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CHAPTER 3

Radio Astronomy
Spectrum Requirements

National Spectrum Requirements

The NTIA Requirements Study addressed 40 radio services and projected U.S. spectrum requirements for a 10-year period based primarily on technical factors. TABLE 3–1 below was taken from the NTIA Requirements Study and depicts the additional U.S. spectrum requirements for both Federal and non-Federal users. NTIA indicated that eight of these radio services needed access to additional spectrum in order to satisfy user requirements to the year 2004.

The NTIA Requirements Study found that a total of 204 megahertz will be needed for land mobile operations within the next 10 years, and that a total of about 3,088 kilohertz additional spectrum in the HF band (3–30 MHz) will be needed for radiocommunications for five radio services: broadcasting, amateur, aeronautical mobile, mobile, and maritime mobile. This report addresses spectrum availability and long-range planning options for the radio astronomy services’s request for additional spectrum as identified in the NTIA Requirements Study. In identifying planning options for the radio astronomy service, NTIA was mindful the criteria should be: (1) the inclusion of the radio astronomy service is reasonable; (2) the options selected would have minimum frequency assignments or licenses; and (3) that any primary users would probably be amenable to allowing the radio astronomy service access to the bands.

Radio Astronomy Spectrum Requirements

NTIA indicated in its NTIA Requirements Study that the additional spectrum requested for the radio astronomy service is about 241 megahertz: 9.6 megahertz of additional allocations, and access to an additional 231 megahertz by local coordination. Spectrum requirements for the radio astronomy service are somewhat different from those of most other radio services in that they are not dictated by predicted traffic requirements and, in the case of spectral lines, involve very specific frequencies.(1)

TABLE 3–1.
Summary of Additional U.S. Spectrum Requirements
(10-Year Projection)
Radio Services Spectrum Requirements
Land Mobile
a) Conventional dispatch, public safety, cellular, PCS, trunked mobile, and paging
b) Intelligent Transportation System
a) 119 MHz Additional below 5 GHz
b) 75 MHz below 10 GHz 10 MHz between 10 and 100 GHz
Aeronautical Mobile 30 kHz Additional (HF) for off-route (OR) and 108 kHz for route (R).(2)
100 kHz Additional (HF) allocated to the Mobile Service.
Maritime Mobile 36–60 kHz Additional (HF)
Mobile-Satellite 60 MHz Additional
Fixed Up To 250 MHz Reduction
Fixed-Satellite 200–400 MHz Additional (Feeder Links)
Broadcasting 1,900 kHz Additional (HF)
Broadcasting-Satellite Present Spectrum Adequate
Radionavigation Present Spectrum Adequate
Radiolocation Present Spectrum Adequate
Radiodetermination-Satellite Present Spectrum Adequate
Inter-Satellite Present Spectrum Adequate
Space Operation Present Spectrum Adequate
Space Services Present Spectrum Adequate
Radio Astronomy 9.6 MHz Additional (see note)
Amateur and Amateur-Satellite 900 kHz Additional (HF) 1280 kHz Additional (VHF)
Standard Frequency and Time Signal Present Spectrum Adequate
Meteorological Aids Present Spectrum Adequate
Note: The radio astronomy community also requested access to an additional 231 megahertz, which could be obtained on a local, coordinated basis.

In their comments to the NTIA Notice of Inquiry, the NSF indicated that the United States radio astronomy frequency allocations should lie at approximately every octave above 30 MHz and should have bandwidths at least one to two percent of the center frequency to improve sensitivity of radio astronomy receivers. Present frequency allocations to radio astronomy in the United States reflect the octave spacing requirement for the most part except for the gap between the 74.6 MHz and the 406.1 MHz allocations. Allocations to cover this gap would allow U.S. radio astronomers to contribute to and expand the research of pulsars, quasars, neutron stars, etc., and would also allow the United States to harmonize radio astronomy allocations with Region 1. Also, increasing the bandwidths to some allocations would increase the sensitivity of observations of the Sun, radio bursts from Jupiter, ionized hot gases between stars, and help define the most probable theory of the origin and evolution of the Universe. (3)

The NSF identified several other radio astronomy bands that have less than the minimum one percent bandwidth. The following three tables (TABLES 3–2, 3–3, and 3–4) reflect this and other additional spectrum requirements for the radio astronomy service.

New Allocations

The additional allocations of 9.6 megahertz are required in the 150.05–153 MHz and 322–328.6 MHz bands. These are the two bands suggested by the NSF in its concern about having octavely-spaced allocations between 74.6 MHz and 406.1 MHz.

TABLE 3–2.
New Allocations Requested for Continuum Observations
Frequency Band Bandwidth
150.05-153 MHz 2.95 MHz
322-328.6 MHz 6.6 MHz
Total Spectrum Requested: 9.55 MHz

Access to Additional Spectrum

In addition to the new allocations shown above, NSF indicated that they needed access to additional spectrum on a coordinated basis. This access would be used to increase sensitivity in some bands that do not have the minimum bandwidth and also for certain spectral-line observations that are not presently supported.(4) The following two tables denote the spectrum requested by the NSF.

Continuum observations

Several radio astronomy bands have less than the minimum one percent bandwidth for continuum observations. The NSF recommended increasing the bandwidths of eight frequency bands(5) as indicated in TABLE 3–3 below.

TABLE 3–3.
Increased Bandwidth Requested for Continuum Observations
Frequency Band Current Bandwidth One Percent Bandwidth Additional Spectrum Requested
13.36-13.41 MHz 50 kHz 134 kHz 84 kHz
25.55-25.67 MHz 120 kHz 256 kHz 136 kHz
406.1-410 MHz 3.9 MHz 4.1 MHz 200 kHz
608-614 MHz 6.0 MHz 6.1 MHz 100 kHz
2690-2700 MHz 10 MHz 27 MHz 17 MHz
4990-5000 MHz 10 MHz 50 MHz 40 MHz
10.6-10.7 GHz 100 MHz 107 MHz 7 MHz
15.35-15.4 GHz 50 MHz 154 MHz 104 MHz
Total Access Requested: 169 MHz

Spectral–Line Observations

Astronomers have identified over 550 spectral lines. The IAU maintains a list of the frequencies it considers most important for spectral-line observations.(6) The frequency bands listed in TABLE 3–4 are those identified by the NSF as necessary to extend protection of the most important spectral lines to more highly redshifted (lower) frequencies or to afford protection to important spectral lines that are not currently within a band allocated exclusively to passive services.(7) The total additional spectrum requested in these bands is 62.3 megahertz.

TABLE 3–4.
Spectrum Access Requested for Spectral-line Observations
Additional Allocation Bandwidth of Allocation
1370-1400 MHz 30 MHz
1606.8-1610.6 MHz 3.8 MHz
1659.8-1660 MHz 200 kHz
1714.8-1722.2 MHz 7.4 MHz
4813.6-4834.5 MHz 20.9 MHz
Total Access Requested: 62.3 MHz

Endnotes

(1)See John B. Whiteoak, The Threat to Radio Astronomy, The Vanishing Universe: Adverse Environmental Impacts on Astronomy, (Derek McNally, ed., 1994) at 76. Spectral-line radiation is produced in the dense envelopes of stars and dense interstellar gas clouds by atoms and molecules when they lose or gain energy due to collisions with other particles, or are “excited” by nearby sources of radiation. Each atom or molecule produces a unique signature of spectral lines. About 1000 spectral lines have been identified by radio astronomers from molecular clouds in our Galaxy. Some spectral lines are more important astrophysically than others, and the IAU, approves an updated list of about 30 of the most important lines. Id.

(2)This is the spectrum requirement as indicated in the NTIA Requirements Study. Certain requirements have increased recently.

(3)Id.

(4)See NSF Comments supra note 26 at 14, 16, and 18, Sep 30, 1992.

(5)See NSF Comments supra note 26 at 14, Sep 30, 1992. The Department of Defense believes some of these bands may be difficult to coordinate in some areas. For example, expansion of the 4990–5000 MHz band would limit use of existing troposcatter systems and airborne data links in this spectrum. See memorandum from Nelson V. Pollack, Air Force Member, Interdepartment Radio Advisory Committee (IRAC), to Chairman, IRAC, at 7, (Oct. 7, 1994) (on file with NTIA).

(6)See NSF Comments, supra note 26 at 17–18, Sep 30, 1992. The list is included in Recommendation 314 of the ITU Radiocommunication Sector 1994 RA Series.

(7)See NSF Comments, supra note 26 at 18–19, Sep 30, 1992; Electronic mail from Andrew Clegg, NSF, to Robin H. Haines, NTIA (Oct. 31, 1994) (printed copy on file with NTIA clarifying the need for the frequency bands).

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