FIGURE 1. Arecibo Sky Coverage was upgraded recently to provide high sensitivity and resolving power (1'FWHM) in the protected band at 5 GHz, and any radiation in this band above the harmful interference limits of CCIR 224-4 will degrade or eliminate the Arecibo 6-cm research. The second concern is not directly addressed by CCIR 224-4, as it involves planetary radar. The 430-kw Arecibo cw radar operates‘on an assigned frequency of 2380 MHz. The receiver is a Jet Propulsion Laboratory maser. The normal observing mode involves transmitting for periods ranging from a few to tens of minutes in order to fill the round-trip travel time window between the earth and the target planet, satellite, or asteroid. A reception period of equal duration then follows. The bandwidth used during reception is set by the nature of the target and ranges from 0.02 Hz for Venus at conjunction to 30 kHz for Saturn’s rings. The harmful interference level calculated for these bandwidths, but otherwise using the same criteria as CCIR 224-4, ranges from 2 -204 to -235 dbW/m -Hz. The latter figure, which applies to "soft" targets
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