WJAZ was the call sign used from 1922 to 1931 by a series of four separate, but closely related, broadcasting stations located in Chicago, Illinois and operated by the Chicago Radio Laboratory/Zenith Radio Corporations.
The original WJAZ was first licensed in the summer of 1922, and the next year began broadcasting from the Edgewater Beach Hotel in Chicago. However, it was soon determined that a suburban transmitter location would be preferable, and Zenith began preparations to re-establish WJAZ's operations at a more suitable site. Following operation for a few weeks by the Chicago Tribune as WGN, the station license for the original WJAZ was sold to the hotel management, and the call letters changed to WEBH.
In order to maintain control of the well-known WJAZ call sign until the new facility was ready, in 1924 Zenith briefly renamed a second Chicago station, WSAX, to WJAZ. Later that year, Zenith prepared a portable broadcasting station, mounted on a truck body, in order to evaluate potential new transmitter locations, and this mobile unit inherited the WJAZ call letters. Roving test broadcasts were made from various sites surrounding Chicago, and Mount Prospect, Illinois was ultimately selected for the new transmitter location. In 1925, the replacement facility was completed, and the WJAZ call sign was transferred from the portable unit to the new station.
The next year WJAZ gained national notoriety, when Zenith made an unauthorized change in its transmitting frequency, directly challenging the Department of Commerce's authority under the Radio Act of 1912 to assign frequencies. The courts sided with WJAZ; as a result the Radio Act of 1927 was enacted, which strengthened the government's regulatory powers and established the Federal Radio Commission.
WJAZ was deleted in 1931, after a co-channel station in Kentucky successfully petitioned for full-time use of the shared frequency.