§ 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(f,th)aug = SQRT { E(f,th)std }2 + A{g(th) cos (180 DA/S  }2

   where:

   E(f,th)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(f,th)aug. is the field in the direction specified above, after
   augmentation.

   A=E(f, O)2aug -E(f, O)2std in which f is the central azimuth of
   augmentation. E(f, O)aug and E(f, 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(f,a)aug is less than
   E(f,th)th at any azimuth or vertical elevation angle.

   g(th) 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(f,a)std, E(f,a)th, and the root sum square (RSS)
   value of the inverse fields of the array elements (derived from the
   equation for E(f,a)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(f,a)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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