Editing Group delay and phase delay (section)

==== Basic modulation system ====

[[File:Outer and Inner LTI Device.png|Figure 1: Outer and Inner LTI Devices|frame]]

A device's group delay can be exactly calculated from the device's phase response, but not the other way around.  The simplest use case for group delay is illustrated in Figure 1 which shows a conceptual [[modulation]] system, which is itself an LTI system with a baseband output that is ideally an accurate copy of the baseband signal input. This system as a whole is referred to here as the outer LTI system/device, which contains an inner (red block) LTI system/device.  As is often the case for a radio system, the inner red LTI system in Fig 1 can represent two LTI systems in cascade, for example an amplifier driving a transmitting antenna at the sending end and the other an antenna and amplifier at the receiving end.