What distinguishes the different IFF modes from one another during operation?

The distinction between different Identification Friend or Foe (IFF) modes primarily arises from the unique characteristics of pulse spacing used during communication. Pulse spacing refers to the timing differences between individual pulses in the radar signal. Each IFF mode utilizes different pulse intervals and structures to convey specific information, helping to differentiate between friendly and hostile targets.

In operational contexts, this pulse spacing is critical as it enables identification systems to accurately interpret and respond to the transmitted signals. As various military platforms may employ separate IFF modes with distinctive pulse spacing parameters, this becomes a foundational aspect of how these systems function to enhance situational awareness.

The other choices, while related to signal transmission, do not capture the core mechanism by which IFF modes are differentiated. Frequency modulation and pulsed amplitude modulation describe general methods of signal alteration, but they do not address the specific criteria pertinent to IFF modes. Signal strength can indicate how well a system is receiving data but does not inherently serve as a means of distinguishing among the operational modes themselves. Thus, pulse spacing stands out as the defining feature that characterizes the various IFF modes during operation.