Sec.  73.686   Field strength measurements.

   (a) Except as provided for in  Sec. 73.612, television 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 rulemaking proceedings
   concerning the amendment of such technical standards. Persons making field
   strength measurements for formal submission to the Commission in rulemaking
   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) At a point exactly 16.1 kilometers (10 miles) from the transmitter,
   each radial is marked, and at greater distances at successive 3.2 kilometer
   (2 mile) intervals. Where measurements are to be conducted at UHF, or over
   extremely rugged terrain, shorter intervals may be employed, but all such
   intervals shall be of equal length. Accessible roads intersecting each
   radial as nearly as possible at each 3.2 kilometer (2 mile) 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 3.2 kilometer (2 mile) marker as nearly as
   possible.

   (2) Measurement procedure. The field strength of the visual carrier shall be
   measured with a voltmeter capable of indicating accurately the peak
   amplitude of the synchronizing signal. All measurements shall be made
   utilizing a receiving antenna designed for reception of the horizontally
   polarized signal component, elevated 9.1 meters (30 feet) above the roadbed.
   At each measuring location, the following procedure shall be employed.

   (i) The instrument calibration is checked.

   (ii) The antenna is elevated to a height of 30 feet.

   (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 30.5 meters (100 feet) is made, which 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 shall 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 61.0 meters (200 feet) of
   the center point of the mobile run.

   (viii) If overhead obstacles preclude a mobile run of at leat 30.5 meters
   (100 feet), 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 shall be within 61.0 meters (200 feet) 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 television 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. The field strength of the visual carrier shall be
   measured, with a voltmeter capable of indicating accurately the peak
   amplitude of the synchronizing signal. All measurements shall be made
   utilizing a receiving antenna designed for reception of the horizontally
   polarized signal component, elevated 9.1 meter (30 feet) above street 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.

   (d) Collection of field strength data to determine television signal
   intensity at an individual location—cluster measurements—(1) Preparation for
   measurements—(i) Testing antenna. The test antenna shall be either a
   standard half-wave dipole tuned to the visual carrier frequency of the
   channel being measured or a gain antenna, provided its antenna factor for
   the channel(s) under test has been determined. Use the antenna factor
   supplied by the antenna manufacturer as determined on an antenna range.

   (ii) Testing locations. At the location, choose a minimum of five locations
   as close as possible to the specific site where the site's receiving antenna
   is located. If there is no receiving antenna at the site, choose the minimum
   of five locations as close as possible to a reasonable and likely spot for
   the antenna. The locations shall be at least three meters apart, enough so
   that the testing is practical. If possible, the first testing point should
   be chosen as the center point of a square whose corners are the four other
   locations. Calculate the median of the five measurements (in units of dBu)
   and report it as the measurement result.

   (iii) Multiple signals. If more than one signal is being measured (i.e.,
   signals from different transmitters), use the same locations to measure each
   signal.

   (2) Measurement procedure. Measurements shall be made in accordance with
   good engineering practice and in accordance with this section of the Rules.
   At each measuring location, the following procedure shall be employed:

   (i) Testing equipment. Measure the field strength of the visual carrier with
   a calibrated instrument with an i.f. bandwidth of at least 200 kHz, but no
   greater than one megahertz (1,000 kHz). Perform an on-site calibration of
   the instrument in accordance with the manufacturer's specifications. The
   instrument must accurately indicate the peak amplitude of the synchronizing
   signal. Take all measurements with a horizontally polarized antenna. Use a
   shielded transmission line between the testing antenna and the field
   strength meter. Match the antenna impedance to the transmission line at all
   frequencies measured, and, if using an unbalanced line, employ a suitable
   balun. Take account of the transmission line loss for each frequency being
   measured.

   (ii) Weather. Do not take measurements in inclement weather or when major
   weather fronts are moving through the measurement area.

   (iii) Antenna elevation. When field strength is being measured for a
   one-story building, elevate the testing antenna to 6.1 meters (20 feet)
   above the ground. In situations where the field strength is being measured
   for a building taller than one-story, elevate the testing antenna 9.1 meters
   (30 feet) above the ground.

   (iv) Antenna orientation. Orient the testing antenna in the direction which
   maximizes the value of field strength for the signal being measured. If more
   than one station's signal is being measured, orient the testing antenna
   separately for each station.

   (3) Written record shall be made and shall include at least the following:

   (i) A list of calibrated equipment used in the field strength survey, which
   for each instrument, specifies the manufacturer, type, serial number and
   rated accuracy, and the date of the most recent calibration by the
   manufacturer or by a laboratory. Include complete details of any instrument
   not of standard manufacture.

   (ii) A detailed description of the calibration of the measuring equipment,
   including field strength meters, measuring antenna, and connecting cable.

   (iii) For each spot at the measuring site, all factors which may affect the
   recorded field, such as topography, height and types of vegetation,
   buildings, obstacles, weather, and other local features.

   (iv) A description of where the cluster measurements were made.

   (v) Time and date of the measurements and signature of the person making the
   measurements.

   (vi) For each channel being measured, a list of the measured value of field
   strength (in units of dBu and after adjustment for line loss and antenna
   factor) of the five readings made during the cluster measurement process,
   with the median value highlighted.

   [ 40 FR 27683 , July 1, 1975, as amended at  50 FR 23701 , June 5, 1985;  64 FR 7127 , Feb. 12, 1999;  64 FR 73433 , Dec. 30, 1999]