External LO

External LO refers to an LO source used with the PXIe-5673/5673E Vector Signal Generator that is not the PXI/PXIe-5650/5651/5652 RF Analog Signal Generator.

By default, a single NI-RFSG session controls all devices in the PXIe-5673/5673E—the PXIe-5611 I/Q Modulator, the PXIe-5450/5451 Waveform Generator, and the PXI/PXIe-5650/5651/5652 LO source. In a PXIe-5673/5673E device configured to use an external LO, the NI-RFSG session controls the I/Q modulator and the AWG, but the LO source is not controlled by the NI-RFSG session. An external LO is useful if you have an LO with lower phase noise, lower harmonics, or faster tuning time than the PXI/PXIe-5650/5651/5652.

Configuring the PXIe-5673/5673E to Use an External LO

After interconnecting multiple PXIe-5673/5673E modules, you can configure the PXIe-5673/5673E to use an external LO in MAX by completing the following steps:

1. Launch MAX by navigating to Start»All Programs»NationalInstruments»NI MAX or by clicking the NI MAXdesktop icon.
2. In the configuration tree, double-click Devices and Interfaces to seethe list of installed devices.
3. Expand your chassis tree item. You will see a list of installeddevices that includes the PXIe-5611 module, the PXIe-5450/5451 module, and thePXI/PXIe-5650/5651/5652 module.
4. Select the PXIe-PXIe-5611.
5. In the Associated Devices section, use the drop-down LO listbox and select External.

You can also configure the PXIe-5673/5673E to use an external LO through the option string input of the niRFSG Initialize With Options VI or niRFSG_InitWithOptions function.

Controlling the PXIe-5673/5673E with an External LO

Complete the following steps to control the PXIe-5673/5673E with an external LO by setting the appropriate frequency and power level:

1. Specify the LO frequency to the NI-RFSG session using the Frequency property or NIRFSG_ATTR_FREQUENCY attribute.
2. Specify the LO power using the LO In Power property or NIRFSG_ATTR_LO_IN_POWER attribute.