Talk:The Radio/@comment-69.76.235.36-20200101162249

The marks (up arrows) on the radio's frequency indicator between the 6 & 7 and between the 11 & 16 indicate the Civil Defense (C-D) channels. Not all radios, even those of the same model, had these marks.

In 1951, a plan was created to shut down all radio and TV broadcasts in case of an enemy attack to prevent bombers from homing in on those broadcasts for navigation. Only two AM channels would still be operating at 640 kHz and 1240 kHz in order to provide the public with necessary information. It was called the CONELRAD (Control of Electromagnetic Radiation) network.

In case of attack, broadcast power for all stations in the network would be reduced to only 5 kW and they would be synchonized to broadcast for only a few minutes at a time, then switch to another tower. This way, the signal would disappear from one location and reappear somewhere else to prevent an enemy from using the signal for guidance. All ham radio operators were required to stop broadcasting.