Earth network

An earth network is an earthing system made up of many metal strips laid in the ground, which is used for the low-resistance earthing of a vertical transmitting antenna . This is particularly necessary for T-antennas and self-radiating transmission masts in the long-wave, long-wave and medium-wave range, in which the required second dipole half is replaced in this way . The decisive factor is the lowest possible earthing resistance of a few ohms , which is well below the foot point impedance of a quarter-wave radiator of only 36 Ω.

General

The earth grid must be able to absorb the current that would actually flow into the lower (buried) dipole half.

The antenna current I supplied by the transmitter oscillates between the grounding network and the antenna in the rhythm of the transmission frequency, which is why the grounding network is also referred to as a “ counterweight ”. The total load resistance of the transmitter is the sum

${\displaystyle R_{Last}=R_{Erdnetz}+R_{Antenne}}$

The respective services are calculated

${\displaystyle P_{Antenne}=I^{2}\cdot R_{Antenne}}$

${\displaystyle P_{Erdnetz}=I^{2}\cdot R_{Erdnetz}}$

So if you want to radiate as much power as possible and only heat the ground a little, the earthing resistance R earth _network must be as low as possible.

An earth network consists of several bands, the lengths of which are at least as high as the height of the transmitting antenna, but are usually a quarter of the wavelength of the frequency to be emitted . In areas with poor soil conductivity, earth networks have also been built whose length exceeds 1.5 times the wavelength to be emitted.

The galvanized steel earth strips are buried at a shallow depth (up to 50 centimeters). If it is impossible to bury them in rocky ground, they may be laid above ground on small masts. Especially in this case one speaks of " radials ". The bands of an earth-web running radially ( radiate ) to the antenna carrier. They are not supposed to cross each other.

In the case of transmitter systems on ships and platforms anchored in the sea, good grounding is guaranteed by the electrically conductive seawater over the hull. In these cases no extensive earth network is required.

literature

• Wolf Siebel: Antenna guide for HF reception. 3rd edition, Siebel Verlag GmbH, Meckenheim, 1987, ISBN 3-922221-23-8
• Herbert Zwaraber: Practical setup and testing of antenna systems . 9th edition, Dr. Alfred Hüthig Verlag, Heidelberg, 1989, ISBN 3-7785-1807-0
• Eberhard Spindlert: The great antenna book. 11th edition, Franzis-Verlag GmbH, Munich, 1987, ISBN 3-7723-8761-6