VLF transmitter DHO38

The Navy radio spot Rhauderfehn with the call sign DHO38 is a VLF transmitter of the Navy, which is subordinate to the Naval Support Command. The official name of NATO is NATO VLF / MSK Marine radio end point Rhauderfehn. It bears this name since the 18th December 1981. The local people, the plant is known as " The Towers ".

The transmitter is located near Saterland - Ramsloh in the district of Cloppenburg ( Lower Saxony). Through the grounds of the Navy radio transmitting site are the borders of the two counties of Cloppenburg and empty. Five antennas are in Ostfriesland, three on Cloppenburger area.

Plant

The masts of the naval radio station among the highest used by the military structures of continental Western Europe. They stand with 352.8 meters in fifth place of the largest buildings in Germany. The eight red - white pylons can be seen up to a distance of more than 30 kilometers.

The grounds of the Navy radio station covers an area of ​​about 540 hectares. The entire area is surrounded by a 12 km long security fence and accessible with paths and road network of about 26 km in length.

The specific conductivity of the Wester Moors played an important role in the choice of location. The wet ground allows the required for the radiation of long waves good grounding, in addition, the long waves can propagate optimally due to the flat terrain structure. To produce a transmission link to submerged submarines a low emission frequency and on the other a high radiated power required for a. Only in this way is required to achieve high received field strength. For technical and economic considerations, the antenna was built as a radiation- coupled system. To ensure high availability, the transmission system is duplicated. The two antenna groups each with four antennas, two shelters and two operations centers.

The entire house technology with the air - conditioning and cooling as well as water and electricity supply are designed such that the Navy radio system is self-sufficient in disturbances of public utilities. Four diesel generators, one spare system in the basement of each Schutzbaues, with a capacity of 550 kVA, automatically take over the complete power supply in case of a power failure. Normally, the power supply of the transmitter system is ensured by a 20 kV supply from the public network of EWE AG. The drinking and industrial water supply is supplied from the public water supply network. In a possible failure of a drinking water container is ready. For cooling systems, fire extinguishing systems and sanitary facilities are available two wells with appropriate pumping equipment.

Transmitter

The transmitter with its eight 100 - kW transmitter amplifiers is designed for long - ( VLF ) or longwave (LF) with frequencies of 14 kHz to 50 kHz and 23.4 kHz currently sends a transmission power of 800 kW. It is technically possible to transmit on a plurality of frequencies. The final stages included (yet) an electron tube with evaporative cooling.

Are sent coded messages to submarines of the Navy and other NATO countries. Due to the very low transmission frequency associated with a high transmission power of the transmitter in the world and to receive up to a water depth of about 30 m.

Antennas

The transmitter uses eight identical screen antennas, each supported by 352.8 -meter-high steel tubular poles. Each mast has a diameter of 2.20 meters. The cylinder designs have here, depending on the local stress, wall thickness from 8 mm to 13 mm. The individual masts stand on each one about 3 feet tall cylindrical ceramic insulator, a so-called Fußpunktisolator, consisting of 16 full- ceramic core supports two levels. The Fußisolator is designed for a load of 4000 tons and can safely isolate a voltage of 250 kV. The masts are fixed by nine guy wires ( backstays ) on three levels. These ropes are transferred to three layers and arranged 120 degrees around the mast and supported by twelve roof parts.

Each of the towers represents a separate antenna system, there are no antenna wires stretched between the masts.

The antenna structure has, as with VLF transmitters usual, an omni-directional characteristics.

Inside the antenna, a lift and a ladder are available for inspection and maintenance. The elevator is moved up and down via a worm gear which engages into a position located in the interior of the pole rack. A ride from the foot up to the roof hatch of the transmission tower takes 18 minutes. It is mandatory that persons using the elevator, wearing life dishes on the body. A maximum of three people can fit in the elevator. Every 60 meters there is lattice planes in the mast, superimposed on which Abseilmaterial and bandages.

Among the four anchor points four vibration absorbers are provided on the outside of the poles (on the images as a thickening can be seen ), so-called oscillation damper is mounted. These are filled with a special granular material and prevent the generation of vibrations which may occur at relatively low wind speeds. You get the stable state of the construction in storms. The total mass of a mast including fixtures and ropes is per 475 tonnes.

Rope anchoring

Supply line and vibration dampers

The control bunker

Abstimmanlagen

To tune the antenna next to each mast antenna tuning house the size of a small apartment blocks. These include meter high capacitors and inductors, as well as other equipment. Thus can be mechanically " extended " to electrically short antennas, which, based on the wavelength. The tuning means are used to adjust the input impedance of the antenna to the impedance of the transmitter amplifier.

Ground network

The ground network is to provide the best possible introduction of the antenna current in the ground. To each of the eight antenna mast about 30 cm below the surface 200 ground wires are designed to radiate. This per 400 m to 450 m long wires have a cross section of 3.5 mm and end in a 3 m long grounding rod made ​​of stainless steel. Serves as corrosion protection, a 1.5 mm thick lead sheath, which ensures the stability of the earth net against the aggressive bog water. The entire floor area around the impact area of ​​the screen antennas is covered by the ground network. Between two adjacent poles, the abutting ends of the earth wires are welded together and share a common ground.

Chronicle

Costs

Signal

The signal is a MSK DHO38 encoded signal with 200 Baud. The transmitter can be received with any receiver or converter which receives the frequency 23.4 kHz. An AM receiver provides a chirping noise.

Since all transmissions are encrypted by DHO38 whose decryption is practically impossible and they do not contain information for civilian users, a civilian use of the signal from DHO38 very rudimentary purposes, such as direction finding, investigation of the propagation conditions at about the wireless weather forecast and the detection of larger concentrations of metal limited in the ground, as these are the propagation direction and polarization of the waves of DHO38 influence.

Criticism

The Navy radio station was for military reasons a long time, a white spot on the map. Were the Saterländer 1973 still glad they did prevent the planned bombing range at the same place, there is now the concern caused by the building radiation exposure could pose a health risk. In addition, the risk to present a target in a crisis or war case exists.

During the planning and construction phase of the transmitter concerns about the environmental impact of the plant have been expressed by various organizations. Due to the extremely restrictive access restrictions, however, have grown up over the years in this part of the Wester Moore's many animal and plant species that are not elsewhere, or only rarely encountered. The Association for Bird Protection admits to have counted 34 species of breeding birds.