US1930693A - Multiplex communication system - Google Patents

Description

Oct. 17, 1933. F. scHRbTER'Er AL MULTIPLEX COMMUNICATION SYSTEM Filed 00$. 18, 1930 INVENTORS FRITZ SCHROTER WALDEMAR ILBERG ATTORNEY reame ca. 17, 1933 MULTIPLEX COIEMUNICATION SYSTEM Fritz Schrtiter and Waldemar Ilberg, Berlin, Germany, assignors to Telefunken Gesellschaft fur Drahtlose Telegraphic m. b. 11., Berlin, Germany, a corporation of Germany Application October 18,

and in Germany October '19, 1929 6 Claims.

Owing to the increasingly greater lack of wavelengths due to the growing number of radiotelegraphic lines or channels there has arisen a need for a method and means whereby it is possible to operate two or moresuch lines or channels upon one and the same carrier wave without any mutual interference or disturbance between signals being caused.

- This is accomplished in the present inventionby insuring that the transmitters working on the same wave on the several channels never radiate waves simultaneously. In accordance with this invention the signals are emitted from thetransmitters alternately at more or less short l5 time intervals. At the same rhythm or cycle,

the several receivers corresponding to the channels operated on the" same wave-length are switched in successively so that at any given instant only that particular receiver apparatus will 50 be operative whose respective transmitter is at the time sending out signals.

The invention has been illustrated in one of its preferred forms by the accompanying drawing,

wherein: Q5 Fig. 1 explains the underlying principle schematically for an arrangement wherein three lines are to be operated simultaneously, and Fig. 2 illustrates a preferredform of receiver device for receiving the signals transmitted. 3T9 Now referring to the drawing and first to the transmitter of Fig. 1, consecutive connection of the three transmitters is here accomplished by revolving switches a1, a2, a: respectively. The contact arms or wipers of these switches are driven by suitable mechanism in synchronism and under co -phasic conditions. Three similar switching devices are provided in the receivers adapted to receive signals from the respective transmitters. These switches are designated by letters b1, b2, b3, and they rotate in synchronism in-relation to one another and with the corresponding transmitter switches. In the drawing it has been supposed that these receiver switches cause rhythmically separationpr breaking of the connection between the output circuit of the radio receivers and the indicators or detector devices. These indicators may be ink recording devices as shown. It will be understood that the switch device may be interposed at any other suitable place in the receiver.

The number of switching cycles per second may be so chosen that the time required for a given cycle to elapse will be less than the briefest telegraphic impulse to be transmitted, in other 1930, Serial No. 489,512,

words, less than a dot in the case of the Morsecode. I

It will then not be necessary to take into consideration at all the questionoi the position at any time of the synchronous switch whether the signals are sent off by hand or from an automatic or machine transmitter. v So far as the receiving end is concerned, it may then be of advantage to storeup the signal beyond the length or duration of a switch cycle in order that the action upon the indicator, such as the ink recorder, of the receiver owing to the division of the signal by the change-over switch of thereceiver may be rendered'harmless. A- practical. example of a scheme of signal accumulation 'comprising the use of a glow-discharge or gaseousconduction-lamp is shown in Fig. 2. The indicator means 8 of the receiver outfit being of the inking kind in this case is here associated by way of main electrodes 9 and 10 forming .a dischargegap 6 with a source of current 7 furnishing a potential ranging between the striking and extinguishing voltage of. the glow-discharge gap so that by itself it will be unable to result in initiation of the glow-discharge. The incoming signal impulses are caused to result in flashing of the glow-discharge gap by way of the segment '4 of the synchronous switch (which in the case of three connections on the same wave-length as here concerned amounts to 360:3=l20) by causing the incoming alternating current potential,

if desired, after'rectification, to act between one electrode 10 and an auxiliary electrode 11 of the glow-discharge gap. After completion of a switching cycle, the glow-discharge current feeding the receiver indicator and released by the. auxiliary ignition potential supplied by the receiver is broken each time by conducting the said glow-discharge current through a second segment 5 of the synchronous switch which comprises almost a complete circle but which has the non-conducting segment 57 interrupting the com- I plete circular conducting path 5. Thus, the voltage of the battery 7 is removed fromacross the tube electrodes 9 and 10 each time the distributor brush contacts with the section or segment 5' oi. the ring 5. When the battery voltage is again applied across the tube 6 by a further rotation of the distributor the incoming signal suppliedto the electrode 11 of the tube 6 serves to trigger the tube and cause continuous operation by virtue of the fact that the distributor .brush contacts now with the segment 5 which continues until the distributor brush-again reaches the segment 5 after which this operation is repeated, provided there isan incoming signal to trigger the tube 6. In the case of a signal of greater length, such as a Morse dash, the glow-discharge gap is immediately re-struck.

The sequence of switch cycles should conveniently not be chosen too rapid inasmuch as with increasing switching speed also the difficulties inherent in synchronization will grow, and since, moreover, owing to the rapid interruption of the transmitters, the side-bands that are radiated oif also grow in size.

Another manner of carrying the basic idea of the invention into effect comprises the employment of automatic or machine transmitters operating with perforated tapes for signal transmission. Inthis case it is feasible to insuretimeconsecution or joining of the equi-wave transmitters by the stepwise production of a certain number of signals by causing the travel or conveyance of the perforated paper tape to proceed alternately in synchronous sections. The arrangements at the receiving end, fundamentally speaking, remain the same as hereinbefore described, though there is here no need for the accumulation of the signals. Whererecorder reception is resorted to, the conveyance of the paper is also conveniently caused by stages or intermittently. While this method reduces the mean speed of telegraphy of each one of the n-many lines to the nth part, this fact is mostly of little importance sofar as the field of application of this method is concerned seeing that the combination of a plurality of lines of communication in one wave is primarily intended and useful for lines carrying usually low loads for which, however, perfect working readiness is a prime desideratum.

For insuring and maintaining synchronism in rotation of the. constituent switches comprised in the transmitter and receiver equipments and of the automatic transmitters and inkers or other recording devices most of the synchronizing methods known in the prior art may be adopted. For instance, tuning forks tuned to the same frequency. in conjunction with synchronous motors could be employed. If necessary, correction of the phase of the synchronized parts may be produced at certain time intervals in known manner by the aid of special impulses radiated of! from the transmitter or else by the telegraphic signals themselves. For the same object a combination of an electric contact-making pendulum and a stepping mechanism could be used.

The arrangement becomes particularly simple in nature when a duplex connection is established in a manner as hereinbefore described inasmuch as in that case the transmitter and receiver switches could then be constructionally combined at each end, or could at least be kept in synchronism by one and the same tuning fork. The method first described above involving a rotation or change-over of the different lines being 'rapid comparatively with the length of the signals, however, is liable to cause difliculties in this case because of thefinite length of travel of the radio signals. If the time of transmission or travel from the sender to the receiver amounts to t seconds, it can be readily found that reception undisturbed by the sending part of the station will be feasible at both ends only if the number of switching periods k per second is equal to:

l T2t2t2t Hence, this difilculty can be obviated by the suitable choice of the switch frequency as shown,

It s etc;

When short waves are used, the spreading or echo effects peculiar thereto and occasioned-by extended or multiplied received signals is liable to result in disturbances of equi-wave operation in so far as signals of one line of communication, after the change-over of the telegraphic channels, are apt to be picked up by the next receiver set in the rotation of connections. This source of trouble may be overcome if the rotation or sequence of the n-many channels or connections is not chosen unduly fast, by making the different switch segments less than 360mm, so that after each switch or signal period there is provided a blank orperiod free from a signal. This scheme would appear of advantage also for the reason that this eliminates slight discrepancies in synchronization.

In what precedes the assumption had been made that the synchronous circuit changes or connections are established by mechanical, more particularly revolving switch mechanism. Of

munication is to be used for picture telegraphy comprising the use of drums, it will not be necessary to stop the picture drums both at the sender and at the receiver during the transmission intervals or spaces. If the duration of the differ-- ent transmission periods is vmade equal to the time required by the picture drums for completing a revolution,' then, for n-many equi-wave lines it is sufl'icient to reduce the axial shift of all picture drums to the nth part of the pitch governed by the width of the picture elements.

Hence, each picture will thus be transmitted inside an n-times long time, but the fineness of the screen or subdivision of the picture will be unimpaired. The sending and receiving switches should in this scheme be constructionally combined-with the picture apparatus in order that their switching rhythm should bear. a suitable relationto the rotation of the picture drums. In this way separate synchronization for the switch mechanism would be dispensed with.

Having now described our invention, what we claim and desire to secure by Letters Patent is the following:

1. In a multiplex communication system, means for transmitting a plurality of messages, means for dividing the time period of transmission between each of said messages into a plurality of sequentially recurring periods each of a duration no greater than the duration of the brieiest signal to be transmitted, means for receiving signal corresponding to each of the independent messages, and means for accumulating the separate message signals for a time period greater than the recurrences of the same message, and means for recording the accumulated message signals.

3. In a multiplex communication system, means for transmitting a plurality of messages, means for dividing the time period of transmission between each of said messages into a plurality of sequentially recurring periods each of a duration no greater than the duration of the briefest signal to be transmitted, means for receiving signals corresponding to each of the independent messages, and a glow discharge relay for accumulating the separate message signals for a time period greater than the time division in periods between successive recurrences of the same message.

4. In a multiplex communication system, the method of receiving a plurality of signals transmitted over a single carrier which includes the steps of transmitting a plurality of messages,

dividing the time period of transmission for each of said messages into a plurality of sequentially recurring periods each of a duration no greater than the time duration of the briefest signal to be transmitted, reeciving all of the signals, and accumulating the separate signals for recording for a time period greater than the time division in theperiods between successive recurrences of the same message signal.

5. In a multiplex communication system, the method of receiving a plurality of signals transmitted over a single carrier which includes the steps of transmitting a plurality of messages,

dividing the time period of transmission for each of said messages into a plurality of sequentially recurring periods each of a duration no greater than the time duration of the briefest signal to be transmitted, receiving all of the signals, accumulating the separate signals for recording for a time period greater than the time-division in the periods between successive recurrences of the same message signal, and'recording each sequentially recurring accumulated signal.

6. In a multiplex communication system, means for transmitting a plurality of messages, means for dividing the time period of transmission between each of said messages into a plurality of sequentially recurring periods each of a duration no greater than the duration of the briefest si nal to be transmitted, means for receiving signals corresponding to each of the independent messages, signal recording means for reproducing the signals, said means being normally slow in responding and rapid in releasing, and a glowdischarge relay for accumulating the separate message signals for a time period greater than the time division in periods between successive recurrences of the same message so as to actuate the signal recording means.

FRITZ SCHRGTER. WALDEMAR ILBERG.

Images