§  15.251   Operation within the bands 2.9-3.26 GHz, 3.267-3.332 GHz,
3.339-3.3458 GHz, and 3.358-3.6 GHz.

   (a) Operation under the provisions of this section is limited to
   automatic vehicle identification systems (AVIS) which use swept
   frequency techniques for the purpose of automatically identifying
   transportation vehicles.

   (b) The field strength anywhere within the frequency range swept by the
   signal shall not exceed 3000 microvolts/meter/MHz at 3 meters in any
   direction. Further, an AVIS, when in its operating position, shall not
   produce a field strength greater than 400 microvolts/meter/MHz at 3
   meters in any direction within +-10 degrees of the horizontal plane. In
   addition to the provisions of §  15.205, the field strength of radiated
   emissions outside the frequency range swept by the signal shall be
   limited to a maximum of 100 microvolts/meter/MHz at 3 meters, measured
   from 30 MHz to 20 GHz for the complete system. The emission limits in
   this paragraph are based on measurement instrumentation employing an
   average detector. The provisions in §  15.35 for limiting peak
   emissions apply.

   (c) The minimum sweep repetition rate of the signal shall not be lower
   than 4000 sweeps per second, and the maximum sweep repetition rate of
   the signal shall not exceed 50,000 sweeps per second.

   (d) An AVIS shall employ a horn antenna or other comparable directional
   antenna for signal emission.

   (e) Provision shall be made so that signal emission from the AVIS shall
   occur only when the vehicle to be identified is within the radiated
   field of the system.

   (f) In addition to the labelling requirements in §  15.19(a), the label
   attached to the AVIS transmitter shall contain a third statement
   regarding operational conditions, as follows:

   *  *  * and, (3) during use this device (the antenna) may not be
   pointed within +-** degrees of the horizontal plane.

   The double asterisks in condition three (**) shall be replaced by the
   responsible party with the angular pointing restriction necessary to
   meet the horizontal emission limit specified in paragraph (b).

   (g) In addition to the information required in subpart J of part 2, the
   application for certification shall contain:

   (1) Measurements of field strength per MHz along with the intermediate
   frequency of the spectrum analyzer or equivalent measuring receiver;

   (2) The angular separation between the direction at which maximum field
   strength occurs and the direction at which the field strength is
   reduced to 400 microvolts/meter/MHz at 3 meters;

   (3) A photograph of the spectrum analyzer display showing the entire
   swept frequency signal and a calibrated scale for the vertical and
   horizontal axes; the spectrum analyzer settings that were used shall be
   labelled on the photograph; and,

   (4) The results of the frequency search for spurious and sideband
   emissions from 30 MHz to 20 GHz, exclusive of the swept frequency band,
   with the measuring instrument as close as possible to the unit under
   test.

   [ 54 FR 17714 , Apr. 25, 1989;  54 FR 32340 , Aug. 7, 1989]

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