Based on these parameters, one can construct a table showing the necessary power reduction (filtering) at the SPS frequency in order to protect a typical radio astronomy system from overload or physical damage. It is possible to achieve filtering that will protect a radio astronomy installation in most cases. A notch filter in the receiver input with a 100 dB loss at 2.45 GHz will probably be difficult to achieve, and it might not be possible to protect observations near the celestial equator where it is likely that the main beam will be pointed at or very near an SPS transmitter. It must be noted that the input filtering needed to protect radio astronomy receivers from the effects discussed here will reduce the sensitivity of the radiometers by introducing loss (0.5 dB) in the signal path and by the thermal radiation of the filter components. The addition of an input filter may increase the system noise temperature 25% or more even if the filter is cooled to the physi- cal temperature of a cooled parameteric amplifier ( 20 K), a quite undesirable degradation of the radiometer performance. One must keep in mind that this discussion estimates the impact of a future system (SPS), one that might be in operation several decades hence, on the performance parameters of a typical radio astronomy system which is currently being used. A future system may be more sensitive to overload and physical damage, but could also be less vulnerable.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==