Neal McLain got it also right but missed one detail. Right now, under federal law, the only EAS alerts any broadcaster/CATV operator is required to carry are federal (Presidential or National Information Center). These are the ones that are sent by FEMA to the 34 or so primary entry points, NPR and XM radio. Every TV station must carry them or shut down. So it does very little harm for the CATV not to interupt the TV Broadcaster. OTOH, since the broadcaster may be doing live captioning, or supply a live video broadcast, or custom graphics, the CATV may be doign more harm thant good. The FCC thus allows this to be negotated.
In the real word, few broadcasters don't carry state or local generated alerts (but they often delay them), and here the issue are as Neal describes. A CATV operator in the finges of a TV station may elect to interupt a TV station to insure local alerts are delivered. In designing the system, the FEMA alerts are passed to the state primarys, then to local primarys. So the state or local EMA is able to interject their message with only minimal cooperation from the SP and LP, and all the local stations have to do to program their endec to process the alerts. Everything but programming the ENDECs is allready required, so it is no cost to them to follow the plan.
The LP and SP stations must carry the alerts, most would anyway, but many accepted a FEMA generator in the past, the retention of which is contingent on them participating. It's an interesting excercise, somewhat like herding cats.
Under an upgrade called CAP (Common Alerting Protocal), this will change somewhat, as state messages will be must carry. Their is some concern over this being used by the governer just to be heard. Other states have already put plans in place, with the help of broadcasters, to allow the Governer to seize the stations for more then the 2 minutes allowed by a EAS compliant alert. (Only State/Local messages are limited to 2 minutes.)
As far as testing the system, CATV operators must perform the required weekly (RWT)and monthly (RMT) tests. The RWT can be any time (but must be varried)selected by the operator. The station must log the recieved tests (from up to 5 stations) and transmit its test, but their doesn't need to be any connection between the two. Only the Header and end of message must be transmitted. The RMT is initated by (or at the direction of) the state, usually through the SP, and alternates between day and night (because of the use of so many AM stations in the chain). Each station must retransmitt the message within 15 minutes of reception. There is a cool feature on some Endecs that will retransmitt the alert in 15 minutes if it is not manually done before then. This is the only test that is required to contain the 2 tone activation tone from the old EBS system.
Somewhat related to Hurricane Katrina, Alabama, Mississippi, and Florida are getting new PEP stations. We need it in alabama to replace the New Orleans station we officially use now. I can't quite make the connection what this has to do with hurricanes. But the PEP stations are the daytime weak link in what is usually a robust, if kludgy, system.
And back to PA, they had their RMT at 0035 today (thursday). Next RMT will be May 15 at 1005. You cable system could air it hours latter if stations up the chain delay it. (I said 15 minutes- some states allow
60 minutes in their official plan, the FCC says 15 minutes in their official instructions required to be in the control room, but I think the supporting law may allow 60 minutes.)Patton Turner FAA Telecommunications snipped-for-privacy@mindspring.com