[Code of Federal Regulations]
[Title 47, Volume 2]
[Revised as of October 1, 2007]
From the U.S. Government Printing Office via GPO Access
[CITE: 47CFR73.152]
[Page 38-41]
TITLE 47--TELECOMMUNICATION
CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION (CONTINUED)
PART 73_RADIO BROADCAST SERVICES--Table of Contents
Subpart A_AM Broadcast Stations
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,
[[Page 39]]
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 Sec.
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
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([phis],[thetas])aug = [radic] { E([phis],[thetas])std {time} \2\+
A{g([thetas]) cos (180 DA/S {time} \2\
where:
E([phis],[thetas])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([phis],[thetas])aug. is the field in the direction specified above,
after augmentation.
A=E([phis], O)\2\aug-E([phis], O)\2\std in which [phis] is the central
azimuth of augmentation. E([phis], O)aug
[[Page 40]]
and E([phis], 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([phis],[alpha])aug is less than E([phis],[thetas])th at any azimuth or
vertical elevation angle.
g([thetas]) is defined in Sec. 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 Sec. 73.150. The effective (RMS) field strength in
the horizontal plane of E([phis],[alpha])std, E([phis],[alpha])th, and
the root sum square (RSS) value of the inverse fields of the array
elements (derived from the equation for E([phis],[alpha])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([phis],[alpha])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 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
------------------------------------------------------------------------
[[Page 41]]
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;
66 FR 20756, Apr. 25, 2001]