By 1930 the disadvantages of the T antenna led broadcasters to adopt the mast radiator antenna. One of the first types used was the diamond cantilever or Blaw-Knox tower. This had a diamond (rhombohedral) shape which made it rigid, so only one set of guy lines was needed, at its wide waist. The pointed lower end of the antenna ended in a large ceramic insulator in the form of a ball-and-socket joint on a concrete base, relieving bending moments on the structure. The first, a half-wave mast was installed at radio station WABC's 50 kW Wayne, New Jersey transmitter in 1931. Radial wire ground systems were also introduced during this era.