"Three-Letter Roll Call" by Thomas H. White (earlyradiohistory.us). When WLB was first licensed in 1922, the dividing line for eastern "W" call letters and western "K" call signs ran along the western borders of the Dakotas. In January 1923 the boundary was shifted to the Mississippi River, which moved Minneapolis into the "K" call letters region.
"New Stations: Special Land Stations", Radio Service Bulletin, April 1, 1920, page 5. The "9" in 9XI's call sign indicated that the station was located in the ninth Radio Inspection district, while the "X" signified that the station was operating under an Experimental license.
"New Stations: Commercial Land Stations", Radio Service Bulletin, February 1, 1922, page 2. At this time there was no differentiation between commercial and non-commercial broadcasting stations. The licenses were not time-stamped, however WLB's Limited Commercial license serial number was #275, and WHA's was #276.
Charles William Taussig (1922). The Book of Radio. pp. 199–201. Retrieved 2018-03-04.
The same equipment was used for both station operations. A photograph of the 9XI-WX2 transmitting equipment is included at the "Radio history at the U of M" webpage.
