Operation
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© 2017 Pico Technology
pv106ug r1
6.3.4
Group delay
Group delay is defined as the rate of change of phase with frequency:
In relatively non-dispersive components such as transmission lines, group delay is the transit time through
the line. However, some components such as filters can exhibit negative group delays so care is needed
when attaching an interpretation to group delay.
The PicoVNA 106 calculates the group delay by dividing the phase change between adjacent sweep points
and dividing by the size of the sweep step. It is usual to apply some degree of trace smoothing to remove
very rapidly changing perturbations from the trace. Care should be exercised to ensure that genuine sharp
group delay variations are not masked by the smoothing.
Displaying the results
Group delay of any S-parameter can be measured. The result can be displayed by selecting the required
parameter and group delay graph from the
Display
window as described in
Display setup
.
6.3.5
Time domain measurements
The time domain facility allows the display of the time domain response of a network under test. For
example, time domain reflectometry (TDR) measurements can be made by first carrying out an S
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calibration using 1024 sweep points. Similarly, time domain transmission (TDT) measurements can be
made by first completing an S
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calibration using 1024 sweep points. The steps necessary are shown in the
flowcharts below.
Performing a TDR measurement
