"New Stations: Special Land Stations"Radio Service Bulletin, 1 July 1921 (No. 51), Bureau of Navigation, Department of Commerce, Washington, D.C., page 4. Special land stations were a class of stations used by experimenters, technical and training schools, and certain amateur radio operators. The "7" in the call sign indicated that the station was located in the 7th Radio Inspection district, while the "Y" reflected that it was a Technical and Training School authorization.
