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 held upright 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 U.S. were built by Blaw-Knox.
Many Blaw-Knox towers, of both conventional (uniform cross-section) and diamond design, remain in use in the United States. Few of the diamond towers were built, and several remain; all transmit AM radio signals:
- WSM, Nashville, Tennessee: 808 ft (246 m); originally 874 ft (267 m); tower located in Brentwood, Tennessee.
- WLW, Cincinnati, Ohio: 747 ft (227 m); originally 831 ft (253 m); tower located in Mason, Ohio.
- WBT, Charlotte, North Carolina: three towers, 428 ft (130 m) each (one original, two reproductions from the original plans after the originals were destroyed by Hurricane Hugo)
- WFEA, Manchester, New Hampshire: 400 ft (121 m)
- WBNS, Columbus, Ohio: 380 ft (116 m)
Several additional diamond-cantilever towers were built at stations in the Central Valley of California but are less well-known. These towers were much smaller in both height and cross-section than the towers listed elsewhere; only one — KSTN, Stockton — remains in use for broadcasting.
The following Blaw-Knox diamond-cantilever towers remain standing in Europe:
- Lisnagarvey Mast (constructed: 1936) at Lisnagarvey, Northern Ireland
- Lakihegy Tower (constructed: 1933, height: 314 metres) at Szigetszentmiklós-Lakihegy, Hungary (The tallest Blaw-Knox tower ever built)
- Vakarel Transmitter (constructed: 1937, height: 215 metres) at Vakarel, Bulgaria
- Stara Zagora Transmitter at Stara Zagora, Bulgaria