throughout the spectrum. Many of the frequencies of interest are spectral lines (often Doppler shifted from their real frequencies). A list of such spectral lines is included in CCIR Report 223 (Appendix A). In order to achieve reasonable interference protection at frequencies outside the bands allocated to radio astronomy, radio observatories have been located in remote areas where man-made interference levels are low. Also, in order to formalize such protection, the FCC established in 1958 a National Radio Quiet Zone surrounding the National Radio Astronomy Observatory in Green Bank, West Virginia and the nearby Naval Radio Research Laboratory in Sugar Grove, West Virginia. Within this quiet zone, FCC licensing procedures are intended to allow only transmitters that produce power fluxes at the observatories of less than 10 W/m . A few broadcasting stations remote from the National Radio Quiet Zone (NRQZ) do exceed these limits, producing power fluxes at the observatories on the order of 10 W/m . Other observatories and the Deep Space Network Station at Goldstone, California have less formal arrangements to minimize local sources of interference, generally based on the requirement that spurious radiation in the protected bands not exceed the levels given in CCIR Report 224-4 (or CCIR Report 685 in the case of the Deep Space Network). Estimates of the side lobe radiation flux from each power satellite vary, - but range as high as 2 x 10 W/m within a few hundred kilometers of the - rectenna, 10 W/m at the grating lobes, and 10 W/m at various peaks out to distances of 4000 km from the rectenna (D0E/ER-0023, Figures 19 and 22). For comparison, the flux of radio and TV broadcast signals in major metropolitan areas (e.g., in Los Angeles at a distance of 20 km from Mt. Wilson) might be of the order 10 W/m . A fully-developed system with 100 satellites serving the entire country would raise the power flux to this value (M0 W/m ) in side lobe peaks over the whole country, since the mean spacing between rectenna sites would then be 300 km. Thus, in a sense, construction of the SPS would make the radio environment of the whole country as unsuitable for sensitive observations as the most densely populated areas are now.
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