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Significant Radio Astronomy Frequencies

The following radio astronomy frequency bands were recognized at the 1979 World Administrative Radio Conference. Many are shared segments, not specifically protected from interference by other authorized users, but are nevertheless generally accepted spectral regions for radio astronomical observation. The lower two segments are generally used for solar and Jupiter observations; the 73, 150 and 406 MHz segments are quite popular for pulsar detection, and the 1400 MHz band is used for hydrogen line measurements.


IAU Protected Segments
Contributed by Hans Brakob, K0HB

At the XXIst General Assembly of the International Astronomical Union, IAU, (Buenos Aires, July 23 - August 1, 1991) the astrophysically most important spectral lines have been carefully reviewed. The IAU listed the revision of these spectral lines as reproduced below. The IAU expressed the continued need to protect these frequency bands from in-band, band-edge and harmonic emissions, especially from space-borne transmitters.

SubstanceRest FrequencyProtected SegmentNotes (1)
Deuterium (DI)327.3840 MHz 327.0 - 327.7 MHz
Hydrogen (HI)1420.406 MHz 1370.0 - 1427.0 MHz2),3)
Hydroxyl radical (OH)1612.231 MHz 1606.8 - 1613.8 MHz3),4)
Hydroxyl radical (OH)1665.402 MHz 1659.8 - 1667.1 MHz4)
Hydroxyl radical (OH)1667.359 MHz 1661.8 - 1669.0 MHz4)
Hydroxyl radical (OH)1720.530 MHz 1714.8 - 1722.2 MHz3),4)
Methyladyne (CH)3263.794 MHz 3252.9 - 3267.1 MHz3),4)
Methyladyne (CH) 3335.481 MHz 3324.4 - 3338.8 MHz 3),4)
Methyladyne (CH) 3349.193 MHz 3338.0 - 3352.5 MHz 3),4)
Formaldehyde (H2CO) 4829.660 MHz 4813.6 - 4834.5 MHz 3),4)
Methanol (CH2OH) 6668.518 MHz 6661.8 - 6675.2 MHz 3),6)
Ionized Helium Isotope (3HeII) 8665.650 MHz 8660.0 - 8670.0 MHz
Methanol (CH3OH) 12.178 GHz 12.17 - 12.19 GHz3),6)
Formaldehyde (H2CO) 14.488 GHz 14.44 - 14.50 GHz3),4)
Cyclopropenylidene (C3H2) 18.343 GHz 18.28 - 18.36 GHz3),4),6)
Water Vapour (H2O) 22.235 GHz 22.16 - 22.26 GHz3),4)
Ammonia (NH3) 23.694 GHz 23.61 - 23.71 GHz4)
Ammonia (NH3) 23.723 GHz 23.64 - 23.74 GHz4)
Ammonia (NH3) 23.870 GHz 23.79 - 23.89 GHz4)
Silicon monoxide (SiO) 42.821 GHz 42.77 - 42.86 GHz
Silicon monoxide (SiO)43.122 GHz 43.07 - 43.17 GHz
Carbon monosulphide (CS)48.991 GHz 48.94 - 49.04 GHz
Deuterated formylium (DCO+) 72.039 GHz 71.96 - 72.11 GHz3)
Silicon monoxide (SiO) 86.243 GHz 86.16 - 86.33 GHz
Formylium (H13CO+) 86.754 GHz 86.66 - 86.84 GHz
Silicon monoxide (SiO) 86.847 GHz 86.76 - 86.93 GHz
Ethynyl radical (C2H) 87.300 GHz 87.21 - 87.39 GHz5)
Hydrogen cyanide (HCN) 88.632 GHz 88.34 - 88.72 GHz4)
Formylium (HCO+) 89.189 GHz 88.89 - 89.28 GHz4)
Hydrogen isocyanide (HNC) 90.664 GHz 90.57 - 90.76 GHz
Diazenylium (N2H) 93.174 GHz 93.07 - 93.27 GHz
Carbon monosulphide (CS) 97.981 GHz 97.65 - 98.08 GHz4)
Carbon monoxide (C18O) 109.782 GHz 109.67 - 109.89 GHz
Carbon monoxide (13CO) 110.201 GHz 109.83 - 110.31 GHz4)
Carbon monoxide (C17O) 112.359 GHz 112.25 - 112.47 GHz6)
Carbon monoxide (CO) 115.271 GHz 114.88 - 115.39 GHz4)
Formaldehyde (H213CO) 137.450 GHz 137.31 - 137.59 GHz3),6)
Formaldehyde (H2CO) 140.840 GHz 140.69 - 140.98 GHz
Carbon monosulphide (CS) 146.969 GHz 146.82 - 147.12 GHz
Water vapour (H2O) 183.310 GHz 183.12 - 183.50 GHz
Carbon monoxide (C18O) 219.560 GHz 219.34 - 219.78 GHz
Carbon monoxide (13CO) 220.399 GHz 219.67 - 220.62 GHz 4)
Carbon monoxide (CO) 230.538 GHz 229.77 - 230.77 GHz 4)
Carbon monosulphide (CS) 244.953 GHz 244.72 - 245.20 GHz6)
Hydrogen cyanide (HCN) 265.886 GHz 265.62 - 266.15 GHz
Formylium (HCO+) 267.557 GHz 267.29 - 267.83 GHz
Hydrogen isocyanide (HNC) 271.981 GHz 271.71 - 272.25 GHz
Dyazenulium (N2H+) 279.511 GHz 279.23 - 279.79 GHz
Carbon monoxide (C18O) 312.330 GHz 329.00 - 329.66 GHz
Carbon monoxide (13CO) 330.587 GHz 330.25 - 330.92 GHz
Carbon monosulphide (CS) 342.883 GHz 342.54 - 343.23 GHz
Carbon monoxide (CO) 345.796 GHz 345.45 - 346.14 GHz
Hydrogen cyanide (HCN) 354.484 GHz 354.13 - 354.84 GHz
Formylium (HCO+) 356.734 GHz 356.37 - 357.09 GHz
Dyazenulium (N2H+) 372.672 GHz 372.30 - 373.05 GHz
Water vapour (H2O) 380.197 GHz 379.81 - 380.58 GHz
Carbon monoxide (C18O) 439.088 GHz 438.64 - 439.53 GHz
Carbon monoxide (13CO) 440.765 GHz 440.32 - 441.21 GHz
Carbon monoxide (CO) 461.041 GHz 460.57 - 461.51 GHz
Heavy water (HDO) 464.925 GHz 464.46 - 465.39 GHz
Carbon (CI) 492.162 GHz 491.66 - 492.66 GHz
Water vapour (H218O) 547.676 GHz 547.13 - 548.22 GHz
Water vapour (H2O) 556.936 GHz 556.37 - 557.50 GHz
Ammonia (15NH3) 572.113 GHz 571.54 - 572.69 GHz
Ammonia (NH3) 572.498 GHz 571.92 - 573.07 GHz
Carbon monoxide (CO) 691.473 GHz 690.78 - 692.17 GHz
Hydrogen cyanide (HCN)797.433 GHz 796.64 - 789.23 GHz
Formylium (HCO+) 802.653 GHz 801.85 - 803.85 GHz
Carbon monoxide (CO) 806.652 GHz 805.85 - 807.46 GHz
Carbon (CI) 809.350 GHz 808.54 - 810.16 GHz

Notes:

  1. If Note 4) or Note 2) are not listed, the band limits are Doppler-shifted frequencies corresponding to radial velocities of +/- 300 km/s (consistent with line radiation occurring in our galaxy).

  2. An extension to lower frequencies of the allocation of 1400-1427 MHz is required to allow for the Doppler shifts for HI observed in distant galaxies.

  3. The current international allocation is not primary and/or does not meet bandwidth requirements. See: ITU-R Radio Regulations (Table 8) for more detailed information.

  4. Because these line frequencies are also being used for observing other galaxies, the listed bandwidths include Doppler shifts corresponding to radial velocities of up to 1000 km/s. It should be noted that HI has been observed at frequencies redshifted to 500 MHz, while some lines of the most abundant molecules have been detected in galaxies with velocities up to 50 000 km/s, corresponding to a frequency reduction of up to 17%.

  5. There are six closely spaced lines associated with this molecule at this frequency. The listed band is wide enough to permit observations of all six lines.

  6. This line is not mentioned in Article 8 of the ITU-R Radio Regulations.


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