For many years the ARRL Antenna Book has provided a table of conductivities and dielectric constants for common types of earth. Antenna analysis programs have adopted the values and they are widely used. However, the table is for the AM broadcast band. Since ground constants are anything but constant, the ARRL values are not suitable for HF where they are commonly employed.
The ARRL data originally appeared in the FCC publication Standards of Good Engineering Practice Concerning Standard Broadcast Stations in 1939. Inductivity is an obsolete term for dielectric constant. Conductivity is in EMU (10−14 = 1 mS/m).
1.8 3.7 5.3 7.1 10.1 14.2 18.1 21.2 24.9 28.5
■ 86.3 119 63.9 128 55.0 133 48.7 137 42.0 142 36.5 148 33.0 152 30.9 154 28.9 157 27.3 159
■ 59.8 40.2 43.0 46.9 36.4 50.7 31.9 54.0 27.1 58.2 23.2 62.6 20.7 65.9 19.3 68.2 17.9 70.6 16.8 72.6
■ 19.8 3.6 17.2 5.0 16.1 5.9 15.2 6.8 14.2 8.0 13.3 9.3 12.7 10.4 12.3 11.2 11.9 12.0 11.6 12.8
■ 13.4 .83 12.2 1.2 11.6 1.5 11.2 1.8 10.7 2.2 10.3 2.6 10.0 3.0 9.8 3.3 9.6 3.6 9.4 3.9
■ 11.0 .44 9.5 .61 8.9 .72 8.4 .82 7.8 .96 7.3 1.1 6.9 1.2 6.7 1.3 6.5 1.4 6.3 1.5
■ 4.7 .071 4.1 .10 3.8 .12 3.6 .14 3.3 .17 3.1 .20 3.0 .22 2.9 .24 2.8 .26 2.7 .28
George Hagn of SRI International developed these curves in the 1980s. The table lists permittivity followed by conductivity in mS/m for the ham bands. Use this interpolator to better represent your terrain.
1.8 3.7 5.3 7.1 10.1 14.2 18.1 21.2 24.9 28.5 ■ 4 3 2 2 1 1 1 1 1 1 ■ 7 4 4 3 2 2 2 2 1 1 ■ 27 17 13 11 9 7 6 6 5 5 ■ 80 50 40 33 27 21 18 17 15 14 ■ 132 89 73 62 51 42 37 34 31 29 ■ 533 348 281 236 192 157 136 123 112 104
This table lists skin depth in feet for the Hagn ground constants. Antenna-induced ground current decays exponentially with depth. It is 37% of the surface value at skin depth and 14% at twice skin depth. Subsurface soil with significant current that differs from surface soil can influence ground constants. Explore the effect.
Seawater permittivity and conductivity are constant over HF but vary with salinity and temperature. In nonpolar, noncoastal regions, permittivity ranges from 70 to 80 and conductivity from 3000 to 6000 mS/m. This map shows conductivity but does not resolve coastal values. Use Deep Dive in this map to find seawater conductivity along the U.S. coast (divide µS/cm by 10 for mS/m). Use this map to find local salinity and temperature. Then calculate permittivity with this program. Absent local data, 75 and 4500 mS/m are reasonable generic values.
Freshwater permittivity is constant over HF but varies with temperature:
°C °F Permittivity 0 32 87.7 5 41 85.8 10 50 83.8 15 59 81.9 20 68 80.1 25 77 78.3 30 86 76.6
Freshwater conductivity is constant over HF but varies with temperature and widely with location, e.g., 4 to 29 mS/m for individual Great Lakes and 20 to 100 mS/m for major rivers. Use Deep Dive in this map to find local U.S. values (divide µS/cm by 10 for mS/m). Absent local data, 15 mS/m is a reasonable generic value for a lake.
A shallow bottom may affect freshwater ground constants in surprising ways. Examine the effect.
50 98 146 ■ 25 170 22 190 21 200 ■ 15 80 15 100 14 110 ■ 11 17 11 25 10.5 33 ■ 7 2.4 7 5 7 7 ■ 3 .4 3 .65 3 .9
Ground constants extracted with straightedges from Figures 22 and 23 in the Hagn paper.
50 98 146 ■ 0.7 0.5 0.4 ■ 1.1 0.8 0.6 ■ 3.5 2.4 1.7 ■ 19.2 9.2 6.6 ■ 75.4 46.4 33.5
Skin depth in feet.
G. H. Hagn, "Ground Constants at High Frequencies (HF)" mistitled "HF Ground and Vegetation Constants" in Proceedings of Third Annual Review of Progress in Applied Computational Electromagnetics, Monterey, CA, 24–26 March 1987.
H. W. Parker and Withan Makarabhiromya, "Electric Constants Measured in Vegetation and in Earth at Five Sites in Thailand," Special Technical Report 43, SRI Project 4240, Stanford Research Institute, Menlo Park, CA, December 1967. Primary data source for the Hagn generic curves.
88–108 MHz