In the mid-1940s, the WMAQ Radio live studios in the Merchandise Mart were converted to TV studios for use by a new television station. Channel 5 signed on the air on October 8, 1948. Its call letters were WNBQ. Those letters combined the initials for National Broadcasting, plus the Q from WMAQ's call sign. That same year, WMAQ also signed on an FM station at 101.1. WMAQ-FM (today WKQX) largely simulcast AM 670 for its first two decades on the air. It was powered at 24,000 watts with its transmitter atop the Civic Opera Building on North Wacker Drive.