§ 87.133   Frequency stability.

   (a) Except as provided in paragraphs (c), (d), (f), and (g) of this
   section, the carrier frequency of each station must be maintained
   within these tolerances:
   Frequency band (lower limit exclusive, upper limit inclusive), and
   categories of stations Tolerance^1 Tolerance^2
   (1) Band-9 to 535 kHz:
   Aeronautical stations 100 100
   Aircraft stations 200 100
   Survival craft stations on 500 kHz 5,000 20 Hz^3
   Radionavigation stations 100 100
   (2) Band-1605 to 4000 kHz:
   Aeronautical fixed stations:
   Power 200 W or less 100 100^8
   Power above 200 W 50 50^8
   Aeronautical stations:
   Power 200 W or less 100^7 100^7 8
   Power above 200 W 50^7 50^7 8
   Aircraft stations 100^7 100^7
   Survival craft stations on 2182 kHz 200 20 Hz^3
   (3) Band-4 to 29.7 MHz:
   Aeronautical fixed stations:
   Power 500 W or less 50
   Power above 500 W 15
   Single-sideband and Independent-sideband emission:
   Power 500 W or less 50 Hz
   Power above 500 W 20 Hz
   Class F1B emissions 10 Hz
   Other classes of emission:
   Power 500 W or less 20
   Power above 500 W 10
   Aeronautical stations:
   Power 500 W or less ^7100 100^7
   Power above 500 W ^750 50^7
   Aircraft stations ^7100 100^7
   Survival craft stations on 8364 kHz 200 50 Hz^3
   (4) Band-29.7 to 100 MHz:
   Aeronautical fixed stations:
   Power 200 W or less 50
   Power above 200 W 30
   Power 50 W or less 30
   Power above 50 W 20
   Operational fixed stations:
   73-74.6 MHz (Power 50 W or less) 50 30
   73-74.6 MHz (Power above 50 W) 20 20
   72-73.0 MHz and 75.4-76.0 MHz 5 5
   Radionavigation stations 100 50
   (5) Band-108 to 137 MHz:
   Aeronautical stations ^450 ^1220
   Emergency locator transmitter test stations 50 50
   Survival craft stations on 121.5 MHz 50 50
   Emergency locator stations 50 50
   Aircraft and other mobile stations in the Aviation Services ^550 ^1330
   Radionavigation stations 20 20
   Differential GPS     2
   (6) Band-137 to 470MHz:
   Aeronautical stations 50 20
   Survival craft stations on 243 MHz 50 50
   Aircraft stations 50^5 30^10
   Radionavigation stations 50 50
   Emergency locator transmitters on 406 MHz N/A 5
   (7) Band-470 to 2450 MHz:
   Aeronautical stations 100 20
   Aircraft stations 100 20
   Aircraft earth station     320 Hz^11
   Aeronautical utility mobile stations on 1090 MHz 1000 1000
   Radionavigation stations:
   470-960 MHz 500 500
   960-1215 MHz 20 20
   1215-2450 MHz 500 500
   (8) Band-2450 to 10500 MHz:
   Radionavigation stations ^6 91250 1250^6 9
   (9) Band-10.5 GHz to 40 GHz:
   Radionavigation stations 5000 5000

   ^1This tolerance is the maximum permitted until January 1, 1990, for
   transmitters installed before January 2, 1985, and used at the same
   installation. Tolerance is indicated in parts in 10^6 unless shown as
   Hertz (Hz).

   ^2This tolerance is the maximum permitted after January 1, 1985 for new
   and replacement transmitters and to all transmitters after January 1,
   1990. Tolerance is indicated in parts in 10^6 unless shown as Hertz
   (Hz).

   ^3For transmitters first approved after November 30, 1977.

   ^4The tolerance for transmitters approved between January 1, 1966, and
   January 1, 1974, is 30 parts in 10^6. The tolerance for transmitters
   approved after January 1, 1974, and stations using offset carrier
   techniques is 20 parts in 10^6.

   ^5The tolerance for transmitters approved after January 1, 1974, is 30
   parts in 10^6.

   ^6In the 5000 to 5250 MHz band, the FAA requires a tolerance of ±10 kHz
   for Microwave Landing System stations which are to be a part of the
   National Airspace System (FAR 171).

   ^7For single-sideband transmitters operating in the frequency bands
   1605-4000 kHz and 4-29.7 MHz which are allocated exclusively to the
   Aeronautical Mobile (R) Service, the tolerance is: Aeronautical
   stations, 10 Hz; aircraft stations, 20 Hz.

   ^8For single-sideband radiotelephone transmitters the tolerance is: In
   the bands 1605-4000 kHz and 4-29.7 MHz for peak envelope powers of 200
   W or less and 500 W or less, respectively, 50 Hz; in the bands
   1605-4000 kHz and 4-29.7 MHz for peak envelope powers above 200 W and
   500 W, respectively, 20 Hz.

   ^9Where specific frequencies are not assigned to radar stations, the
   bandwidth occupied by the emissions of such stations must be maintained
   within the band allocated to the service and the indicated tolerance
   does not apply.

   ^10Until January 1, 1997, the maximum frequency tolerance for
   transmitters with 50 kHz channel spacing installed before January 2,
   1985, is 50 parts in 10^6.

   ^11For purposes of certification, a tolerance of 160 Hz applies to the
   reference oscillator of the AES transmitter. This is a bench test.

   ^12For emissions G1D and G7D, the tolerance is 2 parts per 10^6.

   ^13For emissions G1D and G7D, the tolerance is 5 parts per 10^6.

   (b) The power shown in paragraph (a) of this section is the peak
   envelope power for single-sideband transmitters and the mean power for
   all other transmitters.

   (c) For single-sideband transmitters, the tolerance is:

   (1) All aeronautical stations on land—10 Hz.

   (2) All aircraft stations—20 Hz.

   (d) For radar transmitters, except non-pulse signal radio altimeters,
   the frequency at which maximum emission occurs must be within the
   authorized frequency band and must not be closer than 1.5/T MHz to the
   upper and lower limits of the authorized bandwidth, where T is the
   pulse duration in microseconds.

   (e) The Commission may authorize tolerances other than those specified
   in this section upon a satisfactory showing of need.

   (f) The carrier frequency tolerance of all transmitters that operate in
   the 1435-1525 MHz or 2345-2395 MHz band is 0.002 percent. The carrier
   frequency tolerance of all transmitters that operate in the 5091-5150
   MHz band is 0.005 percent.

   (g) Any aeronautical enroute service transmitter operating in U.S.
   controlled airspace with 8.33 kHz channel spacing (except equipment
   being tested by avionics equipment manufacturers and flight test
   stations prior to delivery to their customers for use outside U.S.
   controlled airspace) must achieve 0.0005% frequency stability when
   operating in that mode.

   [ 53 FR 28940 , Aug. 1, 1988, as amended at  56 FR 38084 , Aug. 12, 1991;
    57 FR 45749 , Oct. 5, 1992;  58 FR 31027 , May 26, 1993;  63 FR 36607 , July
   7, 1998;  64 FR 27474 , May 20, 1999;  66 FR 26799 , May 15, 2001;  69 FR 32880 , June 14, 2004;  76 FR 17350 , Mar. 29, 2011;  78 FR 61205 , Oct. 3,
   2013;  80 FR 38909 , July 7, 2015]

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