§ 76.612   Cable television frequency separation standards.

   All cable television systems which operate in the frequency bands 108-137
   and  225-400  MHz shall comply with the following frequency separation
   standards:

   (a) In the aeronautical radiocommunication bands 118-137, 225-328.6 and
   335.4-400 MHz, the frequency of all carrier signals or signal components
   carried at an average power level equal to or greater than 10−4 watts in a
   25 kHz bandwidth in any 160 microsecond period must operate at frequencies
   offset from certain frequencies which may be used by aeronautical radio
   services operated by Commission licensees or by the United States Government
   or its Agencies. The aeronautical frequencies from which offsets must be
   maintained are those frequencies which are within one of the aeronautical
   bands defined in this subparagraph, and when expressed in MHz and divided by
   0.025  yield an integer. The offset must meet one of the following two
   criteria:

   (1) All such cable carriers or signal components shall be offset by 12.5 kHz
   with a frequency tolerance of ±5 kHz; or

   (2) The fundamental frequency from which the visual carrier frequencies are
   derived by multiplication by an integer number which shall be 6.0003 MHz
   with  a  tolerance  of  ±1 Hz (Harmonically Related Carrier (HRC) comb
   generators only).

   (b) In the aeronautical radionavigation bands 108-118 and 328.6-335.4 MHz,
   the frequency of all carrier signals or signal components carrier at an
   average  power  level  equal to or greater than 10−4 watts in a 25 kHz
   bandwidth in any 160 microsecond period shall be offset by 25 kHz with a
   tolerance of ±5 kHz. The aeronautical radionavigation frequencies from which
   offsets must be maintained are defined as follows:

   (1) Within the aeronautical band 108-118 MHz when expressed in MHz and
   divided by 0.025 yield an even integer.

   (2) Within the band 328.6-335.4 MHz, the radionavigation glide path channels
   are listed in Section 87.501 of the Rules.

   Note: The HRC system, as described above, will meet this requirement in the
   328.6-335.4 MHz navigation glide path band. Those Incrementally Related
   Carriers (IRC) systems, with comb generator reference frequencies set at
   certain  odd multiples equal to or greater than 3 times the 0.0125 MHz
   aeronautical communications band offset, e.g. (6n + 1.250 ±0.0375) MHz, may
   also meet the 25 kHz offset requirement in the navigation glide path band.

   [ 50 FR 29400 , July 19, 1985]

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