WMBR is the MIT-run student broadcasting station. This the third set of call letters for the station.

The first MIT student broadcasting station, WMIT, first signed on on November 25, 1946. It was a "carrier-current " AM transmitter located in the Ware dormitory and broadcasting over power lines at 800, and later 640 kilocycles ("kilocycles per second" being the proper period term for the unit of frequency now called the "kilohertz"). Audible only within a few hundred feet of the dorms, under then-current FCC regulations it could and did broadcast commercials and was self-supporting.

In the mid-1950s, the possibility of an FM license was explored and it was discovered that the call letters WMIT were in use by a North Carolina station. WTBS (for "Technology Broadcasting Service") was chosen as the best alternative. New facilities were constructed in the basement of Walker Memorial, including a switching and mixing console designed by A. R. Kent and Barry Blesser, believed to be one of the very first all-transistorized consoles ever built. On April 10, 1961 WTBS-FM signed on with 14 watts of effective radiated power at 88.1 megahertz FM.

WTBS continued to operate the carrier-current system to the dormitories, with an identical program, except for commercial breaks, during which the noncommercial FM station filled time with public service announcements, and, later, parody "ads" for products such as "Apple Gunkies" and firms such as "Nocturnal Aviation." The all-request "Nite Owl" was a popular weekend feature, and a "Waveform of the Week" was broadcast for the enjoyment of MIT students watching the program on oscilloscopes.

In the late 1970s, Ted Turner, then operator of WTCG in Atlanta, wanted to use the call letters WTBS. Although call letters are not technically for sale, Turner and WTBS worked out a loophole whereby Turner gave a $25,000 donation to WTBS with an agreement that WTBS would apply for new call letters, with a second donation of $25,000 promised if the FCC were to subsequently grant the letters to Turner. All went as planned, WTBS used the donation for new transmitter equipment, and on November 10, 1979 the station signed on as WMBR with 200 watts of power. (Wags nostalgic for the old letters complained that WTBS had sold its birthright for a mess of wattage).