EAS was initially a system that made it possible for the President of the United States to speak directly to the people via AM and FM radio in a time of national emergency. It has never actually been used for that purpose.
EAS is now used by state, regional and local authorities to deliver urgent emergency information via radio and television using the mechanisms originally designed for the presidential message system.
An overview may be found on the Federal Communications website at:
Much more detailed information may be found on the FCC website at:
The actual rules and regulations contained in the Code of Federal Regulations are at:
At the national level certain station(s) in each state are able to receive EAS messages from the federal government. Most states have published plans defining their system.
If you hear an EAS Alert on AM or FM radio, you will hear several bursts of digital data. The data contains an extremely brief description of the emergency (or test), some information on the location and expected duration of the emergency situation. It also includes data showing what agency originated the EAS Alert. These data bursts may be followed by 3 short bursts terminating the message, but in most cases they are followed by a tone of 8-20 seconds duration followed by a voice message which may be as long as 2 minutes.
Plans vary by state, but in most cases the EAS Alert is originated by a state, regional, or county government agency. The EAS is encoded and transmitted to a local radio station and/or some sort of state radio network. It may be transmitted to the National Weather Service in which case they will rebroadcast the alert in a slightly different format (SAME) over NOAA Weather radio transmitters in the area. Some states send the EAS out on a statewide VHF or microwave network.
Most often a primary local station (or several) broadcast the EAS on their transmitters and other stations receive the EAS Alert. Automated EAS receivers at all stations are to monitor at least 2 sources of EAS. These automated receivers detect the EAS from the originating station, record it, authenticate it, and verify that it applies to their broadcast geographical area. After this process the station either manually or automatically will interrupt their programming and broadcast the EAS.
In some locations the relay process from station to station works almost faultlessly, but in some areas it does not. Stations in some areas often miss weekly tests. Often this is due to atmospheric conditions, failure of another station to relay the message, operator error, or equipment malfunction. By monitoring more than the 2 EAS sources required by the FCC and by monitoring NOAA Weather Radio these missed Alerts can be minimized, but can still be a significant delay as the EAS passes through each station for authentication–a possible 2-3 minute delay at each hop.
A statewide communications path can help. In Washington State the EAS alerts from the main emergency management office are distributed on a State Patrol radio link that covers the state. Stations can monitor other radio stations, the National Weather Service, and the Washington State Patrol VHF channel. But a statewide system often involves complexity and a considerable terrestrial infrastructure that can be damaged by natural or manmade disasters. A statewide system that is not dedicated to EAS can also be overloaded with other traffic related to life and property. A dedicated satellite based EAS distribution system can avoid these possible problems.
The primary advantage is the lack of vulnerable terrestrial infrastructure between the Emergency Management Office, radio stations and public safety agencies. Standard telephone lines and internet may fail or be overloaded during emergencies.
A further advantage is that when the EAS goes out on satellite, all stations and agencies receive the information immediately. There is no relay and authentication delay at other facilities and no chance of failure of a relaying station.
Currently an AMBER Alert may be transmitted via EAS. Recently the FCC added a 3 letter code for such alerts. However, the brevity of the digital portion of the EAS does not allow for any useful details regarding an abducted or missing child except in the allowed 2 minute period for a voice announcement.
Normally the Satstream EAS satellite system is transmitting only "idle" data on the satellite channel until an actual EAS alert needs to go out. Even when transmitting the digital EAS or the Alert Tone commands, some of the Satstream system bandwidth is available. The throughput is approximately 3000-4800 bits per second. We have provided a completely separate data channel that can be used at full speed (when EAS is not passing through) in order to transmit AMBER Alert information details in text or graphic form. This data comes out of our receiver on a separate data connector and acts as a completely separate data channel.
SCPC is an abbreviation for Single Channel Per Carrier. This was the primary method of sending TV and audio through satellites for many years. The trend over the last 10 years has been to move away from SCPC and toward use of broadband DVB. The newer technique can mix together dozens of TV, audio and data channels and transmit them through a satellite as a very high bandwidth (broadband) signal. But this mixing must normally be done at a central location. That means terrestrial infrastructure may be necessary to get the EAS from an Emergency Management Office to an uplink site for combination with many other services.
SCPC in our product means narrowband. While a TV channel may occupy an entire 24 MHz (24000 KHz) satellite transponder, our signal requires only about 25-30 KHz of satellite bandwidth. This keeps the cost of satellite time to a minimum.
Another major advantage of SCPC is that the EAS is going out on a fully dedicated channel. No one else uses the frequency. There are other systems used for home or business internet access and for credit card authentication that make use of a high bandwidth shared channel. With those systems the channel is shared and often a complex ground based system is used to control access and repackage the data on the ground. It looks like a satellite system but in fact it depends on considerable earth based infrastructure.
We recommend that our 21521 FSK SCPC Satellite Receiver be located at each media outlet or public safety agency with an outside dish antenna of about 4' diameter aimed at the satellite. The uplink will require our model 21421 FSK SCPC Uplink Modulator and an uplink transmitter. A power output of only 1 or 2 watts is required–another advantage of narrow bandwidth systems.
See the Satstream EAS products page for further details.
All elements of the EAS are digitized at our uplink modulator. We don't transmit the actual EAS tones or FSK signal or voice signal over the satellite. Instead we send a compressed version of each of these signals. At the receiver these digital packet signals are unpacked and regenerated as precise EAS tones and FSK data. The voice announcement is decompressed using AMBE technology provided by Digital Voice Systems.
Besides carrying AMBER Alert details, the second serial data channel can be used to send other messages and notifications to media outlets, law enforcement, and other public safety agencies. If statewide systems fail, Satstream can provide a robust backup digital channel. This channel can carry anything that requires distribution.