Specifies the local oscillator (LO) signal source used to downconvert the RF input signal.

If this property is set to "" (empty string), RFmx uses the internal LO source. For PXIe-5830/5831/5832, if you want to configure or read on LO1 or LO2 channel, use "lo1" or "lo2" as part of the selector string. You do not need to use a selector string or use "lo1, lo2" as part of the selector string if you want to configure this property for both channels. You can also use RFmxInstr Build LO String utility function to create the LO String. For all other devices, lo channel string is not allowed.

If no signal downconversion is required, this property is ignored.

Note This property is not supported on a MIMO session.

You do not need to use a selector string if you want to configure this property for all signal instances. Specify the signal name in the selector string if you want to configure or read on that signal instance. Refer to the Selector string topic for information about the string syntax.

The default value is Onboard.

Supported Devices: PXIe-5644/5645/5646, PXIe-5830/5831/5832/5840/5841/5842

Remarks

The following table lists the characteristics of this property.

Short Name LO Source
Data type cstr.png
Permissions Read/Write
High-level VIs N/A
Resettable Yes
None None

Specifies that no LO source is required to downconvert the RF input signal.
Onboard Onboard

Specifies that the onboard synthesizer is used to generate the LO signal that downconverts the RF input signal.

PXIe-5831: This configuration uses the onboard LO of the PXIe-3622, using the LO2 stage.

PXIe-5831 with PXIe-5653: This configuration uses the onboard LO of the PXIe-5653 when associated with the PXIe-3622.

PXIe-5832: This configuration uses the onboard LO of the PXIe-3623, using the LO2 stage.

PXIe-5832 with PXIe-5653: This configuration uses the onboard LO of the PXIe-5653 when associated with the PXIe-3623.

PXIe-5840 with PXIe-5653: If the center frequency is greater than or equal to 3.2 GHz, this configuration uses the PXIe-5653 LO source. For frequencies less than 3.2 GHz, this configuration uses the PXIe-5840 internal LO. If RFmx is operating in Spectrum mode, this configuration uses the PXIe-5840 internal LO regardless of the frequency.

PXIe-5842: This configuration uses the onboard LO of the PXIe-5655.
LO_In LO_In

Specifies that the LO source used to downconvert the RF input signal is connected to the LO IN connector on the front panel.
Secondary Secondary

Specifies that the LO source uses the PXIe-5830/5831/5832/5840 internal LO. This value is valid on only the PXIe-5840 with PXIe-5653, PXIe-5831 with PXIe-5653 (LO1 stage only), or PXIe-5832 with PXIe-5653 (LO1 stage only).
SG_SA_Shared SG_SA_Shared

Specifies that the internal LO can be shared between RFmx and RFSG sessions. RFmx selects an internal synthesizer and the synthesizer signal is switched to both the RX and TX mixers. This value is valid only on PXIe-5830/5831/5832/5841/5842.

Automatic_SG_SA_Shared Automatic_SG_SA_Shared

Specifies whether RFmx automatically configures the signal analyzer to use the LO utilized by the signal generator on the same vector signal transceiver (VST) based on the configured measurements.

When using instruments that do not have LOs with excellent phase noise and to minimize the contribution of the instrument's phase noise affecting your measurements, NI recommends to share the LO between the signal generator (SG) and the signal analyzer (SA).

This value is recommended in test setups that use a VST with NI-RFSG to generate a signal at the DUT's input and RFmx to measure the signal at the DUT's output.

This value automatically:
  • determines whether the SG LO can be shared with SA based on the test instrument used, selected measurement, and the measurement settings.
  • configures instrument specific properties on SA to share the LO between the generator and analyzer, whenever possible.

To enable automatically sharing SG LO with SA, you must first setup the required device specific physical connections mentioned below and then follow the steps in the recommended order.

PXIe-5840/5841/5842: SG LO is shared with SA via an external path. Hence, you must connect RF Out LO Out to RF In LO In using a cable.

PXIe-5830/5831/5832: SG LO is shared with SA via an internal path. Hence, an external cable connection is not required.

NI recommends the following order of steps:

  1. Set LO Source property to Automatic SG SA Shared in NI-RFSG (or enable Automatic SG SA shared LO on NI-RFSG Playback Library).
  2. Set LO Source property to Automatic_SG_SA_Shared in RFmx.
  3. Configure any additional settings on RFSG and RFmx, including selecting waveforms.
  4. Initiate RFSG.
  5. Initiate RFmx.
Note When using a DPD applied signal for performing measurements like ModAcc, PvT, or TXP, you must set the LO Leakage Avoidance Enabled property to False and LO Source property to Automatic_SG_SA_Shared.

Refer to following VIs for examples in RFmx WLAN and RFmx NR that show the behavior of Automatic SG SA Shared LO.

<LabVIEW directory>\examples\RFmx\WLAN\RFmxWLAN FEM Test with Automatic SG SA Shared LO.vi <LabVIEW directory>\examples\RFmx\NR\RFmxNR FEM Test with Automatic SG SA Shared LO.vi

This value is valid only on PXIe-5830/5831/5832/5840/5841/5842.