§  73.160   Vertical plane radiation characteristics, f(th).

   (a) The vertical plane radiation characteristics show the relative
   field being radiated at a given vertical angle, with respect to the
   horizontal plane. The vertical angle, represented as th, is 0 degrees
   in the horizontal plane, and 90 degrees when perpendicular to the
   horizontal plane. The vertical plane radiation characteristic is
   referred to as f(th). The generic formula for f(th) is:

   f(th) = E(th)/E(O)

   where:

   E(th) is the radiation from the tower at angle th.

   E(O) is the radiation from the tower in the horizontal plane.

   (b) Listed below are formulas for f(th) for several common towers.

   (1) For a typical tower, which is not top-loaded or sectionalized, the
   following formula shall be used:
   eCFR graphic ec13no91.015.gif

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   where:

   G is the electrical height of the tower, not including the base
   insulator and pier. (In the case of a folded unipole tower, the entire
   radiating structure's electrical height is used.)

   (2) For a top-loaded tower, the following formula shall be used:
   eCFR graphic ec13no91.016.gif

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   where:

   A is the physical height of the tower, in electrical degrees, and

   B is the difference, in electrical degrees, between the apparent
   electrical height (G, based on current distribution) and the actual
   physical height.

   G is the apparent electrical height: the sum of A and B; A + B.

   See Figure 1 of this section.
   eCFR graphic ec01mr91.066.gif

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   (3) For a sectionalized tower, the following formula shall be used:
   eCFR graphic ec13no91.017.gif

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   where:

   A is the physical height, in electrical degrees, of the lower section
   of the tower.

   B is the difference between the apparent electrical height (based on
   current distribution) of the lower section of the tower and the
   physical height of the lower section of the tower.

   C is the physical height of the entire tower, in electrical degrees.

   D is the difference between the apparent electrical height of the tower
   (based on current distribution of the upper section) and the physical
   height of the entire tower. D will be zero if the sectionalized tower
   is not top-loaded.

   G is the sum of A and B; A + B.

   H is the sum of C and D; C + D.

   D is the difference between H and A; H-A.

   See Figure 2 of this section.
   eCFR graphic ec01mr91.067.gif

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   (c) One of the above f(th) formulas must be used in computing radiation
   in the vertical plane, unless the applicant submits a special formula
   for a particular type of antenna. If a special formula is submitted, it
   must be accompanied by a complete derivation and sample calculations.
   Submission of values for f(th) only in a tabular or graphical format
   (i.e., without a formula) is not acceptable.

   (d) Following are sample calculations. (The number of significant
   figures shown here should not be interpreted as a limitation on the
   number of significant figures used in actual calculations.)

   (1) For a typical tower, as described in paragraph (b)(1) of this
   section, assume that G = 120 electrical degrees:
   th f(th)
   0  1.0000
   30 0.7698
   60 0.3458

   (2) For a top-loaded tower, as described in paragraph (b)(2) of this
   section, assume A = 120 electrical degrees, B = 20 electrical degrees,
   and G = 140 electrical degrees, (120 + 20):
   th f(th)
   0  1.0000
   30 0.7364
   60 0.2960

   (3) For a sectionalized tower, as described in paragraph (b)(3) of this
   section, assume A = 120 electrical degrees, B = 20 electrical degrees,
   C = 220 electrical degrees, D = 15 electrical degrees, G = 140
   electrical degrees (120 + 20), H = 235 electrical degrees (220 + 15),
   and D = 115 electrical degrees (235-120):
   th f(th)
   0  1.0000
   30 0.5930
   60 0.1423

   [ 46 FR 11993 , Feb. 12, 1981]