Adjustment Components

1. The NI 5610 upconverter module adjusts the NI RF signal generator output signal power level in increments of 1 dB by asserting up to 121 dB of onboard IF and RF attenuation. The NI 5610 upconverter module has a maximum output power level specified at 10 dBm (at room temperature). (Absolute maximum power is a function of frequency and is unit-dependant. Refer to the Allow Out of Specification User Settings property or the NIRFSG_ATTR_ALLOW_OUT_OF_SPECIFICATION_USER_SETTINGS attribute for more information about absolute maximum power). Attenuation settings for given frequencies and temperatures are determined during calibration.
2. The AWG module provides fine signal power adjustment by tuning the main digital-to-analog converter (DAC) attenuation and by scaling the digital waveform. NI-RFSG automatically selects a DAC attenuation setting based on signal power requirements. As more attenuation is required, the following components are adjusted:
   • Main DAC — 3 dB of analog signal attenuation is available (in increments of less than 0.02 dB) by adjusting the NI 5421/5441 module main DAC attenuation. Attenuating the DAC output signal allows very fine resolution control over signal power while maintaining optimal DAC dynamic range, ensuring no bits are lost from the digital representation of the waveform. Adjusting the main DAC does not apply to the NI 5672.
   • Digital Waveform Scaling — If more attenuation is needed, NI-RFSG modifies the digital waveform such that it does not occupy the full-scale output voltage of the DAC. Scaling the digital waveform this way potentially decreases the dynamic range and thus the signal-to-noise ratio, but offers more than 30 dB of attenuation. However, scaling has no effect on observable RF signal generator signal-to-noise ratios because NI-RFSG scales the digital waveform only at power levels , where other components dominate the signal-to-noise ratio (< -85 dBm typical). NI-RFSG performs scaling on both sine waves and arbitrary waveforms as required.

If the frequency output is varied while keeping power output levels constant, NI-RFSG may automatically adjust the attenuator settings and the IF power levels to maintain constant power output.