US1987961A - Multiple transmitting system - Google Patents

Description

MULTIPLE} TRANSMITTING SYSTEM Filed Jan. 14, 1932 M. LANGER W. RABANUS A TTORNEY IN VE N TORS Patented Jan. 15, 1935 UNITED STATES signers to Siemens and Halske Aktiengeselb schaft, Siemensstadt', near Berlin, Germany, a

company of Germany Application January 14, 1932, Serial mama In Germany January 20, I931 p Y 11 Claims. (Cl. 179-78) The invention relates to-amethod of reducingthe cross-talk in multiple lines in which'several lines carry the same signals. Such multiple transmission (news, music, picture signals) may have the advantage that the disturbance or the transmission on one line, such as an interruption or short circuit of the line, does not disturb the transmission on the other lines. Other cases frequently occurring represent the broadcasting systems (wired wireless) common cable or on the same or adjacent carriers, then as soon as voice currents flow in one or more of these lines hereafter referred to as disturbing lines, noise potentials are induced in the other lines hereafter referred to as the disturbed lines, the occurrence of which is known as cross-talk. The greater the amplitudes of these voice currents the greater will be the crossgo talk disturbance. A certain potential level must therefore not be exceeded in the disturbing lines which carry the voice currents, so that noise or cross-talk potentials will remain below the maximum allowable value or limit in the disturbed lines. However, the level of the crosstalk in the disturbed lines rises only to a small extent if severalv disturbing lines are carrying various textssimultaneously instead of one line, since in the individual disturbing lines the peaks of the disturbing potentials occur at different times. a a

It is a different matter, however, if a plurality of disturbing lines are simultaneously carrying the same text, a case which occurs particularly fregrams (music transmission). Here the disturb ing potentials occurring simultaneously through the transmission of the same broadcast performances in adjacent lines, for example of the same noise or cross-talk potential will not be exceeded in the disturbed lines. The reduction of amplitude, however, may be of great disadvantage for the transmission or the performances, since it reduces the ratio of the program transmission level to the noise level of the line.

In accordance with the pres'entinvention the reduction 01' the amplitudes is avoided by the fact that the transmission of the same texts takes place in the individual disturbing lines or groups of lines with a phase displacement.

. For example, it is possible to displace the dis If a number of telephone lines are laid in aquently in the transmission of broadcast pro nothing. came a as i ai ntiaitaesfwan lie; spect to each other in phase electrically or by, very slightamountsof time, inwhich the oscil'1a-.

tions arestill quasi-stationary, so thatthe potentials induced in the, disturbed wires by the adjacent disturbing wires for the mostpart are cancelled in their total effect onaccount otthe mutual phase displacement. Thesmall; tempo; rary displacement may for example, beoi great,

advantage for telegraphy (direct current,.-impulse oralternating current and also infra low frequency telegraphy). Speech ,and music in which small interferences arequasi-stationary,

are also. fieldsptapplication. 3

Another embodiment of theinventive idea may consist in the fact thatdisplacements take place in the individual wires in suchspacesof time that difierent texts, that; iszthe multiple transmissions;

efi'ected, for. example, broadcasttransmissions,

may take place with undiminished-amplitude;

A further advantage of the method inaccordance with the invention that-the cross-talk occurring is unintelligible, I which is veryimuch to be desired from the point of viewoi secrecy. The line level may. also bev rendered dependent only upon the noise level, so the noise level may be permitted tobe higher. p

The invention may be-more-iully understood b referringto the drawing of which:

Fig. 1 illustrates oneembodiment of the invention in which the phases of the disturbing cur rents in the various lines are reversed.

Fig. 2 illustrates another-embodiment of the in. vention in -which the'disturbing, currents are TENT FF-IC transmitted to groups of lines with a time .dis-.

placement.

Fig. 3 shows still another embodiment of the invention employing electrical networks to secure different time delaysin .the disturbingcurrents transmitted to the various linesof the group.

Fig. 1 shows the arrangementin which the energy to be distributed on the cable at l is conveyed to a transformer 2.from whose secondary side two pairsof bus-bars3, 4 are branched off, whose potentials for all the frequencies are displaced in phase by 180. Now if one or more lines such as 11 and 13 of cable 16 are connected to the pair ofbus bars 3. (as shown) they will each induce cross-talkin. other adjacent: lines such, as 15 which. will add directly and give risetothe sum of the cross-talk produced by each of the lines ll or13 alone- Similarly, one or more lines 12 and 14 connected to bus bars 4 will induce crosstalk in the disturbed circuits 15 which are shown connected to other apparatus 18. This cross-talk will be the sum of that induced by each of the lines 12 or 14 alone. .However, since the currents in lines 11 and'13 connected to bus bars 3 are Just opposite to or 180 out of phase with the currents in lines 12 and 14 connected to bus bars 4, the cross-talk current induced by these two groups of lines 11 and 13, and 12 and 14 in the disturbed circuits or lines 15 will also be opposite in phase and therefore will tend toneutralize each other. The resultant cross-talk induced in adjacent circuits or lines 15 from a plurality of disturbing lines or circuits all simultaneously carrying the same signal is thus reduced without reducing the currents in the individual disturbing circuits which are all carrying the same signal.

The cross-talk induced in adjacent circuits may be further reduced by uniformly distributing the lines which are simultaneously carrying the same signal between bus bars 3 and 4 so that approximately the same number of lines are carrying the same message currents with a 180 phase displacement as without this phase displacement. In addition, these lines carrying the same currents may be uniformly distributed throughout cable 16 so that any of the disturbed or adjacent lines 15 will be approximately as close to a line connected to bus bars 3 as to a line connected to bus bars 4. In this manner the resultant crosstalk included in any of these adjacent lines will be substantially neutralized.

It is to be understood that :the cross-sectioned portion of the cable 16 represented by 17 in the drawing is composed of other lines similar to 11, 12, 13, 14 and 15. These lines may be either connected to other equipment such as 18, or evenly distributed between bus bars 3 and 4. However, they have not been individually shown, but rather shown in cross-section so that the distribution of the typical lines illustrated may be easily and clearly shown.

Fig. 2 shows an arrangement of the second type, in which greater temporary phase displacements are obtained by using, for example, a common steel wire of a telegraphone carrying the broadcast transmission currents to magnetic recording device 5. Telegraphone pick-up devices, for example, 6-9, spacially separated from each other lead to diiferent lines or bus bars. In case there are only a small number of lines simultaneously transmitting the same message currents it would probably be desirable to provide a pick-up device for each individual line. However, in the case of a very large number of lines simultaneously transmitting the same message currents, it would be desirable to divide these lines into groups, each group being connected to bus bars which are supplied from an individual pick-up device. Thus, the signals which comprise the entire message as transmitted over each of the different lines or groups of lines are displaced by small time intervals so that the peaks of the signal currents in the different groups do not occur simultaneously. Then the total cross-talk induced in disturbed circuits is not the numerical sum of the instantaneous cross-talk currents induced by each of the disturbing circuits. In this manner multiple transmission may be efiected with a normal level of current'in each of the disturbing circuits or lines without increasing the cross-talk induced in the disturbed circuits or lines above the level encountered when the disturbing circuits are all carrying diiierent signals simultaneously. A special recording device 10 would be provided to remove the magnetism of the steel wire produced by the signals when the wire passes recording device 5.

Instead of using the steel wire greater time retardations may be obtained by apparatus such, for example, as that shown in Fig. 3 in which electrical delay networks K are provided. In order a that a uniform delay of the total voice frequency band may take place, the delay networks may be formed by the series connection of an artificial cable with a phase balancing circuit. Details of representative delay networks and circuit arrangements suitable for use in these circuits may be found in the disclosures of the following U. S. patents; H. Nyquist, 1,607,687, November 23, 1926, H. Nyquist, 1,770,422, July 15, 1930, H. W. Bode, 1,828.454, October 20, 1931.

As illustrated in Fig. 3, the source of the sig .nals to be distributed is connected to bus bars I to which a group of lines illustrated by lines 19 and 20' are connected as well as a group of current delay devices two of which are illustrated by delay network K which are represented in Fig. 3' at 25 and 26. These networks 25 and 26 delay the entire frequency band which is transmitted by different amounts. The outputs of these delay networksare connected through amplifiers V to compensate for the attenuation of these networks and are shown diagrammatically at 27 and 28 in Fig. 3. The outputs of these amplifiers are connected to other bus bars II and III respectively. Connected to each of these bus bars is a group of lines, two of which are shown for purposes of il lustration in Fig. 3 which are 21 and 22, and 23 and 24, respectively. As described above, these lines may also be distributed throughout the cable. This is illustrated in the figure in which only a few of the lines of cable 16 are individually shown in order that the distribution may be clearly illustrated. Furthermore, it is an advantage to evenly distribute the line carrying the same current evenly between the bus bars as shown in Fig. 3 in which two lines are connected to each of the bus bars.

The invention is of particular importance for broadcasting systems. In order that the lines which are not employed for broadcasting but for telephony may have the smallest possible crosstalk, it is necessary to have as uniform as possible a distribution of the texts transmitted with different phase over the subscribers lines.

What is claimed is:

1. Means for reducing the cross-talk in multiple lines several lines of which carry the same message, comprising a telegraphone, several pickup heads associated therewith and so related that they each receive the entire message with a slightly different time displacement, each of said pickup heads being connected to one or more lines of the several lines.

2. A method of reducing cross-talk in a multiple transmission system wherein the same message is simultaneously transmitted over a group of adjacent transmission lines, which comprises, transmitting the entire message over each individual line of the group of lines with a different phase displacement.

3. A method in accordance with claim 2, characterized in this that both the fundamental and over tones of the entire message as transmitted by the individual lines are displaced by the same phase angle.

4. A method according to claim 2 in which the entire message is transmitted over each line of the group of lines with a different time displacement.

5. A method in accordance with claim 2, particularly for broadcasting, characterized in this, that the phase displaced messages are uniformly distributed to the individual lines of the group 7 of lines transmitting the same message.

6. The method of reducing cross-talk disturbances in a multiple transmission system in which the same message is simultaneously transmitted over a plurality of groups of adjacent transmission lines, characterized in this that the entire message is transmitted over each group of lines with a different phase displacement;

'7. The method of reducing cross-talk disturbances in a multiple broadcasting system in which the same message is simultaneously transmitted over a plurality of adjacent groups of transmission lines in a cable, comprising transmitting the entire message over each group of lines with a different time displacement and uniformly distributing the group of lines transmitting these time displaced messages through the cable.

8. In an electrical communication system comprising a source of message currents, a plurality of adjacent transmission lines, a group of current delay devices connected to said source of message currents and to a group of said transmission lines, the method of reducing the cross-talk induced from said group of lines into the other adjacent lines which comprises transmitting all the message currents over each transmission line of said group of lines with a different delay.

9. In an electrical communication system comprising a source of message currents, an electrical communication cable comprising a plurality of adjacent transmission lines, a group of current delay devices each connected between a group of said transmission lines and said source of message currents, a method of reducing the cross-talk between said groups of lines and the remainder of the lines of said cable which comprises transmitting all the message currents over each line of said group of lines and delaying the message currents transmitted to said lines a different amount.

10. In an electrical communication system comprising a source of message currents, an electrical communication cable comprising a plurality of adjacent transmission lines, a group of current delay devices each connected between a group of said transmission lines and said source of message currents, a method of reducing the cross-talk between said groups of lines and the remainder of the lines of said cable which comprises transmitting the message currents over each group of lines with a different delay and uniformly distributing the lines of said groups of lines throughout said cable.

11. In a communication system, comprising a. plurality of adjacent transmission lines, several lines of which carry the same message currents, means for reducing the cross-talk between the several lines carrying the same message current and the remainder of the lines of said transmission lines which comprises electrical delay networks and repeaters so designed and so connected to the several lines that the entire message will be transmitted over each of the several lines with a slightly difierent time displacement.

MAX LANGER. WILHELM RABANUS.

Images