US2803704A - Electrical repeating method and apparatus - Google Patents

Description

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g- 1957 J. GRAMBOW ET AL 2,803,704

ELECTRICAL REPEATING METHOD AND APPARATUS Filed July 11, 1955 4 Sheets-Sheet l DISTRIBUTOR EXCHA NGE I'm/enters w;- WM ssmgg Aug. 20, 1957 J. GRAMBOW ETAL ELECTRICAL REPEATING METHOD ANQ APPARATUS Filed July 11, 1955 4 Sheets-Sheet 2 b y Wmdmu s Srmm Z 1957 J. GRAMBOW EIAL 2,803,704

ELECTRICAL REPEATING METHOD AND APPARATUS Filed July 11, 1955 4 Sheets-Sheet 5 LOUDSPEAKER v A MPL/ TUDE REGULATOR To 54 REGULATOR o o u o n 53 55 55 MAIN TUNED MAIN CIRCUIT TUNED CIRCUIT I I. I g INPUT rurvso 57 CIRCUIT 9W5 57 52 .5 3 ICIRCU/T ggl gzzz I Inventors: Jaewhhn Grambow E wmd I Negev ELECTRICAL REPEATING METHOD AND APPARATUS Filed. July 11, 1955 71957 J. GRAMBOW ET AL 4 Sheets-Sheet 4 Inventors:

J cucha m G-rm United States Patent ELECTRICAL REPEATING METHOD AND APPARATUS Joachim Grambow, Eutingen, Baden, and Ewald Rieger, Villingen, Black Forest, Germany, assignors to Saba August Schwer Siihne G. in. b. H., Villingen, Black Forest, Germany Application July 11, 1955, Serial No. 521,322 Claims priority, application Germany July 9, 1954 5 Claims. (Cl. 179-15) The present invention relates to a new and improved electrical repeating method and apparatus. More particularly, the present invention relates to a new and improved electrical repeating method and apparatus for receiving and simultaneously transmitting electrical transmissions in the communication or broadcasting art.

In order to distribute received wireless transmissions in the communication or broadcasting art, it is known to use electrical repeating apparatus which transmits these received electrical transmissions over different conductors to remotely located subscribers desiring to receive the electrical transmissions. Such repeating apparatus is used, for example, in the television art where one community television antenna placed on a high mast receives the transmitted audio and video signals. Repeating apparatus at the community antenna then retransmits the received electrical transmissions over a plurality of conductors to remote subscribers.

These electrical transmissions may be directly monitored in the lower frequency range, for example, by means of loudspeakers, earphones or other types of acoustic reproducers. However, there are several disadvantages in conventional types of apparatus. One disadvantage is that the number of electrical conductors between the distributing central exchange and each of the subscribers must correspond to the number of electrical transmissions to be distributed. In addition, the quality of the reproducing apparatus and particularly the fidelity of reproduction of the electrical transmission cannot be made sufficiently high.

In order to faithfully reproduce the electrical transmission, the reproducing apparatus must be capable of reproducing a wide band of frequencies. In the broadcasting art this band of frequencies corresponds to about 15,000 cycles per second. In the conventional repeating methods and apparatus, due to the unavoidable capacity and damping introduced by the electrical conductors between the repeating apparatus and the remote subscriber, the high frequency portions of the received message are unnaturally, strongly, attenuated.

On the other hand, the present invention provides a new and improved repeating method and apparatus for receiving and simultaneously distributing electrical transmissions in the communication and broadcasting field wherein difierent types of transmissions can be simultaneously transmitted to a desired number of subscribers for listening, or to be visually displayed on the screens of cathode ray tubes for use in television. The present invention also preferably uses existing conductors such as telephone cables which serve other purposes without affecting the normal usage of these existing conductors.

It is accordingly an object of the present invention to provide a new and improved repeating method and apparatus for receiving and distributingelectrical transmissions in the communications field.

Another object of the present inventionis to. provide a new and improved method and apparatus for receiving and distributing electrical transmissions by using existing ICC 2 conductors between the distributing station and the subscn'ber who is to receive the transmission.

A further object of the present invention is to provide a new and improved repeating method and apparatus for receiving and distributing electrical transmissions to desired subscribers either for aural or visual reproduction.

Still another object of the present invention is to provide a new and improved repeating method and apparatus which transmits a plurality of received electrical transmissions over a single existing conductor which may simultaneously be used for other purposes.

With the above objects in view, the present invention mainly consists of a repeating apparatus adapted to receive a plurality of electrical transmissions and dis tribute the same to a plurality of remote subscribers, and including a plurality of receiving means, each of the receiving means being adapted to receive a different one of the plurality .of electrical transmissions; a plurality of modulating means, each of the modulating means being connected respectively to one of the receiving means and adapted to modulate the electrical transmission received by its respective receiving means, .a plurality of electrical conductors connected between the modulating means and the plurality of remote subscribers, each of the plurality of electrical conductors having one of its ends connected respectively to the plurality of modulating means and its other end connected respectively to one of the plurality of remote subscribers to transmit the modulated electrical transmissions to the remote subscribers, a plurality of groups of selecting means, each group of selecting means being located at one of the remote subscribers respectively and being connected respectively to the other end of the electrical conductor connected to the respective subscriber for selecting at least one of the transmitted, modulated, electrical transmissions to be received by the respective subscriber, a plurality of groups of detectors, each group of detectors being connected respec tively to one of the groups of selecting means for demodulating the transmitted, modulated, electrical transmission selected by its respective group of selecting means, and means respectively located at each of the remote subscribers for reproducing a selected, demodulated, electrical transmission.

The present invention also includes a method for receiving a plurality of electrical transmission and distributing the same to a plurality of remote subscribers and including the steps of receiving each of the plurality of electrical transmissions by means of a respectively different receiver, transferring each of the received electrical transmissions into respectively different frequency channels, transmitting each of the frequency transferred electrical transmissions over at least one electrical conductor to at least one of the remote subscribers, selecting, at the one of the remote subscribers, one of the frequency transferred electrical transmissions transmitted thereto; retransferring the selected one of the transmitted electricaltransmissions back into its original frequency channel, and reproducing at the one of the remote subscribers the retransferred, selected electrical transmission.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both asto its construction and its method of operation, together with additional objects and advantages thereof, will .be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which: I

Fig. 1 is an electrical schematic diagram of a central distributing exchange incorporating the principles of the present invention;

Fig. 2 is a perspective view of a program distributor constructed in accordance with the present invention;

Fig. 3 is a diagrammatic representation of a selecting and detecting apparatus constructed in accordance with the present invention and which is located at the subscriber; v

Fig. 4 is a perspective view of the receiving apparatus located at the site of the remote subscriber; and.

Fig. 5 is a perspective view of the receiver of Fig. 4 mounted on a piece of furniture 1 Referring now to the figures and more particularly to Fig. 1, for the purposes of explaining the present invention, it is assumed that five differentelectrical transmissions are to be received and distributed by apparatus incorporating the present invention and in accordance with the method thereof. These five transmissions may be radio or television programs which have been transmitted into space by the conventionalradio or television transmitter. In accordance with.the present invention these five transmissions are modulated respectively by different high frequency carrier signals, for example, 1.70 megacycles; 1.85 megacycles; 2.00 megacyclesg, 2.15 megacycles ad 2.30 megacycles which lie below the conventional medium-wave broadcast band.

In Fig. 1 it can be seen that the central exchange for the repeating apparatus constructed in accordance with the principles of the present invention can be constructed in the form of a plurality of several similar units indicated by the numerals 1, 2, 3, 4. and 5, respectively. Each unit contains a receiver and modulator which may bequartzcontrolled for accurate tuning to the electrical transmission to be received and also contains a one-stage amplifiera The dotted lines in Fig. 1 indicate separate units for each of the reception and modulation frequencies. The terminals a, b, c, d and e represent the respective inputs to the repeating apparatus and may be antennas for the five electrical transmissions to be received.

The five units 1-5 form a distributor exchange which can be located in a telephone central exchange or in a private branch telephone exchange such as used in a hotel. Each of the units receives an electrical transmission and transfers it into a difierent frequency channel, as indicated above, for example, by modulating the same. The adjacent frequency channels into which the transmissions are transferred are preferably 150 kilocycles apart for the medium-wave broadcasting range.

\ It can be seen that the outputs of the amplifiers of units 1-5 are connected in series and to a cable 6 which is connected between the amplifier of unit 1 and the amplifier of unit 5. The high frequency distribution-of the transferred transmissions emanating from the units 1-5 are carried out by means of the cable 6 the other end of which is connected to paralleled transformers 7, 8, 9, 10 and 11. If the cable 6 is a lead coveredtwo-conductor telephone cable having a characteristic impedance of 100 ohms, the transformers 7-11 are arranged so that the input impedance of the primary windings of the transformers has a corresponding characteristic impedance of 100 ohms.

If there are 500 subscribers connected to the central exchange, these subscribers can be broken down into five groups of 100 each so that the five transmitting systems 7-11 are sufficient. Since the primary windings of the five transformers are connected in parallel and they must have an input impedance of 100 ohms, it is apparent that the input impedance of each of the primary windings must be 500 ohms.

The secondary windings of the transformer systems 7-11 are connected respectively to busbars 12, 12, 12", 12", and 12. The output impedance of each of the secondary windings should be equal to 1 ohm so that the 100 subscribers, connected to each of the busbars, may be connected by means of a lead covered two-conductor telephone cable having a characteristic impedance of 100 ohms. That is, the conductors of the 100 subscribers will all be connected in parallel to their respective busbar and have a combined impedance of 1 ohm.

The telephone cable of the first subscriber is connected to the busbar 12 by means of a high-pass filter 13 constructed of two capacitors. The telephone cable of the second subscriber is connected to the busbar 12 by means of a high-pass filter 14. Similarly, the remaining 98 subscribers connected to the busbar 12, each have their respective telephone cable connected to the busbar 12 through a respective high-pass filter consisting of two capacitors.

The busbar 12' is similarly connected to subscribers 101-200; the busbar 12" to subscribers 201-300; the busbar 12" to subscribers 301-400; and the busbar 12" to subscribers 401-500.

The advantageous arrangement of the present invention is further illustrated in Fig. 1 for only one subscriber. But it should be appreciated that similar apparatus can be arranged at each of the subscribers connected to the busbars. Accordingly, the telephone cable 17 is shown connected to the output of the high-pass filter 13. The normal telephone conversation between the telephone exchange and the subscriber is carried by the telephone'conductor 17. For this purpose the low-pass filter 16 is connected between the cable 17 and the automatic equipment in the telephone exchange. The low-pass filter 18 is connected at the subscribers end between the telephone cable 17 and the subscribers telephone equipment.

The low- pass filters 16 and 18 can be made out of inductors and capacitors and have the overall dimensions of a match box so that they can be made very economically and may easily be positioned at the telephone exchange and at the subscribers telephone apparatus. The low- pass filters 16 and 18 serve to prevent the high frequency used for the transmission of the broadcast transmissions from interfering with the normal telephone conversation carried on over the cable 17.

Similarly, the high-pass filter 13 on the distributing side of the cable 17 permits the distribution of one or more transmissions or programs to a single subscriber. The high-pass filter 19 is located at the subscribers end of the telephone cable 17 to prevent the low frequencies of the telephone conversation from affecting the reproduction of the program to be received.

A shielded two conductor cable 20 is connected between the hig'h-pass filter 19 and the receiving apparatus 21 located at the subscribers end. The input to the receiver 21 and the cable 20 are shielded and connected to ground to prevent any unwanted electrical disturbances from affecting the reproduction of the program. In this manner any cross-talk from the subscribers 2-100, who are also connected to the busbar 12, is avoided. In addition, since the secondary winding of the transformer 7 has an impedance of only 1 ohm, this acts as an effective shortcircuit for any unwanted cross-talk.

The program selection is carried out inthe receive apparatus 21 by the operation of program keys which are illustrated in Fig. l as five switch pairs connected respectively on opposite sides of five respective transformers. For a desired program afixed predetermined tuned circuit is switched in by the corresponding program key. Across the output terminals 22 of the receiver apparatus 21 is connected conventional tunedradio-frequency (TRF) receiving circuits which will be' described further with respect to Fig. 3. These conventional units contain amplifiers and demodulators for receiving the transmitted program. 7

Referring now to Fig. 2 a program distributor is shown mounted on a control console. On the control console is mounted apparatus adapted to receive electrical transmissions or programs which have been transmitted in the usual wireless fashion. Also mounted on the control console is apparatus. adapted to transmit these received messages or programs over conductors to one or more subscribers.

The control console has mounted thereon five receivers 34, 35, 36, 3'7 and 38 which are adapted to receive'respectively the five programs a, b, c, d and e. The control console is provided with a key operated selecting and distributing member 33 for selecting and distributing the broadcast programs.

A plurality of the received programs may be simultaneously transmitted over the telephone cable, after modulation, so that a subscriber may choose any one of the programs which he desires. For the period during which the receivers are tuned in to the transmitters transmitting the programs, the receivers in the control console are separated from the cable of the subscriber circuit so that the adjustments made at the console are not heard at the subscribers location. When such adjust ments are going on it is possible, by means of signal, to indicate to the subscribers receiving apparatus, that the particular frequency channel is undergoing adjustment. Such a signal may be a red light, for example, which indicates to the subscriber that the particular key at the subscribers end, controlling the channel under adjustment, has been separated from the distributing apparatus.

The member 33 contains a plurality of keys 45 which may operate various apparatus located in the control console. For example, it may arrange anyone of the receivers 34-438 to operate in any one of several different frequency ranges, namely long wave, medium wave, short wave, or ultra-short wave. These keys may also connect the magnetic tape recorder 40 to one of the receivers so that the program being received by this receiver may be recorded on magnetic tape. Similarly one of these keys may connect one of the receivers to the disc recording apparatus 42 so that the program being received by this receiver may be recorded on a disc. Also, a desired received program may be connected to the loudspeaker 39 for checking the quality, intensity and the timbre of the program being transmitted to the subscriber. In addition, programs recorded on the magnetic tape or on the disc may be distributed to the subscribers.

Each key of the group of keys 45 is connected to a particular receiver chassis of the receivers 34-38. The group of keys 46 located in the distributor member 33 permit the examination of the high frequency-modulated program being transmitted to the subscribers. These keys '46 permit such examination to be made without interfering with the subscribers reception. Each key 46 of a respective frequency carrier channel corresponds to a key in the group of keys 46 so that by a proper operation of these keys, any one of the receivers 34-48 may be monitored.

In the example chosen for the present application, since there are five program channels, there are correspondingly five keys 45 and five keys 46. In addition a releasing key 45' is provided for the keys 45 and a releasing key 46 is provided for the keys 46. The re leasing key 45 disconnects the program from the subscribers line while the releasing key 46' only disconnects the control apparatus for carrying out the modulation. Each of the receivers 34-38 and the selecting distributing member 33 have control indicators as shown at 47 in member 33, which may be in the form of a magic eye tube. Also provided on the member 33 is a volume control 48 and a tone control 49 which can be used for controlling the volume and tone of the programs being transmitted over the cables to the subscriber.

The key connections are so arranged, that by operating one key of the group 45 or 46, not only the key itself is operated, but also the corresponding receiver is indicated for example, by illuminating the key and scale of the receiver in red.

If now, the release key 45 is depressed, the depressed key of the group of keys 45 is released and the red illumination disappears from the corresponding receiver. Therefore the subscriber receives the particular program in the proper frequency channel since the corresponding 6 receiver chassis is connected to the modulator and the received program is transferred to the proper high frequency channel. At this time, the receiver indicates in the usual manner on the scale indicator such as the magic eye 34 and 35.

In order to check the quality, amplitude and timbre of the program channels corresponding to the received programs, a key of the group of keys 46 can be depressed for the particular channel, whereby without disturbing the reception of the program by the subscriber, the characteristics of the program being sent to the subscriber can be checked. By operating the releasing key 46', the controls can again be disconnected. For checking purposes by means of the keys 46, the scale illuminations of the corresponding receivers 3448, are again switched into the control position.

In a particularly simple manner these operations can be carried out at the control console 31 which operates as a selecting, distributing and testing apparatus for the received programs and for the transmitted high frequency program channels whereby desired selection for a single channel can be made in the central exchange. These selections can include programs being broadcast by wireless transmissions, messages recorded on magnetic tape or phonographs and also programs originating at the console by means of a microphone.

In the arrangement shown in Fig. 2 a desk-shape is provided for the arrangement in accordance with the invention whereby the selecting and distributing member 33 is located in the center of the console 32 on a control table 31. The receiver apparatus 34--33 are arranged about the selecting and distributing members 33. The various operating controls such as the keys and the scales of the various instruments are arranged within easy reach and sight of the control console operator.

Referring now to Fig. 3 the diagrammatic representation of the receiving apparatus located at the site of the subscriber is shown. The input to the receiver is applied to a shielded two-conductor cable 51 which is adapted to be connected to the output terminals 22 of Fig. 1. For use in this type of receiver, it is particularly advantageous to use a tuned-radio-frequency circuit in the form of a two-circuit receiver, as illustrated, for the distribution of different transmitted programs.

The modulated electrical transmissions arrive at the receiving apparatus by means of frequency dividers where by means of mechanical contractors (see 21 in Fig. 1), a particular electrical transmission is chosen by means of fixed tuned circuits. By means of conventional program switching apparatus, advantageously, by using conventional push-button switches, each push-button is arranged to a particular contact so that in Fig. 3 the first program button operates the contacts 52', 52", 52", etc. up to 52. Also other push-buttons can operate the illustrated contacts 53-53"" and 54'54"". Also, by means of these contacts, for each corresponding program channel, the fixed high frequency tuned circuit is switched 1n.

Therefore, for example, in channel I the input circuit 55 with its input coupling and the main circuit 56 with its input coupling can be operated by means of the various contacts 52'-52' for the desired example of a two-circuit TRF receiver. Similarly, the contacts 5353"' in channel II and the contacts 54-54 in channel III can be operated to properly connect the respective input and main circuits such as the illustrated input circuit 57 and main circuit 58.

In Fig. 3 three channels are illustrated but it is apparent that many more channels may be provided as desired. Such additional channels are diagrammatically illustrated by the dots adjacent the switch members 53.

The tuned circuits 55 and 56 may be arranged so that only the inductances are switched in by the pushbutton switches. Therefore all of the input circuits of each of the channels can utilize a fixed tuned circuit capacitor 59 and all of the main circuits can utilize a fixed capacitor 60. Accordingly, by simply operating the switching means, the tuned circuits of the different program channels may be provided so that all the programs are received with similar characteristics. That is, with the same amplitude, quality and timbre. when the push-buttons are operated to switch from one received program to another, the amplitude and timbre of the received program remains the same.

The input circuit 55 in channel I is connected to the main circuit 56 by means of a high frequency amplifier 61. The amplified high frequency emitted from the main circuit 56 is demodulated by a low frequency plate-current detector 62, so that the audio frequencies contained in the received program are available. The utilized voltage corresponding to the maximum permissible amplitude of the audio frequencies is adjusted by means of the regulating members 63. In addition the tone and amplitude may be further regulated by the subscriber by means of regulating members 64 and 65. The loudspeaker 66 is connected to the output of the regulating member 45.

It can be seen that the apparatus located at the subscriber is quite simple and merely includes several similar channels, each of the channels having a respective tuned-radio-frequency circuit for receiving the modulated radio programs transmitted over the telephone cable and for demodulating the same.

The demodulated radio programs can then be heard over the loudspeaker 66 in Fig. 2. In this manner the subscriber has a choice of any one of a plurality of electrical transmissions. It is clear that a cathode ray tube with its attendant operating circuits may also be provided at the subscriber so that a distributed television program may be displayed.

It should be clear that with the present invention the apparatus located at the site of the subscriber is quite simple. A low-pass filter is provided at the telephone of the subscriber so that he may carry on telephone conversations in the usual manner. A high-pass filter is also provided at the telephone cable and is connected to the receiving apparatus. The receiving apparatus is of the simple tuned-radio-frequency type so that it requires no complicated mixing circuits such as are used with superheterodyne receivers. Therefore, simple push button tuning may be provided for selecting the program to which the subscriber desires to listen. It is clear that such apparatus may be provided in hotel rooms, for example, thereby providing the user with a wide selection of radio or television programs without high initial expense to the hotel.

The apparatus located at the repeating station is also relatively simple. If the repeating station or exchange is located at the central ofiice of the telephone exchange, the repeating apparatus may be simply isolated from the automatic equipment of the telephone exchange by the use of low-pass filters. This equipment may also be housed in a control console which occupies relatively little space and which permits the carrying out of all the necessary monitoring functions. It is clear that if television programs are to be received and distributed, a cathode ray tube may be provided at the control console.

Referring now to Fig. 4, a perspective view of the receiving apparatus is provided. The tuned-radio-frequency circuits are located within the housing 7t and the apparatus may be mounted by means of the flanges 71 and 72. The numeral '77 indicates a screw adjustable potentiometer with which the maximum amplitude of the sound may be adjusted and which is set once when the set is installed. The knobs '74 and 75 may be used for regulating the amplitude of the sound and the tone thereof. The push buttons 73 can be used for switching in the desired program and the push button 76 can be used as an on-off switch.

in Fig. the apparatus shown in Fig. 4 is illustrated mounted within a piece of furniture, This piece of Accordingly,

furniture can thereby serve more than one purpose in a hotel room, for example. That is, the furniture may serve, simultaneously, as a chest of drawers and as a program receiving apparatus.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of repeating apparatus differing from the types described above.

While the invention has been illustrated and described as embodied in a new and improved method and apparatus for receiving a plurality of electrical transmissions and distributing the same, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A repeating apparatus adapted to receive a plurality of electrical transmissions and distribute the same to a plurality of remote subscribers, comprising, in combination, a plurality of receiving means, each of said receiving means being adapted to receive a different one of the plurality of electrical transmissions; a plurality of modulating means, each of said modulating means being connected respectively to one of said receiving means and adapted to modulate the electrical transmission received by its respective receiving means; a plurality of electrical conductors connected between said modulating means and said plurality of remote subscribers, each of said plurality of electrical conductors having one of its ends connected respectively to said plurality of modulating means and its other end connected respectively to one of said plurality of remote subscribers to transmit said modulated electrical transmissions to said remote subscribers; a plurality of groups of selecting means, each group of selecting means being located at one of said remote subscribers respectively and being connected respectively to said other end of said electrical conductor connected to the respective subscriber for selecting at least one of said transmitted, modulated, electrical transmissions to be received by the respective subscriber; a plurality of groups of detectors, each group of detectors being connected respectively to tone of said groups of selecting means for demodulating the transmitted, modulated, electrical transmission selected by its respective group of selecting means; and

means respectively located at each of said remote subscribers for reproducing a selected demodulated electrical transmission.

2. A repeating apparatus adapted to receive a plurality of electrical transmissions and distribute the same to a plurality of remote subscribers, comprising, in corn bination, a plurality of receiving means, each of said receiving means being adapted to receive a different one of the plurality of electrical transmissions; a plurality of frequency channel transferring means, each of said frequency channel transferring means being connected respectively to one of said receiving means and adapted to transfer the electrical transmission received by its respective receiving means into a predetermined electrical frequency channel; a plurality of electrical conductors connected between said frequency channel transferring means and said plurality of remote subscribers, each of said plurality of electrical conductors having one of its ends connected respectively to said plurality of frequency channel transferring means and its other end connected respectively to one of said plurality of remote subscribers to transmit said frequency transferred electrical transmissions to said remote subscribers; a plurality of groups of selecting means, each group of selecting means being located at one of said remote subscribers respectively and being connected respectively to said other end of said electrical conductor connected to the respective subscriber'for selecting at least one of said transmitted, and frequency transferred, electrical transmissions to be received by the respective subscriber; a plurality of groups of detectors, each group of detectors being connected respectively to one of said groups of selecting means for retransfern'ng the transmitted and frequency transferred electrical transmission selected by its respective group of selecting means back to its original frequency channel; and means respectively located at each of said remote subscribers for reproducing a selected retransferred electrical transmission.

3. A repeating apparatus adapted to receive a plurality of electrical transmissions and distribute the same to a plurality of remote subscribers, comprising, in combination, a plurality of receiving means, each of said receiving means being adapted to receive a different one of the plurality of electrical transmissions; a plurality of modulating means, each of said modulating means being connected respectively to one of said receiving means and adapted to modulate the electrical transmission received by its respective receiving means; a plurality of amplifying means, each of said amplifying means being connected respectively to one of said modulating means for amplifying the modulated electrical transmission modulated by its respective modulating means; a plurality of electrical conductors connected between said amplifying means and said plurality of remote subscribers, each of said plurality of electrical conductors having one of its ends connected respectively to said plurality of amplifying means and its other end connected respectively to one of said plurality of remote subscribers to transmit said modulated and amplified electrical transmissions to said remote subscribers; a plurality of groups of selecting means, each group of selecting means being located at one of said remote subscribers respectively and being connected respectively to said other end of said electrical conductor connected to the respective subscriber for selecting'at least one of said transmitted, modulated, electrical transmissions to be received by the respective subscriber; a plurality of groups of detectors, each group of detectors being connected respectively to one of said groups of selecting means for demodulating the transmitted, modulated, electrical transmission selected by its respective group of selecting means; and means respectively located at each of said remote subscribers for reproducing a selected demodulated electrical transmission.

4. A repeating apparatus adapted to receive a plurality of electrical transmissions and distribute the same to a plurality of remote subscribers comprising, in combination, a plurality of receiving means, each of said receiving means being adapted to receive a different one of the plurality of electrical transmissions; a plurality of modulating means, each of said modulating means being con- 50 nected respectively to one of said receiving means and adapted to modulate the electrical transmission received by its respective receiving means; a plurality of electrical conductors connected between said modulating means and said plurality of remote subscribers, each of said plurality of electrical conductors having one of its ends connected respectively to said plurality of modulating means and its other end connected respectively to one of said plurality of remote subscribers to transmit said modulated electrical transmissions to said remote subscribers; a plurality of groups of selecting means, each group of selecting means being located. at one of said remote subscribers respectively and being connected re spectively to said other end of said electrical conductor connected to the respective subscriber for selecting at least one of said transmitted, modulated, electrical transmissions to be received by the respective subscriber; a plurality of groups of detectors, each group of detectors being connected respectively to one of said groups of selecting means for demodulating the transmitted, modulated, electrical transmission selected by its respective group of selecting means; and a loudspeaker respectively located at each of said remote subscribers for acoustically reproducing a selected demodulated electrical transmission.

5. A repeating apparatus adapted to receive a plurality of electrical transmissions and distribute the same to a plurality of remote subscribers, comprising, in combination, a plurality of receiving means, each of said receiving means being adapted to receive a different one of the plurality of electrical transmissions; a plurality of frequency channel transferring means, each of said frequency channel transferring means being connected respectively to one of said receiving means and adapted to transfer the electrical transmission received by its respective receiving means into a predetermined electrical frequency channel; a plurality of electrical conductors connected between said frequency channel transferring means and said plurality of remote subscribers, each of said plurality of electrical conductors having one of its ends connected respectively to said plurality of frequency channel transferring means and its other end connected respectively to one of said plurality of remote subscribers to transmit said frequency transferred electrical transmissions to said remote subscribers; a plurality of groups of selecting means, each group of selecting means being located at one of said remote subscribers respectively and being connected respectively to said other end of said electrical conductor connected to the respective subscriber for selecting at least one of said transmitted, and frequency transferred, electrical transmissions to be received by the respective subscriber; a plurality of groups of detectors, each group of detectors being connected respectively to one of said groups of selecting means for retransferring the transmitted and frequency transferred electrical transmission selected by its respective group of selecting means back to its original frequency channel; and a loudspeaker respectively located at each of said remote subscribers for acoustically reproducing a selected retransferred electrical transmission. i

References Cited in the file of this patent UNITED STATES PATENTS 1,754,878 Clement Apr. 15, 1930 1,894,646 Trogner Jan. 17, 1933 1,894,656 Barone Jan. 17, 1933

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