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The field strength must not exceed a maximum value Emax as described in P1546ITU-R P. 1546-1. In principle any correction which increases a field strength must not be allowed to produce values greater than these limits for the family of curves and distance concerned. However, limitation to maximum values should be applied only where indicated in Annex 6 of the ITU-R P.1546-4.
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For land paths less than 15 km one of , the following two methods should be method is used:
Terrain information not available
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The field strength resulting from extrapolation for h1 > 1200 m should be limited if necessary such that it does not exceed the maximum defined in § 2 of P1546Recommendation ITU-R P.1546-4.
This model is not valid for h1 > 3000 m.
Transmitting/base antenna height, h1, in the range 0 m to 10 m
For a land path, the field strength at the required distance d km for 0 £ h1 < 10 m is calculated using:
Interpolation of field strength as a function of distance
Figures 1 to 24 of Recommendation ITU-R P.1546-4 show field strength plotted against distance, d, the range 1 km to 1 000 km. No interpolation for distance is needed if field strengths are read directly from these graphs. For greater precision, and for computer implementation, field strengths should be obtained from the associated tabulations (see Annex 1 of ITU-R P.1546-4, § 3). In this case, unless d coincides with one of the tabulation distances given in Table 1, the field strength, E (dB(mV/m)), should be linearly interpolated for the logarithm of the distance using:
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The field strength resulting from extrapolation for frequency above 2 000 MHz should be limited if necessary such that it does not exceed the maximum value given in § 2 of Recommendation ITU-R P.1546-4.
For sea paths where the required frequency is less than 100 MHz an alternative method should be used, based upon the path lengths at which 0.6 of the first Fresnel zone is just clear of obstruction by the sea surface. An approximate method for calculating this distance is given in § 17 of Recommendation ITU-R P.1546-4.
The alternative method should be used if all of the following conditions are true:
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Table 88: Default clutter height in the P1546ITU-R P.1546-4 model(when clutter height option not activated)Anchor T088 T088
Selected environment | Assumed height of local clutter |
Rural | 10 |
Sub-urban | 10 |
Urban | 20 |
Dense urban | 30 |
Where the receiving/mobile antenna is on land account should first be taken of the elevation angle of the arriving ray by calculating a modified representative clutter height R' (m), given by:
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