Blaw-Knox Towers was once a major force in tower construction. The distinctive diamond shape essentially is created by having to standard self-supporters stacked with the lower one inverted. However, as Watt Hairston notes, the two sections are different. There are some who say there is an electrical benefit to the shape, but the combination of the shape and the heights forced virtually every one of the early users to reduce the height of the upper half. Otherwise, there was severe fading fairly close in - enough to destroy much of the coverage of the former clear channel stations.
According to some, the Blaw-Knox diamond was first constructed for WSM in Nashville in 1932, instead of the typical "T," horizontal wire strung between two towers, with a vertical feed wire. The single tower was said to radiate better and more omni-directionally. According to George Brown, this is a result, but not the reason for the shape.
Essentially, by bringing the structure to a point at the bottom, it dramatically reduces the forces that might try to pull the tower off its foundation, especially the horizontal twisting forces that can come from wind or earth movement, for example. Some more details of this physics of the design are in a paper by Watt Hairston.
Blaw-Knox went out of the tower business in 1958 after several disastrous installation accidents.
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|WSM- Nashville - 1932
808 feet (originally 874 feet)
|WLW - Cincinnati - 1932
747 feet (originally 831 feet)
|WBT - Charlotte
428 feet (two of the towers were
Other Blaw-Knox towers were in Manchester, NH (WFEA- 400 feet), Columbus, OH (WBNS - 380 feet), and