Transponder modes at a glance — interrogation 1030 MHz / reply 1090 MHz
This page is a condensed excerpt from the IFF / SSR reference issued to students in Yankee Actual's EW operations training programs. The complete reference details waveforms, pulse timing, code structures, encryption, and interrogation behavior for every mode — with signal-level analysis exercises from course labs.
| Mode | Classification | Primary Use | Secured |
|---|---|---|---|
| Mode 1 | Military | Mission / sortie identification | None |
| Mode 2 | Military | Aircraft tail-number identification | None |
| Mode 3/A | Military / Civil | ATC identity (squawk) | None |
| Mode C | Military / Civil | Pressure altitude reporting | None |
| Mode 4 | Military | Encrypted challenge–response IFF | Encrypted |
| Mode 5 | Military | Modern crypto-secured IFF with position data | Encrypted |
| Mode S | Military / Civil | Selective interrogation & data link (TCAS) | None |
| ADS-B (1090ES) | Civil / Military | Autonomous position broadcast | None |
COMPLETE MODE-BY-MODE SIGNAL DETAIL PROVIDED IN YANKEE ACTUAL TRAINING PROGRAMS
