§ 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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