[EAS] The Daisy Chain

[Sean Donelan]

On Mon, 16 Aug 2021, Clay Freinwald wrote:
 It would be nice if the PEP's could send an RMT and you could set your box
 to receive it but not relay. At least you could play back the audio as
 recorded in the EAS box and make sure the two-tone attention signal, as sent
 over the satellite, isn't over-driving the input.

 Why not use a DMO?

The National Weather Service includes an audio message in its weekly RWTs.
Broadcasters don't include audio messages to keep the weekly interruption 
as brief as possible, but an audio message is allowed.

There are lots of options. FEMA regularly tests the closed circuit 
portion of PEP, but doesn't test the on-air part of terresterial PEP 
stations of the audio chain because the tests would interrupt normal 
broadcasting (and still FEMA is skittish about the 1971 incident).

The satellite PEPs use non-programming audio channels (barker channel for 
Sirus XM, and closed circuit channels for NPR and Premiere).  So brief 
interruptions may be less of a concern.

The biggest challenge for satellite tests is choosing a testing FIPS code 
which doesn't cause a conflict with actual EAS local areas. Satellite 
operators sometimes use a Washington DC (011001) which conflicts with 
actual tests and alerts in Washington DC.

The National Weather Service uses the undefined FIPS/SAME "999000" for 
practice messages.

RWTs should never be relayed (although a few low-power stations do). FEMA 
says that the "DMO" code is used for testing some outdoor warning sirens, 
although I've never found a jurisdiction which actually uses DMO to 
activate its sirens.

AT&T Long Lines used to force everyone to use the same audio levels.  But 
now everyone does their own thing with audio levels.  Just cram everything 
through an audio processor to make it sound the same on the air. Each 
station in the EAS daisy-chain processes the same audio multiple times, 
in multiple different ways.  Its amazing its still intelligible.