US2124318A - Broadcast system - Google Patents

Description

R. sElDELBAcH 2,124,38

July 19, 1938.

" BROADCAST SYSTEM Filed Mach 31, 193e Patented July 19, 193s V 2,124,318

UNITEDy STATES PATENT oFFicF.

BROADCAST SYSTEM Rudolf Seidelbach, Berlin-Mariendorf, Germany,

assigner to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a German company Application March 31, 1936, Serial No. '71,831 In Germany April 6, 1935 s claims. A(c1. 11s- 2.5)

It is well known in connection with the so Three high frequency transmitters are denoted called subscriber-broadcast to transmit several by I, II, III. By Gn, GT2, GT3 three groups of programmes simultaneously over telephone netsubscriber lines L are designated. In order to works by means of different waves, namely three suit the surge impedance of these lines to the different waves at the present. In order to entransmitter, transformers are used in connection 5, sure a high efficiency of transmission the subwith all the transmitters, the different voltages scrber lines must be subject to certain measures required in accordance with the different wave on the transmitting side. In this connection, lengths being maintained by the transmitters however, difficulties are encountered since the themselves. Group Gm is connected to transsubscriber lines are very different in length. mitter I by a transformer 4. The transmitters 10 There are also difculties due to the number of II, III are likewise connected toy group 'Gl/r1, subscriber lines being liable to variation. In a namely by transformers 5, 6. With respect to practical example of an automatic exchange, the groups GT2, GT3, transformers 1, 8 are pro- 60% of the lines is not longer than 3 kilometers vided. Connected in parallel with the transand 30% not longer than 5 kilometers, the reformers 1, 1', 8 are potentiometers 9, I0, 9', I0', 15

mainder varying between 5 and 15 kilometers in II, I2. The potentials derived from 9, I0, 9' IU', length. In such case the measure to which the II, I2 are conveyed to additional high frequency lines are subject may consist in combining them ampliers I5, I6 to which the groups Grz, Gra are to form groups in accordance with these lengths attached by transformers I3, I4. The connecand to connect them in parallel on the exchange tions between potentiometers 9', IIJ' and ampli- 20 side and further to employ transformers for coufiers I5, I6 are not shown in the drawing. These pling them to the transmitting arrangement. potentiometers, however, are assumed to be con- The primaries of such transformers may be connected in the same manner as potentiometers 9, nected in series to the high frequency generator. I0. The input circuits of the amplifiers I5, I6

The disadvantage of this arrangement is that a are connected to the transmitters II, III by 25 mutual independency of the groups cannot be means of the transformers 1, 8 and potentiomattained. On the contrary, variations of the eters 9 to I2, and in such a manner that the voltsurge impedance of one group or other will influf ages required for the respective wave lengths ence the surge impedance of the other groups, are produced. The surge impedance of the lines this being troublesome especially if the number L in this case is rendered suitable by means of 30 of subscribers, that is, the numberA of connected the transformers I3, I4 which are located in the lines is Afrequently varied. The simplest way output of the amplifiers I5, I6. By I1, I8 filters would be to combine the lines to form groups are denoted. and then to make vthese groups equal to each The advantage of the novel circuit arrangeother by arranging artificial means of attentua' ment is that no energy losses occur and that the 35 tion. AThis lmode however Would entail that regulation of the surge impedance of the several very much energy would be destroyed. For, as groups of lines has no influence on the surge will be seen from the numerical example before impedance of other groups. stated, most of the subscriber stations are com- For the sake of clearness the arrangement 4,0 paratively near to the telephone exchange. The represented nearly contains thevhigh frequency attenuation of all these lines would have to be portion, that is, does not contain the low freaugmented to be of the same value as the attenquency exchange portion and the like. The high uation of the longest subscriber line connected frequency exchange arrangement, and the 10W t0 the exchange, a mOde Which 0f COUTS@ Would frequent one are separated from each other by 1'1V01Ve a great 1055 0f energyfilters in a manner well known in itself. The 45 In Order t0 avoid these dSadVantageS the in* respective details need not be described here vention proposes to combine the subscriber lines Since they are known per se,

to form groups in the manner indicated and to what 1e Claimed is; allot additional high frequency amplifiers to such 1 A broadcast system Comprising e, plurality 5o groups. of high frequency transmitters, a plurality of 50 The invention is described hereafter with ref- Subscribers lines Combined to ferm groups haverence t0 the aCCOmpanyng drawing in Which ing comparatively similar lengths and impedby Way Of exemple a circuit arrangement is ances, a separatel coupling path between each of shown Which iS adapted fOr effecting the these groups and said plurality of transmitters,

invention. an individual amplifying device connected in one 55 or more of said separate paths whereby a desired intensity of signal is produced at the far end of every line, and impedance matching means between said transmitters and said lines.

2. In a wired program broadcast system, a plurality of high frequency transmitters, a plurality of subscribers lines of dierent characteristics associated in groups, within each of which, the lines are of substantially similar characteristics, an individual coupling path from said plurality of transmitters to one of said groups of lines, further individual coupling paths fromv said plurality of transmitters to each other group of lines, impedance matching means in each of said paths and an individual amplifier connected in each one of said further paths and adapted to amplify the power in said one of said paths to such a level relative to the power in the other paths, that the resulting power transmitted to the ends of all lines is substantially the same.

3. AV system according to claim 1, further comprising potentiometers disposed between said individual amplifying devices and said transmitters.

4. A system according to claim 1, wherein the output circuit of said individual amplifying devices is suited to the surge impedance of the subscriber lines.

5. A system according to claim 1, further comprising filters adapted to prevent high frequency energy from passing from one transmitter to another.

6. In a broadcast system the combination of high frequency transmitters with telephonesubscriber lines combined to form groups having comparatively similar lengths and impedances, means connecting these groups to said transmitters, a high frequency amplifier individually coupled toeach one of said groups, an additional group of telephone-subscriber lines fed directly from said transmitters Without the interposition of such an individual amplier, connections from one or more of said high frequency transmitters to the latter group, and means for matching the output circuits of these transmitters to the surge impedance of said last mentioned group of lines.

RUDOLF SEIDELBACH.

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