Sec. 73.314  Field strength measurements.

    (a) Except as provided for in Sec. 73.209, FM broadcast stations 
shall not be protected from any type of interference or propagation 
effect. Persons desiring to submit testimony, evidence or data to the 
Commission for the purpose of showing that the technical standards 
contained in this subpart do not properly reflect the levels of any 
given type of interference or propagation effect may do so only in 
appropriate rule making proceedings concerning the amendment of such 
technical standards. Persons making field strength measurements for 
formal submission to the Commission in rule making proceedings, or 
making such measurements upon the request of the Commission, shall 
follow the procedure for making and reporting such measurements outlined 
in paragraph (b) of this section. In instances where a showing of the 
measured level of a signal prevailing over a specific community is 
appropriate, the procedure for making and reporting field strength 
measurements for this purpose is set forth in paragraph (c) of this 
section.
    (b) Collection of field strength data for propagation analysis.
    (1) Preparation for measurements. (i) On large scale topographic 
maps, eight or more radials are drawn from the transmitter location to 
the maximum distance at which measurements are to be made, with the 
angles included between adjacent radials of approximately equal size. 
Radials should be

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oriented so as to traverse representative types of terrain. The specific 
number of radials and their orientation should be such as to accomplish 
this objective.
    (ii) Each radial is marked, at a point exactly 16 kilometers from 
the transmitter and, at greater distances, at successive 3 kilometer 
intervals. Where measurements are to be conducted over extremely rugged 
terrain, shorter intervals may be used, but all such intervals must be 
of equal length. Accessible roads intersecting each radial as nearly as 
possible at each 3 kilometer marker are selected. These intersections 
are the points on the radial at which measurements are to be made, and 
are referred to subsequently as measuring locations. The elevation of 
each measuring location should approach the elevation at the 
corresponding 3 kilometer marker as nearly as possible.
    (2) Measurement procedure. All measurements must be made utilizing a 
receiving antenna designed for reception of the horizontally polarized 
signal component, elevated 9 meters above the roadbed. At each measuring 
location, the following procedure must be used:
    (i) The instrument calibration is checked.
    (ii) The antenna is elevated to a height of 9 meters.
    (iii) The receiving antenna is rotated to determine if the strongest 
signal is arriving from the direction of the transmitter.
    (iv) The antenna is oriented so that the sector of its response 
pattern over which maximum gain is realized is in the direction of the 
transmitter.
    (v) A mobile run of at least 30 meters is made, that is centered on 
the intersection of the radial and the road, and the measured field 
strength is continuously recorded on a chart recorder over the length of 
the run.
    (vi) The actual measuring location is marked exactly on the 
topographic map, and a written record, keyed to the specific location, 
is made of all factors which may affect the recorded field, such as 
topography, height and types of vegetation, buildings, obstacles, 
weather, and other local features.
    (vii) If, during the test conducted as described in paragraph 
(b)(2)(iii) of this section, the strongest signal is found to come from 
a direction other than from the transmitter, after the mobile run 
prescribed in paragraph (b)(2)(v) of this section is concluded, 
additional measurements must be made in a ``cluster'' of at least five 
fixed points. At each such point, the field strengths with the antenna 
oriented toward the transmitter, and with the antenna oriented so as to 
receive the strongest field, are measured and recorded. Generally, all 
points should be within 60 meters of the center point of the mobile run.
    (viii) If overhead obstacles preclude a mobile run of at least 30 
meters, a ``cluster'' of five spot measurements may be made in lieu of 
this run. The first measurement in the cluster is identified. Generally, 
the locations for other measurements must be within 60 meters of the 
location of the first.
    (3) Method of reporting measurements. A report of measurements to 
the Commission shall be submitted in affidavit form, in triplicate, and 
should contain the following information:
    (i) Tables of field strength measurements, which, for each measuring 
location, set forth the following data:
    (A) Distance from the transmitting antenna.
    (B) Ground elevation at measuring location.
    (C) Date, time of day, and weather.
    (D) Median field in dBu for 0 dBk, for mobile run or for cluster, as 
well as maximum and minimum measured field strengths.
    (E) Notes describing each measuring location.
    (ii) U.S. Geological Survey topographic maps, on which is shown the 
exact location at which each measurement was made. The original plots 
shall be made on maps of the largest available scale. Copies may be 
reduced in size for convenient submission to the Commission, but not to 
the extent that important detail is lost. The original maps shall be 
made available, if requested. If a large number of maps is involved, an 
index map should be submitted.
    (iii) All information necessary to determine the pertinent 
characteristics

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of the transmitting installation, including frequency, geographical 
coordinates of antenna site, rated and actual power output of 
transmitter, measured transmission line loss, antenna power gain, height 
of antenna above ground, above mean sea level, and above average 
terrain. The effective radiated power should be computed, and horizontal 
and vertical plane patterns of the transmitting antenna should be 
submitted.
    (iv) A list of calibrated equipment used in the field strength 
survey, which, for each instrument, specifies its manufacturer, type, 
serial number and rated accuracy, and the date of its most recent 
calibration by the manufacturer, or by a laboratory. Complete details of 
any instrument not of standard manufacture shall be submitted.
    (v) A detailed description of the calibration of the measuring 
equipment, including field strength meters, measuring antenna, and 
connecting cable.
    (vi) Terrain profiles in each direction in which measurements were 
made, drawn on curved earth paper for equivalent 4/3 earth radius, of 
the largest available scale.
    (c) Collection of field strength data to determine FM broadcast 
service in specific communities.
    (1) Preparation for measurement. (i) The population (P) of the 
community, and its suburbs, if any, is determined by reference to an 
appropriate source, e.g., the 1970 U.S. Census tables of population of 
cities and urbanized areas.
    (ii) The number of locations at which measurements are to be made 
shall be at least 15, and shall be approximately equal to 0.1(P)1/
2, if this product is a number greater than 15.
    (iii) A rectangular grid, of such size and shape as to encompass the 
boundaries of the community is drawn on an accurate map of the 
community. The number of line intersections on the grid included within 
the boundaries of the community shall be at least equal to the required 
number of measuring locations. The position of each intersection on the 
community map determines the location at which a measurement shall be 
made.
    (2) Measurement procedure. All measurements must be made using a 
receiving antenna designed for reception of the horizontally polarized 
signal component, elevated 9 meters above ground level.
    (i) Each measuring location shall be chosen as close as feasible to 
a point indicated on the map, as previously prepared, and at as nearly 
the same elevation as that point as possible.
    (ii) At each measuring location, after equipment calibration and 
elevation of the antenna, a check is made to determine whether the 
strongest signal arrives from a direction other than from the 
transmitter.
    (iii) At 20 percent or more of the measuring locations, mobile runs, 
as described in paragraph (b)(2) of this section shall be made, with no 
less than three such mobile runs in any case. The points at which mobile 
measurements are made shall be well separated. Spot measurements may be 
made at other measuring points.
    (iv) Each actual measuring location is marked exactly on the map of 
the community, and suitably keyed. A written record shall be maintained, 
describing, for each location, factors which may affect the recorded 
field, such as the approximate time of measurement, weather, topography, 
overhead wiring, heights and types of vegetation, buildings and other 
structures. The orientation, with respect to the measuring location 
shall be indicated of objects of such shape and size as to be capable of 
causing shadows or reflections. If the strongest signal received was 
found to arrive from a direction other than that of the transmitter, 
this fact shall be recorded.
    (3) Method of reporting measurements. A report of measurements to 
the Commission shall be submitted in affidavit form, in triplicate, and 
should contain the following information:
    (i) A map of the community showing each actual measuring location, 
specifically identifying the points at which mobile runs were made.
    (ii) A table keyed to the above map, showing the field strength at 
each measuring point, reduced to dBu for the actual effective radiated 
power of the station. Weather, date, and time of each measurement shall 
be indicated.
    (iii) Notes describing each measuring location.

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    (iv) A topographic map of the largest available scale on which are 
marked the community and the transmitter site of the station whose 
signals have been measured, which includes all areas on or near the 
direct path of signal propagation.
    (v) Computations of the mean and standard deviation of all measured 
field strengths, or a graph on which the distribution of measured field 
strength values is plotted.
    (vi) A list of calibrated equipment used for the measurements, which 
for each instrument, specifies its manufacturer, type, serial number and 
rated accuracy, and the date of its most recent calibration by the 
manufacturer, or by a laboratory. Complete details of any instrument not 
of standard manufacture shall be submitted.
    (vii) A detailed description of the procedure employed in the 
calibration of the measuring equipment, including field strength meters, 
measuring antenna, and connecting cable.

[ 40 FR 27682 , July 1, 1975;  40 FR 28802 , July 9, 1975, as amended at  48 FR 29508 , June 27, 1983]