CONELRAD may sound like the name of a fictional android, but it is actually an acronym for control of electronic radiation. This was a system put in place by the United States at the height of the cold war (from 1951 to 1963) with two purposes: One was to disseminate civil defense information to the population and, also, to eliminate radio signals as homing beacons for enemy pilots.
How CONELRAD Worked
Here’s how it worked: In case of an attack, certain key stations were notified. They would use a very simple sequence to indicate there was an alert. All FCC-licensed stations had to cease transmission once the alert sounded. This wasn’t a bad idea. In World War II, bombers used radio stations to find nearby targets.
However, it did leave the government without a way to communicate with the people. Through advertising, the US let people know that in an emergency they should tune to 640 kHz or 1240 kHz. Certain commercial radio stations would move to those frequencies and take turns transmitting the same information. One station would transmit for a few minutes before another took over. This way there wasn’t a lengthy transmission for enemy bombers to home in on.
Tuning During an Air Raid
Special receivers that could pick up the CONELRAD signal were available. In addition, all AM radios were required to have markings at the CONELRAD frequencies (see triangle on the radio dial below).
Detecting the alert was simple but error prone. The key stations would stop transmitting for five seconds, returning to the air for five seconds, and then shut down for another five seconds. The station would then return to the air and transmit a 1 kHz tone for fifteen seconds.
It wasn’t unusual to get false alarms. Also, some transmitters would fail because of the rapid on/off cycling. This led to the replacement of the system by 1963 with the Emergency Broadcasting System. Most monitors would simply look for a signal on one of the two CONELRAD frequencies. Others would look for the tone along with an ordinary station dropping out.
Luckily, the CONELRAD system was never used for a real event. Unlike later systems, CONELRAD was not used for severe weather alerts. You have to wonder about its success had it been activated. There were still tube sets and the transmitters of the day were probably all tube-based. But electromagentic pulse effects would have certainly taken out the transistor devices that did exist. On top of that, bomb air burst would have played havoc with radio communications anyway.