BotGadget: Radio Apocalypse: The Emergency Broadcast System

Some sounds are capable of evoking instant terror. It might be the shriek of a mountain lion, or a sudden clap of thunder. Whatever your trigger sound, it instantly stimulates something deep in the lizard brain that says: get ready, danger is at hand.

For my part, you can’t get much scarier than the instantly recognizable two-tone alert signal (audio link warning) from the Emergency Broadcast System (EBS). For anyone who grew up watching TV in the 60s and 70s in the US, it was something you heard on at least a weekly basis, with that awful tone followed by a grave announcement that “the broadcasters of your area, in voluntary cooperation with the FCC and other authorities, have developed this system to keep you informed in the event of an emergency.” It was a constant reminder that white-hot death could rain from the sky at any moment, and the idea that the last thing you may ever hear was that tone was sickening.

While I no longer have a five-year-old’s response to that sound, it’s still a powerful reminder of a scary time. And the fact that it’s still in use today, at least partially, seems like a good reason to look at the EBS in a little more depth, and find out the story behind the soundtrack of the end of the world.

Replacing the CONELRAD System

The EBS system was developed as a response to shortcomings in the CONELRAD system for civil preparedness announcements. As Al Williams noted in his recent article on CONELRAD, the system was troubled by nuisance alarms and a complicated operating procedure that required every TV and radio transmitter to go dark and have designated AM stations retune their transmitters to one of the two CONELRAD frequencies. Expecting broadcast engineers to perform these tasks under the threat of sudden annihilation was probably something that should have been subjected to a little human-factors testing.

As a response to this, EBS was first fielded in 1963. It was designed to deal with the changing nature of the threat; CONELRAD imposed radio silence to deny bomber pilots of electronic landmarks, while EBS recognized that ballistic missiles needed no such aids. EBS was more inclusive, too, requiring TV stations and FM broadcasters to participate, in a tacit acknowledgment that AM radio was no longer the big kid on the block.

The EBS system did take cues from CONELRAD, though. The basic architecture was the same — to create one nationwide network that the government could use to transmit consistent messages and instructions quickly and efficiently. Linking the national carriers into a single network was initiated by a teletype message with codeword authentication to primary stations like the Big Three networks and news services like UPI and AP. To get the attention of station employees tasked with monitoring teletypes in station newsrooms often full of the clattering devices, this Emergency Action Notification (EAN) was preceded by a line of X characters and a bunch of control-Gs to sound the teletype’s bell.

Once the codeword was authenticated — it was changed daily — the transmitter was turned off then back on again twice in a row, followed by a 15-second transmission of a 1,000 Hz attention tone. Again, this was a holdover from the “carrier drop” signaling of the CONELRAD system, often wryly referred to by broadcaster engineers as the “EBS stress test” for its ability to kill transmitters. The loss of carrier in the specific pattern dictated by the EBS rules would activate decoders in the other stations, allowing the seamless network to be stitched together rapidly.

Recognizing that carrier-drop signaling was no longer optimal, in 1976 the EBS system was changed to support the now-familiar two-tone Attention Signal. A form of in-band signaling, the two pure sine tones of 853 Hz and 960 Hz were chosen so that false decoding of normal audio programming would be unlikely. The Attention Signal also had the advantage of being discordant and unpleasant to hear, therefore standing out from normal programming. The initiation process would then be followed by the official announcement of the end of the world.

EBS Goes Digital

Faced with changing technology, the EBS system was scrapped in 1997 in favor of the Emergency Alert System. The EAS includes not only terrestrial broadcasters but cable providers, satellite services, digital radio, and smartphones. EAS incorporates Specific Area Message Encoding (SAME), a digital header that’s pretty terrifying in its own right, which allows targeting emergency messages to specific geographic areas. This is the system used in weather radios to issues severe storm warnings to specific locations.

While none of these emergency notifications systems has ever been used to announce the apocalypse, the later versions have been activated many times for smaller-scale disaster, both natural and man-made. EBS was activated something like 20,000 times for weather alerts, and EAS warnings down to the level of Amber Alerts regularly appear on smartphones. While there’s no such thing as a minor emergency when it’s happening to you, here’s hoping we continue to use these systems for everyday emergencies rather than their intended purpose.