Blaw-Knox tower

The Blaw-Knox company was a manufacturer of steel structures and construction equipment based in Pittsburgh, Pennsylvania. The company is today best known for its radio towers, most of which were constructed during the 1930s in the United States. Although Blaw-Knox built many kinds of towers, the term Blaw-Knox tower (or radiator) usually refers to the company's unusual "diamond cantilever" design, which is stabilized by guy wires attached only at the vertical center of the mast, where its cross-section is widest. A 1942 advertisement claims that 70% of all radio towers in the US were built by Blaw-Knox.

The distinctive diamond-shaped towers became an icon of early radio. Several are listed on the US National Register of Historic Places and the diamond antenna design has been incorporated into logos of various organizations related to radio, for example the Country Music Hall of Fame and Museum.

Design

The diamond-shaped tower was patented by Nicholas Gerten and Ralph Jenner for Blaw-Knox July 29, 1930. and was one of the first mast radiators. Previous antennas for medium and long wave broadcasting usually consisted of wires strung between masts, but in the Blaw-Knox antenna, as in modern AM broadcasting mast radiators, the metal mast structure itself functioned as the antenna. To prevent the high frequency potential on the mast from short-circuiting to ground, the narrow lower end of the tower rested on a ceramic insulator about 3 feet wide, shaped like a ball and socket joint. Thus the tower required guy lines to hold it upright.