Specific Area Message Encoding

History

From the 1960s to the 1980s, a special feature of the NOAA Weather Radio (NWR) system was the transmission of a single 1050 Hz attention tone prior to the broadcast of any message alerting the general public of significant weather events. This became known as the Warning Alarm Tone (WAT). Although it served NWR well, there were many drawbacks. Without staff at media facilities to manually evaluate the need to rebroadcast an NWR message using the Emergency Broadcast System (EBS), automatic rebroadcasting of all messages preceded by just the WAT was unacceptable and impractical. Even if stations and others with the need were willing to allow for this type of automatic capture, assuming the events for activation were critical, there was no way for automated equipment at the station to know when the message was complete and restore it back to normal operation.

SAME had its beginnings in the early 1980s when NOAA's National Weather Service (NWS) began experimenting with system using analog tones in a dual-tone multi-frequency (DTMF) format to transmit data with radio broadcasts. In 1985, the NWS forecast offices began experimenting with placing special digital codes at the beginning and end of every message concerning life- or property-threatening weather conditions targeting a specific area. The intent of what became SAME was to ultimately transmit a code with the initial broadcast of all NWR messages. The NWS started implementing SAME on the full NWR system in 1998. In 2003, NOAA established a SAME technology standard for weather radio receivers. However, the roll-out moved slowly until 1995, when the U.S. Government provided the budget needed to develop the SAME technology across the entire radio network. Nationwide implementation occurred in 1997, when the Federal Communications Commission (FCC) adopted the SAME standard as part of its new Emergency Alert System (EAS).

The SAME technique was later adopted by the U.S. Federal Communications Commission (FCC) in 1997 for use in the EAS as well as by Environment Canada for its Weatheradio Canada service in 2004. Much like the original EBS dual-tone  Attention Signal , this produces a distinct sound (the  SAME header ) which is easily recognized by most individuals due to its use in weekly and monthly broadcast tests, as well as weather alert messages. During the said events, viewers and/or listeners will hear these digital codes in the form of buzzes, chirps, and clicking sounds (or what broadcast engineers affectionately call "duck farts") just before the attention signal is sent out and at the conclusion of the voice message.

Format of the digital parts

In the SAME system, messages are constructed in four parts, the first and last of which are digital and the middle two are audio. The digital sections of a SAME message are AFSK data burst, with each individual bit lasting 1920 μs (1.92 ms) each, giving a bit rate of 520 ⁵⁄₆ bits per second. A mark bit is four complete cycles of a sine wave, translating to a mark frequency of 2083 ¹⁄₃ Hz, and a space bit is three complete sine wave cycles, making the space frequency 1562.5 Hz.

The data is sent isochronously and encoded in 8-bit bytes with the most-significant bit of each ASCII byte set to zero. The least-significant bit of each byte is transmitted first, including the preamble. The data stream is bit and byte synchronized on the preamble.

Since there is no error correction, the digital part of a SAME message is transmitted 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. However, consumer weather radio receivers often activate (unmute the audio) after hearing only one out of the three headers (with a significant delay).

Header format

The text of the header code is a fixed format:

<Preamble>ZCZC-ORG-EEE-PSSCCC+TTTT-JJJHHMM-LLLLLLLL-

This is broken down as follows:

1. A preamble of binary 10101011 (0xAB in hex) repeated sixteen times, used for "receiver calibration" (i.e., clock synchronization), then the letters ZCZC as an attention to the decoder (a message activation method inherited from NAVTEX).

2. ORG — Originator code; programmed per unit when put into operation

PEP – Primary Entry Point Station

President or other authorized national officials

CIV – Civil authorities

i.e. Governor, state/local emergency management, local police/fire officials

WXR – National Weather Service (or Environment Canada.)

Any weather-related alert

EAS – EAS Participant

Broadcasters. Generally only used with test messages.

EAN – Emergency Action Notification Network

Used to send Emergency Action Notifications.

3. EEE — Event code; programmed at time of event

4. PSSCCC — Location codes (up to 31 location codes per message), each beginning with a dash character; programmed at time of event

In the United States, the first digit (P) is zero if the entire county or area is included in the warning, otherwise, it is a non-zero number depending on the location of the emergency.

In the United States, the remaining five digits are the FIPS state code (SS) and FIPS county code (CCC). The entire state may be specified by using county number 000 (three zeros).

In Canada, all six digits specify the Canadian Location Code, which corresponds to a specific forecast region as used by the Meteorological Service of Canada. All forecast region numbers are six digits with the first digit always zero.

5. TTTT — Purge time of the alert event (from exact time of issue)

In the format hhmm, using 15 minute increments up to one hour, using 30 minute increments up to six hours, and using hourly increments beyond six hours. Weekly and monthly tests sometimes have a 12-hour or greater purge time to assure users have an ample opportunity to verify reception of the test event messages; however; 15 minutes is more common, especially on NOAA Weather Radio's tests.

For short term events (like a tornado) this value could be set to 0000 (four zeros), which will purge the warning immediately after the message has been received. However, this is not typical, and FCC guidelines suggest a minimum of 15 minutes purge time.

The purge time is not intended to coincide with the actual end of the event. Longer events that may not end for days (like hurricanes) may have a purge time of only a few hours. That an event message has been purged does not indicate or imply that the threat has passed.

6. JJJHHMM — Exact time of issue, in UTC, (without time zone adjustments).

JJJ is the Ordinal date (day) of the year, with leading zeros

HHMM is the hours and minutes (24-hour format), in UTC, with leading zeros

7. LLLLLLLL — Eight-character station callsign identification, with "/" used instead of "–" (such as the first eight letters of a cable headend's location, WABC/FM for WABC-FM, or KLOX/NWS for a weather radio station programmed from Los Angeles).

Each field of the header code is terminated by a dash character, including the station ID at the end; individual PSCCC location numbers are also separated by dashes, with a plus (+) separating the last location from the purge time that follows it.

Full message format

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

1. Header.
2. Attention signal — Sent if any message is included (normally sent with all messages except RWT on broadcast radio/TV); must be at least eight seconds long. (On Weatheradio in Canada the 1050 Hz tone is only used with three event codes: RMT, SVR & TOR.)
3. Single  1050 Hz  audio tone for Weatheradio.
4. Combined  853 and 960 Hz  tones for broadcast radio/TV.
5. Message — Audio, video image or video text.
6. Tail — (Preamble) NNNN (EOM).

There is one second of blank audio between each section, and before and after each message. For those used to packet communications systems where each packet has a checksum, note that there is no checksum used in the message format. Each message is supposed to be transmitted 3 times, and the receiver is obliged to implement columnar parity correction.

The combined tones date back to 1976 when they were made part of the Emergency Broadcast System, the EAS' predecessor.

Event codes

There are roughly 80 different event codes that are used in EAS. These codes are defined federally by the FCC for use in the EAS system and publicly by the Consumer Electronics Association (CEA) standard for SAME protocol weather radio receiver decoder units.

All but the first six of these used to be optional and could be programmed into encoder/decoder units at the request of the broadcaster. However, a July 12, 2007 memo by the FCC now requires mandatory participation in state and local level EAS by broadcasters. Furthermore, the creation and evolution of a voluntary standard by the CEA in December 2003 has provided participating manufacturers of weather radio receivers a single definitive reference to use when designing and programming receivers. In addition, some receiver manufacturers have added an additional layer as to whether or not an event code can be user-suppressed (e.g., a Hurricane Warning in a Midwest US State) or will never be allowed to be suppressed (e.g., nuclear power plant warning).

Key for event code tables Event codes in use: The following event codes have been implemented by agencies in the United States and/or Canada, and CIRES A.C. in Mexico. ** While the CEA standard lists the FZW event code as "Freeze Warning", Environment Canada refers to it as a "Frost Warning". However, it will be displayed as a "Freeze Warning" on receivers that are compliant to the CEA standard. † Environment Canada additionally uses the WSW event code to refer to any of the following weather conditions: Blowing Snow Warning, Freezing Drizzle Warning, Freezing Rain Warning, Snowfall Warning, Snow Squall Warning *** The EQW and VOW event codes are used in Mexico as part of the Seismic Alert System (also known as SASMEX. The receivers are known as Seismic Alert Radio, and the system known as SARMEX). EQW is referred as "Alerta Sísmica", while VOW is referred to as "Alerta Volcánica". Other event codes are being tested, such as Hurricane Warning (HUW), Hurricane Watch (HUA) and Hurricane Statement (HLS). Required Weekly Tests (RWT) are conducted every three hours to make sure receivers are working properly. Internal use only: Receiver decoders that comply to the CEA standard will neither display the messages below, nor activate a warning tone if applicable. While the message will be stored in memory, it will not be displayed to the user. The FCC has also designated these event codes as being for "internal use only", and not for display. Environment Canada lists these messages as "Administrative Bulletins". Future implementation: The following codes are part of the CEA standard for receiver decoders, but are not listed as being in use by any agencies in the United States. Environment Canada lists these codes as being "for future implementation". None of these event codes are being implemented in Mexico, as Mexico's network is for seismic and volcanic alerts at this time. Future Proposal: The following codes are not part of the CEA standard for receiver decoders, nor are they listed as being in use by any agencies in the United States. The National Weather Service has requested the FCC to create and adopt these codes for future implementation.

The FCC established naming conventions for EAS event codes. The third letter of the code must be one of the following.

The exception to this convention is for "TOR" (tornado warning), "SVR" (Severe Thunderstorm Warning), "EVI" (Evacuation Immediate), the EAS national activation codes, and administrative messages.

SAME on weather radio receivers

There are many weather/all-hazards radio receivers that are equipped with the SAME alert feature. It allows users to program SAME/FIPS/CLC codes for their designated area or areas of their interest and/or concern rather than the entire broadcast area. (Examples given: If a person were to live in Irving, Texas, he or she would program a FIPS code for Dallas County. However, if he or she needs to be in the know of severe weather from the west and northwest ahead of time, the user would program additional FIPS codes for Denton and Tarrant Counties.) On a more specialized receiver, a user has the option to eliminate any SAME alert codes that may not apply to their area such as a "Special Marine Warning" or a "Coastal Flood Warning". Once the SAME header is sent by NOAA/NWS and if it matches the desired code(s), the receivers then decode the event, scroll it on their display screens, and sound an alarm.

Receivers receive on one of the following National Weather Service network frequencies (in MHz): 162.400, 162.425, 162.450, 162.475, 162.500, 162.525, and 162.550. The signals are typically receivable up to 50 miles from the transmitters.

SAME in popular culture

The SAME EOM (end of message) tone was heard in the movie trailer for Knowing and in the series Jericho where its familiar emergency use and its increasing cadence create a sense of foreboding. It was used in the movie trailer for Olympus Has Fallen and The Purge. These uses have since been heavily discouraged on-air by the FCC (outside of public service announcements demonstrating SAME and EAS technology), and stations and networks using them (for instance, TBS and WNKY-TV in Bowling Green, Kentucky) in advertising or promotions have been fined for doing so.