NL63459C - - Google Patents

Abstract

582,737. Secret transmission. PATELHOLD PATENTVERWERTUNGS- & ELEKTRO-HOLDING AKT.-GES. April 5, 1944, No. 6377. Convention date, April 5, 1943. [Class 40 (iv)] In a system of secret telephony wherein the speech band is converted into a number of adjacent but transposed sub-bands of which the relative widths are constantly varying, the arrangement is such that at least one subband is inverted and at least one is not inverted. As shown in Fig. 4, the speech band e0 modulates successively a fixed frequency g1 and a varying frequency g2, the lower side-band being selected in each case to give the band e2. This then modulates a pair of frequencies g3, g4 spaced by the width of the band to give an inverted double-band e3 and also another pair of frequencies g5, g6 to give an erect doubleband e5. Complementary portions e4, e6 are selected from these double-bands and combined to form a double-band e7, from which the central portion is taken and shifted to produce a final band e10 comprising four subbands of varying width, two being erect and two inverted. In another arrangement of a similar character, different transpositions of the sub-bands are obtainable by a choice of carrier frequencies at the intermediate modulation stages. One or more of the sub-bands may be retarded ih relation to the remainder of the band ; for example, the selected portion e4 may be retarded by means of a telegraphone before combination with the portion e6. The speech band may be subjected to variable attenuation before scrambling. When the arrangement is applied to a multi-channel system, several speech channels may be grouped together for the purpose of scrambling.