Field cable construction

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The Feldkabelbau one of the wire-line communication tools .

The field cable technology was already used in the world wars and until recently also by the German Bundeswehr , which is now increasingly switching to fiber optic cables. It is still used today by civil protection and disaster control , especially by the Technical Relief Organization (THW). The aim of field cable technology or OB technology is to add or temporarily replace the existing GSM and radio network , which is overloaded or unusable during large-scale operations (such as the ICE disaster in Eschede , Elbe flood, etc.) , quickly and temporarily .

In addition to the old OB technology, the technical relief organization also uses AWITEL field technology .

Cable types

Field cable (Fkb)

The twisted field cable consists of two wires . These are called a-wire and b-wire (see ab interface ). The field cable is kept on a field cable drum. A field cable reel is usually 800 m long, but can hold up to 850 m of cable. A drum with cable weighs about 14 kg and the length of the cable has a DC resistance of about 100 ohms. A plastic-coated core consists of three galvanized steel wires and four tinned copper wires . The diameter of a wire is 2.1 mm. The cable has a breaking load of about 390 N / mm². Under favorable conditions (good cable, no interference, optimal cable routing), the range for voice connections is up to 15 km in civil engineering (laying on the ground) and up to 40 km in building construction (laying over masts, trees, etc.).

Remote field cable (FFkb)

Several connection cable drums

The remote field cable with a round sheath consists of four cores (ie two pairs or two twin cores [DA]), is plastic-insulated and shielded. The remote field cable drum comprises 400 m of cable and weighs 45 kg. Thanks to the low loop resistance of around 20 ohms per drum, a range for voice connections of 50 km can be achieved. The installation of remote field cables is more difficult due to its weight, but it is very similar to the construction technology of the field cable.

Connection cable (AnKb or AKb)

The connection cable looks similar to the FFkb because it is kept on similar or identical drums. However, the plugs are significantly larger in diameter. The cable has 20 poles, i.e. 10 pairs (also referred to as 10 "). Each length is 230 m.

30-pin connection cable (VerBkb)

The short (usually 1–10 m, rarely up to 30 m) cables are used to connect the tens exchanges and lightning junction boxes or junction boxes . Despite their 30 possible contacts, often only 10 pairs, i.e. 20 poles, are used. There are adapters on connection cables.

Lightning protection

The overvoltage protection or lightning protection must be installed on both telecommunication line ends depending on the line length. In the case of tents without a floor, however, it should be noted that the earthing point must remain 20 m away from the actual tent . Problems rarely arise in field operation with OB technology. For ZB (analog) and especially for DSL (U K0 ), the breakdown voltage of the surge arrester must be observed.

Lightning protection cartridges

The functional principle of the lightning protection device is comparable to a fuse, except that the filling of the cartridge hardly conducts and only becomes conductive in the event of overvoltage. Thus, the cartridge connects the telecommunication line (each wire separately) with the grounding device and is intended to conduct harmful currents downwards. Glass cartridges with a red ring contain radioactive gas. Therefore they must be disposed of properly. If the glass cartridge breaks in a closed room, the room must be immediately ventilated and hermetically sealed from other rooms; it may then not be entered for at least 30 minutes.

10 lightning protection junction box

The 10 lightning connection box has ten pairs of rotating terminals, an earth connection, a 30-pin knife socket (also known as a bar) and 20 lightning protection cartridges.

Application:

  • Connection of field telecommunication lines via the lightning protection device to OB / ZB exchanges or telecommunications systems
  • Distributor to adapt from an AKb to individual terminals (10 pairs) via an adapter on a 30-pin male connector.
  • do not use with DSL.

Terminal box AK 70

The AK 70 junction box has 30 pairs of spring clamps, an earth connection, two 30-pin knife sockets (also called bars) and 30 lightning protection cartridges.

Application:

  • Connection of field telecommunication lines via the lightning protection device to OB / ZB exchanges or telecommunications systems
  • Distributor to adapt from an AKb via an adapter to a 30-pin male connector to individual terminals (AKb only uses ten pairs).
  • Looping through of AKb using two adapters on a male connector so that ten pairs can be tapped on individual contacts
  • Connection of two AK 70s using a 30-pin cable for 15-pair wiring
  • Mixed operation possible (1 a / b to 10 a / b are compatible with 10 lightning protection and AKb), 11a / b to 15a / b are only compatible with a direct connection using a 30-pin cable and another AK 70

One and two-pair lightning protection

Colloquially known as "NATO rolls". Olive's box, slightly larger than a beer mat and a good 5 cm thick, external grounding screw, hinged, all-round sealing lip, inside four or eight clamps and two or four lightning protection cartridges. Installation by means of an earthing rail (sheet metal strip) directly on the earthing spike so that the lightning protection does not lie on the ground and therefore in the water.

Construction engineering

Construction crew

The construction team consists of a squad leader and several telecommunications. At the THW, this task is carried out by the telecommunications team of the leadership / communication department (FGr FK). At the DRK, the IuK (information and communication) (telecommunications service) specialist service, in particular the telecommunications team, takes on this task.

Types

There are three types of construction:

  • Building construction means that the field cable is installed as high as possible (typically 4.50 m to 5.50 m) in order to reduce the attenuation by e.g. B. to reduce damp grass and to avoid damage or sabotage or at least make it more difficult. Therefore, building construction is the preferred type. The minimum construction height must be high enough that trucks (4.20 m) can drive through it.
  • The civil engineering is the fastest method of construction, since the cable is simply placed on the floor. However, care must be taken to ensure that the cable is laid in such a way that no one can accidentally trip over it.
  • In the protected underground construction , the cable is buried in the ground. This method takes the most time and effort, but represents the least hindrance to people and traffic and is best protected against espionage and sabotage.

Construction work

Field cable construction can be carried out in two ways:

  • In the case of a closed construction , the field cable is laid out in one operation and installed immediately. This type of construction is recommended when the unconstrained field cable is a hazard. This construction method is carried out by a construction team.
  • With the separate design , the field cable is laid out in the first step and installed in the second step. This type of construction is recommended if the field cable laid out does not pose a risk, as the line is then available more quickly. This type of construction can be carried out by one or more construction teams, working together or apart, and can accordingly require more staff.

Construction equipment

Construction cart (sulki) with 2 removable wheels with pneumatic tires, drawbar with T-handle, loaded with backpack and 3 field cable drums

The most important devices in field cable construction are:

  • Back carrier: The field cable drum is transported on the back carrier. When laying out cables, it is carried on the back, when picking up it is carried in front of the stomach. In addition, a guide device for the cable (spindle and shuttle) is attached for picking up. The roller can be cranked in particular to take up cables.
  • Wire fork: The wire forks are used to lay the field cable in building construction and install the construction hooks.
  • Construction hook: The construction hook enables the field cable to be installed in high places that have no natural or structural storage points for the field cable.
  • Construction poles with extension pieces: The field cable is laid with construction poles in building construction if there is no other option. Construction poles are usually needed especially for road crossings. With two construction poles (2.25 m each) and an extension (1.25 m), a construction height of up to 5.50 m can be achieved.
  • Anchor posts and ropes: Construction poles are guyed and anchored with anchor posts and ropes.
  • Poles: Poles are used to create holes for setting poles.
  • Ground pipes and plugs: An earth connection (ground) is established with ground pipes and plugs .
  • Lightning protection connection strips: The ends of the field cable are connected to the lightning protection connection strips in order to divert overvoltages from lightning that could strike the field cable into the ground before the field telephone . There are, for example, strips with ten connections (10-pair) or with only one connection (1-pair).
  • Telephone construction trolleys: The construction trolleys are used to transport the necessary building materials if no motor vehicle is available or the site does not allow motor vehicles . A back stretcher is attached to the construction cart, in which the drum is attached for laying out. Two more drums can be carried as a reserve, and wire forks, construction poles, post irons and anchor posts are belted on just above axle height.

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