Goto Section: 73.685 | 73.687 | Table of Contents
FCC 73.686
Revised as of October 2, 2015
Goto Year:2014 |
2016
§ 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 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) NTSC—Collection of field strength data to determine NTSC 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.
(e) DTV—Collection of field strength data to determine digital 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]
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Goto Section: 73.685 | 73.687
Goto Year: 2014 |
2016
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