Editing Ground (electricity) (section)

=== Design ===
A standard ground system widely used for [[mast radiator]] broadcasting antennas operating in the [[medium frequency|MF]] and [[low frequency|LF]] bands consists of 120&nbsp;equally-spaced, buried, radial ground wires extending out one quarter of a [[wavelength]] (<math>\ \tfrac{ 1 }{ 4 } \lambda\ </math>, or 90&nbsp;electrical degrees{{efn|name=electrical_degrees_note}}) from the antenna base.<ref name=Carr-2001/><ref name=ARRL-AntBk-2000/><ref name=Johnson-1993/><ref name=NAB-Hdbk-2007>
{{cite book
 |editor-last1 = Williams  |editor-first1 = Edmund
 |display-editors=etal
 |year   = 2007
 |title  = NAB Engineering Handbook
 |edition = 10th
 |publisher= [[National Association of Broadcasters]] (NAB) / Taylor and Francis
 |pages  = 718–720
 |isbn   = 9780240807515
 |url    = https://books.google.com/books?id=V8Lk2ghPl7IC&pg=PA718
 |via    = Google books
}}
</ref>
[[American wire guage|AWG]]&nbsp;8 to AWG&nbsp;10 soft-drawn copper wire is typically used, buried 4–10&nbsp;inches deep.<ref name=Johnson-1993/> For [[AM broadcast band]] antennas this requires a circular land area extending from the mast {{convert|47-136|meter|ft}}. This is usually planted with grass, which is kept mowed short, as tall grass can increase power loss in certain circumstances. If the land area available is too limited for such long radials, they can in many cases be adequately replaced by a greater number of shorter radials, or a smaller number of longer radials.<ref name=NAVELEX/><ref name=ARRL-AntBk-2000/>

In transmitting antennas a second cause of power wastage is [[dielectric loss|dielectric power losses]] of the [[electric field]] ([[displacement current]]) of the antenna passing through the earth to reach the ground wires.<ref name=NAB-Hdbk-2007/> For antennas near a half-wavelength high (180&nbsp;electrical degrees{{efn|
name=electrical_degrees_note|
An ''electrical degree'' is a frequency-relative and material-relative measure of length, with 360&nbsp;electrical degrees representing one full [[wavelength]], as it appears in the medium the [[radio wave]]s happen to be traveling through, for whatever [[radio frequency]] the waves happen to be oscillating at. Hence a quarter-wavelength is <math>\ \tfrac{\ 1\ }{ 4 } \times 360^\circ = 90^\circ\ ,</math> and a half-wavelength is  <math>\ \tfrac{\ 1\ }{ 2 } \times 360^\circ = 180^\circ ~.</math>
}}) the antenna has a voltage maximum ([[antinode]]) near its base, which results in strong electric fields in the earth above the ground wires near the mast where the [[displacement current]] enters the ground. To reduce this loss these antennas often use a conductive copper ground screen under the antenna connected to the buried ground wires, either lying on the ground or elevated a few feet, to shield the ground from the electric field.

In a few cases where rocky or sandy soil has too high a resistance for a buried ground, a [[Counterpoise (ground system)|counterpoise]] is used.<ref name=ARRL-AntBk-2000/> This is a radial network of wires similar to that in a buried ground system, but lying on the surface or suspended a few feet above the ground. It acts as a [[capacitor]] plate, capacitively coupling the feedline to conductive layers of the soil.