Goto Section: 73.185 | 73.187 | Table of Contents
FCC 73.186
Revised as of October 2, 2015
Goto Year:2014 |
2016
§ 73.186 Establishment of effective field at one kilometer.
(a) Section 73.189 provides that certain minimum field strengths are
acceptable in lieu of the required minimum physical heights of the antennas
proper. Also, in other situations, it may be necessary to determine the
effective field. The following requirements shall govern the taking and
submission of data on the field strength produced:
(1) Beginning as near to the antenna as possible without including the
induction field and to provide for the fact that a broadcast antenna is not
a point source of radiation (not less than one wave length or 5 times the
vertical height in the case of a single element, i.e., nondirectional
antenna or 10 times the spacing between the elements of a directional
antenna), measurements shall be made on six or more radials, at intervals of
approximately 0.2 kilometer up to 3 kilometers from the antenna, at
intervals of approximately one kilometer from 3 kilometers to 5 kilometers
from the antenna, at intervals of approximately 2 kilometers from 5
kilometers to 15 kilometers from the antenna, and a few additional
measurements if needed at greater distances from the antenna. Where the
antenna is rurally located and unobstructed measurements can be made, there
shall be at least 15 measurements on each radial. These shall include at
least 7 measurements within 3 kilometers of the antenna. However, where the
antenna is located in a city where unobstructed measurements are difficult
to make, measurements shall be made on each radial at as many unobstructed
locations as possible, even though the intervals are considerably less than
stated above, particularly within 3 kilometers of the antenna. In cases
where it is not possible to obtain accurate measurements at the closer
distances (even out to 8 or 10 kilometers due to the character of the
intervening terrain), the measurements at greater distances should be made
at closer intervals.
(2) The data required by paragraph (a)(1) of this section should be plotted
for each radial in accordance with either of the two methods set forth
below:
(i) Using log-log coordinate paper, plot field strengths as ordinate and
distance as abscissa.
(ii) Using semi-log coordinate paper, plot field strength times distance as
ordinate on the log scale and distance as abscissa on the linear scale.
(3) However, regardless of which of the methods in paragraph (a)(2) of this
section is employed, the proper curve to be drawn through the points plotted
shall be determined by comparison with the curves in § 73.184 as follows:
Place the sheet on which the actual points have been plotted over the
appropriate Graph in § 73.184, hold to the light if necessary and adjust
until the curve most closely matching the points is found. This curve should
then be drawn on the sheet on which the points were plotted, together with
the inverse distance curve corresponding to that curve. The field at 1
kilometer for the radial concerned shall be the ordinate on the inverse
distance curve at 1 kilometer.
(4) When all radials have been analyzed in accordance with paragraph (a)(3)
of this section, a curve shall be plotted on polar coordinate paper from the
fields obtained, which gives the inverse distance field pattern at 1
kilometer. The radius of a circle, the area of which is equal to the area
bounded by this pattern, is the effective field. (See § 73.14.)
(5) The antenna power of the station shall be maintained at the authorized
level during all field measurements. The power determination will be made
using the direct method as described in § 73.51(a) with instruments of
acceptable accuracy specified in § 73.1215.
(b) Complete data taken in conjunction with the field strength measurements
shall be submitted to the Commission in affidavit form including the
following:
(1) Tabulation by number of each point of measurement to agree with the maps
required in paragraph (c) of this section, the date and time of each
measurement, the field strength (E), the distance from the antenna (D) and
the product of the field strength and distance (ED) (if data for each radial
are plotted on semilogarithmic paper, see paragraph (a)(2)(ii) of this
section) for each point of measurement.
(2) Description of method used to take field strength measurements.
(3) The family of theoretical curves used in determining the curve for each
radial properly identified by conductivity and dielectric constants.
(4) The curves drawn for each radial and the field strength pattern.
(5) The antenna resistance at the operating frequency.
(6) Antenna current or currents maintained during field strength
measurements.
(c) Maps showing each measurement point numbered to agree with the required
tabulation shall be retained in the station records and shall be available
to the FCC upon request.
[ 28 FR 13574 , Dec. 14, 1963, as amended at 41 FR 44178 , Oct. 7, 1976; 46 FR 11995 , Feb. 12, 1981; 49 FR 49851 , Dec. 24, 1984; 50 FR 18843 , May 2, 1985;
50 FR 47055 , Nov. 14, 1985; 51 FR 2707 , Jan. 21, 1986; 52 FR 10570 , Apr. 2,
1987; 66 FR 20757 , Apr. 25, 2001]
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Goto Section: 73.185 | 73.187
Goto Year: 2014 |
2016
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