Friday, June 10, 2005
radio was an early casualty of the atomic age...
CONELRAD was born in 1951 as an acronym for "Control of Electromagnetic Radiation." The general idea was to deny the Soviets the ability to home in on specific broadcast stations.
Under CONELRAD all normal broadcasting would stop when a signal was given by the Civil Defense Department. At that time, all broadcasts would either cease or move to the designated frequencies of 640 and 1240 AM. the idea was the if all these transmitters were broadcasting the same synchronized emergency information, they would be unusable for navigation. Stations not broadcasting this signal each were required to monitor that was. (this included even ham radio) CONELRAD had a simple system for alerting the public and other "downstream" stations that consisted of a sequence of shutting the station off for five seconds, returning to the air for five seconds, again shutting down for five seconds, and then transmitting a tone for 15 seconds.
In 1953, all new radios sold were required by law to carry a Civil Defense triangle at 640 and 1240 AM on the dial. The triangles were referred to as CD marks, for Civil Defense. I cant figure out when they were allowed to drop that.
By the early 1960's the development of Soviet missiles had made the CONELRAD system obsolete. This system was succeeded by the EBS system in the 1963. The Emergency Broadcast System, which was less stupid in that stations did not have to change frequencies, some stations still had to be ready to shut down and flip to monitor mode.
Pics of CONELRAD devices: http://www.oldradio.com/current/bc_conel.htm
In 1997 EBS was dropped in favor of an automated system, the Emergency Announcement System or EAS for short. This modern system had the bonus of eliminating the intermediate station monitoring and the reliance on station personel.