§  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]

   return arrow Back to Top