DE569790C - Procedure for the secrecy of electrically transmitted messages - Google Patents

Description

GERMAN EMPIRE

ISSUED ON
FEBRUARY 8, 1933

REICH PATENT OFFICE

PATENT LETTERING

M 569790 CLASS 21 a 2 GROUP 37 ₀₂

Siemens & Halske Akt.-Ges. in Berlin-Siemensstadt *)

Procedure for the secrecy of electrically transmitted messages

Patented in the German Empire on March 1, 1930

There are already methods for keeping electrical messages secret, e.g. B. Language became known in which the frequency range to be transmitted is divided into individual subbands disassembled and the sub-bands in their mutual position interchanged and if necessary, their frequency sequence has been reversed. So was z. B. a voice band broken down into three sub-bands by filters and the sub-bands with auxiliary frequencies like this modulated so that they interchanged their mutual position and, if necessary, their frequency sequence reversed.

The frequency reversal and swapping of the bands were made so that the The width of the entire tape after the conversion was the same as before. The disadvantage This method consisted in dividing the frequency band to be transmitted the edge frequencies of the permeability ranges of the filters are lost through filters. The same disadvantages occur in the previously proposed method with a voiceband division and the individual subbands with different delays subject to secrecy.

Furthermore, information about such procedures for secrecy has already become known, according to which a voice band should be subdivided into sub-bands by filters with the frequency ranges 200 to 800, 800 to 1400 and 1400 to 2000 Hertz. Based on this information, it could perhaps be assumed that the filters are responsible for the separation of the sub-bands should have overlapping permeability areas. The usage However, such a filter per se is not yet able to remove the reduction in intelligibility, even if it does not Frequencies in the transition areas are suppressed because the currents in the overlapping Frequency ranges by the converting devices for secrecy depending on the channel in which they are transmitting will take part in various confidentiality conversions so that these streams after being put together on the Line can no longer be deciphered.

The areas of overlap then not only fall as a contribution to clarity off, but even provide background noise.

According to the invention, these disadvantages in methods for secrecy of electrically transmitted messages, speech or the like, in which the frequency band to be transmitted is divided into individual bands with the aid of filters with a somewhat overlapping permeability range, and in particular the sub-bands are offset from one another or reversed in their frequency sequence or both or also individual sub-bands

*) The patent seeker stated as the inventor:

Dipl.-Ing. Ladislaus Fenyö in Berlin-Siemensstadt.

Claims (1)

are delayed, thereby eliminated that, according to the invention, the sub-bands before they on the common transmission medium, e.g. B. line, are given, moved apart so that they no longer overlap during transmission. The shifting of the frequency bands is expediently done by using modulation an auxiliary frequency. In the case of confidentiality facilities, which with delay of the sub-bands can work, the shifting of the frequency bands before or after the delay circuit lie. If the bands are shifted from one another to maintain secrecy and if the frequency is partially reversed of the ligaments, the displacement of the ligaments is done in a simple manner immediately during the rearrangement. In the figures, the subject matter of the invention is based on an exemplary embodiment are explained in more detail. Fig. Ι shows schematically the conversion of a frequency band known for secrecy, z. B. voice band, in an incomprehensible form. At A , the band to be transmitted is drawn divided into three sub-bands, where the abscissas are the frequencies and the ordinates to identify the sub-bands and the frequency sequence different heights, which z. B. amplitudes are plotted. After conversion by modulation with auxiliary frequencies, the sub-bands are brought into the order shown at B. The bands 2 and 3 have swapped places and 3 also reversed its frequency sequence. When the signs are received in the form of B , the reverse conversion takes place in an analogous manner. Fig. 2 shows the attenuation curves of the three filters used to separate the sub-bands according to the known design shown in Fig. 1. As can be seen from Fig. 2, the frequencies at the edges of the transmission ranges are between 1 and 2, 2 and 3. Due to the lack of these edge frequencies, the intelligibility is of course reduced after deciphering at the receiving station. Fig. 3 now shows schematically the known transmitting and receiving circuits used for frequency conversion AB according to Fig. 1. The sub-band / is sent and received unchanged, for example. The frequency band 2 is offset by the action of the modulator M ₂ and the sideband used is allowed to pass through the filter F ₂ ' . On the receiving side, the frequency band converted in this way is received and fed via the filter F _{2 to} the modulator ^, which converts it back into the original band 2, which is then fed to the subscriber of the receiving station via a filter / ^. Volume 3 is treated in an analogous manner. The effect of the filters and modulators in the previously known device can be seen from Fig. 4. In A , the omission of the edge frequencies is indicated in accordance with the attenuation curves of the sub-filters. At B the converted frequency band is shown in a similar way. In contrast, Figs. 5 and 6 show how the edge frequencies are maintained according to the invention. The permeability range of the filter, F ₂ and F _s is chosen to overlap somewhat according to Fig. 5, as this has perhaps already been done, and the filters F ₂ ' and F ₃ ' are used with approximately the same hole width, but with areas moved apart, as can be seen from Fig. 6. For the modulators ^ and A1 _S , the frequency is also chosen a little differently in order to achieve the desired shifting of the frequency bands. On the receiving side, the reverse conversion takes place, whereby the filters shown in the figure correspond to those of the transmitter station with the same name. The total range of the sub-bands is naturally somewhat larger in B than in A, but this small disadvantage is by far outweighed by the better intelligibility that results from the complete transmission of all frequencies in the range. PATENTANSI'KUCH: Method for the secrecy of electrically transmitted messages, characters or the like, in which the frequency band to be transmitted is divided into individual subbands and in particular the subbands are offset from one another or reversed in their frequency sequence or both or individual subbands are delayed and when the subbands are separated Filters with a somewhat overlapping practical permeability range are used, characterized in that the sub-bands prior to transmission n ₀ to the common medium, e.g. B. the line, preferably by modulation with auxiliary frequencies so far apart that there is no overlap of the sub-bands during transmission. 1 sheet of drawings