Crosstalk Power Research Articles

Signal-to-Crosstalk Power Radio in Smoothly Limited Multichannel FDM Signals

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.

A Six-Channel Station Carrier System

There is an increasing need for a low-cost, reliable station carrier system for use in the outside telephone plant. The system design constraints of cable attenuation, including bridge taps, cable crosstalk, switching noise, and remote power feed considerations are discussed. The particular design choices that have been made with respect to the modulation plan, carrier transmission levels, line impedance matching, system power, and signaling are described for a six-channel station carrier system. A repeater is used with this system with nominal span loss of 35 dB at 112 kHz, but the loss may be as little as 20 dB to as much as 40 dB. No adjustments or building-out networks are required. The system is installed and maintained in operation without adjustment or alignment, because automatic level regulation and coordination is provided.