the current logo of the emergency alert system

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Technical conceptEdit

Main article: Specific Area Message Encoding Messages in the EAS are composed of four parts: a digitally encoded SAME header, an attention signal, an audio announcement, and a digitally encoded end-of-message marker. [1][2]A Sage EAS ENDEC unit. The [3] SAME header (help·info) is the most critical part of the EAS design. It contains information about who originated the alert (the President, state or local authorities, the National Weather Service, or the broadcaster), a short, general description of the event (tornado, flood, severe thunderstorm), the areas affected (up to 32 counties or states), the expected duration of the event (in minutes), the date and time it was issued (in UTC), and an identification of the originating station. (See SAME for a complete breakdown of the header.)

30+ radio stations are designated as National Primary Stations in the Primary Entry Point (PEP) System to distribute Presidential messages to other broadcast stations and cable systems.[2] The Emergency Action Notification is the notice to broadcasters that the President of the United States or his designee will deliver a message over the EAS via the PEP system. "You {AM and FM broadcasters} will hear the following Emergency Action Notification Message from the EAS decoder. This is an Emergency Action Notification requested by the White House. All broadcast stations will follow activation procedures in the EAS Operating Handbook for a national level emergency. The President of the United States or his representative will shortly deliver a message over the Emergency Alert System."[3]

[edit]Communications linksEdit

The FEMA National Radio System (FNARS) "Provides Primary Entry Point service to the Emergency Alert System," acts as an emergency presidential link into the EAS, and is capable of phone patches. The FNARS net control station is located at the Mount Weather Emergency Operations Center.[4]

[edit]What the national level EAS would not doEdit

In a The New York Times article (correction printed January 3, 2002)[5] the lack of news coverage by station WNYC FM, New York, was explained by the destruction of its broadcast transmitters with the collapse of the World Trade Center north tower on 9/11. "No president has ever used the current [EAS] system or its technical predecessors in the last 50 years, despite the Soviet missile crisis, a presidential assassination, the Oklahoma City bombing, major earthquakes and three recent high-alert terrorist warnings.... Michael K. Powell, chairman of the Federal Communications Commission, which oversees the Emergency Alert System, pointed to 'the ubiquitous media environment,' arguing that the system was, in effect, scooped by CNN, MSNBC, Fox News Channel and other channels.... [FEMA] activates the alert system nationally at the behest of the White House on 34 50,000-watt stations that reach 98 percent of Americans.... Beyond that, the current Emergency Alert System signal is an audio message only—which pre-empts all programming—so that viewers who were watching color images of the trade center on Sept. 11 would have been able to see only a blank screen along with a presidential voice-over, if an emergency message had been activated."[5]
Other than the on-screen scrolling message accompanying the initial activation, the Federal Communications System EAS TV Handbook - 2007 does not include any sort of visual element. Under the SAME protocol, precise emergency information would be delivered aurally.

[edit]EAS headerEdit

Because the header lacks error detection codes, it is repeated three times for redundancy. However, the repetition of the data can itself be considered an error detection and correction code—like any error detection or correction code, it adds redundant information to the signal in order to make errors identifiable. EAS decoders compare the received headers against one another, looking for an exact match between any two, eliminating most errors which can cause an activation to fail. The decoder then decides whether to ignore the message or to relay it on the air if the message applies to the local area served by the station (following parameters set by the broadcaster).
The SAME header bursts are followed by an [4] attention signal (help·info) which lasts between eight and 25 seconds, depending on the originating station. The tone is [5] 1050 Hz (help·info) on a NOAA Weather Radio station, while on commercial broadcast stations, it consists of a "two tone" combination of 853 Hz and 960 Hz sine waves and is the same attention signal used by the older Emergency Broadcast System. The "two tone" system is no longer required as of 1998 and is to be used only for audio alerts before EAS messages.[6] Like the EBS, the attention signal is followed by a voice message describing the details of the alert.

[6][7]A Gorman-Redlich rack mounted CAP-to-EAS converter which translates CAP formatted alerts into EAS headers. The message ends with three bursts of the AFSK "EOM", or End of Message, which is the text NNNN, preceded each time by the binary10101011 calibration.

The White House has endorsed the migration to the Common Alerting Protocol (CAP) and FEMA is in the process of testing implementation.[7][8]

Station RequirementsEdit

.The FCC requires all broadcast stations to install and maintain EAS decoders and encoders at their control points. These decoders continuously monitor the signals from other nearby broadcast stations for EAS messages. For reliability, at least two other source stations must be monitored, one of which must be a designated local primary. Stations are to retain the latest version of the EAS handbook.

Stations are required by law to keep full logs of all received and transmitted EAS messages. Logs may be kept by hand but are usually kept automatically by a small receipt printer in the encoder/decoder unit. Logs may also be kept electronically inside the unit as long as there is access to an external printer or method to transfer them to a personal computer.
In addition to the audio messages transmitted by radio stations, television stations must also transmit a visual message. A text "crawl" is displayed at the top of the screen. A color coded "crawl" system is often used where the color signifies the priority of the message. Some television stations transmit only the visual message which is outside of the requirements. A television station may be used for monitoring by another station and thus the audio is necessary.[6]
Upon reception of an alert, a station must relay EAN (Emergency Action Notification) and EAT (Emergency Action Termination) messages immediately (US FCC 7). Stations traditionally have been allowed to opt out of relaying other alerts such as severe weather, and child abduction emergencies (AMBER Alerts) if they so choose. Under new rules published on July 12, 2007, the FCC intends to require all stations to relay state and local alerts that are approved by their states' governors (pending approval of the CAP standard).
Some stations may be non-participating, and do not relay messages. Instead they transmit a message instructing listeners/viewers to tune to another station for the information, and they must then suspend their operation.

[edit]FCC equipment certificationEdit

EAS equipment must be FCC certified for use as described above. The following companies have been certified by the FCC to manufacture such equipment.[9]
Companies certified to manufacture encoder/decoder units
Company Name FCC ID
Burk Technology Inc. MPEEAS
Cadco Systems, Inc. ND2EAS
Digital Alert Systems, LLC R8VDASDEC-1EN
Gorman-Redlich Manufacturing Co. MVZEAS1
Hollyanne Corp. GRQMIP-921
M&N Electronics LLC M46HU-961
Multi-Technical Services, Inc. HTG3000D
Sage Alerting Systems, Inc. MAX1822
Trilithic, Inc. P4V-EASYPLUS-1
Companies certified to manufacture decoder-only units
Company Name FCC ID
Digital Alert Systems, LLC R8VDASDEC-1EN
Gorman-Redlich Manufacturing Co. MVZEAS1
Trilithic, Inc.


All EAS equipment must be tested weekly. The required weekly test (RWT) consists of the header and the end-of-message SAME bursts. The RWT does not need an audio or graphic message announcing the test, although many stations will provide them as a courtesy to the listener or viewer. Television stations are not required to transmit a video message for weekly tests. RWTs are scheduled by the station, alternating between night and day, and are not relayed.[6]Edit

On cable systems before the start of the EAS test, all of a system's channels, both on cable ready televisions directly connected to the coaxial cable, and those on cable boxes, are redirected to one digital channel which is received on all tiers of service, but doesn't usually give out news or weather information (such as the TV Guide Network, QVC, HSN, or a public access station), where the test occurs from the local headend office or from the system's master office elsewhere in the region. Newer technology allows cable DVR and video on demand systems to interrupt playback of a program for an EAS test. After the test ends, the one channel usually remains on screen for 5-10 additional seconds before the original station/network is returned to.[citation needed]
Required Monthly Tests (RMTs) are generally originated by the primary relay station or a State's EAS agency, relayed by broadcast and cable stations. RMTs are conducted with the following procedure:
  1. Normal programming is suspended (commonly during commercial breaks), and an announcement may be made such as: "The following is a monthly test of the Emergency Alert System. This is only a test."
  2. The SAME Header burst is sent, perhaps followed by an attention signal.
  3. Another voice message is sent, which runs something like this:
    "This is a coordinated monthly test of the broadcast stations in your area. Equipment that can quickly warn you during emergencies is being tested. If this had been an actual emergency such as a tornado warning or severe thunderstorm warning, official messages would have followed the alert tone. This concludes this test of the Emergency Alert System."
  4. The SAME EOM burst is sent.
RMTs must be performed between 8:30 a.m. and local sunset during odd numbered months, and local sunset to 8:30AM for even months. Received tests must be retransmitted within 60 minutes from receipt.[6] Additionally, an RMT cannot be scheduled or conducted during an event of great importance such as a pre-announced Presidential speech, coverage of a national election or a major sporting event such as the Olympic Games, the Super Bowl or the World Series as mentioned in individual EAS state plans.
An RWT is not required during a calendar week in which an RMT is scheduled. No testing has to be done at all during a calendar week in which the EAS has been legitimately activated. Coordinated national tests are conducted at least once every year and are very similar to RMTs

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