# Using the NI RF Signal Conditioning Devices With RF Vector Signal Analyzers

NI RF Signal Conditioning Devices Help (NI-5690 14.5)

Edition Date: March 2015

Part Number: 371326D-01

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The NI RF signal conditioning devices are designed to work with NI RF vector signal analyzers such as the NI PXI‑5660, NI PXI‑5661, and NI PXIe‑5663. NI RF signal conditioning devices are analog devices that amplify or attenuate their input signal according to the specified path and gain settings. No triggering scheme is required.

## Reference Level Settings

When using the NI RF signal conditioning devices with an NI RF vector signal analyzer, consider the following factors when determining the NI RF vector signal analyzer reference level setting.

1. The NI RF vector signal analyzer reference level specifies the expected total integrated power, in dBm, of the NI RF vector signal analyzer input signal.
2. The gain specified in the ni5690 Configure Gain VI or the ni5690_configureGain function is applied before the signal is passed to the NI RF vector signal analyzer.
3. Therefore, when using an NI RF vector signal analyzer with NI RF signal conditioning devices, set the NI RF vector signal analyzer reference level according to the following equation:

expected signal power + actual gain as returned by the ni5690 Get Actual Gain VI or the ni5690_getActualGain function

For example, to obtain an input signal with a total integrated power of less than –30 dBm using a gain setting of 30 dB in the signal conditioning device, the proper NI RF vector signal analyzer reference level setting is 0 dBm.

## Linearity

Consider the following linearity factors when using NI RF signal conditioning devices.

Given an output third-order intercept (output TOI) specification, you can determine the intermodulation distortion (IMD) created by the RF amplifier or attenuator nonlinearity. For example, using a two-tone signal, the IMD is expressed by the following equation.

IMD (dBc) = 2 × [output fundamental tone level (dBm) – output TOI (dBm)]

For example, if the NI RF signal conditioning device output TOI at your frequency is +10 dBm, and your application requires better than –60 dBc of IMD, then your output fundamental tone level must be ≤–20 dBm. In this case, if gain is 30 dB, then the input fundamental tone level must be ≤–50 dBm. Notes  CH 1 main path linearity factors are as follows. NI RF signal conditioning device TOI is specified at maximum gain. Typically, TOI does not change significantly with lower gain settings. Referred to the input (for a fixed input power level), the preceding linearity factor in statement 2 translates to improved linearity due to lower gain yielding lower outputs, while the output TOI is typically maintained. Referred to the output (for a fixed output power level), the linearity factor in statement 2 translates to tolerating higher level signals at the input, while linearity is typically maintained.