page_title: Radio masts and towers
section_title: History
hierarchical_section_title: Radio masts and towers / History
caption_attribution_description: English: Multiwire T aerial of radio station WBZ in Springfield, Massachusetts, USA, in 1925. Licensed on September 15, 1921, it is claimed to be the first commercially licensed broadcast station in the US (although other stations like WWJ and KDKA had been broadcasting under other licenses for several years). Located at the Westinghouse plant in East Springfield, it broadcast on a wavelength of 360 meters (833 kHz) with a power of 2000 W. The antenna is typical of the wire antennas used for mediumwave broadcasting in the 1920s. The vertical wire connecting to the middle of the antenna is the radiating element, and the multiwire horizontal part is the capacitive "top load"; its function is to increase the oscillating currents in the vertical wire to increase the radiated power.
context_page_description: Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. There are two main types: guyed and self-supporting structures. They are among the tallest human-made structures. Masts are often named after the broadcasting organizations that originally built them or currently use them.
  In the case of a mast radiator or radiating tower, the whole mast or tower is itself the transmitting antenna.
context_section_description: The first experiments in radio communication were conducted by Guglielmo Marconi beginning in 1894. In 1895–1896 he invented the vertical monopole or Marconi antenna, which was initially a wire suspended from a tall wooden pole. He found that the higher the antenna was suspended, the further he could transmit, the first recognition of the need for height in antennas.  Radio began to be used commercially for radiotelegraphic communication around 1900. During the first 20 years of radio, long distance radio stations used long wavelengths in the very low frequency band, so even the tallest antennas were electrically short and had very low radiation resistance of 5-25 Ohms, causing excessive power losses in the ground system. Radiotelegraphy stations used huge capacitively-toploaded flattop antennas consisting of horizontal wires strung between multiple 100–300 meters (330–980 ft) steel towers to increase efficiency.
  AM radio broadcasting began around 1920. The allocation of the medium wave frequencies for broadcasting raised the possibility of using single vertical masts without top loading. The antenna used for broadcasting through the 1920s was the T-antenna, which consisted of two masts with a wire topload strung between them, requiring twice the construction costs and land area of a single mast. In 1924 Stuart Ballantine published two historic papers which led to the development of the single mast antenna. In the first he derived the radiation resistance of a vertical conductor over a ground plane. He found that the radiation resistance increased to a maximum at a length of ​¹⁄₂ wavelength, so a mast around that length had an input resistance that was much higher than the ground resistance, reducing the fraction of transmitter power that was lost in the ground system without using a capacitive top-load. In a second paper the same year he showed that the amount of power radiated horizontally in ground waves reached a maximum at a mast height of ​⁵⁄₈ wavelength.
  By 1930 the expense of the T-antenna led broadcasters to adopt the mast radiator antenna, in which the metal structure of the mast itself functions as the 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 665 foot (203 m) half-wave mast was installed at radio station WABC's 50 kW Wayne, New Jersey transmitter in 1931. During the 1930s it was found that the diamond shape of the Blaw-Knox tower had an unfavorable current distribution which increased the power emitted at high angles, causing multipath fading in the listening area. By the 1940s the AM broadcast industry had abandoned the Blaw-Knox design for the narrow, uniform cross section lattice mast used today, which had a better radiation pattern.
  The rise of FM radio and television broadcasting in the 1940s and 50s created a need for even taller masts. The earlier AM broadcasting used LF and MF bands, where radio waves propagate as ground waves which follow the contour of the Earth. The ground-hugging waves allowed the signals to travel beyond the horizon, out to hundreds of kilometers. However the newer FM and TV transmitters used the VHF band, in which radio waves travel by line-of-sight, so they are limited by the visual horizon. The only way to cover larger areas is to raise the antenna high enough so it has a line-of-sight path to them.
  Until August 8, 1991, the Warsaw radio mast was the world's tallest supported structure on land; its collapse left the KVLY/KTHI-TV mast as the tallest. There are over 50 radio structures in the United States that are 600 m (1968.5 ft) or taller.
caption: Multiwire broadcast T-antenna of early AM station WBZ, Springfield, Massachusetts, 1925.
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