Technical data

5-19
Operating Concepts
Analyzer Display Formats
Figure 5-12. Real Format
Imaginary Format
The IMAGINARY, 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 5-13.