CONELRAD

CONELRAD (pronounced kon-ill-rad or kon-ill-rid)

The short form of CONtrol of ELectromagnetic RADiation.

Exclusive to the US, CONELRAD was a nationally standardized system of emergency public broadcasting (on the AM (amplitude modulation) medium-wave band at 640 & 1240 KHz) intended to operate in the event of enemy attack during the Cold War.  The original specifications for what emerged as CONELRAD was first discussed in March 1951 at the Informal Government-Industry Technical Conference and later published by the FCC (Federal Communications Commission):

"The primary plan for alerting broadcast stations that is currently being considered by the FCC Study Group is known as the Key Station System.  The arrangement requires certain telephone circuits (private wire or direct line to Toll Board) between the Air Defense Control Centers (ADCC) and specified radio stations to be known as Basic Key Stations & Relay Key Stations”.

The essence of the system was each Basic Key Station upon receiving an alert or warning signal from the ADCC would, upon instruction, broadcast a predetermined message and also relay the message by telephone to all Relay Key Stations assigned to each Basic Key Station.  As a diversified network designed to be able to continue functioning even if various parts were destroyed, it was conceptually similar to a later US military project which would later evolve into the internet.  Intended to be simple, robust and able to reach as wide a possible audience in the shortest possible time, CONELRAD used simple protocols for alerting the public and other "downstream" stations, consisting 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.  Key stations would be alerted directly and all other broadcast stations would monitor a designated station in their area.

In the event of an attack on the US, all domestic television and FM (frequency modulation) radio stations were required instantly to cease broadcasting and upon alert, all most AM stations shut down, those remaining on-air transmitting either on 640 or 1240 kHz.  No transmission would last more than a few minutes and upon one going “off-air” another would take over the frequency on a ”round robin” chain, this to confuse enemy aircraft which might be navigating using Radio Direction Finding (RDF), a technique first widely used in the early days of World War II (1939-1945).  In the US, all radio sets manufactured between 1953-1963 were required to have the two frequencies marked by the triangle-in-circle (CD Mark), the symbol of Civil Defense organizations.