The PXIe-5654 RF signal generator has two modes for power level adjustment: automatic leveling control (ALC) disabled (open-loop mode) and ALC enabled (closed-loop mode).

Note When using the PXIe-5654 as a stand-alone device, only open-loop mode is supported because the ALC is in the PXIe-5696 Amplitude Extender module. When you use the PXIe-5654 with the PXIe-5696 , both open-loop and closed-loop modes are supported.

ALC Disabled (Open-Loop Mode)

As a stand-alone device, the PXIe-5654 open-loop operation mode provides fine amplitude adjustment over the power control range and is temperature compensated over the operating temperature range. With the PXIe-5654 stand-alone device, you can adjust the power level in 0.01 dB steps.

ALC Enabled (Closed-Loop Mode)

When you pair the PXIe-5654 with an PXIe-5696 , a 110 dB mechanical step attenuator extends the power adjustment range, and the power accuracy improves by engaging the ALC loop.

The ALC loop performs fine amplitude adjustment, and the step attenuator performs coarse attenuation in 10 dB steps. The ALC is calibrated for amplitude and temperature variation and is used to adjust the power within the power control range of the PXIe-5654 . NI-RFSG uses the ALC and step attenuator together to optimize the absolute and relative accuracy at the specified power[1]1 Power accuracy varies depending on power level..

When the ALC is closed, NI-RFSG sets the amplifier to use the low harmonic path or the high power path based on frequency and power settings. Power settings are independent of the ALC; however, power level accuracy increases in closed-loop mode.

Note Refer to the NI PXIe-5654 Specifications document for guaranteed output power range and accuracy.

1 Power accuracy varies depending on power level.