The fashionable headgear shown here from a hundred years ago is being donned by an engineer at WDAP in Chicago. The station had these so that the quality of the station’s transmission could be checked at any time anywhere in the studio. The crystal set was mounted on a pair of headphones, which meant that there was no need to sit down at a standard receiver.

Later that year, the station was purchased by the Chicago Tribune, which changed the call letters to WGN, for World’s Greatest Newspaper.

These images appeared in the March 1924 issue of Popular Mechanics.