Jump to content

Specific Area Message Encoding

Add links
From Wikipedia, the free encyclopedia
This is an old revision of this page, as edited by Radiojon (talk | contribs) at 05:12, 14 August 2003 (moving SAME-specific info from EAS page & organizing it). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)

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 ___Hz mark tone and ___Hz space tone. The data is encoded in 7-bit ASCII, with no parity bit and one stop bit ("7-N-1").

In the SAME system, messages are originated in four parts. 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. Alternating 01010101 "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 Header Breakdown

The EAS header contains these elements, in this transmitted sequence:

  1. (Preamble) ZCZC-org-eee-pssccc-pssccc+tttt-jjjhhmm-llllllll
  2. Attention (two-tone) signal
  3. Message - audio, video image or video text
  4. (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
  • tttt: Duration of alert (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
  • 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 forty-nine optional headers that users may program

Required

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

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: Civil emergency message
  8. CFA: Coastal flood watch
  9. CFW: Coastal flood warning
  10. DMO: Demonstration message
  11. DSW: Dust storm warning*
  12. EQW: Earthquake warning*
  13. EVI: Evacuation Immediate
  14. FFA: Flash flood watch
  15. FFW: Flash flood warning
  16. FFS: Flash flood statement
  17. FLA: Flood watch
  18. FLW: Flood warning
  19. FLS: Flood statement
  20. FRW: Fire warning*
  21. HUA: Hurricane watch
  22. HUW: Hurricane warning
  23. HLS: Hurricane statement
  24. HMW: Hazardous materials warning*
  25. HWA: High wind watch
  26. HWW: High wind warning
  27. LAE: Local area emergency*
  28. LEW: Law enforcement warning*
  29. NIC: National Information Center
  30. NMN: Network message motif*
  31. NPT: National periodic test
  32. NUW: Nuclear plant warning*
  33. RHW: Radiological hazard warning*
  34. SMW: Special marine warning*
  35. SPS: Special weather statement
  36. SPW: Shelter in place warning*
  37. SVA: Severe thunderstorm watch
  38. SVR: Severe thunderstorm warning
  39. SVS: Severe weather statement
  40. TOA: Tornado watch
  41. TOE: 911 telephone outage emergency*
  42. TOR: Tornado warning
  43. TRA: Tropical storm watch
  44. TRW: Tropical storm warning
  45. TSA: Tsunami watch
  46. TSW: Tsunami warning
  47. VOW: Volcano warning*
  48. WSA: Winter storm watch
  49. WSW: Winter storm warning

(*new codes added in 2002)

Retrieved from "https://en.wikipedia.org/w/index.php?title=Specific_Area_Message_Encoding&oldid=1289836"