§ 73.686 Field strength measurements. ( a ) Except as provided for in § 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 the most recent official decennial U.S. Census population data as identified by the Media Bureau in a Public Notice. (See § 73.620(b)).
( 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 ) [Reserved]
( e ) *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 center frequency of the channel being tested 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 test site, 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 a 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 dBμ) and report it as the measurement.
( iii ) *Multiple signals* — ( A ) If more than one signal is being measured (*i.e.,* signals from different transmitters), use the same locations to measure each signal.
( B ) For establishing eligibility of a satellite subscriber to receive distant network signals, only stations affiliated with the network in question that are located in the same Nielsen Designated Market Area (DMA) as the test site may be considered and tested.
( 2 ) *Measurement procedure.* Measurements shall be made in accordance with good engineering practice and in accordance with this section of this chapter. At each measuring location, the following procedure shall be employed: ( i ) *Testing equipment.* Perform an on-site calibration of the test instrument in accordance with the manufacturer's specifications. Tune a calibrated instrument to the center of the channel being tested. Measure the integrated average power over the full 6 megahertz bandwidth of the television signal. The intermediate frequency of the instrument should be set to 100 kilohertz unless the instrument is specifically designed by the manufacturer to use an alternative i.f. setting. The instrument must be capable of integrating over the selected i.f. for the 6 megahertz channel bandwidth. 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 un-balanced line, employ a suitable balance. Take account of the transmission line loss for each frequency being measured.
( ii ) *Weather.* Do not take measurements during periods of inclement weather, including, but not limited to, periods of heavy rainfall, snowfall accumulation, high windspeed, or any combination thereof.
( 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 dBμ 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; 75 FR 81498, Dec. 28, 2010; 89 FR 7253, Feb. 1, 2024]