This test might fail due to incorrect calibration data of the 8494 and 8496 step attenuators. Make sure you have entered the calibration data for the step attenuators that you're using. Please refer to the Equipment Calibration Data section in the N7800A TME Help for details on how to enter this data. You must enter the data for the following columns to obtain valid results: Attn(dB), Uncert(dB) and ReflSize.