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Very low frequency
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Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave as the wavelengths range from one to ten myriameters. Due to its limited bandwidth, audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines.
A VLF receiving antenna at Palmer Station, Antarctica, operated by Stanford University
A VLF receiving antenna at Palmer Station, Antarctica, operated by Stanford University
Central mast of a similar "trideco" antenna of the NATO VLF transmitter at Anthorn radio station, UK, showing 6 insulator strings attaching the toploa
Central mast of a similar "trideco" antenna of the NATO VLF transmitter at Anthorn radio station, UK, showing 6 insulator strings attaching the toploads to the 6 vertical radiator wires
Umbrella antenna of the Omega navigation system beacon on Tsushima Island, Japan, which transmitted at 10-14 kHz; 389 meters high, it was dismantled i
Umbrella antenna of the Omega navigation system beacon on Tsushima Island, Japan, which transmitted at 10-14 kHz; 389 meters high, it was dismantled in 1998.
Flattop antenna towers of the Grimeton VLF transmitter, Varberg, Sweden
Flattop antenna towers of the Grimeton VLF transmitter, Varberg, Sweden
T-antenna
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A ‘T’-antenna, ‘T’-aerial, or flat-top antenna is a monopole radio antenna consisting of one or more horizontal wires suspended between two supporting radio masts or buildings and insulated from them at the ends. A vertical wire is connected to the center of the horizontal wires and hangs down close to the ground, connected to the transmitter or receiver. The shape of the antenna resembles the letter "T", hence the name. The transmitter power is applied, or the receiver is connected, between the bottom of the vertical wire and a ground connection.
A 1935 photo of WOR / 710AM's facility in Carteret, New Jersey. In this case there are three radiators: the two towers and the center ‘T’-antenna, sus
A 1935 photo of WOR / 710AM's facility in Carteret, New Jersey. In this case there are three radiators: the two towers and the center ‘T’-antenna, suspended in the middle.
Multiwire broadcast T-antenna of early AM station WBZ, in Springfield, MA, 1925.
Multiwire broadcast T-antenna of early AM station WBZ, in Springfield, MA, 1925.
One of the first uses of ‘T’ aerials in the early 20th century was on ships, since they could be strung between masts. This is the antenna of RMS Tita
One of the first uses of ‘T’ aerials in the early 20th century was on ships, since they could be strung between masts. This is the antenna of RMS Titanic, which broadcast the rescue call during her sinking in 1912. It was a multiwire ‘T’ with a 50 metre (160′) vertical wire and four 120 metre (400′) horizontal wires.
An amateur radio cage ‘T’-antenna 60 ft high by 90 ft long built in 1922, owned by the Historic Radio Engineers Club, Riverhead, New York. The conduct
An amateur radio cage ‘T’-antenna 60 ft high by 90 ft long built in 1922, owned by the Historic Radio Engineers Club, Riverhead, New York. The conductor is made of a 'cage' of 6 wires held apart by wooden spreaders. This antenna achieved transatlantic contacts on 1.5 MHz, at a power of 440 W.