{"data":{"id":"us/47-cfr-87.133","jurisdiction":"us","citation":"47 CFR 87.133","heading":"Frequency stability.","body":"(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:\nFrequency band (lower limit exclusive, upper limit inclusive), and categories of stations Tolerance 1 Tolerance 2\n(1) Band-9 to 535 kHz:\nAeronautical stations 100 100\nAircraft stations 200 100\nSurvival craft stations on 500 kHz 5,000 20 Hz 3\nRadionavigation stations 100 100\n(2) Band-1605 to 4000 kHz:\nAeronautical fixed stations:\nPower 200 W or less 100 100 8\nPower above 200 W 50 50 8\nAeronautical stations:\nPower 200 W or less 100 7 100 7 8\nPower above 200 W 50 7 50 7 8\nAircraft stations 100 7 100 7\nSurvival craft stations on 2182 kHz 200 20 Hz 3\n(3) Band-4 to 29.7 MHz:\nAeronautical fixed stations:\nPower 500 W or less 50\nPower above 500 W 15\nSingle-sideband and Independent-sideband emission:\nPower 500 W or less 50 Hz\nPower above 500 W 20 Hz\nClass F1B emissions 10 Hz\nOther classes of emission:\nPower 500 W or less 20\nPower above 500 W 10\nAeronautical stations:\nPower 500 W or less 7 100 100 7\nPower above 500 W 7 50 50 7\nAircraft stations 7 100 100 7\nSurvival craft stations on 8364 kHz 200 50 Hz 3\n(4) Band-29.7 to 100 MHz:\nAeronautical fixed stations:\nPower 200 W or less 50\nPower above 200 W 30\nPower 50 W or less 30\nPower above 50 W 20\nOperational fixed stations:\n73-74.6 MHz (Power 50 W or less) 50 30\n73-74.6 MHz (Power above 50 W) 20 20\n72-73.0 MHz and 75.4-76.0 MHz 5 5\nRadionavigation stations 100 50\n(5) Band-108 to 137 MHz:\nAeronautical stations 4 50 12 20\nEmergency locator transmitter test stations 50 50\nSurvival craft stations on 121.5 MHz 50 50\nEmergency locator stations 50 50\nAircraft and other mobile stations in the Aviation Services 5 50 13 30\nRadionavigation stations 20 20\nDifferential GPS 2\n(6) Band-137 to 470MHz:\nAeronautical stations 50 20\nSurvival craft stations on 243 MHz 50 50\nAircraft stations 50 5 30 10\nRadionavigation stations 50 50\nEmergency locator transmitters on 406 MHz N/A 5\n(7) Band-470 to 2450 MHz:\nAeronautical stations 100 20\nAircraft stations 100 20\nAircraft earth station 320 Hz 11\nAeronautical utility mobile stations on 1090 MHz 1000 1000\nRadionavigation stations:\n470-960 MHz 500 500\n960-1215 MHz 20 20\n1215-2450 MHz 500 500\n(8) Band-2450 to 10500 MHz:\nRadionavigation stations 6 9 1250 1250 6 9\n(9) Band-10.5 GHz to 40 GHz:\nRadionavigation stations 5000 5000\n1 This 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).\n2 This 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).\n3 For transmitters first approved after November 30, 1977.\n4 The 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.\n5 The tolerance for transmitters approved after January 1, 1974, is 30 parts in 10 6.\n6 In 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).\n7 For 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.\n8 For 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.\n9 Where 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.\n10 Until 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.\n11 For purposes of certification, a tolerance of 160 Hz applies to the reference oscillator of the AES transmitter. This is a bench test.\n12 For emissions G1D and G7D, the tolerance is 2 parts per 106.\n13 For emissions G1D and G7D, the tolerance is 5 parts per 106.\n(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.\n(c) For single-sideband transmitters, the tolerance is:\n(1) All aeronautical stations on land—10 Hz.\n(2) All aircraft stations—20 Hz.\n(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.\n(e) The Commission may authorize tolerances other than those specified in this section upon a satisfactory showing of need.\n(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.\n(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.","path":["Title 47—Telecommunication","CHAPTER I—FEDERAL COMMUNICATIONS COMMISSION","SUBCHAPTER D—SAFETY AND SPECIAL RADIO SERVICES","PART 87—AVIATION SERVICES","Subpart D—Technical Requirements"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-47.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:28Z","sha256":"8c1fa96d981a2caa16aaa013207911749ac55f1ffa05071b0c82547f20609f97","source_id":"us-cfr","stale":true,"prev":"us/47-cfr-87.131","next":"us/47-cfr-87.135"},"notice":"GroundRules: Original legal text. Not legal advice."}