Mast radiator
A self- radiating transmitter mast is a base station, in which the entire structure acts as an antenna. It is often used as a transmitting antenna for long - or medium-wave. Unlike the antenna carrier, which serves only as a mechanical support for the attached at its upper portion ( relatively small ) transmitting antenna, such as for FM broadcast or mobile.
Depending on the requirements, a self- radiating transmission tower isolated from earth or be grounded. In the first case, the feed is usually close to the ground. In the latter case, the transmission power needs to be fed to the tower, for example, at a certain height over backstays.
Known representatives of the design with feed on the backstays are the transmission towers in Aholming and Donebach for the long-wave transmitter of the Germany radio.
Electrical connection
Isolated self-radiating transmission towers stand during transmission where high voltages (up to 300 kV) and therefore must be protected against unauthorized approach. Matching between the line and the impedance of the coaxial cable is effected by a Antennenfußpunktes resonant transformer is accommodated in the Abstimmhaus.
Since such masts are sometimes very high, even a flight safety lighting is often necessary. This is fed through a cable which is passed through a coil which forms a blocking circuit for the transmission frequency with a parallel-connected capacitor. In this way, a mast mounted on the transmission antenna for FM can be fed. In the adjacent figure, such a coupling in the form of two circular interlocking coils, each rotated by 90 °, the left can be seen next to the base insulator. Right next to the insulator there is a spark gap to electrostatic atmospheric -related charges, according to thunderstorms dissipate. The outer wall of behind it Abstimmhauses is provided with a grounded wire mesh for the purpose of shielding.
Rarely, an illumination of the mast top with the help of Skybeamern is performed, as in 1939 when radio mast of Germany transmitter in Herzberg on the Elster.
Vibration damping
In order to dampen wind-induced vibrations are used in some self-radiating tubular steel masts cylindrical vibration that look like cylindrical thickened. Such dampers are used for example in the masts of DHO38 in Ramsloh in Saterland. They are also directly in the separator equipped with insulators masts of anti-fading transmit antennas of medium wave transmitter Hamburg, Wolfsheim and Ismaning above the separating insulator available.
Electrical isolation of the bracing
The guy ropes even more radiant transmission towers may not resonate with the radiated frequency. Therefore, they are usually divided by insulators. During thunderstorms, high voltages can occur as a result of the electrostatic charge on the ropes the backstays, which can lead to flashovers on the insulators.
Alternatively, the guy wires can be tuned via coils or their length are chosen so that at the transmission frequency used no resonance occurs. The latter design has the advantage that no maintainable only at great expense insulators and surge arresters are needed in the backstays. Also plastic ropes have been used for the bracing of radiating transmitting masts. However, there are problems with such ropes with aging, so that their use is not widespread.
There are poles, which are divided by a plurality of insulators electrically into a plurality of sections. They can be fed several times and allow a shallow angle ( shrinkage -reducing antenna). Such constructions are used in the transmitters in Muehlacker, Ismaning, Hamburg and Wolfsheim ( Rheinsender ). Solid core insulators are made of fired steatite used as insulators for the bracing. As isolation of mast construction to earth serve hollow body made of steatite. Due to the high hardness and the associated low fracture toughness of advanced ceramics are special requirements for the design and installation.
Maintenance
Since the insulated against ground radiating transmitting masts are under a high electric voltage, make maintenance a particular challenge either the antenna must be completely shut down, or a special insulated platform is used to allow installers secure access. In the first case, a spare antenna must be present when it should not cause an interruption of the transmission mode.
On most radiating transmitting masts people may linger during transmission, as similar to a bird sitting on a power line, the antenna current flows past this. However, this does not work for some types shrinkage -reducing transmit antennas. Here, the ladder is insulated from the mast structure and between the two lies during a performance at a high voltage. However, you can compensate for this potential and thus make access to the ladder for maintenance possible. Transmission towers must be always off when maintenance work on insulators or in its immediate vicinity are pending, since always a high voltage when transmitting.
As with normal transmission towers also, a ladder is present in radiating transmitting masts. They may be placed inside or outside of the mast construction. Especially with tubular steel poles it is usually assembled from weather protection reasons inside the transmitter tower. As already mentioned, this ladder can also serve as a conduit for the supply of lying above a separating insulator mast parts, but for which an isolated mounting on the transmission tower is necessary.
In some radiating transmitting masts also an elevator system was installed, which is designed for the sake of mast statics mostly as a self-propelled climbing elevator. The drive is provided as a rule with an electric, sometimes with an internal combustion engine. The power supply to the elevator car is done either via busbars ( Ramsloh in Saterland ) or via a trailing cable is firmly connected. It is used along with the lines of flight safety lights passed through the coil of a blocking group for the transmission frequency, which lies between Earth and the transmission tower.
Designs
A special design even more radiant transmission towers is built particularly in the U.S. before the Second World War Blaw -Knox transmission tower. This design resembles the shape after a double pyramid. However, it has lower radiation properties than conventional guyed masts and is therefore no longer used since 1940.
Another unusual feature are freestanding towers, which are isolated from earth. A well-known representative is the radio tower in Berlin, but was never used as a self-oscillating transmission tower. Further towers of this design are the antenna towers of Radio Luxembourg in Junglinster and Blosenbergturm in Beromunster.
On May 18, 1974, the 646 meter high self-radiating radio transmission tower in Warsaw Konstantynów, Poland was completed. The used as a long-wave transmitter "Radio Warsaw " rope tensed steel tower was up to its collapse on 8 August 1991, the tallest building in the world.
Maximum voltage
The mast at maximum applied voltage is given by
Wherein the transmission output power at the unmodulated carrier, the radiation resistance at the transmission frequency, the reactance is at the transmission frequency. designates the modulation degree. For amplitude-modulated transmitter, it can be a maximum of 1, for frequency-modulated transmitters it is 0
Gallery
Tower of NDBs NKR - sizing Ochsenbach
The former radio mast in Konstantynów in Poland (height: 646 meters )
Base of the transmitter and radio technology museum in King Wusterhausen