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Ch1neg10: the correction Ch1 in dB calculated using equation (12) in § 4.3 of ITU-R P.1546-4 at the required distance for h1 = 10 m
E10 and E20 : the field strengths in dB(V/m) calculated according to § 4.1 of ITU-R P.1546-4 at the required distance for h1 = 10 m and h1 = 20 m respectively..
Note that the corrections C1020 and Ch1neg10 should both evaluate to negative quantities.
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
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dB (Eq. 246)
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at the required distance for h1 =
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E10 and E20 : the field strengths in dB(μV/m) calculated according to § 4.1 of ITU-R P.1546-4
...
dB(μV/m) (Eq. 244)
where:
d : distance for which the prediction is required
dinf : nearest tabulation distance less than d
dsup : nearest tabulation distance greater than d
Einf : field-strength value for dinf
Esup : field-strength value for dsup.
This model is not valid for values of d less than 1 km or greater than 1 000 km.
Interpolation and extrapolation of field strength as a function of frequency
Field-strength values for the required frequency should be obtained by interpolating between the values for the nominal frequency values of 100, 600 and 2000 MHz. In the case of frequencies below 100 MHz or above 2 000 MHz, the interpolation must be replaced by an extrapolation from the two nearer nominal frequency values. For most paths interpolation or extrapolation for log (frequency) can be used, but for some sea paths when the required frequency is less than 100 MHz it is necessary to use an alternative method.
For land paths, and for sea paths where the required frequency is greater than 100 MHz, the required field strength, E, should be calculated using:
dB(μV/m) (Eq. 243)
where:
f : frequency for which the prediction is required (MHz)
finf : lower nominal frequency (100 MHz if f < 600 MHz, 600 MHz otherwise)
fsup : higher nominal frequency (600 MHz if f < 600 MHz, 2 000 MHz otherwise)
Einf : field-strength value for finf
Esup : field-strength value for fsup.
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:
- The path is a sea path.
- The required frequency is less than 100 MHz.
- The required distance is less than the distance at which a sea path would have 0.6 Fresnel clearance at 600 MHz, given by D06(600, h1, 10) as given in § 17 of P1546-4.
If any of the above conditions is not true, then the normal interpolation/extrapolation method given by equation (14) should be used.
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
where:
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
d600 : distance at which the path has 0.6 Fresnel clearance at 600 MHz calculated as D06(600, h1, 10) as given in § 17 of P1546-4
df : distance at which the path has 0.6 Fresnel clearance at the required frequency calculated as D06( f, h1, 10) as given in § 17 of P1546-4
Ed600 field strength at distance d600 and the required frequency calculated using equation (14).
Interpolation of field strength as a function of percentage time
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:
...
at the required distance for h1 = 10 m and h1 = 20 m respectively..
Note that the corrections C1020 and
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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(μV/m)), should be linearly interpolated for the logarithm of the distance using:
dB(μV/m) (Eq. 247)
where:
d : distance for which the prediction is required
dinf : nearest tabulation distance less than d
dsup : nearest tabulation distance greater than d
Einf : field-strength value for dinf
Esup : field-strength value for dsup.
This model is not valid for values of d less than 1 km or greater than 1 000 km.
Interpolation and extrapolation of field strength as a function of frequency
Field-strength values for the required frequency should be obtained by interpolating between the values for the nominal frequency values of 100, 600 and 2000 MHz. In the case of frequencies below 100 MHz or above 2 000 MHz, the interpolation must be replaced by an extrapolation from the two nearer nominal frequency values. For most paths interpolation or extrapolation for log (frequency) can be used, but for some sea paths when the required frequency is less than 100 MHz it is necessary to use an alternative method.
For land paths, and for sea paths where the required frequency is greater than 100 MHz, the required field strength, E, should be calculated using:
dB(μV/m) (Eq. 248)
where:
f : frequency for which the prediction is required (MHz)
finf : lower nominal frequency (100 MHz if f < 600 MHz, 600 MHz otherwise)
fsup : higher nominal frequency (600 MHz if f < 600 MHz, 2 000 MHz otherwise)
Einf : field-strength value for finf
Esup : field-strength value for fsup.
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:
- The path is a sea path.
- The required frequency is less than 100 MHz.
- The required distance is less than the distance at which a sea path would have 0.6 Fresnel clearance at 600 MHz, given by D06(600, h1, 10) as given in § 17 of P1546-4.
If any of the above conditions is not true, then the normal interpolation/extrapolation method given by equation (14) should be used.
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
where:
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
...
d600 : distance at which the path has 0.6 Fresnel clearance at 600 MHz calculated as D06(600, h1, 10) as given in § 17 of P1546-4
df : distance at which the path has 0.6 Fresnel clearance at the required frequency calculated as D06( f, h1, 10) as given in § 17 of P1546-4
Ed600 field strength at distance d600 and the required frequency calculated using equation (14).
Interpolation of field strength as a function of percentage time
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. 245)
where:
...
(Eq. 249)
where:
t : percentage time for which the prediction is required
...
The field-strength values given by the land curves and associated tabulations in this model are for a reference receiving/mobile antenna at a height, R (m), representative of the height of the ground cover surrounding the receiving/mobile antenna, subject to a minimum height value of 10 m. Examples of reference heights are 20 m for an urban area, 30 m for a dense urban area and 10 m for a suburban area.
Table 8890: Default clutter height in the ITU-R P.1546-4 model(when clutter height option not activated)Anchor T088T090T088 T090
...
m (Eq. 238250)
where h1 and R (m) and distance d (km). Note that for h1 < 6.5d + R, R′ ≈ R. The value of R' must be limited if necessary such that it is not less than 1 m.
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Correction 
dB for h2 < R′ (Eq. 239251)
dB for h2 ≥ R′
...
Correction = 
(Eq. 240252)
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 P1546-4, 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.
...
dB (Eq. 241)
where:
K = 1.2, for receivers with antennas below clutter height in urban or suburban environments for mobile systems with omnidirectional antennas at car-roof height
K = 1.0, for receivers with rooftop antennas near the clutter height
K = 0.5, for receivers in rural areas
f : required frequency (MHz).
In SEAMCAT depending on the selected system the standard deviation is defined as follow:
Mobile: when “< 2 km radius” and “< 50 km radius” is selected, 4 dB and 8 dB are added to the calculated standard deviation respectively. This responds to the note of the Recommendation stating that if the area over which the variability is to apply is greater than 500 m ´ 500 m, or if the variability is to relate to all areas at a given range, rather than the variation across individual areas, the value of sL will be greater. Empirical studies have suggested that location variability is increased (with respect to the small area values) by up to 4 dB for a 2 km radius and up to 8 dB for a 50 km radius.
Broadcasting, digital: the standard deviation is set to a constant value of 5.5 dB. No correction is added.
Broadcasting, analogue: The standard deviation is defined as follow and no correction is added:
dB (Eq. 242 dB (Eq. 253)
where:
K = 1.2, for receivers with antennas below clutter height in urban or suburban environments for mobile systems with omnidirectional antennas at car-roof height
K = 1.0, for receivers with rooftop antennas near the clutter height
K = 0.5, for receivers in rural areas
f : required frequency (MHz).
In SEAMCAT depending on the selected system the standard deviation is defined as follow:
Mobile: when “< 2 km radius” and “< 50 km radius” is selected, 4 dB and 8 dB are added to the calculated standard deviation respectively. This responds to the note of the Recommendation stating that if the area over which the variability is to apply is greater than 500 m ´ 500 m, or if the variability is to relate to all areas at a given range, rather than the variation across individual areas, the value of sL will be greater. Empirical studies have suggested that location variability is increased (with respect to the small area values) by up to 4 dB for a 2 km radius and up to 8 dB for a 50 km radius.
Broadcasting, digital: the standard deviation is set to a constant value of 5.5 dB. No correction is added.
Broadcasting, analogue: The standard deviation is defined as follow and no correction is added:
dB (Eq. 254)
In addition, SEAMCAT allows you to select a standard deviation value which overwrites any predefined value when selecting the “use user specified standard deviation” switch.