James F Buddenhagen

US Patent:

43631274, Dec 7, 1982

Filed:

Jan 12, 1981

Appl. No.:

6/224367

Inventors:

Randall G. Evans - San Jose CA
James F. Buddenhagen - San Jose CA

Assignee:

Ford Aerospace & Communications Corporation - Detroit MI

International Classification:

H03K 1322

US Classification:

375 30

Abstract:

Statistical properties of a signal are used to distinguish between a voice signal and an "on hook" indication on a low bandwidth digital data link. Noise is intentionally added to the voice signal to guarantee a minimum power level, while not disrupting normal demodulation. A digital signal, having a known maximum power level upon demodulation, is used to represent the "on hook" condition. Upon demodulation, the minimum power level of the noise-colored voice signal is greater than the maximum power level of the "on-hook" signal, and the two signals can be distinguished by a power level threshold detector. This apparatus and technique is particularly well-suited to under-sampled, such as CVSD (continuously variable slope delta), data links, which are usually noisy and distorted. It alleviates the need for direct access to the digital link and simplifies the required hardware and retrofit modifications.