A while back I bought an EAS ENDEC (encoder/decoder) from a hamfest for a song. I’ve since dove deep.
It had an interesting side-effect of letting me look at how a “production” one was set up. It was configured to relay the following alerts:
| Code | Event Type | Remarks |
|---|---|---|
| EAN | Emergency Action Notification | Required. |
| EAT | Emergency Action Termination | Once required, now obsolete. |
| RMT | Required Monthly Test | Required. Allowed to wait up to 60 minutes to relay. |
| RWT | Required Weekly Test | Required to originate weekly, and log what is received (AFAICT), but other stations’ RWTs are not relayed. (For some reason mine was set up to do so.) |
| CEM | Civil Emergency Message | “An emergency message regarding an in-progress or imminent significant threat(s) to public safety and/or property” at weather.gov |
| CAE | Child Abduction Emergency | |
| HUW | Hurricane Warning | |
| SMW | Special Marine Warning | |
| SVR | Severe Thunderstorm Warning | Radar- or spotter-indicated, and focused more on winds and potential for tornadoes than the lightning itself. |
| FFW | Flash Flood Warning | |
| TOR | Tornado Warning | Note an important difference: a tornado watch (TOA) indicates a tornado could form, while a tornado warning (TOR) indicates a tornado has formed, as confirmed by radar or a trained spotter. |
An interesting takeaway here is that the only mandatory events are the Presidential alerts (EAN), a system which has never been used for any actual emergency, and the required tests. Stations that relay emergency weather alerts, etc., are technically doing so voluntarily. See this NPRM, FCC 21-36 [PDF], which states (footnotes elided):
The primary purpose of the EAS is to provide the President with “the capability to provide immediate communications and information to the general public at the National, State and Local Area levels during periods of national emergency.” The EAS also is used to distribute alerts issued by state, local, Tribal, and territorial governments, as well as by the National Weather Service (NWS). Although EAS Participants are required to broadcast Presidential alerts, they participate in broadcasting state and local EAS alerts on a voluntary basis.
The NPT (National Periodic Test) appears to be mandatory now as well, but wasn’t at the time this unit was in service at a now-defunct FM station.
The Daisy Chain
An interesting bit to me about the design of EAS is that every participating station monitors at least two EAS stations. The SAME headers allow detecting duplicate (already-heard) messages and ignoring them, basically as a core part of the design.
State EAS plans often prescribe something like a tiered hub-and-spoke model. In NH, for example, the state can originate alerts which are carried to a handful of UHF relays, which are monitored by a handful of designated broadcast stations. Other stations monitor those broadcast stations. But the system is not required to be this hierarchical — it’s designed for survivability and resiliency, where getting an alert nearly anywhere in the chain should result in it propagating to the other stations monitoring for the matching FIPS codes.
RWTs / RMTs
The Boston/Norton, MA (BOX) office conducts their weekly tests on Wednesdays at 11am Eastern. (Also confirmed through observation in January of 2023.) It appears that the Grey, Maine (GYX) office, which serves New Hampshire, originates theirs at 11:25am on Wednesdays.
The NH Association of Broadcasters (NHAB) has an EAS page which includes their monthly RMT schedule. They note that NPR airs a FEMA-originated RWT Tuesdays at 1:15pm. (This may be NHPR-specific, or only stating that it’s sent over their satellite link. WGBH-FM in MA did not seem to air an RWT at that time.)
The Massachusetts Broadcasters Association also has an EAS page with schedules.
PEP
With the original purpose of the EAS as being in place to disseminate nationwide alerts originated by the President, there exists a network of radio stations known as Primary Entry Points (PEPs), which are fed directly by FEMA. For a long time, PEPs were (almost?) entirely AM radio stations. In much of New England, we’re served by WBZ-AM, which has its transmitter site in a marshy area of Hull. The importance to the government of continuing this service is perhaps underscored by the upgrades at WBZ conducted by FEMA in 2021.
These days, satellite distribution is also available. NPR’s satellite distribution network (the Public Radio Satellite System, or PRSS) feeds programming to their stations; their “Cue” or “Squawk” channel over satellite is where their alerts originate, allowing NPR stations nationwide to act as a de facto entry point. Local area EAS plans don’t seem to include them as a PEP. It’s unclear if this is just because the role is already filled by WBZ, or if they’re not fully approved.
Within the last few years, SiriusXM has been approved for monitoring as a PEP source, and via their free preview channels no less. The article also notes that another satellite syndication network, Premiere Networks (owned by iHeartMedia), serves a similar role.
Of course, the nationwide PEP is designed for nationwide alerts. It’s a good source for broadcast stations to monitor, but shouldn’t be used on its own as local alerts would be missed — and local stations will relay those signals.