Conventional SSR and Mode S use 1030 MHz for interrogations and 1090 MHz for replies (supplementary reading, Mode S).

Pulse spacing is drawn schematically, not to scale.

Callsigns and flight details are fictional. Correlation is simplified; real systems also use track position and code-change handling.

Illustrative. The pulse patterns are simplified; overlapping pulses are shown merging.

Illustrative. The spread of positions is exaggerated to make the difference visible.

Which parameters appear depends on the aircraft’s equipment and the ATM system. Values shown are fictional.