Goto Section: 73.685 | 73.687 | Table of Contents
FCC 73.686
Revised as of October 1, 2011
Goto Year:2010 |
2012
§ 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 dBu) 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 dBu 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]
Goto Section: 73.685 | 73.687
Goto Year: 2010 |
2012
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