§ 73.314   Field strength measurements.

   (a) Except as provided for in § 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
   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
   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.

   (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]

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