Radio might not be quite the media force it once was, but there are still thousands of stations around the country, and the call letters for almost every one of them begin with either "K" or "W."

Why? Because the government said so.

In the days of the telegraph, operators started the practice of using short letter sequences as identifiers, referring to them as call letters or call signs. Early radio operators continued the practice, but without a central authority assigning call letters, radio operators often chose letters already in use, leading to confusion.

To alleviate the problem, the Bureau of Navigation (part of the Department of Commerce) began assigning three-letter call signs to American ships in the early 1910s. Ships in the Atlantic and Gulf of Mexico got a K prefix; in the Pacific and the Great Lakes, a W. The precise reasons for choosing these two letters, if there were any, are unknown (bureaucracy works in mysterious ways). At the 1912 London International Radiotelegraphic Convention, ranges of letters were assigned to each of the participating nations and the U.S. was told to keep using the W and most of the K range. (Military stations used N.)

When the federal government began licensing commercial radio stations soon after, it had planned to assign call letters to the land-based stations in the same way. Somehow, things got flipped during implementation, though, and Eastern stations got W call signs and the Western ones got Ks. Where exactly does the Bureau of Navigation draw the line between East and West? For a while it ran north along state borders from the Texas-New Mexico border, but shifted in 1923 to follow the Mississippi River.

Some areas, however, might have both a K and W station in the same vicinity. Why? When the dividing line switched, some stations were made to change their call signs, while others weren't. For about a year in the 1920s, the Bureau of Navigation decided that all new stations were going to get a K call sign no matter where they were located. Still other exceptions were made by special request, station relocations, ownership changes, and even human error.

As for the rest of the call sign: That sometimes includes the station (ABC, NBC), but can also be an acronym. WGN stands for "World's Greatest Newspaper" (as it was considered the Chicago Tribune's radio station) while Chicago's WTTW is "Window to the World." But nothing beats St. Louis sports station KRAP, which gave itself the very self-aware label in 2014. “Our signal is KRAP,” reads their website. “Our studios are KRAP. Even our staff is KRAP.”

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