[Code of Federal Regulations]
[Title 47, Volume 4]
[Revised as of October 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 47CFR73.151]

[Page 37-38]
 
                       TITLE 47--TELECOMMUNICATION
 
                    CHAPTER I--FEDERAL COMMUNICATIONS
                         COMMISSION (CONTINUED)
 
PART 73_RADIO BROADCAST SERVICES--Table of Contents
 
                     Subpart A_AM Broadcast Stations
 
Sec. 73.151  Field strength measurements to establish performance of 
directional antennas.

    (a) In addition to the information required by the license 
application form, the following showing must be submitted to establish, 
for each mode of directional operation, that the effective measured 
field strength (RMS) at 1 kilometer (km) is not less than 85 percent of 
the effective measured field strength (RMS) specified for the standard 
radiation pattern, or less than that specified in Sec. 73.189(b) for 
the class of

[[Page 38]]

station involved, whichever is the higher value, and that the measured 
field strength at 1 km in any direction does not exceed the field shown 
in that direction on the standard radiation pattern for that mode of 
directional operation:
    (1) A tabulation of inverse field strengths in the horizontal plane 
at 1 km, as determined from field strength measurements taken and 
analyzed in accordance with Sec. 73.186, and a statement of the 
effective measured field strength (RMS). Measurements shall be made in 
the following directions:
    (i) Those specified in the instrument of authorization.
    (ii) In major lobes. Generally, one radial is sufficient to 
establish a major lobe; however, additional radials may be required.
    (iii) Along additional radials to establish the shape of the 
pattern. In the case of a relatively simple directional antenna pattern, 
a total of six radials is sufficient. If two radials would be more than 
90[deg] apart, then an additional radial must be specified within that 
arc. When more complicated patterns are involved, that is, patterns 
having several or sharp lobes or nulls, measurements shall be taken 
along as many as 12 radials to definitely establish the pattern(s). 
Pattern symmetry may be assumed for complex patterns which might 
otherwise require measurements on more than 12 radials.
    (2) A tabulation of:
    (i) The phase difference of the current in each element with respect 
to the reference element, and whether the current leads (+) or lags (-) 
the current in the reference element, as indicated by the station's 
antenna monitor.
    (ii) The ratio of the amplitude of the radio frequency current in 
each element to the current in the reference element, as indicated on 
the station's antenna monitor.
    (3) A monitoring point shall be established on each radial for which 
the construction permit specifies a limit. The following information 
shall be supplied for each monitoring point:
    (i) Measured field strength.
    (ii) An accurate and detailed description of each monitoring point. 
The description may include, but shall not be limited to, geographic 
coordinates determined with a Global Positioning System receiver.
    (iii) Clear photographs taken with the field strength meter in its 
measuring position and with the camera so located that its field of view 
takes in as many pertinent landmarks as possible.
    (b) For stations authorized to operate with simple directional 
antenna systems (e.g., two towers) in the 1605-1705 kHz band, the 
measurements to support pattern RMS compliance referred to in paragraphs 
(a)(1)(ii) and (a)(1)(iii) of this section are not required. In such 
cases, measured radials are required only in the direction of short-
spaced allotments, or in directions specifically identified by the 
Commission.

[36 FR 919, Jan. 20, 1971, as amended at 42 FR 36828, July 18, 1977; 49 
FR 23348, June 6, 1984; 50 FR 32416, Aug. 12, 1985; 56 FR 64862, Dec. 
12, 1991; 63 FR 33876, June 22, 1998; 66 FR 20756, Apr. 25, 2001]