HP 8753E User Manual page 321

Group delay measurements can be made on linear frequency, log frequency, or list frequency
sweep types (not in CW or power sweep). Group delay aperture varies depending on the
frequency spacing and point density, therefore the aperture is not constant in log and list
frequency sweep modes. In list frequency mode, extra frequency points can be deiined to
ensure the desired aperture.
To obtain a readout of aperture..values at different points on the trace, turn on a marker. Then
aperture is varied its value in Hz is displayed below the active entry area.
Application and Operation Concepts