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Protocol References

This directory contains technical / engineering-level references for the on-air signalling protocols EAS Station™ produces and consumes. They describe the bit-level frame format, modulation parameters, error-detection and forward-error-correction schemes, and how each protocol is implemented in this codebase.

These documents are aimed at developers and operators who need to debug waveforms, verify implementations against external decoders, or extend the protocol support. Operator-facing setup instructions live under docs/guides/ instead.

Protocol Document Modulation Implementation
SAME — Specific Area Message Encoding (FCC 47 CFR §11.31, NRSC-4-B §4) SAME.md AFSK · 520.83 baud · 2083.33 / 1562.5 Hz app_utils/eas_fsk.py, app_utils/eas.py, app_utils/eas_decode.py, app_utils/eas_demod.py
MDC1200 — Motorola 1200-baud FFSK selective calling MDC1200.md FFSK · 1200 baud · 1200 / 1800 Hz app_utils/mdc1200.py
Alpha M-Protocol — Alpha Sign Communications Protocol (9708-8061F) for the Alpha 9120C LED sign ALPHA_M_PROTOCOL.md RS-232/RS-485 or TCP · framed serial scripts/led_sign_controller.py

For the broader RBDS Annex-D treatment of SAME (as embedded in NRSC-4-B for FM broadcasters), see also ../NRSC4B_SAME_STANDARD.md.

For a behavioral reference and gap analysis against the commercial Sage Digital ENDEC appliance — its serial/network device protocols (raw EAS encoder, decoder status, Generic CGEN, News Feed) and incoming-alert filtering/priority model — see SAGE_ENDEC.md.

How they are combined

Every EAS Station™ broadcast — auto-forwarded CAP/IPAWS, OTA EAS relay, or manually-authored alert — passes through the same composite-audio assembly in EASAudioGenerator.build_files (and build_manual_components for operator-authored events). The on-air timeline is:

flowchart LR PRE["Pre-alert signal<br/>(optional)<br/><i>MDC1200 PTT-ID Pre fits here</i>"] SAME["3 × SAME header<br/>ZCZC-…"] TONE["Attention tone<br/>8 s · 853 + 960 Hz"] VOICE["Voice narration<br/>TTS / mp3"] EOM["3 × SAME EOM<br/>NNNN"] POST["Post-alert signal<br/>(optional)<br/><i>MDC1200 PTT-ID Post fits here</i>"] PRE --> SAME --> TONE --> VOICE --> EOM --> POST classDef signal fill:#fef3c7,stroke:#92400e,color:#78350f; classDef same fill:#dbeafe,stroke:#1e40af,color:#1e3a8a; classDef voice fill:#dcfce7,stroke:#166534,color:#14532d; class PRE,POST signal; class SAME,EOM same; class TONE,VOICE voice;

The signal slots are protocol-agnostic — they accept any of the profiles listed in app_utils/eas.ALERT_CHIME_PROFILES (bell, beep, three_tone, qc2, dtmf, mdc1200). When MDC1200 is selected for both ends and the op-code preset is ptt_id_pre (the default), the post side automatically substitutes ptt_id_post so subscriber radios see a complete bookend pair. This is what enables the two-way LMR forwarding use case described in MDC1200.md.

Back to Documentation Index

This document is served from docs/reference/protocols/README.md in the EAS Station™ installation.