[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: 47CFR73.150]
[Page 35-38]
TITLE 47--TELECOMMUNICATION
CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION (CONTINUED)
PART 73_RADIO BROADCAST SERVICES--Table of Contents
Subpart A_AM Broadcast Stations
Sec. 73.150 Directional antenna systems.
(a) For each station employing a directional antenna, all
determinations of service provided and interference caused shall be
based on the inverse distance fields of the standard radiation pattern
for that station. (As applied to nighttime operation the term ``standard
radiation pattern'' shall include the radiation pattern in the
horizontal plane, and radiation patterns at angles above this plane.)
(1) Parties submitting directional antenna patterns pursuant to this
section and Sec. 73.152 (Modified standard pattern) must submit
patterns which are tabulated and plotted in units of millivolts per
meter at 1 kilometer.
Note: Applications for new stations and for changes (both minor and
major) in existing stations must use a standard pattern.
(b) The following data shall be submitted with an application for
authority to install a directional antenna:
(1) The standard radiation pattern for the proposed antenna in the
horizontal plane, and where pertinent, tabulated values for the
azimuthal radiation patterns for angles of elevation up to and including
60 degrees, with a separate section for each increment of 5 degrees.
(i) The standard radiation pattern shall be based on the theoretical
radiation pattern. The theoretical radiation pattern shall be calculated
in accordance with the following mathematical expression:
[GRAPHIC] [TIFF OMITTED] TC13NO91.014
where:
E([phis],[thetas])th Represents the theoretical inverse
distance fields at one kilometer for the given azimuth and elevation.
k Represents the multiplying constant which determines the basic pattern
size. It shall be chosen so that the effective field (RMS) of the
theoretical pattern in the horizontal plane shall be no greater than the
value computed on the assumption that nominal station power (see Sec.
73.14) is delivered to the directional array, and that a lumped loss
resistance of one ohm exists at the current loop of each element of the
array, or at the base of each element of electrical height lower than
0.25 wavelength, and no less than the value required by Sec.
73.189(b)(2) of this part for a station of the class and nominal power
for which the pattern is designed.
n Represents the number of elements (towers) in the directional array.
i Represents the i\th\ element in the array.
Fi Represents the field ratio of the i\th\ element in the
array.
[thetas] Represents the vertical elevation angle measured from the
horizontal plane.
fi ([thetas]) represents the vertical plane radiation characteristic of
the ith antenna. This value depends on the tower height, as well as
whether the tower is top-loaded or sectionalized. The various formulas
for computing fi ([thetas]) are given in Sec. 73.160.
Si Represents the electrical spacing of the ith tower from
the reference point.
[phis]i Represents the orientation (with respect to true
north) of the ith tower.
[phis] Represents the azimuth (with respect to true north).
[psi]i Represents the electrical phase angle of the current in the
ith tower.
The standard radiation pattern shall be constructed in accordance
with the following mathematical expression:
[[Page 36]]
[GRAPHIC] [TIFF OMITTED] TC01MR91.063
where:
E([phis],[thetas])std represents the inverse distance fields
at one kilometer which are produced by the directional antenna in the
horizontal and vertical planes. E([phis],[thetas])th
represents the theoretical inverse distance fields at one kilometer as
computed in accordance with Eq. 1, above.
Q is the greater of the following two quantities: 0.025g([thetas])
Erss or 10.0g([thetas]) [radic] PkW
where:
g([thetas]) is the vertical plane distribution factor, f([thetas]),
for the shortest element in the array (see Eq. 2, above; also see Sec.
73.190, Figure 5). If the shortest element has an electrical height in
excess of 0.5 wavelength, g([thetas]) shall be computed as follows:
[GRAPHIC] [TIFF OMITTED] TC01MR91.064
Erss is the root sum square of the amplitudes of the
inverse fields of the elements of the array in the horizontal plane, as
used in the expression for E([phis],[thetas])th (see Eq. 1,
above), and is computed as follows:
[GRAPHIC] [TIFF OMITTED] TC01MR91.065
PkW is the nominal station power expressed in kilowatts,
see Sec. 73.14. If the nominal power is less than one kilowatt,
PkW=1.
(ii) Where the orthogonal addition of the factor Q to E([phis],
[thetas])th results in a standard pattern whose minimum
fields are lower than those found necessary or desirable, these fields
may be increased by appropriate adjustment of the parameters of
E([phis], [thetas])th.
(2) All patterns shall be computed for integral multiples of five
degrees, beginning with zero degrees representing true north, and, shall
be plotted to the largest scale possible on unglazed letter-size paper
(main engraving approximately 7[min] x 10[min]) using only scale
divisions and subdivisions of 1,2,2.5, or 5 times 10nth. The
horizontal plane pattern shall be plotted on polar coordinate paper,
with the zero degree point corresponding to true north. Patterns for
elevation angles above the horizontal plane may be plotted in polar or
rectangular coordinates, with the pattern for each angle of elevation on
a separate page. Rectangular plots shall begin and end at true north,
with all azimuths labelled in increments of not less than 20 degrees. If
a rectangular plot is used, the ordinate showing the scale for radiation
may be logarithmic. Such patterns for elevation angles above the
horizontal plane need be submitted only upon specific request by
Commission staff. Minor lobe and null detail occurring between
successive patterns for specific angles of elevation need not be
submitted. Values of field strength on any pattern less than ten percent
of the maximum field strength plotted on that pattern shall be shown on
an enlarged scale. Rectangular plots with a logarithmic ordinate need
not utilize an expanded scale unless necessary to show clearly the minor
lobe and null detail.
(3) The effective (RMS) field strength in the horizontal plane of
E([phis],[thetas])std, E([phis],[thetas])th and
the root-sum-square (RSS) value of the inverse distance fields of the
array elements at 1 kilometer, derived from the equation for
E([phis],[thetas])th. These values shall be tabulated on the
page on which the horizontal plane pattern is plotted, which shall be
specifically labelled as the Standard Horizontal Plane Pattern.
(4) Physical description of the array, showing:
(i) Number of elements.
(ii) Type of each element (i.e., guyed or self-supporting, uniform
cross section or tapered (specifying base dimensions), grounded or
insulated, etc.)
(iii) Details of top loading, or sectionalizing, if any.
(iv) Height of radiating portion of each element in feet (height
above base insulator, or base, if grounded).
(v) Overall height of each element above ground.
(vi) Sketch of antenna site, indicating its dimensions, the location
of the antenna elements, thereon, their spacing from each other, and
their orientation with respect to each other and to true north, the
number and length of the radials in the ground system about each
element, the dimensions of ground screens, if any, and bonding between
towers and between radial systems.
[[Page 37]]
(5) Electrical description of the array, showing:
(i) Relative amplitudes of the fields of the array elements.
(ii) Relative time phasing of the fields of the array elements in
degrees leading [+] or lagging [-].
(iii) Space phasing between elements in degrees.
(iv) Where waiver of the content of this section is requested or
upon request of the Commission staff, all assumptions made and the basis
therefor, particularly with respect to the electrical height of the
elements, current distribution along elements, efficiency of each
element, and ground conductivity.
(v) Where waiver of the content of this section is requested, or
upon request of the Commission staff, those formulas used for computing
E([phis],[thetas])th and E([phis],[thetas])std.
Complete tabulation of final computed data used in plotting patterns,
including data for the determination of the RMS value of the pattern,
and the RSS field of the array.
(6) The values used in specifying the parameters which describe the
array must be specified to no greater precision than can be achieved
with available monitoring equipment. Use of greater precision raises a
rebuttable presumption of instability of the array. Following are
acceptable values of precision; greater precision may be used only upon
showing that the monitoring equipment to be installed gives accurate
readings with the specified precision.
(i) Field Ratio: 3 significant figures.
(ii) Phasing: to the nearest 0.1 degree.
(iii) Orientation (with respect to a common point in the array, or
with respect to another tower): to the nearest 0.1 degree.
(iv) Spacing (with respect to a common point in the array, or with
respect to another tower): to the nearest 0.1 degree.
(v) Electrical Height (for all parameters listed in Section 73.160):
to the nearest 0.1 degree.
(vi) Theoretical RMS (to determine pattern size): 4 significant
figures.
(vii) Additional requirements relating to modified standard patterns
appear in Sec. 73.152(c)(3) and (c)(4).
(7) Any additional information required by the application form.
(c) Sample calculations for the theoretical and standard radiation
follow. Assume a five kilowatt (nominal power) station with a
theoretical RMS of 685 mV/m at one kilometer. Assume that it is an in-
line array consisting of three towers. Assume the following parameters
for the towers:
------------------------------------------------------------------------
Field Relative Relative Relative
Tower ratio phasing spacing orientation
------------------------------------------------------------------------
1............................. 1.0 -128.5 0.0 0.0
2............................. 1.89 0.0 110.0 285.0
3............................. 1.0 128.5 220.0 285.0
------------------------------------------------------------------------
Assume that tower 1 is a typical tower with an electrical height of
120 degrees. Assume that tower 2 is top-loaded in accordance with the
method described in Sec. 73.160(b)(2) where A is 120 electrical degrees
and B is 20 electrical degrees. Assume that tower 3 is sectionalized in
accordance with the method described in Sec. 73.160(b)(3) where A is
120 electrical degrees, B is 20 electrical degrees, C is 220 electrical
degrees, and D is 15 electrical degrees.
The multiplying constant will be 323.6.
Following is a tabulation of part of the theoretical pattern:
------------------------------------------------------------------------
Vertical
Azimuth 0 30 60 angle
------------------------------------------------------------------------
0........................... 15.98 62.49 68.20
105......................... 1225.30 819.79 234.54
235......................... 0.43 18.46 34.56
247......................... 82.62 51.52 26.38
------------------------------------------------------------------------
If we further assume that the station has a standard pattern, we
find that Q, for [thetas]=0, is 22.36.
Following is a tabulation of part of the standard pattern:
------------------------------------------------------------------------
Vertical
Azimuth 0 30 60 angle
------------------------------------------------------------------------
0........................... 28.86 68.05 72.06
105......................... 1286.78 860.97 246.41
235......................... 23.48 26.50 37.18
247......................... 89.87 57.03 28.87
------------------------------------------------------------------------
[[Page 38]]
The RMS of the standard pattern in the horizontal plane is 719.63
mV/m at one kilometer.
[36 FR 919, Jan. 20, 1971, as amended at 37 FR 529, Jan. 13, 1972; 41 FR
24134, June 15, 1976; 46 FR 11991, Feb. 12, 1981; 48 FR 24384, June 1,
1983; 51 FR 2707, Jan. 21, 1986; 52 FR 36877, Oct. 1, 1987; 56 FR 64861,
Dec. 12, 1991; 57 FR 43290, Sept. 18, 1992]