This is a relatively new invention as well. When radio first started in the US (late 1890s), callsigns were arbitrary. I believe the Kxxx and Wxxx divide starte

This is a relatively new invention as well. When radio first started in the US (late 1890s), callsigns were arbitrary. I believe the Kxxx and Wxxx divide started in the 1920s. Also, this callsign convention applies for TV broadcast as well.