Starting 1 July 1995, two tone encoders MAY be modified to transmit the attention signal for 8 to 25 seconds. The shortened tone was suggested by NAB in their EBS petition. The 8 second minimum with a decode time maximum of four seconds insures broadcast stations will continue to properly receive the EBS tones.
Starting 1 July 1995, stations MAY start using the new EAS codes in addi tion to the shortened EBS tone.
Starting 1 July 1996, stations MUST use the new EAS codes along with the shortened EBS tone.
Starting 1 July 1997, stations no longer need to maintain the existing two tone decoders. All station alerting is done by the new EAS codes. Stations MUST continue to broadcast the two tone "attention signal" during monthly tests and during emergencies. Paragraph 95 of the Report and Order indicates that retention of the tone or not making it excessively short was due to comments from a couple organizations representing disabled persons. It was thought that the tones would catch someone's attention better than a short audio frequency shift keyed (AFSK) chirp. In addition, though not mentioned in the Report and Order, there are several thousand consumer receivers in operation around the country that detect the dual tone attention signal. Continued use of the two tone attention signal allows these receivers to continue to operate.
PREAMBLE] ZCZC-ORG-EEE-PSSCCC+TTTT-JJJHHMM-LLLLLLLL- (one second pause) [PREAMBLE] ZCZC-ORG-EEE-PSSCCC+TTTT-JJJHHMM-LLLLLLLL- (one second pause) [PREAMBLE] ZCZC-ORG-EEE-PSSCCC+TTTT-JJJHHMM-LLLLLLLL- (one or more second pause) (two tone attention signal for 8 to 25 seconds) (emergency audio programming) [PREAMBLE] NNNN (one second pause) [PREAMBLE] NNNN (one second pause) [PREAMBLE] NNNN (one or more second pause)
ORG is a three character identifier indicating who originated the activation of the EAS. Only five ORG codes are assigned. These are EAN (Emergency Action Notification network of program networks and suppliers for a national alert), PEP (Primary Entry Point, key broadcast stations which can provide national emergency information if EAN fails), WXR (National Weather Service), CIV (civil authorities, such as EAS activations by state or county governments), and EAS (Emergency Alert System activations by broadcast or cable systems).
EEE is a three character "event code" that identifies the type of emergency. These are listed in figure 2.
EAN National Emergency Action Notification EAT National Emergency Action Termination NIC National Information Center NPT National Periodic Test RMT Required Monthly Test RWT Required Weekly Test TOA Tornado Watch TOR Tornado Warning SVA Severe Thunderstorm Watch SVR Severe Thunderstorm Warning SVS Severe Weather Statement SPS Special Weather Statement FFA Flash Flood Watch FFW Flash Flood Warning FFS Flash Flood Statement FLA Flood Watch FLW Flood Warning FLS Flood Statement WSA Winter Storm Watch WSW Winter Storm Warning BZW Blizzard Warning HWA High Wind Watch HWW High wind Warning HUA Hurricane Watch HUW Hurricane Warning HLS Hurricane Statement TSA Tsunami Watch TSW Tsunami Warning EVI Evacuate Immediate CEM Civil Emergency Message DMO Practice/Demo Warning ADR Administrative Message
Figure 2 - EAS Event Codes
PSSCCC defines the location of the emergency. Each state is assigned a number (SS). Each county is assigned a number (CCC). If the CCC is 000, the emergency covers the whole state. P is 0 if the emergency covers the whole county. P can be a number 1 through 9 to cover nine portions of a county (generally scanning west to east, north to south).
TTTT defines the valid duration of the emergency in HHMM format with 15 minute resolution below one hour, then 30 minute resolution.
JJJHHMM defines the time the message was originally released. JJJ is a three digit number representing the day of year (1 January is 001). HHMM is the time in UTC (the old GMT). The use of UTC was selected since emergency messages may cross time zones.
LLLLLLLL is the identity of the station CURRENTLY transmitting the code. When packets are relayed, this is the ONLY field that is changed.
NNNN is an End Of Message indicator. It can mute consumer receivers or return stations to normal programming automatically.
The rules do not specify the contents of the one second pause. It COULD be one second of silence, one second of normal program audio or one second of 2083.3 Hz. Paragraph 110 of the R&O refers to "unobtrusive tests" of the system where only the EAS data is sent. They estimate the tests would take about six seconds and be unintelligible to listeners. If an average alerting packet runs 58 bytes (including preamble) and each byte is 10 bits (including start and stop bits), it would take a little over a second to transmit. The End Of Message packets are considerably shorter, running 20 bytes with the preamble. These each take about 400 milliseconds. It SEEMS that the "unobtrusive test" would be less obtrusive if program audio were allowed in the pause periods. The data bursts would then sound something like the data bursts we currently hear on some networks for station equipment control.
Decoders must receive two identical headers (of the three transmitted) to be considered valid. This is the system error checking.
It seems that local EAS plans should be set up to either include separate distribution webs for each language spoken in an area (and broadcast), or a single web could be used with the emergency operations center giving the emergency instructions in several languages sequentially (like the announcements in airports).
I see the EAS as a web of nodes, all interconnected by several communications paths. National, state and local emergency agencies have several entry points to the web. A county emergency operations center might have an EAS encoder driving phone lines or a county radio system driving the EAS decoders at several stations in the area. When an emergency occurs, the emergency official could push a button on a map of the county identifying which area(s) require notification. She/he would then push a button marked "Evacuate Immediate" (or other event code) and wait for the "green light". The green light would be lit after the three EAS headers and the two tone attention signal are sent. The official would then give the emergency instructions and push the EOM button. This audio (AFSK datastream, attention signal and voice announcement) would be sent to several stations in the area. Stations that have programmed their EAS systems for this area and event type would immediately broadcast the EAS codes (regenerating them, substituting their own call letters) followed by the attention signal, the emergency audio and the EAS EOM. Since it takes time to fully decode the EAS datastream and regenerate it, it's necessary to buffer the audio. The new EAS systems will include a two minute (minimum) audio storage. Other stations monitoring this station will similarly receive the EAS datastream and rebroadcast it. The "immediate" retransmission is required only for national (EAN) messages. State and local messages may be delayed up to 15 minutes (see 11.51(k)(2)). It appears that EAS systems COULD be designed to interface with program automation systems to run the emergency message during the next break, avoiding program interruption. This, however, seems to add unnecessary complexity. If the use of EAS is indeed reserved for true emergencies, it appears immediate retransmission is appropriate.
A "integrated" EAS unit would be required to have at least two audio inputs. These would monitor other EAS sources, such as other broadcast stations, state and local emergency communications circuits, weather service radios, etc. A state EAS plan provides the monitoring assignments for each station. The topology is designed to provide several paths from an originating point to all participants so a failure at any one point does not disrupt the system.
I'd suggest a "program loop through" similar to many existing EBS systems. The loop through should be designed to consider the varieties of program transmission methods. At a minimum, I'd suggest a way of handling balanced stereo audio and composite stereo. On receiving appropriate EAS codes, the system would drop whatever audio is being passed through and substitute its audio (the EAS tones, attention signal, time delayed emergency program, EAS EOM), then return to normal audio.
The system will have a display and keyboard that are used to program the system and display information pulled from received EAS headers.
The systems will also have a serial data port to relay EAS data to and receive EAS data from non-audio circuits (digital data circuits, RBDS encoder/decoder, etc.). It appears (based on 11.32(a)(2), 11.32(a)(3), and 11.32(a)(1)) that the EAS systems do a speed conversion from 83 bps used over audio channels to 1200 bps for digital circuits.
Once again, I invite you to read the Report and Order yourself. It's available via internet or fax, as described above.