This noise power would be focused differently from the signal. Each tube would feed one element of a phased array, each element have an effective area of about one square meter, with a forward gain of 30 dB at the design frequency, falling off slowly (1 dB/100 MHz) with frequency. The signal beam from the 1 km diameter phased array would subtend an angle of less than an arcminute, placing more than 90 percent of the signal in an area 10 km across the earth’s surface. However, the noise voltages would not be correlated from one Amplitron to the next. Hence the noise beamwidth would be defined by the pattern of the individual elements, about 10°. The noise would therefore be distributed over an area some thousands of miles in diameter centered on each receiving site. The study proposes reducing this noise level, which is unacceptable even for commercial communications services, by further development of the Amplitron tubes and by filtering the signal from the tubes before it reaches the antenna elements. The filtering requirements are severe if permanent damage to radio and radar astronomy is to be avoided. The unfiltered noise signal with current tube designs would be -153 dBW m^ Hz”l at the earth’s surface. The harmful interference levels defined in the CCIR report lies some 80 to 90 dB below this level in the 2-3 GHz region. Even if adequate filters could be designed, the failure of a single one of the 10$ filters could produce a noise level in excess of the harmful limits of CCIR 224-4. (These limits apply when the radio telescope is pointed away from the satellite; in a small area around the satellite’s position the interference would be much worse). There are several other mechanisms by which serious out-of-band interference might be generated by virtue of extremely high r-f power levels. These include non-linear effects in the earth’s atmosphere and in metallic structures in the satellite or on the earth’s surface. In addition to the problems from the noise power, the signal power itsd.f will be so high that there could be substantial interference due to the energy which goes into directions other than the main beam, and to frequencies outside the intended band. It is never possible to confine all the energy of a radio signal to the main beam and the assigned frequency band, but with normal transmitters the out-of-beam and out-of-band levels are usually low enough to be negligible. The situation would be quite different for the very powerful transmitters being considered here, especially for interference to the very sensitive receivers used in radio astronomy. Many observatories could be affected by any of the types of interference considered above; major U.S. installations are currently located at Green Bank, WV; Socorro, NM; Tucson, AZ; Hat Creek and Owens Vally,(sic) CA; Marfa, TX; Arecibo, PR; Amherst and Westford, MA, and Danville, IL. A remote location provides no protection from satellite interference. National borders are equally ineffective; Canadian installations in Algonquin Park, Ontario, and Penticton, BC, would also be affected. A particularly severe problem would exist for the world’s most powerful and sensitive radar system, located at Arecibo, as its assigned operating frequency of 2380 MHz lies just outside the 2400-2500 MHz band currently under consideration for use by the power satellite.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==