Thursday, August 14, 2008

LP1 and LP2 are SAME

The EAS (Emergency Announcement System) has gone through a number of changes since Conelrad. The currently system debuted January 1, 1997. It's functional, but gets serious criticism over some very real flaws. While reading about this I came across an acronym I didn't' know. It wasn't very arcane in the end, but some of those small details are very revealing to the outsider. So we proceed.Every State has it's own EAS plan. The idea is that a central agency (varies) will arrange for emergency information to be broadcast on radio stations around the state to disseminate critical information. It might be a weather warning, child abduction, chemical spill, riot... etc. But no one central agency should have to tell every radio station individually. That's kind of cumbersome, not any one agency knows everything, and even if they did it'd create one of those dreaded single points of failure we hear so much about.

Instead it's broken down into states, regions, counties and etc. Also multiple agencies can issue alerts. Depending on the state, any number of local authorities, or even the National Weather Service can issue warnings. The president of the United States may as well. (This is a shame since our current one cant be trusted to operate a salad bar.) Depending on the scope of the problem different sets of stations will receive the data first. Obviously a station in San Diego does not need to run an alert for a Mud Slide in Uriah California. One station may be primary for multiple counties, but that's going to vary state to state. So what you get is the following
LP1 - Local Primary 1
LP2 - Local Primary 2

WXR - National Weather service Radio

CIV - Civil Authorities

PEP - Primary Entry Point (30 nationally just for the Prez)

Now the message has all sorts of requirements as will the station itself. San Francisco (for example) does the following:

5.1.2: Write your 50-60 second WARNING message to be broadcast by all AM, FM, TV stations and cable television companies in this FCC Local Area Emergency Alert System plan. To assure broadcast and timely rebroadcasts, you should keep your message under one (1) minute. Be sure to include the Who, What, Where, When, Why, and the How in your message. Never dictate the message to an LP1 employee; you are the announcer.

5.1.3: Telephone the primary (LP1) EAS station KCBS (or KQED) at:
a. KCBS (LP1) xxx-xxx-xxxx or xxx-xxx-xxxx
or if no contact, call:
b. KQED (LP2) xxx-xxx-xxxx
NOTE: If you are equipped with an EAS terminal and a CLERS
radio, separate instructions and procedures below will apply.

5.1.4: Identify yourself by name and title.
State that you want to activate the Emergency Alert System for (give the nature of the emergency). Authenticate in accordance with COO No. 7.
Speak clearly and distinctly.
Say "3 - 2 - 1" and read your message. Remain quiet at the end until the station employee speaks to you. The radio station will now do the rest.

That's actually pretty well thought out. But it's a state with a lot of brush fires so I'm sure they've learned a little. But it does not explain the mechanics so here we go:

All radio stations must have an EAS decoder. It's a rack mountable device that receives the EAS signal on a designated frequency. These decoders continuously monitor the signals from other nearby broadcast stations for EAS messages. For redundancy at minimum of two other LP1 stations must be monitored.

This signal is preceded by a S.A.M.E. header (Specific Area Message Encoding.) The system transmits digital tones over normal audio using AFSK, with a 2083.3 Hz mark tone and 1562.5 Hz space tone, lasting 1920 μs (1.92 ms) each. The data is encoded in 7-bit ASCII but uses all 8 bits, with no parity bit and no stop bit ("8-N-0"), at a bitrate of 520.83 bits per second. the message contains location data, identifies the sender, duration of alert, and event codes.