Preparing Engineering Data For FCC FORM 301
The most significant factor in assuring a successful filing of Form 301 is to supply all the specific data in complete detail. Thus, in planning a new station or changes in an existing station, a broadcaster should be familiar with the engineering know-how required. Familiarity with the FCC Rules will aid in making the necessary decisions regarding site location, equipment requirements, and antenna location and construction. The engineering staff should therefore be acquainted with the following: Vol. 1, Nov. 1963: Part 1—Practice and Procedure; Part 17—Construction, Marking, and Lighting of Antenna Structures; Vol. III, Jan. 1964: Part 73— Radio Broadcast Services; NAB Engineering Handbook 5th Edition, Section 2—Antennas, Towers and Wave Propagation.
Section V-A of the form applies to standard broadcast (AM) engineering data, Section V-B to FM data, and Section V-C to TV engineering data. Section V-G of the application specifically pertains to antenna and site information.
Application Considerations
Applications lacking complete
answers, or supplementary documents and engineering data, may
be returned for additional information or corrections. While the
application may be resubmitted,
and no additional fee is required,
approval for construction and
operation will obviously be delayed, possibly resulting in unplanned financial loss. To minimize the possibility of such a
delay, a cardinal rule is to become
familiar with the instructions on
the cover page of Form 301 and
the applicable sections of Part 73
of the FCC Rules.
Cost Considerations
One of the first points to be
considered about costs is whether
the chief engineer or a consulting
engineer should make the calculations and perform the tests to obtain the necessary data. While
many chief engineers may be
capable of preparing much of the
data required, it is generally advisable to use the services of an
engineering consultant, especially
if the antenna system is complex
(such as a directional array).
Also, present-day regulations
make it almost mandatory to enlist the aid of a consultant in making an allocations study and report for proposed facilities. In an
operating station, engineering
time is too valuable to perform
the technical determinations. For
a new station, however, it is most practical and economical for the
chief engineer to work with a
consulting engineer.
Engineering personnel assigned
to the project should be advised of
the necessity for keeping within the budget. Total cost for the
engineering data will vary widely
from station to station and area
to area. As required tower heights
and power outputs increase, costs
will increase proportionately.
Selecting a Frequency
Available frequencies for FM
broadcasting are listed in Par.
73.201: Numerical Designation of
FM Broadcast Channels, Subpart
B—FM Broadcast Stations (Vol.III of the Rules). The channel
you request must be one assigned
to your community (Table of Assignments, Par. 73.202). If your
community has no channel assigned, or is not within 25 miles of the assignment, or if there are
stations already on the channels
in your area, a petition must be
filed with the FCC to change the
Table of Assignments as required
by Par. 73.203.
Antenna Site Considerations
Applicants who propose to operate an FM antenna in the immediate vicinity (200 ft. or less) of
another FM antenna, or TV an tenna with frequencies adjacent
to the FM band, must describe the
effect the two systems will have
upon each other.
If an FM antenna is to be
mounted on a nondirectional
standard broadcast antenna tower, new resistance measurements
must be made after the FM antenna is installed and tested. During the installation, and until the
new resistance measurements are approved, the AM license should
apply for authority (informal application) to use the indirect
method of measuring power. The
FM application will not be considered until the new resistance
measurements are filed for the
AM station. If the FM antenna is
to be mounted on an element of an
AM directional array, or on a
tower in the vicinity of a directional array, a full engineering study of the effect on the performance of the AM array must
be filed with application. In some
cases, the FCC may require readjustment and certain field intensity measurements of the AM
system when the FM antenna is
in operation.
Section V-B
If you plan to use a dual polarized antenna, Tables I and II list data for horizontal and vertical
polarization. Fig. 1 shows how
data for dual polarization is entered on the form.
The height of the radiation center is the physical center of the
radiating elements if uniform
power distribution is used. If a
split-feed or power divider system
and nonuniform power distribution are employed, the height of
the radiation center is not the
same as the physical center (the
manufacturer will furnish this
data).
A directional antenna may not be used solely for the purpose of
reducing minimum mileage separation requirements; it is permissible if it will improve service,
or permit the use of a particular
site, and is designed for a noncircular radiation pattern. Directional antennas with a ratio of
15 db maximum to minimum radiation in the horizontal plane are
not allowed.
Horizontal and vertical plane
radiation patterns showing
the free space field strength
in mv m at 1 mile and ERP
in dbk for each direction: a
complete description of how
the measurements were made, including the type
equipment used and a tabulation of the measured data.
If you compute directivity,
methods used, formulae, sample calculations and tabulations of the data must accompany the application.
Radiation characteristics
above and below the horizon tal plane illustrated by vertical paterne. Complete information and patterns for
angles of ±.10° from the horizontal plane, and the portion
lying between +10° and the zenith of —10° and the nadir, to conclusively demonstrate the absence of undesirable lobes in these areas.
The horizontal plane pattern
must be plotted on polar coordinate paper with reference to true north. The vertical plane must be plotted on
rectangular coordinate paper with reference to the horizontal plane.
Transmission Lines
Fig. 3 shows entries for the required information on the trans mission line. These characteristics
vary with frequency: size in
inches, coaxial or waveguide, efficiency to produce the desired ERP
and, of course, cost considerations. The total length in feet includes the horizontal run from the
harmonic filter to the base of the
antenna tower and the length up
the tower to the antenna terminal
point where the gain is rated.
Power loss for this length may be
determined from the manufacturer's specifications. (See Table IV.)
Expected Coverage Information
Profile graphs of the terrain, from 2 to 10 miles for 8 or more radials from the transmitter location, must accompany the application. One or more radials must extend through the principal city. All radials should be plotted on a topographic map.
The graph for each radial
should be plotted by contour intervals of from 40 to 100 feet and,
where the data permits, at least
50 points of elevation should be
used for each radial. The graphs
should indicate the topography accurately and should be plotted with the distances in miles as the
abscissa, and the elevation in feet
above the mean sea level as the
ordinate. The elevation of the antenna radiation center and the
source of the topographic data
should be indicated on each graph.
The F(50,50) field strength
chart, Fig. 4, is used to predict
field strength of the contours
(Fig. 1 of Par. 73.33 may also be
used). The chart is based on an
effective power of 1 kw radiated
from a half-wave dipole in free
space, which produces an attenuated field strength at 1 mile of 103-
db above 1 p.v/m (137.6 mv m ) .
The chart may be used for other powers; the sliding scale associated with the chart serves as the
ordinate. Par. 73.313: Prediction
of Coverage, explains its use.
If the terrain departs widely
from the average elevation of the
2 to 10 mile sector, in one or more
directions from the antenna site,
the prediction method may indicate distances that are different
from what may be expected in
practice. For example, a mountain ridge may indicate the practical limit of service, while the prediction method indicates otherwise; the prediction method
should be followed, accompanied
by a supplemental exhibit concerning the contour distances as
determined by a method based on
actual conditions. The exhibit
shoula describe the procedure employee and include sample calculations. Maps of predicted coverage should include both methods
of prediction.
When measurements are required, these should include the
area obtained by the regular
method and area obtained by the
supplemental method. In directions where the terrain is such
that negative antenna heights or
heights below 100 feet for the 2
to 10 mile sector are encountered,
a supplemental showing of expected coverage must be included with
a description of the method used in predicting the coverage. The
Commission may require additional information about terrain and
coverage in such cases.