Concerning Optimum Frequencies for Space Vehicle Communication

Optimum frequencies for the varied needs of space vehicle communication can best be determined from the estimated system performance. Each of the contributing equipment and propagation factors over the range of the radio frequency spectrum affects the minimum tolerable signal-to-noise power ratio at the receiver. Over the range of the radio frequency spectrum, the behavior of the individual building blocks, as factors, will vary so as to exhibit a preponderance of either desirable or undesirable characteristics. Some of the newer technical developments that increase sensitivity to weak signals are evaluated for their potential increase in the distance of communication. Then the individual building blocks are married to each other in operating systems that determine the optimum portions of the frequency spectrum. The equipment factors are examined first, both as to their individual characteristics and their dependence on each other. Next, the propagation factors are examined for their effect over the range of the radio frequency spectrum in providing windows for communication through the earth's atmosphere, troposphere, and ionsphere to outer space. Some consideration is given to the effects of auroral displays, water vapor and gaseous absorption, Faraday rotation of polarization, and radio star scintillations. In addition, there is a discussion of noises arising from various causes. Measurements by radio astronomers demonstrate that equivalent noise temperature is a more useful measure of signal-to-noise ratio of receiver performance than the standard noise figure definition.