HP 54753A User Manual page 218

Figure 10-9
Errors present in the TDR normalization waveform (bottom) are visible in the measured waveform
(top)
Improving Time Domain Network Measurements
Removing Measurement Errors
In both cases, the measured waveforms are stored and subtracted directly from
the measured DUT response before the response is filtered. Ideally, these
normalization waveforms are flat lines. Any non-flatness or ringing is
superimposed on the measured DUT response and represents a potential
measurement error source. These errors are not related to the magnitude of
the response of the DUT. Therefore, it is valid to subtract them directly. Notice
in Figure 10-9 that the errors present in the TDR normalization waveform
(bottom) are also visible in the measured DUT waveform (top), particularly at
the left side of the figure.
10-12