page_title: VLF Transmitter Cutler
section_title: Antenna
hierarchical_section_title: VLF Transmitter Cutler / Antenna
caption_attribution_description: English: Diagram of the antenna array at the U.S. Navy Cutler VLF transmitter facility at Cutler, Maine. It transmits operational orders one-way to submerged U.S. submarines worldwide at a frequency of 24 kHz. With a transmitter power of 1.8 megawatts, it is known as the most powerful radio transmitter in the world. It consists of two identical antenna arrays called the 'North array' and 'South array', driven from a transmitter building between them. This type of antenna is called a trideco or umbrella antenna, a form of capacitively top-loaded electrically-short monopole antenna. Each array consists of a hexagonal pattern of 13 vertical steel masts attached at the top to a system of 6 diamond-shaped fans of cables suspended above the ground. The vertical masts actually radiate the VLF radio waves, while the top cables form a large capacitor with the ground, which serves to increase the efficiency of the antenna. Under each mast there is also a system of cables suspended a few feet above the ground radiating from the mast base, called a counterpoise (not shown) which functions as the other plate of the capacitor. Each central mast is 304 m (997.5 ft) high, and has a 'helix house' at its base, which contains massive coils of wire needed to match the antenna to the transmission line, which travels through an underground tunnel from the transmitter.
context_page_description: The VLF Transmitter Cutler is the United States Navy's very low frequency shore radio station at Cutler, Maine. The station provides one-way communication to submarines in the Navy's Atlantic Fleet, both on the surface and submerged. It transmits with call sign NAA, at a frequency of 24 kHz and input power of up to 1.8 megawatts, and is one of the most powerful radio transmitters in the world.
context_section_description: The extensive antenna system consists of two separate identical umbrella antenna arrays, designated the “north array” and the “south array”. Each array consists of a ring of 13 tall metal masts connected at the top by a network of horizontal cables. The cables form six diamond-shaped "panels" radiating from the central tower in a hexagonal pattern shaped like a snowflake. The two arrays normally operate together as one antenna, but each is designed to function independently to allow maintenance on the other array. The central tower of each antenna system is 304 m (997.4 ft) tall. It is surrounded by six 266.7 m (875 ft) tall
  masts, placed on a ring with a radius of 556 m around the central tower. The remaining six towers of the array are 243.5 m (799 ft) tall, placed on a circle of 935.7 m (3070 ft) around the central tower.
  Each element (“panel”) of the antenna is suspended between the central tower, two towers of the inner ring and one tower of the outer ring. The entire array is 6140 ft (1.871 km or 1.16 miles) in diameter.
  This type of antenna array is called a trideco or umbrella antenna, a type of antenna which can radiate power efficiently at the low 24 kHz frequency used. It functions as a capacitively top-loaded electrically short monopole antenna. Vertical wires at the central mast of the antenna radiate the VLF radio waves, while the suspended horizontal cable array functions as a large capacitor, increasing the efficiency of the vertical radiators. At the base of each mast is a star-shaped network of cables suspended a few feet above the ground, extending out hundreds of feet, called a counterpoise, which serves as the bottom plate of the "capacitor".
  The climate in Maine results in severe icing of the antenna wires during the winter, resulting in unacceptably large loads on the supporting structures. Therefore, the antennas have a deicing system which runs large 60 Hz electric currents through the wires, heating them, to melt the ice. The power required for deicing is 3 MW, higher than the transmitter output power. An antenna array cannot transmit while it is being deiced, and one reason for having two arrays was to allow one array to be deiced while the other provides crucial uninterrupted transmission capability. Repairs and adjustments to an array can also be made without interrupting transmission.
caption: Diagram of Cutler antenna array
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