1. Verify that the discrepancy between the PXIe-5663E and the source is within the error limits of the devices.
    1. Verify the absolute amplitude accuracy of the PXIe-5663E using the appropriate value.
    2. Verify the level accuracy of the input signal into the receiver.
  2. Check for cable loss, which can be substantial. For example, an RG58 coaxial cable loses about 2.1 dB of signal amplitude per foot at 2 GHz. Unless you are using high-quality cables, expect losses when working with high-frequency signals.
  3. Perform a self-calibration for the PXIe-5663E.

If errors continue, contact NI technical support or visit ni.com/support.