"New Stations" (Special Land), Radio Service Bulletin, June 1, 1921, page 3. The "7" indicated that the station was located in the 7th Radio Inspection District, and the "Y" specified that the station was operating under a "Technical and Training School" authorization.
"New Stations" (Special Land), Radio Service Bulletin, November 1, 1923, page 4.
"New Stations", Radio Service Bulletin, April 2, 1923, page 8.
Polich, Edward L. (1950). A history of Portland's secondary school system with emphasis on the superintendents and the curriculum (Thesis/dissertation). University of Portland. pp. 67, 71, 81, 160. OCLC232551057.