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. It was originally located
in Arlington, Virginia. Original Arlington Virginia station
The station began operations in 1913 as a radio telegraphy station call sign NAA
in Arlington, Virginia, at a facility next to Fort Myer. Although its
broadcasts occasionally included band concerts and speeches, it was most
famous for its nightly time signals. The three towers known then as “The Three
Sisters” stood 600 feet, 450 feet and 200 feet above the ground. The site was
referred to as “Radio”, Virginia. The towers were the second largest man-made
structure in the world behind only the Eiffel Tower. The word “Radio” was first
used instead of “Wireless,” in the name of this Naval Communications facility.
The First Trans-Atlantic voice communication was made between this
station and the Eiffel Tower in 1915. The Nation set its clocks by the signal
and listened for its broadcast weather reports. The Towers were dismantled in
1941 as a menace to aircraft approaching the new Washington National Airport. The
towers stand today at United States Naval Academy in Maryland, on the edge
of the Chesapeake Bay. Move to Cutler Maine
The current Cutler Naval Station was built in 1960 and became operational on
January 4, 1961. It has a transmission power of 2 megawatts, and it was at one
time, and perhaps still is, the most powerful radio transmitter in the world.
As with all VLF stations, the transmitter has a very small bandwidth,
and so cannot transmit audio but only coded text messages, at a relatively low
data rate. The transmission consists of a continuously encrypted minimum-shift
keying signal capable of multi channel operations. The transmitter operates on
24.0 kHz. In the past it operated on 17.8 kHz. The callsign of the station is
The extensive antenna system consists of two separate identical 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 tall. It is
surrounded by six 266.7 m 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 tall
and placed on a circle of 935.7 m around the central tower.
Each element 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
in diameter. This type of antenna array is called a
trideco or umbrella antenna. It functions as a capacitively top-loaded
electrically short monopole antenna. The vertical steel masts of the antenna
radiate the VLF radio waves, while the suspended 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.
Antenna maintenance Antenna maintenance is performed during
the summer months. During maintenance periods the station transmits on one
array while work is performed on the other array, which is grounded. This
allows continuous transmission, crucial since the Navy closed Annapolis, the
only other East Coast VLF station. The region where the two arrays come
close together, near the transmitter house, is called the “bow-tie area”.
There are two panels and three towers from each array in this area. The fields
on the grounded array are highest in the bow-tie area due to proximity to the
active array. The present station operating procedure, based on a past
RADHAZ survey, does not allow work on the bow-tie area towers or panels while
transmitting on the other array. There is an ongoing tower painting project at
Cutler scheduled for completion over the next few years. Under the present
station policy, completion of this project would require several months of
total downtime, which is unacceptable. Test transmissions have been arranged,
during which, only four panels of one array are connected to the transmitter.
The objective of the four-panel tests was to allow painting and normal
maintenance on the bow-tie area towers of the inactive array. A secondary
objective of the tests is to characterize the antenna operating
parameters which had not been measured since changing to 24.0 kHz.
See also Jim Creek Naval Radio Station
Naval Communication Station Harold E. Holt
Lualualei VLF transmitter List of masts
References Further reading