Antenna to reduce shrinkage

from Wikipedia, the free encyclopedia

A shrinkage- reducing antenna is a transmission antenna for long and medium waves , which relocates the area of near fading as far away from the transmission location as possible. This cannot be achieved with a high transmission power - an antenna must be used that suppresses the steep radiation with an elevation angle of more than 50 degrees as much as possible. This avoids interference between the radio wave reflected by the ionosphere and the ground wave .

Vertical radiator

Isolator on the former medium wave transmission mast of the Rhine transmitter (Wolfsheim)

It can be a mast radiator are used, with a separating insulator is divided electrically into two parts, wherein the feeding of the uppermost mast part either an inside of the mast laid cable or moved in the interior of the pole ladder takes place. Alternatively, wires that are attached outside the mast construction can also be used to feed the upper mast part . The medium wave transmitters of the transmitter Muehlacker , Wolfheim and the broadcast Transmitter Hamburg-Billstedt use such antennas.

There are also shrinkage-reducing transmitter masts in which the mast is divided by two isolators, as is the case with the Ismaning transmitter .

Since such isolation insulators are more sensitive than the rest of the mast construction, greater horizontal forces that can be caused by wind-induced vibrations should be avoided if possible. For this purpose, some transmission masts were equipped with built-in isolators with cylindrical vibration dampers directly above the isolators. These vibration dampers look like cylindrical bulges in the mast construction. Such vibration dampers can be found on the transmission masts in Ismaning, Wolfsheim and Hamburg.

Such subdivided antenna masts can change their radiation pattern electrically.

Another possibility is to use such a length of the (undivided) insulated mast that best suppresses the upward side lobe. This is a length of a little more than half a wavelength, namely 0.528 (190 °). The horizontal radiation is reduced by about 1 dB, but the best shrinkage-reducing properties are achieved. An example of such a mast is the Wilsdruff transmitter with a transmission frequency of 1044 kHz and a height of 153 m.

dipole

Alternatively, dipoles at a certain height above the surface of the earth can also be used as anti-fading antennas .

Another possibility for the implementation of a shrinkage-reducing antenna is the circular group radiator . For this purpose, several self-radiating transmission masts are arranged in a circle and fed in phase. With such systems, very flat radiation characteristics can also be achieved, but are very expensive because of the number of transmission masts required. Such a plant used the now disused Orlunda radio transmitter of the Swedish Radio .

alternative

In contrast to the flat radiating shrinkage-reducing antenna described here, shrinkage is also reduced with particularly steep radiation (see NVIS from Near Vertical Incidence Skywave). There are steep antennas used.

literature

Individual evidence

  1. ↑ http://www.bbceng.info/Install/Transmitter%20Projects/Reminiscences/Lisnagarvey/Lisnagarvey_Blaw-Knox.htm Aubrey McKibben: Lisnagarvey and the Blaw-Knox mast , accessed June 11, 2020