THE DESIGN AND DEVELOPMENT OF THE R-1084 SINGLE-SIDEBAND RADIO RECEIVER

A time invariant system is said to be physially realzable if its unit impulse response, ht, is zero for t 0. It is often assumed in treatments of physical realizability that the Fourier transform of ht is square integrable L sub 2 neg. infinity, pos. infinity. Some use is then made of the regularity of the transform for real frequencies, to derive further properties of the transform. The condition that the system be stable leads to a different assumption, that the absolute value of ht be integrable is L negative infinity, positive infinity this implies only uniform continuity of the transform for real frequencies. Physically realizable, stable systems are discussed, and several necessary, and a few sufficient, conitions on the Fourier transform of ht are summarized. In particular, the behavior of the transform for complex frequencies, the Bode relations, and the Paley-Wiener criterion are reviewed. Author