Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses (2007) / Chapter Skim
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4 Technical Aspects of Protection for the Scientific Use of the Radio Spectrum
4 Technical Aspects of Protection for the Scientific Use of the Radio Spectrum
Pages 79-90
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From page 79... ...
.1 The threshold levels of interference to radio astronomy bands are published in Recommendation ITU-R RA.769, "Protection Criteria for Radioastronomical Measurements."2 With the increasing commercial use of the spectrum, it is ever more important to implement ways to protect radio astronomy and other services from adjacent and neighboring band interference resulting from air-to-ground and space-to-ground transmissions. 4.1 INTERFERENCE DETRIMENTAL TO RADIO ASTRONOMY 4.1.1 Radio Astronomy Signals The threshold levels of interference detrimental to radio astronomy3 given in Recommendation ITU-R RA.769 are specified in both power flux density (pfd)
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From page 80... ...
In Tables 1 and 2 of Recommendation ITU-R RA.769, values of FH and SH are given for representative radio astronomy bands across the spectrum for both continuum and spectral line observations. For continuum observations, the bandwidth used is the width of the allocated radio astronomy band; for spectral line (multichannel)
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From page 81... ...
This interference level is determined by fixing the unwanted signal level below 20 percent of ∆P = k∆TeB, where ∆Te is the sensitivity of passive radiometric sensors, k is Boltzmann's constant, and B is the receiver bandwidth. Recommendation ITU-R SA.1028 provides the performance criteria for satellite passive remote sensing, and ITU-R SA.1029.1 provides the interference criteria that are compatible with those performance objectives by defining the maximum permissible interference level within a reference bandwidth which is not necessarily the same as any particular sensor's bandwidth.
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From page 82... ...
satellite in a band adjacent to a radio astronomy band is provided by a European television broadcast satellite transmitting in the Fixed Satellite Service band 10.7-10.95 GHz. A measured spectrum showed that at 10.7 GHz, the upper edge of a primary radio astronomy band, the spfd from the satellite was approximately 39 dB greater than the corresponding threshold value for continuum observations in Table 1 of Recommendation ITU-R RA.769.
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From page 83... ...
For example, coordination zones are used for cases in which the radio astronomy band is shared with the terrestrial mobile service (see Box 4.1)
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From page 84... ...
"In the bands 1350-1400 MHz and 4950-4990 MHz, every practicable effort will be made to avoid the assignment of frequencies to stations in the fixed and mobile services that could interfere with radio astronomy observations within the geographic areas given above. In addi tion, every practicable effort will be made to avoid assignment of frequencies in these bands to stations in the aeronautical mobile service which operate outside of those geographic areas, but which may cause harmful interference to the listed observatories.
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From page 85... ...
For example, any filter preceding the first amplifier must have sufficiently low insertion loss so as not to dominate the noise figure. This constraint on the filter's insertion loss limits the order of the filter design, which in turn limits the rate of attenuation with increasing frequency separation.
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From page 86... ...
One method of control of the sidebands of these and similar types of digital modulation is through the use of modulation techniques that control the rate of change of amplitude or phase at the transitions and thereby greatly reduce the level of unwanted frequency components that cause the sidebands. Several practical modulation systems of this type have been developed -- for example, 7For background information from technical papers regarding the mitigation of radio-frequency interference, see the following: American Geophysical Union, "Mitigation of Radio Frequency Interference in Radio Astronomy," Radio Science, Vol.
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From page 87... ...
4.3.2 Filtering in Radio Astronomy Receivers As explained in §4.2.2, the ability of passive services to employ filtering of sufficiently high order to mitigate the deleterious effects of emissions outside the radio astronomy band is severely limited by the need to achieve an extremely low noise figure. The requirements for a filter designed to mitigate outof-band emission effectively must take into account (1)
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From page 88... ...
These are related to the fringe oscillations that occur as the relative phase of the signal from the two antennas varies, and, for wideband systems, to the decorrelation that results from the difference in the time delays of the interfering signals in reaching the two antennas. The treatment of interference in these cases is more complicated than for a single antenna.
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From page 89... ...
. Strong efforts must be made to protect radio astronomy bands from interference due to air- or space-to-ground transmissions in other bands.8 Passive services are particu 8See Appendix A for ITU definitions relating to interference.
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From page 90... ...
Modernization of these standards would be useful to other services as well as to radio astronomy. This is particularly the case with airborne and satellite transmitters because of the potential clear line of sight to the radio telescope and devices that do not require licensing.
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