§  76.612   Cable television frequency separation standards.

   All cable television systems which operate analog NTSC or similar
   channels in the frequency bands 108-137 MHZ and 225-400 MHz shall
   comply with the following frequency separation standards for each NTSC
   or similar channel:

   (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, as amended at  83 FR 7630 , Feb. 22, 2018]