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 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 ° 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]