§ 73.152   Modification of directional antenna data.

   (a) If, after construction and final adjustment of a directional antenna, a
   measured inverse distance field in any direction exceeds the field shown on
   the  standard  radiation pattern for the pertinent mode of directional
   operation, an application shall be filed, specifying a modified standard
   radiation  pattern and/or such changes as may be required in operating
   parameters so that all measured effective fields will be contained within
   the  modified  standard radiation pattern. Permittees may also file an
   application specifying a modified standard radiation pattern, even when
   measured radiation has not exceeded the standard pattern, in order to allow
   additional tolerance for monitoring point limits.

   (b) If, following a partial proof of performance, a licensee discovers that
   radiation exceeds the standard pattern on one or more radials because of
   circumstances beyond the licensee's control, a modified standard pattern may
   be requested. The licensee shall submit, concurrently, Forms 301-AM and
   302-AM.  Form  301-AM  shall  include an exhibit demonstrating that no
   interference would result from the augmentation. Form 302-AM shall include
   the  results  of  the  partial  proof, along with full directional and
   nondirectional measurements on the radial(s) to be augmented, including
   close-in  points  and a determination of the inverse distance field in
   accordance with § 73.186.

   (c) Normally, a modified standard pattern is not acceptable at the initial
   construction permit stage, before a proof-of-performance has been completed.
   However,  in certain cases, where it can be shown that modification is
   necessary, a modified standard pattern will be acceptable at the initial
   construction permit stage. Following is a non-inclusive list of items to be
   considered  in determining whether a modification is acceptable at the
   initial construction permit stage:

   (1) When the proposed pattern is essentially the same as an existing pattern
   at the same antenna site. (e.g., A DA-D station proposing to become a DA-1
   station.)

   (2) Excessive reradiating structures, which should be shown on a plat of the
   antenna site and surrounding area.

   (3) Other environmental factors; they should be fully described.

   (4)  Judgment and experience of the engineer preparing the engineering
   portion of the application. This must be supported with a full discussion of
   the pertinent factors.

   (d)  The  following  general principles shall govern the situations in
   paragraphs (a), (b), and (c) in this section:

   (1) Where a measured field in any direction will exceed the authorized
   standard pattern, the license application may specify the level at which the
   input power to the antenna shall be limited to maintain the measured field
   at a value not in excess of that shown on the standard pattern, and shall
   specify the common point current corresponding to this power level. This
   value of common point current will be specified on the license for that
   station.

   (2) Where any excessive field does not result in objectionable interference
   to another station, a modification of construction permit application may be
   submitted  with a modified standard pattern encompassing all augmented
   fields.  The  modified standard pattern shall supersede the previously
   submitted standard radiation pattern for that station in the pertinent mode
   of directional operation. Following are the possible methods of creating a
   modified standard pattern:

   (i) The modified pattern may be computed by making the entire pattern larger
   than the original pattern (i.e., have a higher RMS value) if the measured
   fields systematically exceed the confines of the original pattern. The
   larger pattern shall be computed by using a larger multiplying constant, k,
   in the theoretical pattern equation (Eq. 1) in § 73.150(b)(1).

   (ii) Where the measured field exceeds the pattern in discrete directions,
   but objectionable interference does not result, the pattern may be expanded
   over  sectors  including these directions. When this “augmentation” is
   desired, it shall be achieved by application of the following equation:

   E(φ,θ)aug = √{ E(φ,θ)std }2 + A{g(θ) cos (180 DA/S  }2

   where:

   E(φ,θ)std is the standard pattern field at some particular azimuth and
   elevation  angle,  before  augmentation,  computed  pursuant to Eq. 2,
   § 73.150(b)(1)(i).

   E(φ,θ)aug.  is  the  field  in  the  direction  specified above, after
   augmentation.

   A  =  E(φ,  O)2aug−E(φ,  O)2std  in  which φ is the central azimuth of
   augmentation. E(φ, O)aug and E(φ, O)std are the fields in the horizontal
   plane at the central azimuth of augmentation.

   Note:  “A”  must  be positive, except during the process of converting
   non-standard patterns to standard patterns pursuant to the Report and Order
   in Docket No. 21473, and in making minor changes to stations with patterns
   developed during the conversion. However, even when “A” is negative, “A”
   cannot be so negative that E(φ,α)aug is less than E(φ,θ)th at any azimuth or
   vertical elevation angle.

   g(θ) is defined in § 73.150(b)(1)(i).

   S is the angular range, or “span”, over which augmentation is applied. The
   span is centered on the central azimuth of augmentation. At the limits of
   the span, the augmented pattern merges into the unaugmented pattern. Spans
   may overlap.

   DA  is  the absolute horizontal angle between the azimuth at which the
   augmented  pattern  value is being computed and the central azimuth of
   augmentation. (DA cannot exceed 1/2 S.)

   In the case where there are spans which overlap, the above formula shall be
   applied  repeatedly, once for each augmentation, in ascending order of
   central azimuth of augmentation, beginning with zero degrees representing
   true North. Note that, when spans overlap, there will be, in effect, an
   augmentation of an augmentation. And, if the span of an earlier augmentation
   overlaps the central azimuth of a later augmentation, the value of “A” for
   the later augmentation will be different than the value of “A” without the
   overlap of the earlier span.

   (iii) A combination of paragraphs (d)(2)(i) and (d)(2)(ii), of this section,
   with (d)(2)(i) being applied before (d)(2)(ii) is applied.

   (iv) Where augmentation is allowable under the terms of this section, the
   requested amount of augmentation shall be centered upon the measured radial
   and shall not exceed the following:

   (A) The actual measured inverse distance field value, where the radial does
   not involve a required monitoring point.

   (B) 120% of the actual measured inverse field value, where the radial has a
   monitoring point required by the instrument of authorization.

   Whereas  some pattern smoothing can be accommodated, the extent of the
   requested  span(s) shall be minimized and in no case shall a requested
   augmentation  span  extend  to a radial azimuth for which the analyzed
   measurement data does not show a need for augmentation.

   (3) A Modified Standard Pattern shall be specifically labeled as such, and
   shall be plotted in accordance with the requirements of paragraph (b)(2) of
   § 73.150. The effective (RMS) field strength in the horizontal plane of
   E(φ,α)std, E(φ,α)th, and the root sum square (RSS) value of the inverse
   fields of the array elements (derived from the equation for E(φ,α)th), shall
   be tabulated on the page on which the horizontal plane pattern is plotted.
   Where  sector augmentation has been employed in designing the modified
   pattern, the direction of maximum augmentation (i.e., the central azimuth of
   augmentation) shall be indicated on the horizontal plane pattern for each
   augmented sector, and the limits of each sector shall also be shown. Field
   values within an augmented sector, computed prior to augmentation, shall be
   depicted by a broken line.

   (4) There shall be submitted, for each modified standard pattern, complete
   tabulations  of  final  computed data used in plotting the pattern. In
   addition, for each augmented sector, the central azimuth of augmentation,
   span, and radiation at the central azimuth of augmentation (E(φ,α)aug) shall
   be tabulated.

   (5) The parameters used in computing the modified standard pattern shall be
   specified with realistic precision. Following is a list of the maximum
   acceptable precision:

   (i) Central Azimuth of Augmentation: to the nearest 0.1 degree.

   (ii) Span: to the nearest 0.1 degree.

   (iii) Radiation at Central Azimuth of Augmentation: 4 significant figures.

   (e) Sample calculations for a modified standard pattern follow. First,
   assume  the  existing standard pattern in § 73.150(c). Then, assume the
   following augmentation parameters:
   Augmentation number Central azimuth Span Radiation at central azimuth
   1                               110   40                        1,300
   2                               240   50                           52
   3                               250   10                          130

   Following is a tabulation of part of the modified standard pattern:
   Azimuth    0       30     60   Vertical angle
   0          28.86  68.05  72.06
   105     1,299.42 872.14 254.21
   235        39.00  35.74  38.71
   247       100.47  66.69  32.78

   [ 46 FR 11992 , Feb. 12, 1981, as amended at  56 FR 64862 , Dec. 12, 1991;  66 FR 20756 , Apr. 25, 2001]

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