Note: Applications for new stations and for changes (both minor and major) in existing stations must use a standard pattern.
where:
E([PHI],[THETA])th Represents the theoretical inverse distance fields at one kilometer for the given azimuth and elevation.
k Represents the multiplying constant which determines the basic pattern size. It shall be chosen so that the effective field (RMS) of the theoretical pattern in the horizontal plane shall be no greater than the value computed on the assumption that nominal station power (see § 73.14 ) is delivered to the directional array, and that a lumped loss resistance of one ohm exists at the current loop of each element of the array, or at the base of each element of electrical height lower than 0.25 wavelength, and no less than the value required by § 73.189(b)(2) of this part for a station of the class and nominal power for which the pattern is designed.
n Represents the number of elements (towers) in the directional array.
i Represents the ith element in the array.
Fi Represents the field ratio of the ith element in the array.
[THETA] Represents the vertical elevation angle measured from the horizontal plane.
fi ([THETA]) represents the vertical plane radiation characteristic of the ith antenna. This value depends on the tower height, as well as whether the tower is top-loaded or sectionalized. The various formulas for computing fi ([THETA]) are given in § 73.160 .
Si Represents the electrical spacing of the ith tower from the reference point.
[PHI]i Represents the orientation (with respect to true north) of the ith tower.
[PHI] Represents the azimuth (with respect to true north).
[PSI]i Represents the electrical phase angle of the current in the ith tower.
The standard radiation pattern shall be constructed in accordance with the following mathematical expression:
where:
E([PHI],[THETA])std represents the inverse distance fields at one kilometer which are produced by the directional antenna in the horizontal and vertical planes. E([PHI],[THETA])th represents the theoretical inverse distance fields at one kilometer as computed in accordance with Eq. 1, above.
Q is the greater of the following two quantities: 0.025g([THETA]) Erss or 10.0g([THETA]) [RADIC] PkW
where:
g([THETA]) is the vertical plane distribution factor, f([THETA]), for the shortest element in the array (see Eq. 2, above; also see § 73.190 , Figure 5). If the shortest element has an electrical height in excess of 0.5 wavelength, g([THETA]) shall be computed as follows:
Erss is the root sum square of the amplitudes of the inverse fields of the elements of the array in the horizontal plane, as used in the expression for E([PHI],[THETA])th (see Eq. 1, above), and is computed as follows:
PkW is the nominal station power expressed in kilowatts, see § 73.14 . If the nominal power is less than one kilowatt, PkW = 1.
Tower | Field ratio | Relative phasing | Relative spacing | Relative orientation |
1 | 1.0 | -128.5 | 0.0 | 0.0 |
2 | 1.89 | 0.0 | 110.0 | 285.0 |
3 | 1.0 | 128.5 | 220.0 | 285.0 |
Assume that tower 1 is a typical tower with an electrical height of 120 degrees. Assume that tower 2 is top-loaded in accordance with the method described in § 73.160(b)(2) where A is 120 electrical degrees and B is 20 electrical degrees. Assume that tower 3 is sectionalized in accordance with the method described in § 73.160(b)(3) where A is 120 electrical degrees, B is 20 electrical degrees, C is 220 electrical degrees, and D is 15 electrical degrees.
The multiplying constant will be 323.6.
Following is a tabulation of part of the theoretical pattern:
Azimuth | 0 | 30 | 60 | Vertical angle |
0 | 15.98 | 62.49 | 68.20 | |
105 | 1225.30 | 819.79 | 234.54 | |
235 | 0.43 | 18.46 | 34.56 | |
247 | 82.62 | 51.52 | 26.38 |
If we further assume that the station has a standard pattern, we find that Q, for [THETA] = 0, is 22.36.
Following is a tabulation of part of the standard pattern:
Azimuth | 0 | 30 | 60 | Vertical angle |
0 | 28.86 | 68.05 | 72.06 | |
105 | 1286.78 | 860.97 | 246.41 | |
235 | 23.48 | 26.50 | 37.18 | |
247 | 89.87 | 57.03 | 28.87 |
The RMS of the standard pattern in the horizontal plane is 719.63 mV/m at one kilometer.
47 C.F.R. §73.150