Sec. 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.
    (b) 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.
    (c) The following general principles shall govern the situations in 
paragraphs (a) and (b) 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

[[Page 39]]

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 measured 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 measured 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 
Sec. 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(,aug =  { 
    E(,std }2+ 
             A{g(A/S }2

where:

    E(,std is the standard 
pattern field at some particular azimuth and elevation angle, before 
augmentation, computed pursuant to Eq. 2, Sec. 73.150(b)(1)(i).
    E(,aug. is the field in 
the direction specified above, after augmentation.
    A=E(, 
O)2aug-E(, 
O)2std in which  is the central azimuth 
of augmentation. E(, O)aug and 
E(, 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(,)aug is less than 
E(,th at any azimuth or 
vertical elevation angle.


    g(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 (c)(2) (i) and (ii), of this 
section, with (i) being applied before (ii) is applied.
    (iv) Where the measured inverse distance field exceeds the value 
permitted by the standard pattern, and augmentation is allowable under 
the terms of this section, the requested amount of augmentation shall be 
centered upon the azimuth of the radial upon which the excessive 
radiation was measured 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.

[[Page 40]]

    (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 Sec. 73.150. The effective (RMS) field strength in 
the horizontal plane of E(,)std, 
E(,)th, and the root sum square 
(RSS) value of the inverse fields of the array elements (derived from 
the equation for E(,)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(,)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.
    (d) Sample calculations for a modified standard pattern follow. 
First, assume the existing standard pattern in Sec. 73.150(c). Then, 
assume the following augmentation parameters:

                                                                        
------------------------------------------------------------------------
                                                               Radiation
                                             Central               at   
            Augmentation number              azimuth    Span    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:

                                                                        
------------------------------------------------------------------------
                                                                Vertical
           Azimuth                0          30         60       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]