The aperture defaults to the smallest setting for the frequency range
and number of data points selected. This value is displayed in the Set
Scale key menu when measuring group delay (Figure 8-19).
Group delay applications are found throughout the microwave indus-
try, although the majority of such measurements are made in the tele-
communications area.
One occurrence of group delay that you may have experienced is with
a long-distance telephone call. Occasionally a phone call can be dis-
turbing because of the delay in time from when you speak and when
the other person responds. If there is simply a delay, then time de-
lay—or linear group delay—has occurred. But if the voices are also dis-
torted, then non-linear group delay has occurred. It is this distortion
that we must avoid. We can avoid linear group delay by measuring
group delay both during the design and development stages and dur-
ing recalibration in the field.
One final group-delay application is found in the development of com-
ponents. In this application, group delay is measured for the transit
time of a signal through the device. When time is of the essence in a
fast switching system, as in a modern computer, the travel time
through a device is critical.
37xxxE OM 8-23
MEASUREMENTS GROUP DELAY
S 2 1 F O R W A R D T R A N S M I S S I O N
G R O U P D E L A Y R E F = 1 . 0 0 0 n S 6 0 0 . 0 0 0 p S / D I V
9 . 0 0 0 0
3 . 0 0 0 0
G H z
Figure 8-19. 37xxxE Aperture