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World Atlas of Ground Conductivity

Serge Stroobandt, ON4AA

Copyright 2002-2016, licensed under Creative Commons BY-NC-SA

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TO DO: WWV & References

Importance

It is important to know the conductivity (and permittivity!) of the soil around your HF station for two good reasons:

  1. It allows to model power loss to the ground in the near-field of HF antennas —both vertical and horizontal—,
  2. It allows to accurately calculate radiation patterns of HF antennas, taking into account ground reflections.

Measurement

In literature, a number of ways to measure ground conductivity and permittivity have been described. Most notably, Rudy Severns, N6LF wrote two excellent papers on the subject.

Nonetheless, it is not particularly inciting having to construct a measuring apparatus just for using it once or twice. Moreover, the area of land that most influences the radiation pattern is at about 10λ away from your antenna, and is therefore often not accessible for measurements. I am by no means discouraging ground conductivity measurements. However, in practice, most people —including myself— prefer spending time differently.

Ground conductivity atlas

ITU-R
Quite a while ago, the CCIR (now ITU-R) published Recommendation 832, containing a detailed world atlas of ground conductivities. The maps are for VLF and MF frequencies, though the MF maps still remain useful for the lower HF frequencies. One can easily be misled by the bookmarks in this PDF document. Be sure to scroll down at least to Figure 7 in this atlas to get to the MF maps; preceeding maps are for VLF! An example MF conductivity map of my home country Belgium is shown below.

Download

ground-conductivity-atlas.vlf&mf.pdf [3.9MB]

Belgian MF ground conductivity map in mS/m, standardised at 1MHz. Source: CCIR Rec. 832

Belgian MF ground conductivity map in mS/m, standardised at 1MHz. Source: CCIR Rec. 832

Ground types

Ground types as used by L. B. Cebik, W4RNL
soil description ground quality σ (S/m) εr
cities, industrial areas very poor 0.001 5
sandy, dry, flat, coastal poor 0.002 10
rocky soil, steep hills, typically mountainous poor 0.002 13
pastoral, medium hills, forestation, heavy clay soils good/average 0.005 13
pastoral, low hills, rich soil very good 0.0303 20
salt water excellent 5.0 81
Ground types as defined in 4nec2
soil description σ (S/m) εr
polar ice cap 0.0001 1
city industrial area 0.0001 3
polar ice 0.0003 3
city industrial; maximum attenuation 0.0004 3
arctic land 0.0005 3
sea ice 0.001 4
poor 0.001 5
city industrial; average attenuation 0.001 5
dry, sandy, coastal 0.001 10
fresh water 0.001 80
fresh water 10°C @100MHz 0.001 84
mountainous hills <1000m 0.002 5
fertile land 0.002 10
rocky, steep hills 0.002 15
moderate 0.003 4
medium hills and forest 0.004 13
average 0.005 13
highly moist ground 0.005 30
fresh water 20°C @100MHz 0.005 80
pastoral hills, rich soil 0.007 17
marshly land, densily wooded 0.0075 12
marshly, forested, flat 0.008 12
good 0.010 4
rich agric land, low hills 0.010 15
sea water 20°C <1GHz 4.0 73
sea water 10°C <1GHz 4.0 80
sea water 5.0 81

WWV

In the United States, call signs generally start with the letter “K” for stations located west of the Mississippi River, whereas stations east of the Mississippi generally have a call sign starting with the letter “W”.[@Wikipedia.Call_sign]

References

  1. http://www.antennasbyn6lf.com/measurement_of_soil_characteristics/
  2. https://en.wikipedia.org/wiki/Near_and_far_field
  3. https://en.wikipedia.org/wiki/Call_sign
  4. http://tf.nist.gov/general/pdf/1434.pdf
5
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Last update: Sunday, August 13, 2017.