Radio Apocalypse: Hardening AM Radio Against Disasters

May 15, 2023

If you’ve been car shopping lately, or even if you’ve just been paying attention to the news, you’ll probably be at least somewhat familiar with the kerfuffle over AM radio. The idea is that in these days of podcasts and streaming music, plain-old amplitude modulated radio is becoming increasingly irrelevant as a medium of mass communication, to the point that automakers are dropping support for it from their infotainment systems.

The threat of federal legislation seems to have tapped the brakes on the anti-AM bandwagon, at least for now. One can debate the pros and cons, but the most interesting tidbit to fall out of this whole thing is one of the strongest arguments for keeping the ability to receive AM in cars: emergency communications. It turns out that about 75 stations, most of them in the AM band, cover about 90% of the US population. This makes AM such a vital tool during times of emergency that the federal government has embarked on a serious program to ensure its survivability in the face of disaster.

In the United States, it has always been the case that the grant of a government license to operate on the public airwaves carries the potential to turn a radio station over to authorities in a time of emergency, at least temporarily. That's been the case ever since the Federal Communication Commission (FCC) sprang into being in 1934, but the emergencies imagined back then were strictly local in scope, or perhaps at most a regional disaster, like a hurricane. It really wasn't until the dawn of the nuclear age that a nationwide emergency was even really possible, and with that potential came the need for a systematic method of reaching the entire population at a moment's notice.

The earliest Cold War approach to emergency alerts was the CONELRAD system, which was geared mainly at denying incoming enemy bombers of easy radio waypoints for navigation while still getting emergency instructions out to the public. The idea was that all AM stations would switch their transmitters to one of two frequencies, either 640 kHz or 1240 kHz, and transmit in a round-robin fashion, limiting each station's transmission to just a few minutes. At best it was an awkward system that quickly became obsolete once ICBMs became the preferred delivery system for nuclear weapons.

The successors of CONELRAD focused much more on the rapid assembly of a nationwide network of radio stations than on the control of emissions. The most recognizable element of the current system is probably the Emergency Alert System (EAS), with its distinctively discordant two-tone alert and shrill Specific Area Message Encoding (SAME) digital header. But EAS is just one of many methods of disseminating alerts to the public, all of which fall under a complex and hierarchical architecture known as the Integrated Public Alert and Warning System, or IPAWS.

The complexity of IPAWS is understandable given its mission and the rapidly changing communications ecosystems. Rather than relying solely on terrestrial broadcasters to disseminate emergency alerts, IPAWS rolls cellular carriers, satellite and cable providers, ISPs, and even local alert systems like sirens and electronic signboards. Additionally, IPAWS allows for a wide range of alerting authorities to access the system, meaning that it can be used not only for presidential messages in times of national emergency, but for everything from regional alerts for severe weather to Amber alerts for missing or abducted children.

Despite this increased mission scope, terrestrial broadcasters still play an outsized role in IPAWS. There are currently 77 radio stations across the United States and associated territories that are designated as Primary Entry Point stations for the Emergency Alert System (EAS). PEP stations tend to be so-called "clear-channel" AM stations, which operate at a high effective radiated power — at least 10,000 Watts — and on frequencies that are least subject to interference from other stations. The vast geographic reach of these PEP stations is one of the keys to the EAS network, since all participating stations are required to monitor signals from at least two different PEP stations, and to follow specific procedures if and when the PEP stations initiate an emergency alert.

PEP stations, in turn, are required to maintain a direct connection to the Federal Emergency Management Agency (FEMA) Mount Weather Emergency Operations Center in Virginia. Mount Weather is one of the many relocation facilities intended for continuity of government in times of national emergency, and is designed with maximum survivability in mind. It is also the primary point of access for the president to the EAS. Details of the links between Mount Weather and the PEP stations are limited, of course, but multiple redundant fiber optic lines and satellite links certainly play a role.

Since the EAS network is a daisy chain system, with messages flowing through the system from the top down, the survivability of the PEP stations is critical. PEP stations have always been mandated to have redundant systems, including auxiliary and backup transmitters, backup power generation, and staffing requirements, but as a result of increasing awareness of the vulnerability of critical infrastructure to attacks by electromagnetic pulse (EMP) or the possibility of Carrington Event-level damage, FEMA undertook a program designed to substantially harden the majority of PEPs.

The upgrade effort began in earnest in 2016, with station WJR in Detroit and WLW in Cincinnati, although it appears that at least some stations were being upgraded as early as 2011. The basic "station-in-a-box" seems to consist of a pair of modified 20-foot shipping containers that are prefabricated and transported to either the station's primary or auxiliary transmitter. One container is devoted to power generation and distribution, while the other houses studio equipment and transmitters. The studio container for some of these installations seems to have extra protection in the form of a reinforced concrete enclosure around the container, presumably for protection against storm damage.

In most cases, the shelters are installed adjacent to the station's antenna farm inside security fences with other equipment including satellite dishes, a likely link to FEMA's operations center. Provision seem to have been made for local hazards, though; the shelter at WWL in New Orleans, a stone's throw from the Mississippi River, has been installed on a raised platform to avoid flood damage.

Detailed specifications of the PEP upgrades haven't been easy to locate online, but press releases and local news coverage contain some tantalizing clues as to the thought process behind the design. The shelters are described as "all-hazard" hardened against chemical, biological, and nuclear threats, as well as reports of being Faraday shielded to withstand EMPs. The studio shelters are equipped with air filtration systems, a 60-day supply of food and water, and bunk space and hygiene facilities for two. Backup generators and a large stockpile of fuel are provided, although we very much doubt the 60,000-gallon figure cited by one article.

In short, these facilities are built to survive, and to keep the broadcast engineers inside alive and working. It's not clear if these shelters are to be staffed at all times; indeed, since station KIRO in Seattle is reported to have a standing order with the local Coast Guard station to transport engineers to its hardened transmitter on Vashon Island at a moment's notice, it seems not. But that only proves the point about how serious FEMA is about the survivability of the PEP system as a whole.