Specific Area Message Encoding

Specific Area Message Encoding or SAME is the protocol used to encode the Emergency Alert System in the U.S. for broadcast stations. It was originally created for weatheradio by the National Weather Service, and was later adopted by the FCC for regular broadcasters on radio, television, and cable.

The system transmits digital tones over normal audio using AFSK, with a 2083.3Hz mark tone and 1562.5Hz space tone, lasting 1920μs (1.92ms) each. The data is encoded in 7-bit ASCII but uses all 8 bits, with no parity bit and no stop bit ("8-N-0"), at a bitrate of 520.83 bits per second.

In the SAME system, messages are constructed in four parts, the first and last of which are digital. The first part is the AFSK-encoded header message in 7-bit ASCII text. It is repeated three times, so that decoders can pick "best two out of three" for each byte, thereby eliminating most errors which can cause an activation to fail. The text of the header code contains:

1. A preamble of binary 10101011 (0xAB in hex) repeated sixteen times, used for "receiver calibration", then the letters ZCZC as an attention to the decoder
2. Information about the originator of the alert:
   • EAN - national authorities, including the President
   • CIV - civil authorities, such as president, governor or local city/county emergency management agency
   • WXR - National Weather Service weatheradio
   • EAS - broadcasters, such as radio & TV stations, or cable TV companies
3. Event type (see below)
4. Areas affected (up to 32), usually designated by county (or parish in Louisiana, or borough in Alaska), but which may be designated for the whole state by using county number 000.
5. Duration of alert, normally in increments of 15 minutes from time of issue
6. Exact time of issue, in UTC, without time zone adjustments
7. Eight-character station callsign identification, with / used instead of - .

Full Message Breakdown

An EAS message contains these elements, in this transmitted sequence:

1. Header: (Preamble) ZCZC-org-eee-pssccc-pssccc+tttt-jjjhhmm-llllllll
2. Attention (two-tone) signal
3. Message - audio, video image or video text
4. Tail: (Preamble) NNNN (EOM)

There is one second of blank audio between each section, and before and after each message.

• (Preamble): Signal that clears and resets the receiving system; factory-programmed
• ZCZC: Start of ASCII code; factory-programmed
• org: Originator code; programmed per unit when put into operation
• eee: Event code; programmed at time of event
• pssccc: County-location codes (up to 32 locations); programmed at time of event
  • ss is the state or equivalent water area code
  • ccc is the county/borough/parish, independent city, or equivalent (000 for entire state)
  • p is the part of the county, or 0 for the entire county
• tttt: Duration the alert is valid (hhmm format); programmed at time of event
• jjjhhmm: Date and Time-of-Day; encoded automatically, based on settings
  • jjj is the Julian date day of the year, in UTC, with leading zeros
  • hhmm is 24-hour hours and minutes, in UTC, with leading zeros
• llllllll: Eight-Character ID; programmed per unit when put into operation
  • broadcast station callsign, such as WXXX/FM
  • NWS location, such as KDEN/NWS for Denver, Colorado
• Attention signal: Sent if any message is included (normally sent with all messages except RWT); must be at least eight seconds long
• NNNN: End-of-message code (EOM)

Event codes

There are two types of event codes, four that are required to be encoded in every unit used, and 49 optional headers that users may program

Required

1. EAN: Emergency action notification
2. EAT: Emergency action termination
3. RMT: Required monthly test
4. RWT: Required weekly test

Optional

1. ADR: Administrative message
2. AVA: Avalanche watch
3. AVW: Avalanche warning
4. BZW: Blizzard warning
5. CAE: Child abduction emergency*
6. CDW: Civil danger warning
7. CEM: Dust storm warning*
8. EQW: Earthquake warning*
9. EVI: Evacuation Immediate
10. FFA: Flash flood watch
11. FFW: Flash flood warning
12. FFS: Flash flood statement
13. FLA: Flood watch
14. FLW: Flood warning
15. FLS: Flood statement
16. FRW: Fire warning*
17. HUA: Hurricane watch
18. HUW: Hurricane warning
19. HLS: Hurricane statement
20. HMW: Hazardous materials warning*
21. HWA: High wind watch
22. HWW: High wind warning
23. LAE: Local area emergency*
24. LEW: Law enforcement warning*
25. NIC: National Information Center
26. NMN: Network message motif*
27. NPT: National periodic test
28. NUW: Nuclear plant warning*
29. RHW: Radiological hazard warning*
30. SMW: Special marine warning*
31. SPS: Special weather statement
32. SPW: Shelter in place warning*
33. SVA: Severe thunderstorm watch
34. SVR: Severe thunderstorm warning
35. SVS: Severe weather statement
36. TOA: Tornado watch
37. TOE: 911 telephone outage emergency*
38. TOR: Tornado warning
39. TRA: Tropical storm watch
40. TRW: Tropical storm warning
41. TSA: Tsunami watch
42. TSW: Tsunami warning
43. VOW: Volcano warning*
44. WSA: Aural example of SAME transmission