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m for d <= 3 km (Eq. 232)
m for 3 km < d < 15 km
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m (Eq. 233)
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If the value of h1 coincides with one of the eight heights for which curves are provided, namely 10, 20, 37.5, 75, 150, 300, 600 or 1 200 m, the required field strength may be obtained directly from the plotted curves or the associated tabulations. Otherwise the required field strength should be interpolated or extrapolated from field strengths obtained from two curves using:
dB(μV/m) (Eq. 234)
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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:
dB(μV/m) (Eq. 235)
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dB(μV/m) (Eq. 236)
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If all of the above conditions are true, the required field strength, E, should be calculated using:
dB(μV/m) for d <= df
dB(μV/m) for d > df
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Emax : maximum field strength at the required distance as defined in § 2 of P1546-4
maximum field strength at distance df as defined in § 2 of P1546-4
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Field-strength values for a given percentage of time between 1% and 50% time should be calculated by interpolation between the nominal values 1% and 10% or between the nominal values 10% and 50% of time using:
dB(μV/m) (Eq. 237)
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Table 88: Default clutter height in the ITU-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:
m (Eq. 238)
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Correction 
dB for h2 < R′ (Eq. 239)
dB for h2 ≥ R′
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v = 
m
degrees
f: frequency (MHz).
In cases in an urban environment where R' is less than 10 m, the correction should be reduced by Kh2 log(10/R′). Where the receiving/mobile antenna is on land in a rural or open environment the correction is given by equation 
for all values of h2 with R' set to 10 m.
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Correction = 
(Eq. 240)
where ha is the antenna height above ground (m) (i.e. height of the mast) and R is representative of the height of the ground cover surrounding the receiving/mobile antenna as defined in § 9 of P1546Recommendation ITU-R P. 1546-4, which also represents the height of ground cover surrounding the transmitting/base antenna. This correction only applies when d is less than 15 km and h1 − R is less than 150 m.
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dB (Eq. 241)
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dB (Eq. 242)
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