Proper noun
CONELRAD
(US, historical) Acronym of control of electromagnetic radiation: a method of emergency broadcasting to the public of the United States in the event of enemy attack during the Cold War, rapidly switching the television or radio transmitter stations to make the broadcasts unsuitable for bombers that might attempt to home in on the signals.
CONELRAD radio information systems were adopted, whereby the commercial radio sector (later supplemented by the National Emergency Alarm Repeaters ) would broadcast on two AM frequencies in the event of a Civil Defense (CD) emergency. Source: Internet