HP 54753A User Manual page 220

Figure 10-10
The lower waveform is a copy of the upper waveform with the voltage scale greatly expanded about
the baseline to show more clearly the shape of the secondary reflection
Improving Time Domain Network Measurements
Removing Measurement Errors
BNC connector. A secondary reflection from the DUT is visible at the right end
of the baseline. Notice that the secondary reflection is indeed quite small. It
has a peak voltage value of about 1.5 mV at 40 ps risetime, which is about 0.75%
of the 200 mV incident step.
In step TDNA, a section of airline may be placed between the test port and the
DUT to provide time separation between the primary reflection and secondary
reflections. Figure 10-11 illustrates the use of this technique. A secondary
reflection is visible very close to the primary reflection in the top waveform. It
is difficult to tell them apart. A short section of airline was placed between the
DUT and the test port, resulting in the lower waveform. Note that the primary
and secondary reflections are clearly separated. When the primary and
secondary reflections are close together, the shapes of both may be distorted.
If they are adequately separated in time, as is the case in the lower waveform,
they no longer have a significant effect on each other.
10-14