Gretag Aktiengesellschaft

Pierre Schmid

Eduard Brunner

Walter Stofer

Walter R Widmer

Hans-Jorg Klemenz

A method and an installation for masked or scrambled speech transmission utilize a time-scrambling unit for dividing the speech band into at least two sub-bands, for delaying the one sub-band with respect to the other, and for forming an aggregate signal, and a frequency-scrambling unit for dividing the aggregate signal into at least two second sub-bands of variable band-width, for their cyclic interchanging, and for forming a transmission signal capable of being transmitted over a transmission channel, in order to mask not only the sound character of the speech signals but also the speech rhythm, thus ensuring increased privacy of transmission with high code-changing speed and low sensitivity to distortion.

Method and installation for masked speech transmission over a telephone

A system for inserting extra-information bits into a bit sequence to be transmitted over a transmission channel and for suppressing such bits from the transmitted bit sequence, the system having an inserter at the transmitting end and a suppressor at the receiving end, the inserter converting an input bit sequence which it receives at a first repetition frequency into a second repetition frequency which is higher to correspond to the inserted extra bits, by the insertion of m extra bits per m.k.n bits of the input bit sequence k, n and m denoting integers which are greater than zero, the suppressor restoring the original input bit sequence at the first repetition frequency and the extra-information bits from the output bit sequence which it receives from the transmitter at the second repetition frequency, the inserter comprising a first repetition frequency generator which derives the output bit sequence repetition frequency from the input sequence repetition frequency and complies with the condition n.k.gtoreq. 50.

Data transmission system

A method of scrambling and unscrambling speech transmissions by first dividing the speech frequencies into two frequency bands and reversing their order by modulating the speech information, the width of the bands being varied by varying the carrier frequency used in the modulation process, adding to the reversed frequency bands at least one supplementary signal derived from the modulation process and transmitting the resultant signal. The transmitted signal is unscrambled by first subtracting from it a supplementary signal which is generated at the receiving station from the received scrambled signal, the last mentioned supplementary signal being identical to that added to the reversed frequency band signal prior to transmission and then subjecting the resultant signal to the same modulation processes as referred to above to reassemble the frequency bands into a frequency band containing substantially the same speech frequencies as those that are scrambled. Apparatus for carrying out the above method can comprise a separate transmitter and receiver or a single transmitter/receiver whose mode of operation is controlled by a speech key, the transmitter and receiver each including a frequency scrambling device employing modulators and a time scrambling device for generating the supplementary signal.

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Oberweningen, Switzerland

Pierre Schmid