US2292944A - System for transmitting telegraph signals - Google Patents

Description

Aug. 11, 1942. E. HUDEC SYSTEM FOR TRANSMITTING TELEGRAPH SIGNALS 4 Sheets-Sheet 1 Aug. 11, 1942. E. HUDEC I SYSTEM FOR TRANSMITTING TELEGRAPH SIGNALS 4 Sheets-Sheet 2 Filed Oct. 29, 1938 Aug. 11, 1942. E. HUDEC 2,292,944

SYSTEM FOR TRANSMITTING TELEGRAPH SIGNALS I Filed Oct. 29, 1938 4 Sheets-Sheet 5 as! I l I j WZJ l 3 27 2a 29 30 13, ill IT +TF J; :37!

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Aug. 11, 1942. E. HUDEC SYSTEM FOR TRANSMITTING TELEGRAPH SIGNALS Filed Oct. 29, 1938 4 Sheets-Sheet 4 Patented Aug. 11, 1942 SYSTEM FOR ANSMITTING TELEGRAPH SIGNAL i Erich Hudec, Berlin, Germany Application October 29, 1938, Serial No. 237,708

In G

Claims.

This invention relates to telcg 'aphy by pulses on electric waves and has for its principal object to compensate at the receiver any phase shift of the pulses received which may be caused by deviations between the synchronizing frequencies at the receiver and at the transmitter or by distortions on the way from the transmitter to the receiver or by any other distortions.

Another object of this invention is to provide means for shifting the phase of the receiver pulses in small steps to any degree beyond 360 or multiples of 360.

Another object of this invention is to provide ermany. January 4, 1938 means for compensating the slightest phase shift between the pulses received from the transmitter and the pulses produced at the receiver, so that the variations of the telegraph signals will be very small.

Another object of this invention is to provide means for compensating also a large phase shift of the duration of a signal element.

It has been suggested to compensate fading and echo effects by transmitting merely the commencements or the ends of the telegraph signals by means of short pulses and to convert the pulses received into telegraph signals.

Furthermore it has been suggested to generate pulses at the receiver at equal intervals of time and to transmit only the missing pulses which are necessary for composing the telegraph signals at the receiver. It is to this system of telegraphy to which the present invention is particularly applicable. Such a system is described in detail in the copending application U. S. Serial No.

226,259, filed August 23, 1938, and comprises at the transmitting end a synchronizing frequency generator which controls a pulse generator for generating short periodic control pulses. This generator is preferably of the relaxation type. It is also provided with a motor driven distributor comprising a plurality of contacts connected to several teletype machines, as is conventional in multiplex telegraphy. The telegraph signals received from the teletype machines and the control pulses generated by the pulse generator are applied to a converter which generates a short telegraph or transmission pulse at the commencement or end of each telegraph signal, according to various schemes described in the copending application referred to above. The short telegraph pulses are transmitted and reconverted into telegraph signals at the receiving end of the system. The receiver is also provided witha synchronizing frequency generator which controls a pulse generator for generating short periodic control pulses of the same periodicity as those generated at the receiver. These locally generated pulses, as well as the received telegraph pulses, are applied to a converter, preferably a relaxation device; by means of which the received telegraph pulses are converted into telegraph signals. These signals are then applied to several teletype machines in receiving position corresponding to those at the transmitting end, by means of a rotating distributor which is also controlled by the synchronizing frequency generator at the receiver. In this case the intervals between the fixed commencements (or ends) of the telegraph signals at the transmitter and at the receiver must coincide with extreme accuracy. In the case of picture telegraphy there is required a coincidence of at least 1.10- per cent of the transmission frequency.

According to the invention deviations between the fixed commencements or ends of the signals are compensated by shifting the phase of the locally generated receiver control pulses.

If e. g. the synchronisation frequencies at the transmitter and at the receiver differ from each other by more than l.10-' per cent of their value, but from their intended value by less than 1.10"" per cent, the phase of the receiver control pulses is shifted at constant speed in such a manner that invariable telegraph signals are'reproduced continuously in like fashion during the transmission.

The requisite rate of phase shift is determined in the most simple form with the aid of a few trial transmissions. If, for example, the synchronisation frequencies differ from each other by ().5.10- per cent, it is necessary that the rate of the phase shift be adjusted with an accuracy of 1.10" per cent. By the use of a synchronous motor, which is driven by a frequency-regulated alternating current supply or better by a subharmonic of the synchronizing frequency, this accuracy can be realised and the deviation of the two synchronisation frequencies accordingly reduced to the amount of 1.10- per cent.

If the synchronisation frequencies at the transmitter and (or) the receiver do not remain constant with the requisite accuracy, the phase between the receiver and transmitter impulses must be frequently checked, and if necessary regulated.

For this purpose synchronizing pulses of predetermined constant duration and phase are transmitted from the transmitter to the receiver at certain predetermined intervals. The phase relation between the received synchronizing pulses and the receiver control pulses must always be the same. If deviations from this predetermined relation occur, the phase of the receiver control pulses is shifted in accordance with pulses produced at the receiver.

Fig. 5 illustrates the operation 'of the devices according to Figs. 4 and 6.

Fig. 6 shows on the right side a device for producing the telegraph signals and on the left side a device for controlling the phase shifter according to Fig. 1- by synchronizing pulses received from the transmitter and control pulses produced at the receiver.

pulse occurs during each cycle of the control frequency and also duri'ngeach telegraph unit of the telegraph signals produced by means of the teletypers and the distributor 4. The control pulses and the telegraph signals derived from the contacts of the distributor l are applied to a transmission pulse generator 6 and more speclijically to the control grid of a negatively biased electron'discharge tube in such a manner that ajtelegraph or transmission pulse is generated in the plate circuit of the electron discharge tube whenever a marking unit of the telegraph signals to be transmitted occurs. During occurrence of a spacing unit in the telegraph signal, no transmission pulse or telegraph pulse is developed. During occurrence of a synchronizing sig- Fig. 7 is a diagram showing the distribution at I the receiver of telegraph pulses received from the transmitter and control pulses produced at the receiver of the reproducing telegraph signals and illustrates the operation of the phase shifting arrangement of Fig. 8. I

Fig. 8 shows a device for shifting the receiver control pulses in both directions according to the phase of the synchronizing pulses received from the transmitter.

Fig. 9 shows a complete arrangement at the transmitting and at the receiving side for carrying out the invention A Means forproducing telegraph pulses at the beginning or at the end or in the middle of a telegraph signal, means for producing local pulses at the receiving end for fixing either the termination or the commencement of the telegraph signals, and means for converting the pulses received into telegraph signals have been described 'in my corresponding application Ser. No. 226,259

filed Aug. 23, 1938, referred to above.

' Fig. 9 schematically shows a complete system for transmitting and receiving telegraph signals in accordanc with the present invention. For the purpose of clearness, all electrical connections between the units represented by the blocks I to I9 are indicated by single heavy lines.

At the transmitting end, there 'is provided a synchronizing frequency generator, preferably comprising a tuning fork generator capable of deliveringelectrical oscillations at 1,000 0. P. S. Connected to the generator I is a control frequency generator 2, tuned to a subharmonic of the synchronizing frequency and accurately synchronized therewith. The control frequency signal generated is used for controlling the motor driving a distributor 4, and for controlling a relaxation generator 3 which generates control pulses of relatively short duration, as compared with a telegraph signal unit or baud. The distributor 4 preferably comprises 32 contacts which are closed once during each revolution of the distributor spindle. contacts are used for scanning the contacts of 6 tape transmitters (not shown) and 2 contacts are used forv generating testing signals for synchronizing the receiving apparatus. The control pulses developed by the generator 3 are periodic and so spaced that one of the radio transmitter 8 nal, however, a synchronizing pulse is developed which is transmitted, together with the telegraph pulses, so that the transmission pulses comprise telegraph' and synchronizing pulses. Wherever the distance between the telegraph station and the radio transmitter makes it desirable, a line carrier frequency generator 5 is provided, preferably generating a frequency which is harmonic of, the synchronizing frequency developed by the generator I. This intermediate carrier is modulated or keyed by the-telegraph and synchronizing pulses and then transmitted by way of a wire line to the actual radio transmitter. At

the transmitter, there is provided a demodulator I for demodulating the keyed intermediate carrier. The telegraph pulses and synchronizing pulses are then applied to the modulating stage which transmits a carrier signal keyed or modulated in accordance with transmission pulses comprising telegraph I and synchronizing pulses to be transmitted. At

the receiving end there are provided two antennas, preferably directive, connected to two receivers 9 and I0. At the receivers, the received keyed carrier is demodulated and the demodulated transmission pulses are again modulated upon an intermediate carrier and supplied to an amplifier and demodulator I6.

At the receiver there is also provided a synchronizing frequency generator II, preferably comprising a tuning fork generator capable of developing electrical oscillations having a frequency of 1,000 C. P. S. The frequency of this generator can be adjusted within narrow limits by means of condensers and is adjusted to substantially the same frequency as that of the generator I at the transmitting end. The synchronizing frequency is applied to a phase shifter I2 in which the phase of the synchronizing frequency can be advanced or retarded, thereby to adjust the phase of the periodic receiver control pulses by the pulse generator I3. Adjustment of the phase of the synchronizing frequency is affected in such a manner that the phase of the receiver control pulses remains in predetermined constant phase relation with respect to the received transmission pulses, particularly the received synchronizing pulses. The receiver control pulses are preferably produced by means of a harmonic generator in the same way as the control pulses at the transmitting station. The generator I3 is tuned to a subharmonic of the synchronizing frequency generated by the generatorII and is synchronized by the phase-adjusting synchronizing frequency, that is, the output of the phase shifter I2. The periodicity of the receiver control pulse is substantially the same as that of the control pulses generated at the transmitting end. The control pulses are and long receiver control pulses.

utilized for controlling the motor of the distributor l8 which distributes the reproduced telegraph signals to the various teletype machines. There are also provided two relaxation generators l4 and 15 for producing relatively short and relatively long receiver control pulses, respectively. The distributor I9 comprises 30 contactsfor 6 teletype machines, 2 contacts for phase control and a glow lamp for testing the phase of the distributor.

The demodulated transmission pulses comprising telegraph and synchronizing pulses are applied to a converter H in which the pulses of relatively short duration are converted into signals having durations equal to telegraph units. For this purpose, the short receiver control pulses developed by-the generator H are applied to the converter H. The reproduced telegraph signals are applied to the teletype machines by means of the contacts of the distributor I9. For the purpose of comparing the phase of the received synchronizing pulses with that of the receiver control pulses, there is provided a phase comparator l8 to which received synchronizing pulses and receiver control pulses are applied. In the phase comparator l8, the phase of the leading edges of the received synchronizing pulses is compared with the phase of the leading edges of the short For proper phase relation, the short receiver control pulses must occur within the duration of the received synchronizing pulses and the latter must occur within the duration of the long receiver control pulse. Whenever short receiver control pulses are in advance of the received synchronizing pulses, the motor of the phase shifter I2 is energized to vary the constants of the phase shifter l2 so that the phase of, the synchronizing frequency is shifted backwards. Whenever the received synchronizing pulses are in advance of the long receiver control pulses, the motor of the phase shifter I2 is controlled in the opposite sense.

An arrangement for carrying out the phase shift of the receiver-control pulses is illustrated in Fig. 1. It consists of two independent phase shifters, by means of which the phase of the potential applied to the control grid of an electron discharge tube can be shifted by almost 180 in relation to the plate potential of the preceding tube.

The resistances shifters are coupled together, so that they always have the same values.

Fig. 2 illustrates the operation of the arrangement of Fig. l. The potential in the current branches l--3-2 or -'|--6 is and in the current branches |-4--2 or 586 L]! J.R

From this it follows that the points 3 and 4 'or i and 8 in Fig. 2 move diametrically on a circle in the case of variable R. U2 accordingly varies its phase in relation to U1 without varying its amplitude.

The resistances R, in accordance with Fig. 3, are designed as rotary resistances and are rotated simultaneously. They commence simultaneously with the value W, vary step by step up to a maximum finite value, then jump to infinity, and then after a complete revolution suddenly return to R0. The phase angle #1 between the potentials U1 and U: varies thereby in small stages from approximately 0' to 180 and then suddenly jumps back to approximately 0. Accordingly the phase angle between the output potential U and the input potential Uo'increases from approximately 0 to 360 and then suddenly drops back to.approximately 0.

If the four resistances in Figs. 1 and 3 do not pass simultaneously from the final contact segment to the first one, the phase of the output potential U can assume for a brief period the value of 180 or even drop in its amplitude to zero.

Thesedistortions can be reduced by adjusting the contact segments in Fig. 3 very exactly one above the other; they cannot, however, be completely eliminated.

The remaining errors are eliminated according to the invention by controlling by the output potential U a tube generator, a relaxation generator or a synchronous motor-arrangements which exhibit inertia in face of a variation in phase. Therefore the jump from 360 to 0 is not observable, so that if the phase shifter according to Figs. land 3 rotates beyond 360 or any multiple of 360, the phase of the receiver pulses will be shifted beyond 360 or any multiple of 360.

In Fig. 3 there are shown by way of example switches having 21 steps. The distributor brushes for the switches are located on the same of an intermediate reduction gear (not shown).

R' of each of the two phase The resistances for the single steps are so calculated that the phase angle between the input potential U0 and the output potential U in Fig. 1 varies from step to step' by the same angle A The angle ,0 between the potentials U1 and Us in Fig. 2 is determined by the equation The resistances R for the single steps should be selected according to this relation.

However, the phase angle between the input potential U0 and the output potential U of the phase shifting device is of ultimate concern, rather than the phase angle between the potential U1 and U2. The phase angle between U0 and U for various values of R can be determined by means of a vector diagram with consideration of the vacuum tube impedances, the transformers, and the load resistors W.

The lowest value of the resistors R of Figs. 1 and 3 is equal to that of the resistors Ru. At the second and following contactsof the switches in Fig. 3, the values of their resistors R- increase until they bec ""e.; infinity at the twenty-first contact for he phase angle between U0 and U is K 3 f at the second contact, it is K 360+l8, andincreases in steps of from contact to contact.

If the steps A by which the phase'angle is varied are to be reduced, it is necessary to increase the number of segments of the rotating switch, but the required accuracy with which changes from contact to contact must be effected also increases, so that a practical limit for the number of contact signals is soon reached. The amount A may also be decreased by shifting the phase of a higher harmonic of the frequency required and reducing it to the desired frequency by means of a vacuum tube frequency divider or a relaxation generator.

distributor arm and the generation of the receiver control pulses are so tuned that a control pulse commences just at that moment at which the arm reaches a new contact segment. If the received synchronizing pulses commencing at the same moment, there is produced a spacing or blank interval upon the contact of the distributor brush with the first signal segment of the distributor and a signal is produced upon the contact of the brush with the second signal segment.

If the phase'of the received transmission pulses is leading in phase with regard to the receiver vention testing pulses of predetermined constant wave shape and periodicity are transmitted at predetermined intervals, asexplained below in detail. Y

In broad terms, it is a feature of the present invention periodically to generate synchronizing signals of constant wave shape and periodicity, preferably at the end of each revolution of the distributor arm of a multiplex system, to convert these synchronizing signals into synchronizing pulses with the aid of control pulses, in the same manner as the telegraph signals are converted into telegraph pulses, and to transmit the transmission pulses comprising telegraph and synchronizing pulses. At the receiving end of the system, control pulses are generated having substantially the same periodicity as those generated at the transmitter. The receiver control pulses are to be held in synchronism and in phase with the received telegraph and synchronizing pulses, which, if transmitted through the ether, may suffer phase distortion due to echo eflects. The control pulses generated at the receiver are utilized to convert the received telegraph and synchronizing pulses into signals. In order to maintain phase identity between the control pulses locally generated at the receiver and the received transmission pulses, the phases of both are compared in a phase comparator device to produce a controlfeflect which is utilized to adjust the phase of the receiver control pulses to a predetermined relation with respect-to the phase of the received transmission pulses, If correction is to be effected for both a lead and lag in the phase of the receiver control pulses with respect to the received pulses, two types of receiver pulses are generated of equal periodicity but of different wave shape. Both these types of pulses are compared with the received pulses to produce control effects adapted control pulses, the signal already commences wh the distributor brush is still on the first sync onizin signal segment. This part of the signal acts by way of the first synchronizing signal segment on the grid of the electronic valve i in Fig. 4 and causes the condenser C to become charged to an extent which is all the greater the greater'the phase shift is between the transmission pulses and the locally generated receiver control pulses. During the succeeding contact of the distributor brush with telegraph signal segments connected to the teletype receiver the condenser controls the electronic valve 2, the plate current of whichis used to actuate an electro-motor M. This motor varies the resistance R in Fig. 1, and accordingly shifts the phase of the synchronisation frequency at the receiver which also determines the phase of the receiver control pulses. Shortly before the distributor arm of the multiplex apparatus moves on to the first synchronizing segment the condenser is discharged by way of a contact of the distributor apparatus or, in accordance with Fig. 4, by way of a relaxation apparatus, which is made to be ourrent-transmissive by a distributor contact schematically indicated at S. When the distributor arm again reaches the first synchronizing signal segment this occurrence is repeated, if the received transmission synchronizing pulses do not coincide with the receiver control pulses.

If the phase of the testing pulses received from the transmitter is lagging in regard to the receiver control pulses, the signal commences only during the wiping of the second synchronizing signal segment. This error can also be compensated by allowing the signal to act, in a negative diretcion by way of the second synchronizing signal segment on the grid of the electronic valve l in Fig. 4, which in this case is positively biased. The positive grid bias should be so great that the same is just compensated by the negato correct the lead and lag, respectively, of the receiver control pulses.

For distributing the received telegraph signals to the difierent telegraph receiving apparatus thereare provided at the receiving end of a system operating in accordance with the multiplex method of telegraphy a plurality of telegraph signal contact segments, which are contacted successively by a distributor arm and. contact brush. Generally there are provided for each receiving apparatus 5 segments corresponding to the 5 units of the telegraph code.

For compensating the error in synchronism.

thereare required two synchronizing segments tive signal potential. If the signal by way of the second synchronizing segment initiates too late, the positive bias is eiiective for a time, so that the condenser C is charged. Apart from this the operation is the same as in the first example, In this case the motor must rotatein the opposite direction.

If the phase of the received transmission pulses sometimes is leading and sometimes lagging, there are required two arrangements according to Fig. 4, the one of which is connected with the first synchronizing signal segment and the'other with the second synchronizing signal segment. There can be provided two arrangements according to Fig. 1, which are independent of each other, or the two motors M can act in opposite directions on the same resistances R in Fig, 1.

In the case of image telegraphy the same method can be employed, although in this case it may be diiiicult to close the synchronizing contacts exactly for the duration of one screen period. If the phase of the received transmission pulses is leading, there are preferably produced at the receiver special synchronizing pulses, which are of longer duration and greater amplitude than the synchronizing pulses received from the transmitter, both pulses being superimposed in opposite polarity to one another during the synchronizing period. The testing pulses received from the transmitter are rendered completely inefiectlve by the receiver control pulses when they coincide. If on the other hand the synchronizing transmission pulses are in advance (compare Fig. a), they are effective for the time up to the commencement of the receiver control pulses. They are allowed to control a motor, the velocity of which is adjusted according to the degree'of phase displacement. By this motor the resistances of a phase shifter (for example according to Fig. l) are altered, and in this way there is corrected the phase of the testing receiver pulses relatively to the synchronizing pulses received from the transmitter.

In order to ensure that errors do not occur in the case'of image telegraphy the synchronizing period at the transmitter is made to be greater than at the receiver, so that it is ensured that at the receiver only synchronizing pulses are received during the synchronizing period. This method can be carried out in a manner similar to that in the described example of multiplex telegraphy according to Fig. 4.

If, contrary to the last example, the phase of the synchronizing pulses received from the transmitter lags with respect to the phase of the receiver control pulses, the receiver control pulses are adjusted according to Fig. 512. They are made of shorter duration and smaller amplitude than the synchronizing pulses, so that they are only effective when they lead the synchronizing pulses in phase. In this case, therefore, the electronic valve l in Fig. 4 is controlled by the receiver control pulses, and the latter are applied in opposite polarity with respect to received synchronizing pulses. The condenser C is charged exactly as in the previous example, but only when the received synchronizing pulses lag behind the control pulses. Apart from this the compensation occurs exactly as in the previous example. Finally, it is also possible according to this method tocompensate the errors in phase when the synchronizing pulses received from the trans mitter alternately lead or lag behind the receiver control pulses. There are then required at the receiver two different control pulses, viz.according to Figs. 5a and 5b, and two arrangements according to Fig. 4. The phase of the receiver control pulses is advanced by means of one of these arrangements and retarded by the other.

The arrangement according to Fig. 4 operates faultlessly, but it has the disadvantage that a comparatively large shift must take place between the transmission and receiver impulses before the condenser has been sufficiently charged to control the motor.

This disadvantage is avoided in the arrangement according to Fig. 6 in which a very slight advance of the receiver pulses already causes a displacement of the phase shifter, so that there occur only very small difierences in the duration of the telegraph signals reproduced at the receiver.

According to the invention this is accomplished by controlling, during the synchronizing period, a relaxation device in accordance with tlireceiver control pulses and transmitted synchronilring pulses, which are appliedin opposite polarity and so tude. The relaxation device is caused to relax, for

example, by the receiver control pulses alone. 7

whereas it is not affected by the transmitted synchronizing pulses. Shortly prior to the synchronizing period the relaxation device is caused to relax into the other position by means'of a special contact, hence preparing it for reception of a receiver control pulse. This method is described indetail and illustrated in the following for a multiplex telegraph system.

At the transmitter and at the receiver there is provided a distributor having, for example, 31 segments, of which 6X5 segments are employed for the telegraph signals of 6 telegraph apparatus, while the thirty-first segment is used to transmit upon each revolution a synchronizing pulse, which corresponds in wave shape to the other telegraph pulses. It differs from these merely by the fact that it is always transmitted, whereas the telegraph pulses are transmitted or not transmitted dependent on the combination of the telegraph signal to be transmitted. The generation of the telegraph pulses is described in the patent application (Ser. No. 226,259 of Aug. 23, 1938).

At the receiver the transmission pulses comprising telegraph and testing pulses are preferably picked up by means of a plurality of aerials and a plurality of independent receiving sets and transmitted overseparate wire lines to a telegram collecting oflice by means of an intermediate carrier frequency. The intermediate carrier is amplified and demodulated and the demodulated telegraph and testing pulses applied together to a limiting device, for example an electronic valve or a relaxation device, which is so sensitive that it can be fully or practically fully controlled by the pulses received from one receiver.

In Fig. 6 a device for producing the telegraph signals and the synchronisation signals according to the invention is illustrated by way of example. It is divided into its two parts by the thin broken line. I

For reproducing the telegraph signals by means of the received telegraph pulses there is provided the grid-controlled relaxation device Kl, which is connected in series relation with the v resistance R1 and to a source of unidirectional adjusted that they have nearly the same amplipotential of preferably 50 volts. The control grid of K1 is controlled by the transmitted telegraph and synchronizing pulses SI applied at terminals 8 and Land the receiver control pulses EI applied at terminals 10 and l l, which are produced at the commencement of each telegraph unit by the compensated receiver synchronisation frequency. The grid bias is so adjusted by means of the potentiometer W1 that the upper relaxation potential U is above and the lower relaxation potential I l below the plate potential U (=50 v.). By means of the receiver control pulses the two relaxation potentials are preferably increased, so that the relaxation device K1 does not transmit current. Owing to the received telegraph and synchronizing pulses applied to the control grid of K1, the relaxation potentials are reduced, so that K1 becomes conductive.

The printing apparatus at the receiver are preferably so connected that the receiving relays actuate the permutation bars when they are not excited by the telegraph signals, as in this way the operation of the relays can readily be checked, no signals being transmitted to the receiver. The device according to Fig. 6 is adapted to this form of operation of the printing appa ratus.

If, at the commencement ofa telegraph unit, no transmission pulse is received. the relaxation device Kr is rendered non-conductive by a receiver control pulse. Therefore there is no negative bias at the resistance R1, so that plate current flows in the plate circuit of the amplifying valve V1 for the duration of the next telegraph unit. This plate current flows by way of the distributor connected to terminals and 2 to one of the five receiving relays of a printing apparatus.

Since the received transmission pulses exceed the receiver control pulses in amplitude and duration (the resistances W1. W3 and W4 are adjusted accordingly) it is thus assured that the relaxation device becomes conductive when a telegraph pulse is received. Upon arrival of a telegraph pulse a negative voltage drop is devel oped across R1, by means of which the amplifying valve V1 is blocked, so that the appertaining receiving relay remains unexcited and the permutation bar is actuated.

All remaining parts in Fig.v 6 are intended for the regulation of the synchronism. The amphfying valve V2, which is connected in parallel with the valve V1, feeds a glow lamp, which is connected by way of a transformer ii and the terminals 6 and 1 and lights a stroboscopic disc in the distributor. If no telegraph pulses are transmitted by the transmitter there is only transmitted a synchronizing pulse upon each revolution of the contact drum of the distributor, by way of the distributor contact 3| of Fig. 8, a synchronizing pulse is received at terminals 8 and 9 by means of which K1 is rendered current-transmissive and V2 is blocked. The pulse developed thereby in the transformer '6' causes the glow lamp to light and can accordingly be employed for phase adjustment.

The relaxation device K: and the amplifying valve V: are used for adjusting the phase of the receiver pulses. The grid of the relaxation de vice K2 is normally supplied by way of a highresistance R4 with a negative bias, which is so adjusted that the plate vo tage of 50 volts lies the lower relaxation potential 13.

By means of a distributor contact, the terminals 3 and 5 are conductively connectcd. In this manner the received synchronizing pulses applied from the distributor synchronizing signal contacts to terminals and 9 and the receiver control pulses applied at terminals l2 and ii are applied to thecontrol grid of the relaxation device K: by way of potentiometers W5 and W2.

device K2 must not be caused thereby. For this reason, the grid bias of the relaxation device K: must be so adjusted by means of the potentiometer W: that the platemotential is considerablycloser to the lower relaxation potential g than to the upper relaxation potential-fl of the device K2.

It is only approximately after one revolution of the drum, shortly before the contact 3| of Fig. 8 is closed, that the grid of the relaxation device K2 is connected with a source of positive bias by way of a conductive connection between terminals 3 and 4 effected by a distributor contact and K2 is rendered conductive. The amplifying valve V3 and the relay P are thus deprived of current, and the motor M is disconnected. It remains stationary for such time until the receiver pulse is in advance of the transmission pulse and causes the relaxation device K: to be come non-conductive.

When the synchronizing pulses received from the transmitter are leading the receiver control pulses in phase, receiver control pulses are employed, which are adjusted to be greater in amplitude and longer in duration than the synchronizing pulses received from the transmitter. As soon as the synchronizing pulses received from the transmitter are slightly ahead of thecontrol pulses produced at the receiver, they control a phase shifter, by means of which the phase of the synchronization frequency at the receiver is shifted in' the forward direction until the synchronizing pulses received from the transmitter are in phase with the receiver control pulses.

The synchronizing pulses received from the transmitter then become ineffective, so that the I phase shifter remains stationary.

' from the transmitter become effective after the and We and W2, respectively. The potentiom-. I

eters W5 and We are so adjusted that the transmission synchronizing pulses exceed the receiver control pulses in their amplitude and render the latter ineffective when they occur simultaneously. 'If, on the other hand, the receiver control pulses ,are somewhat in advance, th relaxation device K2 is made non-conductive. Therefore, there is no negative bias at R2, so that a plate current flows in the valve V3 and actuates the relay P. The relay P switches a motor on by way of the terminals l4 and I 5, whichactuates the phase shifter in accordance with Figs. 1 and 3 and brings the rotation of the distributor arm and the receiver control pulses again in phase with the received synchronizing pulses.

If the duration of the received testing pulse extends beyond the termination of the relatively short receiver control pulse, relaxation of the end of the corresponding receiver control pulses. The phase of the receiver pulses is then incorrectly shifted in the forward direction and the synchronism is disturbed.

This drawback is eliminated by superimposing the synchronizing pulses received from the transmitter and the receiver control pulses in opposite polarity by means of a special distributor testing contact, which limits the effective duration of the synchronizing pulses received from the transmitter. I

In Figs. 7 and 8 this method is illustrated by way of example as applied to multiplex telegraphy wherein the phase of the receiver control pulses may be shifted in both directions.

In Fig. 7a there-are shown the receiver control V pulses EI, which are employed together with the received transmission pulses comprising telegraph and synchronizing pulses SI (Fig. 7b) for reproducing the telegraph signals TZ (Fig. 7c). In Fig. 7b it is assumed that duration of the received transmission pulses SI is extended up to 50% of the telegraph signal unit due to echo effects. The telegraph signals are distributed to the receiving relays of the telegraph printers by means of the receiver distributor EV. In Fig. 7d there are shown the distributor contacts 26 30, which lead to the teletype printer VI. There are actuated by the telegraph signal TZ of Fig. 70, for example, the first, second and fifth receiving relays, while the third and fourth are in the stationary position. This combination represents the letter W in the international telegraph code.

According to Fig. 7d, the distributor contacts are closed only for one-half of the duration of a telegraph signal unit. If the received trfansmission pulses coincide in phase withg the receiver control pulses, as illustrated in Fig 'la-d, the time during which the distributor ntacts are closed falls exactly in the middle oi, he telegraph signal unit. Since the receiver control pulses and the receiving distributor. arev controlled by the same synchronization frequency at the receiver, the mutual phase relation between the receiver control pulses EI and the closing of the distributor contacts EV always remains the same.

If the received transmission pulses are shifted in the forward direction, a signal unit of the reproduced telegraph signal released by a transmission pulse is not varied at all, as long as the receiver control pulse occurs within the duration of the transmission pulse. On the other hand a portion of a preceding spacing unit is changed into a telegraph marking signal shortly prior to the termination of the spacing unit. This short,

Fig. 7g shows synchronizing pulses according to Fig. 7b and receiver control pulses accordfaulty telegraph marking signal, with the as sumed closing time of the distributor contacts, remains Without effect as long as it is less than of the duration of a normal signal unit. If it becomes longer, it can incorrectly actuate the receiving relay connected to the telegraph signal contact of the distributor preceding the synchronizing contact.

If the received transmission pulses shift backwards, a telegraph signal marking unit is correspondingly shortened in its duration below that of a normal signal unit. In the case of a shifting of 25%, however, the part of the signal unit acting on the receiving relay is not varied. But if the transmission pulses are lagging behind the receiver control pulses by more than 25% of the signal unit the duration of the reproduced telegraph signal may possibly no longer be sufficient to actuate the receiving relay.

In order that the permissible shifting of the received transmission pulses be as large as possible, the contact duration of the distributor contacts must be so chosen that it is just sufficient to permit actuation of the receiving relay. In order to shorten the permissible contact duration the receiving relays are preferably actuated by way of storage condensers.

After the final signal unit for the final telegraph printer (corresponding to contact of Fig. '7) a pulse is omitted upon each revolution of the distributor at the transmitter and following thereon there is transmitted the synchronizing pulse which is designated P in Fig. 1b. This synchronizing pulse, in the same manner as the other transmission pulses, produces a telegraph signal in conjunction with a receiver control pulse. This telegraph signal is not further employed in the following operation.

The synchronizing pulse P received from the transmitter is superimposed by way of the contacts 3m upon the receiver testing pulses Eli and in opposite polarity thereto, is superimposed by Way of the contact 3l'b upon the receiver control pulses E12 also in opposite plurality thereto. The contacts 3la and b are closed simultaneously at the centre of the interval spacing unit before the transmission pulse P is received from the transmitter, and are opened one-quarter of a signal unit following the initiation of the transmission synchronizing pulse P. Consequently they remain closed for 75% of a signal unit.

and

ing to Fig. 7e superimposed upon each other in opposite polarity for the duration of the contact 3Ia. The remainder of the synchronizing pulse P received from the transmitter, which occurs outside of the contact period of 3m, is represented in broken lines in Fig. 7g (and also in the following figures). In Fig. 7g the received syn chronizing pulse is in phase with the receiver control pulse and the latter is just compensated, so that the phase shifter is not actuated.

In Fig. 7h it is assumed that P lags to a slight extent. The receiver control pulse is no longer rendered ineffective and causes the receiver synchronisation frequency and together therewith the receiver control pulses and the distributor to be shifted in phase for such time until the receiver control pulses assume the position according to Fig. 7g.

In Fig. 71' there is indicated the extreme permissible lag of P which can still be properly compensated. If the phase of P is shifted still further to the right, the receiver control pulse is rendered ineffective by the telegraph pulse which should fall on the distributor contact 30 and the regulation of the synchronism is cut off. With the assumed duration of the received transmission pulses the greatest permissible lag accordingly amounts to 1 signal telegraph units or bauds.

Ifon the other hand the transmission pulses are extended by echo effects to the duration of a signal unit, the greatest permissible lag of the pulses P'amounts to merely one signal unit. It

is true that with a considerable lag of this kind incorrect signals are received, but the regulation of the synchronism still operates in faultless manner, so that the transmission and receiver control pulses are again phased.

In order that considerable deviations in the phase of P from a predetermined value and the telegraphic errors thus caused do not remain unnoticed, there is provided an auxiliary contact H1, by way of which a relaxation device is actuated by thecounter-connection of P and E12, If P lags behind the contact H1, EIZ actuates a relaxation device, which actuates a relay and an indicating device.

In Fig. 7k there are shown the testing pulses P and receiver control pulses E12 superimposed upon each other in opposite polarity during the duration of contact 3Ib.. P and E12 are in phase, so that the effect of P is just eliminated by E12. If, on the other hand, P is slightly in advance as in Fig. 71, P actuates the phase shifter. The receiver control pulses and the distributor contacts are shifted slightly in phase, so that they again assume the position according to Fig. 71c.

In Fig. 7m there is shown the extreme permissible advance of P, in the case of which the phase of the receiver control pulses is still just corrected by Way of the testing contact 3H); In this connection it is assumed that P by reason of echo effects has been increased exactly to the extent of one-half of the duration of a signal unit. In the case of greater increase the advance of P may be more, but in the case of smaller increase less. Taking the most unfavourable case the maximum permissible advance amounts to approximately 75% of a signal unit.

With this considerable advance of P, as in the case of a very considerable lag, incorrect telegraph signals are recorded. Also in this case the great advance is recorded by way of the auxiliary contact H but only if P has not been too greatly extended by echo effects. For this event there is provided a special auxiliary contact H2, by way of which there are actuated by P a relaxation device and an indicating device if P is too greatly in advance in relation to.

the receiver testing pulses.

The contacts 3la and b and also HI and H! are preferably so designed that they can be varied within narrow limits.

In Fig. 8 there is shownan arrangement for carrying out the method according to Fig. 7. The received transmission pulses 81 act together with the receiver control pulses EU or E12 on the grid of the relaxation device K1 or K2. By means of the contacts 3m and Slb these pulses are applied to the grids only during the synchronizing period.

If P lags, K1 is negatively biased by Eli and is thus made non-conductive. The negative drop in potential at R11 is eliminated, so that the valve V1 becomes current-transmissive and the con-tact a1 is closed. The brush B of the motor M is connected with the potential 0, and the motor turns the phase shifter in such fashion that the receiver pulses are shifted backwards.

The relaxation device K1, shortly prior to the commencement of the testing period, is positively biased by the contact 30a (compare Figs. 7d and 8) and thus rendered conductive. Owing to the weak negative bias of v, applied to its grid by way of the resistance R1 the relaxation device Kl remains in the condition to which it has been brought by way of the contacts 3|a. or 30a.

In the case of advance of P the relaxation device K2 is positively biased by? by way of the synchronizing contact 3lb and made currenttransrnissive. A negative voltage drop is then developed across the resistor R2: which blocks the valve V2, so that the relay is actuated and the contact a: is closed. By means of the contact a: the brush B of the motor M is connected with the potential +220 v.. so that the motor rotates in the opposite direction as compared with the above example and shifts the phase of the receiver control pulses in the forward direction.

Shortly prior to the testing period the relaxation device K2 is made non-conductive by way of the contact 30b (compare Figs. 7d and 8) As in the relaxation device K1 a negative bias of ---10 v. is used in order that the relaxation device K: may remain in the condition into which it has been brought by way of the contacts 3!!) and 30b.

The receiver control pulses are produced in the most simple form by means of a relaxation oscillation generator, which is controlled by the synchronisation potential or a frequency derived from the same. The short receiver control pulses used for synchronizing are preferably produced by the same relaxation oscillation generator, by which the other receiver control pulses are produced, which latter serve to convert the received telegraph pulses into telegraph signals. On the other hand the long, receiver control pulses must be produced by another relaxation generator, which is controlled either with the short receiver pulses or with the same synchronisation potential as the short pulses. In the latter case there must be provided a special phase shifter, by means of which the long receiver control pulses can be brought into phase with the remaining receiver control pulses.

The method according to Figs. 7 and 8 is not limited to multiplex telegraphy. It can be employed to any other telegraph system, and more particularly also for image telegraphy.

I claim as my invention:

i. In a system for transmitting and receiving intelligence telegraphically in which unidirectional telegraph pulses and synchronizing pulses of relatively short and substantially equal duration are transmitted, said pulses first being derived from electrical telegraph signals representative of the intelligence to be transmitted and periodically interspersed with synchronizing signals, and wherein the received telegraph pulses are reconverted into electrical telegraph signals with the aid of periodic control pulses 1ocally generated at a receiving station and synchronized with said synchronizing pulses, receiving apparatus including a relaxation device capable of assuming a first condition and a second condition characterized by the absence .or presence respectively of an electron discharge in said device, means for applying the received unidirectional telegraph pulses to said device for transfer thereof from said first condition to said second condition, means for applying said locally generated control pulses to said device for transfer thereof from said second condition to said first condition for reproducing electrical telegraph signals of the same character as those from which said telegraph pulses were derived, means for applying the reproduced telegraph signals to apparatus for reproducing the transmitted intelligence, and means responsive to the received synchronizing pulses and said locally generated control pulses for developing a control effect dependent upon the phase relation between said synchronizing pulses and said control pulses and adapted to initiate synchronization of said control pulses with said synchronizing pulses.

2. In a system for transmitting and receiving intelligence telegraphically in which unidirectional telegraph pulses and synchronizing pulses of relatively short and substantially equal duration are transmitted, said pulses first being derived from electrical telegraph signals representative of the intelligence to be transmitted and periodically interspersed with synchronizing signals, and wherein the received telegraph pulses are reconverted into electrical telegraph signals with the aid of periodic control pulses locally generated at a receiving station and synchronized with said synchronizing pulses, receiving apparatus including a grid-controlled relaxation discharge device having a cathode, a control grid and an anode, an output resistor connected in the anode circuit of said device, means for applying a biasing potential to said grid, means for applying the received unidirectional telegraph pulses and said locally generated control pulses to said control grid in opposite polarity thereby to elevate the lower relaxation potential above the anode potential for termination of an electron discharge in said. device and tolower the upper relaxation potential below said anode potential for initiation of an electron discharge in said device, thereby to produce across said output resistor telegraph signals of the same character as those from which said telegraph pulses were derived, means for coupling said output resistor to apparatus for reproducing the transmitted intelligence, means responsive to the received synchronizing pulses and said locally generated control pulses for developing a control effect adapted to initiate synchronization of said control pulses with said synchronizing pulses.

3. In a system for transmitting and receiving intelligence telegraphically in which unidirectional telegraph pulses and synchronizing pulses of relatively short and substantially equal duration are transmitted, said pulses first being derived from electrical telegraph signals representative of the intelligenc to be transmitted and periodically interspersed with synchronizing signals andwherein the received telegraph pulses are reconverted into electrical telegraph signals with the aid of periodic control pulses locally generated at a receiving station and synchrosecond condition, and means controlled by said control signal and adapted to initiate a shifting of the phase of said locally generated control pulses to produce synchronism thereof with said received synchronizing signals.

4. In a system for transmitting and receiving intelligence telegraphically in which unidirectional telegraph pulses and synchronizing pulses of relatively short and substantially equal duration are transmitted, said pulses first being derived from electrical telegraph signals representative of the intelligence to be transmitted and periodically interspersed with synchronizing signals and wherein the received telegraph pulses are reconverted into electrical telegraph signals with the aid of periodic control pulses electrically generated at a receiving station and synchronized with said synchronizing pulses, receiving apparatus including a relaxation device capable of assuming a first condition and a second condition characterized by the absence or presence, respectively, of an electron discharge in said device, means for applying said control pulses and the received synchronizing pulses to said device for transfer thereof from said first condition to said second condition upon non-coincidence of said pulses, means for deriving a control signal from said device in its second condition, means controlled by said control signal and adapted to initiate a shifting phase of said locally generated control pulses to produce synchronism thereof with said received synchronizing signals, and means for periodically returning said device to said first condition prior to application of said pulses thereto.

5. In a system for transmitting and receiving intelligence telegraphically in which unidirectional telegraph pulses and synchronizing pulses of relatively short and substantially equal duration are transmitted, said pulses first being derived from electrical telegraph signals represen tative of the intelligence to be transmitted and periodically interspersed with synchronizing signals, and wherein the received pulses are reconverted into electrical telegraph signals with the aid of periodic control pulses locally generated at a receiving station and synchronized with said synchronizing pulses, receiving apparatus including a relaxation device capable of assuming a first condition and a second condition characterized by the absence or presence, respectively, of an electron discharge in said device, a first contact means normally open and adapted to be closed periodically for applying said locally generated control pulses and the received synchronizing pulses to said device for transfer thereof from said first condition into said second condition upon non-coincidence of said pulses, means for deriving a control signal from said device upon non-coincidence of said pulses, means controlled by said control signal and adapted to initiate a shifting of the phase of said locally generated control pulses, and a second contact means normally open and adapted to be closed periodically for applying a predetermined potential to said device for returning the same to said first condition prior to application of said control and synchronizing pulses thereto.

ERICH HUDEC.

CERTIFICATE OF CORRECTION.

ERICK gumzc It is hereby certified that Lani-er appears 1n the printed specification or theatpve numbered petent requiring co rreefloxi gplto llow a y Page-'3', neeline k7, after 'I1ea" 1naert '--betwe en the 'fippe'r rel-fitted potentialyu Y and-'--; pigs 7 {first/calm lme'69-70, 'atrik e 'out "interv al'; and w 0nd column, line 50; for "519ml telegraph read -te1eg1 'r su -se t'the eaid Letter; Patent. should bereed with this correction therein "that the heme may c'ontormto the record of the cage in the Patent Office. 4

'Signed and sealed thie 20th day .of October; A. n. 1912.

' Henry Van Aradale, 9 Acting commissioner of Patents.

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