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| You can actually identify any American radio made between 1953 and 1963. Just look for the Conelrad markers. Usually an inverted triangle. But some were inverted triangles in circles..... |
The Conelrad stations were the direct predecessors of the annoying EAS data bursts you hear on the radio today. They were originally a civil defense method of warning radio listeners in the event of a nuclear attack.
There was no music or lite talk on Conelrad stations. They were strictly for emergency information.
One of the biggest questions I get asked is why were Conelrad stations on those frequencies? And why weren't any on FM?
First, all but two broadcast frequencies (all other AM radio stations, including TV and FM stations) were required to go off the air FM radio was still in it's infancy. Most radios were AM only and in the '50s, FM had very few listeners by comparison. TV was also still fairly new and TV wouldn't reach coast to coast and ubiquitous in homes until the early '60s. These wouldn't be the best mediums to inform the public of a national emergency. Secondly, the nature of FM/TV broadcasting would make these stations "sitting ducks" for enemy aircraft with radio direction finding.
It was through radio direction finding that Japanese aircraft were able to attack Pearl Harbor by homing in on the signal of KGU, Honolulu.
The 640 and 1240 AM frequencies were selected to confuse enemy aircraft RDF. One radio station would broadcast for a few seconds go off the air, then change over to the next station in a chain that would alternate between 640 and 1240. By doing this, it would be very difficult for enemy aircraft with RDF to get a "lock" on any signal accurately.
And yes, there were some actual radio stations on these frequencies. 640 was occupied by 50,000 watt radio stations KFI Los Angeles and WGST Atlanta and 1240 (which was occupied by many lower power 1,000 watt radio stations.)
It looked brilliant in theory. But in practice, it was pretty clumsy. Higher power radio transmitters (especially the older ones at some radio stations.) weren't made to be shut on and off like that and some transmitters failed.
Conelrad was replaced by the Emergency Broadcast System when missiles could be launched instead of dropped from airplanes. Where designated radio stations in each area served as the primary EBS radio stations. Stations in surrounding areas would relay these broadcasts over their signals or would refer the listeners to tune to the originating station. They also broadened their services to include emergency information of severe weather or man-made/natural disasters.
Here's a video tape from 1990 that explains how the EBS worked on the radio/TV station level.
Under the EAS system of today, ALL radio stations regardless of signal reach or MUST participate. The EAS also provides Amber Alerts for missing kids as well as other emergency information.
This site archives the endless sights and sounds of this nervous era. If you're old enough to remember the Cold War, you'll be in for a really cool flashback and if you're not, welcome to the bomb shelter....
http://www.conelrad.com/index.php
