Abstract
The passage of multichannel frequency division multiplexed (FDM) signals through an amplitude limiting nonlinear device produces crosstalk in each channel output due to intermodulations among signals in all channels. The signal power S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> to crosstalk power N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> ratio in any particular channel determines signal degradation. This paper considers multichannel FDM signals passing through a saturated bandpass amplifier with transfer characteristic of smoothly limiting error function curve, and determines a lower bound of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S_{0}/N_{c}</tex> as a function of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</tex> , which is related to the limiting level. By invoking the central limit theorem, the FDM signals are represented by a Gaussian noise, excepting the signal in the channel where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S_{0}/N_{c}</tex> is to be determined. The signal in the channel under consideration is represented by a constant amplitude sine wave. When an assumption that the input noise power spectral density is symmetric about the center band is made, such as a Gaussian power spectrum considered in the analysis, the computation of a lower bound for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S_{0}/N_{c}</tex> was equivalent to the consideration of the center channel, where the crosstalk power is maximum. The problem is an extension of an earlier work by Cahn, who considered an idealized saturation amplifier. The result is presented in a graph where it is seen that an infinite clipping case of the present analysis agrees with that of Cahn.
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