Ground dipole

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A floor dipole is a special form of a dipole antenna for the transmission of radio signals, especially at extremely low frequencies, the longest waves or even lower ( Extremely Low Frequency ).

A bottom dipole consists of an electrical line fed in the middle, the ends of which are grounded as far as possible from one another with the lowest possible resistance .

Ground dipoles have a very low efficiency (less than 1%) and are only used as a transmitting antenna in professional communications engineering if conventional antennas cannot be implemented for economic and technical reasons, as antenna sizes are usually determined by the wavelength and this is due to extreme longitudinal waves Kilometer range (up to well over 1000 km).

By terminating one end with an earthing resistor and moving the feed point, the bottom dipole is given a preferred orientation. The arrangement is called a beverage antenna . This long-wire antenna is only possible for higher frequencies, e.g. B. 160 m band and smaller wavelengths.

history

When submerged, submarines are shielded from all normal radio signals by the sea water and are therefore cut off from communication with the military command authorities. VLF radio waves can penetrate 10 to 30 meters into seawater and have been used to communicate with submarines since WWII, but the submarine has to rise close to the surface which makes it more noticeable. The realization that ELF waves can penetrate deeper into seawater, to normal submarine operating depths, led to US physicist Nicholas Christofilos suggesting that the US Navy could use them to communicate with submarines in 1958 . The US military researched many different types of antennas for use on ELF frequencies. Cristofilos suggested applying currents to the earth to create a vertical loop antenna, and it became clear that this was the most practical design. The feasibility of the ground dipole idea was tested in 1962 with a 42 km leased power line in Wyoming and in 1963 with a 176 km prototype wire antenna that stretched from West Virginia to North Carolina.

Individual evidence

  1. ^ Lewis Coe: Wireless Radio: A History . 2006, ISBN 0-7864-2662-4 , pp. 143-144 ( google.com ).
  2. ↑ a b c Walter Sullivan: HOW HUGE ANTENNA CAN BROADCAST INTO THE SILENCE OF THE SEA. October 13, 1981, accessed January 25, 2020 .

literature

  • Gerd Klawitter: Antenna advisor receiving antennas for all wave ranges. 6th edition. Verlag für Technik und Handwerk, Baden-Baden 2005, ISBN 3-88180-613-X .