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Operating Concepts
Analyzer Display Formats
Real Format
The softkey displays only the real (resistive) portion of the measured data on a
Cartesian format. See Figure 7-13. This is similar to the linear magnitude format, but can
show both positive and negative values. It is primarily used for analyzing responses in the
time domain, and also to display an auxiliary input voltage signal for service purposes.
Figure 7-13 Real Format
Imaginary Format
The softkey displays only the imaginary (reactive) portion of the measured
data on a Cartesian format. This format is similar to the real format except that reactance
data is displayed on the trace instead of resistive data.
Group Delay Principles
For many networks, the amount of insertion phase is not as important as the linearity of
the phase shift over a range of frequencies. The analyzer can measure this linearity and
express it in two different ways: directly, as deviation from linear phase, or as group delay,
a derived value.
Group delay is the measurement of signal transmission time through a test device. It is
defined as the derivative of the phase characteristic with respect to frequency. Since the
derivative is basically the instantaneous slope (or rate of change of phase with respect to
frequency), a perfectly linear phase shift results in a constant slope, and therefore a
constant group delay. See Figure 7-14.
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