardware Configuration NI-RFSA and NI-RFSG LO Source Values
Property Value Attribute Value
PXIe-5655 (independent configuration) Onboard
  • NIRFSA_VAL_ONBOARD_STR
  • NIRFSG_VAL_LO_SOURCE_ONBOARD_STR
External device LO connected to PXIe-5655LO 0 IN or LO 1 IN (independent configuration) LO In
  • NIRFSA_VAL_LO_IN_STR
  • NIRFSG_VAL_LO_SOURCE_LO_IN_STR
PXIe-5655 (shared configuration using LO0) SG SA Shared
  • NIRFSA_VAL_LO_SOURCE_SG_SA_SHARED_STR
  • NIRFSG_VAL_LO_SOURCE_SG_SA_SHARED_STR

When using the PXIe-5841 with the PXIe-5655, setting the LO Source property to SG SA Shared in an NI-RFSG session enables NI-RFSA to share the internal LO0 synthesizer if requested by NI-RFSA. If an NI-RFSG session has already set the LO Source property to something other than SG SA Shared property value in an NI-RFSG session, you cannot request sharing using NI-RFSA.

Setting the LO Source property to SG SA Shared in an NI-RFSA session results in using the PXIe-5655 LO0 synthesizer. You can also choose not to use the LO0 shared configuration in the NI-RFSA session by instead setting the LO Source property to Onboard or LO In.

Note Output power levels at LO 0 OUT may vary slightly (<1 dB, typical) when set to SG SA Shared as NI-RFSA connects or disconnects the shared signal.