| 摘要 |
Undesired oscillations in a communications conferencing network are reduced and/or eliminated by frequency shifting signals passing through the conferencing network by a small amount for each pass therethrough. Electrical information signals from a plurality of individual communication sets are individually summed, frequency shifted by a predetermined amount, and coupled back to individual ones of the communication sets, less their individual signal contributions. Frequency shifting is performed on analog electrical information signals by modulating the sum signals, filtering the modulated signals and remodulating the filtered signals with a second carrier signal train having a frequency which differs from the frequency of the first carrier signal train by a predetermined amount, and filtering the signals resulting from the second modulating step. Frequency shifting on digital information signals is performed by digitally expanding the spectral range of the sum signals to provide a plurality of replicas of the spectral content of the signals distributed over a wide spectral range, digitally filtering the expanded signals to filter out predetermined portions of the expanded range, digitally shifting the frequency of the remaining replicas by a second expansion, and digitally filtering the frequency shifted replicas to filter out unwanted portions of the shifted spectrum.
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