To consider, based on the results of ITU R studies, any further regulatory measures to facilitate introduction of new aeronautical mobile (R) service (AM(R)S) systems in the bands 112-117.975 MHz, 960-1 164 MHz and 5 000-5 030 MHz in accordance with Resolutions 413 (Rev.WRC 07), 417 (WRC 07) and 420 (WRC 07).
The primary concern for radio astronomy is the potential for out-of-band emission from transmitters providing surface applications at airports in the 5000-5030 MHz band that would cause interference in the primary RAS allocation, 4990-5000 MHz, and the secondary RAS allocation, 4800-4990 MHz. Nearly all centimeter-wavelength radio telescopes operate in the 4800-5000 MHz band to study the continuum radio emission from stars, galaxies, quasars, gamma-ray bursts, and other sources of galactic and extragalactic thermal and nonthermal continuum radiation.
A one-watt EIRP transmitter located 25 km (line of sight) from a radio astronomy facility needs to have its combined excess path loss and out-of-band emissions under -72 dBc to conform to the level specified in Recommendation ITU-R RA.769 that is, of a power density of less than -171 dBW/m2 for continuum observations in the 5 GHz RAS band. The corresponding value in Recommendation ITU-R RA.769 for spectral-line observations is a spectral power density of less than -230 dBW/m2/Hz, so that if the one watt transmitter has a bandwidth of 10 kHz the combined excess path loss and out-of-band emissions need to be less than -91 dBc.
Recommendation: Transmitters providing surface applications at airports in the 5000-5030 MHz band should have sufficient suppression of out-of-band emissions to avoid interference in the adjacent 5 GHz Radio Astronomy Service band in accord with Recommendation ITU-R RA.769.