Goto Section: 73.187 | 73.190 | Table of Contents
FCC 73.189
Revised as of December 4, 2012
Goto Year:2011 |
2013
§ 73.189 Minimum antenna heights or field strength requirements.
(a) Section 73.45 requires that all applicants for new, additional, or
different broadcast facilities and all licensees requesting authority
to move 0the transmitter of an existing station, shall specify a
radiating system, the efficiency of which complies with the
requirements of good engineering practice for the class and power of
the station.
(b) The specifications deemed necessary to meet the requirements of
good engineering practice at the present state of the art are set out
in detail below.
(1) The licensee of a AM broadcast station requesting a change in
power, time of operation, frequency, or transmitter location must also
request authority to install a new antenna system or to make changes in
the existing antenna system which will meet the minimum height
requirements, or submit evidence that the present antenna system meets
the minimum requirements with respect to field strength, before
favorable consideration will be given thereto. (See § 73.186.) In the
event it is proposed to make substantial changes in an existing antenna
system, the changes shall be such as to meet the minimum height
requirements or will be permitted subject to the submission of field
strength measurements showing that it meets the minimum requirements
with respect to effective field strength.
(2) These minimum actual physical vertical heights of antennas
permitted to be installed are shown by curves A, B, and C of Figure 7
of § 73.190 as follows:
(i) Class C stations, and stations in Alaska, Hawaii, Puerto Rico and
the U.S. Virgin Islands on 1230, 1240, 1340, 1400, 1450 and 1490 kHz
that were formerly Class C and were redesignated as Class B pursuant to
§ 73.26(b), 45 meters or a minimum effective field strength of 241 mV/m
for 1 kW (121 mV/m for 0.25 kW). (This height applies to a Class C
station on a local channel only. Curve A shall apply to any Class C
stations in the 48 conterminous States that are assigned to Regional
channels.)
(ii) Class A (Alaska), Class B and Class D stations other than those
covered in § 73.189(b)(2)(i), a minimum effective field strength of 282
mV/m for 1 kW.
(iii) Class A stations, a minimum effective field strength of 362 mV/m
for 1 kW.
(3) The heights given on the graph for the antenna apply regardless of
whether the antenna is located on the ground or on a building. Except
for the reduction of shadows, locating the antenna on a building does
not necessarily increase the efficiency and where the height of the
building is in the order of a quarter wave the efficiency may be
materially reduced.
(4) At the present development of the art, it is considered that where
a vertical radiator is employed with its base on the ground, the ground
system should consist of buried radial wires at least one-fourth wave
length long. There should be as many of these radials evenly spaced as
practicable and in no event less than 90. (120 radials of 0.35 to 0.4
of a wave length in length and spaced 3° is considered an excellent
ground system and in case of high base voltage, a base screen of
suitable dimensions should be employed.)
(5) In case it is contended that the required antenna efficiency can be
obtained with an antenna of height or ground system less than the
minimum specified, a complete field strength survey must be supplied to
the Commission showing that the field strength at a mile without
absorption fulfills the minimum requirements. (See § 73.186.) This
field survey must be made by a qualified engineer using equipment of
acceptable accuracy.
(6) The main element or elements of a directional antenna system shall
meet the above minimum requirements with respect to height or effective
field strength. No directional antenna system will be approved which is
so designed that the effective field of the array is less than the
minimum prescribed for the class of station concerned, or in case of a
Class A station less than 90 percent of the ground wave field which
would be obtained from a perfect antenna of the height specified by
Figure 7 of § 73.190 for operation on frequencies below 1000 kHz, and
in the case of a Class B or Class D station less than 90 percent of the
ground wave field which would be obtained from a perfect antenna of the
height specified by Figure 7 of § 73.190 for operation on frequencies
below 750 kHz.
[ 28 FR 13574 , Dec. 14, 1963, as amended at 31 FR 8069 , June 8, 1966; 33 FR 15420 , Oct. 17, 1968; 44 FR 36038 , June 20, 1979; 50 FR 18844 , May
2, 1985; 51 FR 2707 , Jan. 21, 1986; 51 FR 4753 , Feb. 7, 1986; 52 FR 10570 , Apr. 2, 1987; 56 FR 64868 , Dec. 12, 1991]
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Goto Section: 73.187 | 73.190
Goto Year: 2011 |
2013
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