US2737544A - Telegraph repeaters - Google Patents

Description

March 6, 1956 E. P. e. WRIGHT ETAL 2,737,544

TELEGRAPH REPEATERS 5 Sheets-Sheet 1 Filed March 15, 1953 Inventor E. P. G. WRIGHT- D. A. EI R f. Attorney March 1956 E. P. G. WRIGHT EIAL 2,737,544

TELEGRAPH REPEATERS 5 Sheets-Sheet 2 Filed March 13, 1953 TIME SCALE sr TSP 7/38 D. A.WElR.

S M j Inventor E. P G WRIGHT- SPA c5 A ttorney March 6, 1956 E. P. G. WRIGHT ETAL 2,737,544

TELEGRAPH REPEATERS 5 Sheets-Sheet 3 Filed March 13, 1953 OD EV SPACE MARK .lnventor E.P- G. WRI GHT D. A. WEIR 7 Attorney March 6, 1956 E. P. G. WRIGHT ETAL 2,737,544

TELEGRAPH REPEATERS Filed March 15, 1953 5 Sheets-Sheet 4 I l I I I I I I T/ME SCALE I I I L J s7 F/ G .4.

r/3/ sp GZ/CQQ SPAC 90/ MARK I ,4 6/9 7/3 In ventor E. R G. WRIGHT D. A, w El R Attorney March 1956 E. P. G. WRIGHT ET'AL 2,737,544

TELEGRAPH REPEATERS 5 Sheets-Sheet 5 Filed March 13, 1953 T/ME SCALE F/GS.

SP F

SPACE v G/S Inventor E.R G.WR| GHT- A. WEIR Attorney.

United States Patent TELEGRAPH REPEATERS Esmond Phiiip Goodwin Wright and Donald Adams Weir, London, England, assignors to International Standard Electric Corporation, New York, N. Y.

Application March 13, 1953, Serial No. 342,124

, Claims priority, application Great Britain March 17, 1952 13 Claims. (Cl. 178-2) This invention relates to electric telegraph systems in which intelligence is conveyed in the form of signal combinations, each combination consisting of an invariable number of signal elements, and each element being of two possible kinds.

The object of the invention is to increase the amount of intelligence which can be transmitted in a given period of time.

In is broadest aspect, the invention provides a telegraph system comprising means for transmitting combinations of elements of two kinds, each of which combinations consists only of a start element and a constant number of intelligence elements, the start element of any signal combination being always of opposite kind to that of the last intelligence element of the immediately preceding combination.

It is to be understood that by the term intelligence elements are meant the elements whose selection and arrangement vary according to the character represented by the combination.

In the conventional start-stop teleprinter code, each signal combination consists of an invariable start element of one kind (e. g. space), (usually) five permutable intelligence elements of either kind and an invariable stop element of opposite kind to the start element.

According to a second aspect of the invention there is provided a telegraph system comprising means for receiving combinations of elements of two kinds, each of which combinations consists of invariable start and stop elements and a constant number of intelligence elements, which system further comprises meansfor converting the received combinations into other combinations, each of which consists only of a start element and a constant number of intelligence elements, the start element of any sig nal combination being always of opposite kind to that of the last intelligence element of the immediately preceding combination, together with means for transmitting the converted combinations.

According to a further aspect of the invention there is provided a telegraph system comprising means for receiv ing combinations of elements of two kinds, each of which consists only of a start element and a constant number of intelligence elements, the start element of any signal combination being always of opposite kind to that of the last intelligence element of the immediately preceding combination, which system further comprises means for converting the received combinations into other combinations each of which consists of invariable start and stop elements and a constant number of intelligence elements, together with means for transmitting the converted combinations.

Assuming the conversion is made from seven-element teleprinter code combinations each having five intelligence elements, it becomes possible to retransmit six-element combinations having the same five intelligence elements, thus saving considerable transmission time.

Alternatively, seven-element signal combinations may be transmitted, each having six intelligence elements. The

additional intelligence element may be used to convey further information such as a case shift signal individual to each combination. On the other hand, as will be explained more fully later, the additional element may be used in connection with an error-checking system.

An embodiment of the invention together with various modifications thereof will now be described with reference to the accompanying drawings of which:

Fig. 1 is a block schematic diagram of an electronic regenerative repeater adapted to receive ordinary startstop seven-unit teleprinter signal combinations and to convert them into six-unit combinations comprising a pseudostart signal element according to the invention,

Fig. 2 is a block schematic diagram of an electronic regenerative repeater adapted to receive six-unit combinations comprising a pseudo-start signal element according to the invention and to convert them into ordinary startstop seven-unit teleprinter signal combinations, I

Fig. 3 shows a modification of the circuit of Fig. 1 adapted to add a seventh, error-checking code element to each transmitted combination,

Fig. 4 shows a modification of the circuit of Fig. 2

adapted to examine the seventh, error-checking code elesuitable references have been given to other specifications from which full particulars may be obtained. Thus, the drawings are functional in nature and are intended to show the processes involved rather than the actual means.

used.

The various symbols will be explained as they enter the description.

In this embodiment, the invention is applied to the typeof cold-cathode regenerative repeater which forms the subject of the co-pending application of V. J. Terry, D. S. Ridler, and D. A. Weir, filed March 29, 1949, and bearing Serial No. 84,104.

Referring to Fig. 1 ordinary seven-unit start-stop teleprinter signal combinations are supplied to the Mark and Space input leads shown in the lower part of 'the figure. They are examined by gates G1 and G2 at times determined by examining pulsesapplied at point P+. These examining pulses are of positive polarity and have a repetition frequency of five kilocycles per second. Gates G1 and G2 each require two inputs before they can produce an output as denoted by the numeral 2 within the gate symbol. A gate of this type is disclosed in the specification of British Patent No. 636,700 and its operation is there fully explained.

In the stop condition, marking potential is present on the line so that positive pulses are passed through gate G1 on to lead M.

When a start element is received, the opposite gate G2 conducts and pulses appear on lead S. These pulses pass to the start tube ST of a two-condition device represented by the divided block F1. This device may conveniently comprise a pair of trigger tubes interconnected in Well known manner whereby the conduction of either tube effects the extinction of its partner. Normally the stop tube SP is fired but the first pulse from gate G2 changes over the condition of F1 by firing the start tube ST.

The firing of the start tube of F1 causes a pulse to be passed to a two-input gate G4. The other input to gate G4 comes from a five kilocycles-per-second negative pulse source P synchronised with the source of positive pulses P+. When gate G4 is energised from the start tube of F1, these negative pulses are passed to a time scale circuit comprising three multi-gap gas-filled dischargetubesshown' as blocksCi, C2, and C3; and two further gas-filled trigger tubes shown as gating devices G and G6.- The time scale circuit is connected-and designed to operate in the same manner as that shown and described in said co-pending application. It s function is to count five-kilocycle negative pulses applied at points marked P. As explained in the last mentioned specification, C1 is arranged to count all the pulses, C2 to count every tenth pulse and C3 to count every hundredth pulse. At any particular time after counting begins, a discharge will be present across aparticular gap in each tube, which gap will depend upon the number of pulses counted and hence upon the time that has elapsed. Thus after, say, 175 pulses have been counted, gap 1 in the hundreds tube C3 will be fired together with gap 7 in the tens tube C2 and gap 5 in the units tube C1. Since there are five pulses every millisecond it will be apparent that the time interval which must elapse before the above-condition can be reached is 175+5=35 milliseconds. In saidv co-pending application it is further explained and shown how the simultaneous firing oftwo or three specific gaps in respective tubes may be used to open a gating. circuit at a particular time.

In order to reduce the complexity of Figs. 1 and 2 of the present case, circuits for connecting the outputs of the counting tubes with various gates' which are required to be opened at specific times have been omitted but, instead, the times at which potentials are derived from the timescale circuit are shown against various conductors connected to gates thus: T1, 21, 41, etc. These figures are the time intervals in milliseconds when counting tube outputs are obtained after the starting of the time scale circuit. In order to determine which gaps must be fired at a particular time it is only necessary to multiply the time in milliseconds by five. Thus at time T21, 105 pulses will have been counted and the gaps fired will be gap 5 of C1, gap 0 of C2 and gap 1 of C3.

The first action performed under the control of the time scale circuit is the transmission of the pseudostart element which, as has already been explained, is always arranged to be of opposite polarity to the standing line condition at the end of the preceding element.

At milliseconds, an examining pulse from the time scale circuit is applied to two examining gates G7 and G8 eachof which requires one other input. These other inputs are taken respectively from the space and mark tubes of an output two-condition device F3 similar to F1.

If the output device F3 is in the space condition at 10 milliseconds (i. e. the last element of the previous combination was a space) the' gate G7 opens and applies a pulse to the mark lead which in turn changes over F3 to the mark condition.

If the output device F3 is in the mark condition at 10 milliseconds (i. e. the last element of the previous combination was a mark) the gate G8 opens and applies a pulse to the space lead which in turn changes over F3 to the space condition.

It will be evident that the interconnection of gates G7 and G8 with the output device F3 is such that at 10 milliseconds the line conditions are always reversed so inserting the pseudo-start element already referred to.

In regenerative repeaters it is' the invariable custom to examine each of the seven elements of the incoming slgnal combinations in turn at their respective centres. In the present case this examination is confined to the five intelligence-bearing permutable elements. The ex- 811111131101! is carriedout under the control of pulses derived at 30, 50, 70, 90 and 110" milliseconds from thetime scale circuit and applied to two-examining gates G11 and G12. Gate G11 opens: for a mark element and passes a pulse forward-to fire the: mark tubeofoutput device F3. Similarly gate G12 opens for a space element and passes a pulse forward to fire the space tube of F3.

At 138 milliseconds the stop tube SF of the twocondition device F1 is fired, so extinguishing the start tube ST and cutting off the supply of pulses to the time scale circuit. At 138 milliseconds the number of pulses which has been counted by the time scale circuit is l38 5=690. This means that a discharge is present across gaps t a and 6 respectively of tubes C1, C2 and C3. It is thus necessary to reset only tubes C2 and C3 to the initial condition i. e. with the discharge across gap 0 in either tube. This resetting is done by a transient voltage pulse produced (for example by reactive coupling) as F1 changes over. In the drawings, this transient output is differentiated from the other outputs by being shown as emanating from the end and not the sides of the block.

The output signal combinations from the device F3 will comprise the pseudo-start signal and five intelligencebearing permutable elements. These will be followed by an interval of at least. anotherelements duration during which the polarity of the line will remain the same as that of the last permutable element. At the end of this interval the next psuedo-start element will arrive, of opposite. polarity to the last permutable element. Thus the interval between successive outgoing combinations will be at least 140 milliseconds which is, of course, the minimum interval between successive incoming combinations. In order to effect a saving in transmission time, the outgoing combinations may be recorded on a medium such as a magnetic tape. They can then be reproduced in such a manner that the above-mentioned interval is eliminated and each combination takes only milliseconds6 element periods-to transmit.

At the receivingstation it would be necessary to provide complementary recording and reproducing equipment so as to spread the signal combinations out before converting them to ordinary seven-unit teleprinter code combinations each lasting for at least milliseconds.

In the embodiment being considered, it is assumed that the output terminals of Fig. 1 are directly connected over a transmission circuit to the input terminals of Fig. 2.

The input circuit of Fig. 2 is similar to that of Fig. 1, the gates G14 and G15 being respectively analogous to the gates G1 and G2. During a mark signal, positive pulses appear on the mark lead M (via gate G14) and during a space signal, pulses from the same source appear on the space lead S.

An output device F5, analogous to the device F3 in Fig. 1, comprises a pair of tubes for spaces and marks and these provide respective inputs to. two gates G16 and GT7 which are provided to detect the pseudo-start element. Gate G16 has another input connected to space tube S in the device F5 and gate G17 has an input connected to the mark tube of the same device.

If the device F5 is left in the mark condition it means that the next pseudo-start element will be a space and accordingly a second input is applied to gate G17 thereby conditioning the. gate to detect it. If on the other hand the pseudo-start signal is a mark after an interval of space it will be detected by the opposite gate G16.

Whichever of'thesev gates open, a pulse is passed to fire the start tube ST of a two-condition device F4. This acts in the same way as the device F1 in Fig. 1 and starts a time scale circuit of the same type as that used in the circuit of Fig. 1.

At 10 milliseconds the space tube S of the output twocondition device F5 is fired thereby forcibly inserting the invariable start element which precedes each teleprinter signal combination.

The five permutableelements of the received signal combinations are examined in the usual manner by gates G19 and G20 (analogous to gates G11 and G12 in Fig. 1) and the output device F conditioned accordingly.

At 130 milliseconds, the mark tube M of the output device F5 is fired thereby forcibly inserting the invariable stop signal which concludes each teleprinter signal combination.

At 138 milliseconds the time scale circuit is stopped and reset in the same manner as the time scale circuit of Fig. 1.

If a six-unit code is to be received over the line the input to F5 (Fig. 2) at T130 is omitted and the input to F4 at T138 is changed to T118. The intelligencebearing elements are recorded, for example, on a magnetic tape recorder and the usual invariable start and stop elements added when the signals are reproduced.

It has already been explained that if seven-unit code combinations are transmitted, each comprising a pseudostart element and five permutable elements, the remaining element may be used to provide a simple error-checking device. This can be achieved by modifying the circuits of Figs. 1 and 2 as will now be described with reference to Figs. 3 to 5. In these latter figures, the items common to the earlier figures have been accorded the same references.

Briefly, the method of error-checking comprises the steps of counting the number of space elements in each code combination (not counting the start element), and inserting a space for the seventh element if the number of spaces is odd and a mark if the number of spaces is even. At the receiver a similar evaluation is made and the two check elements are compared so as to see if an error has taken place.

Referring to Fig. 3, the space content of the incoming code combinations is determined by a two-stage counting device C4 comprising (for example) two gas discharge gaps for registering odd and even totals respectively. At 2 milliseconds after the beginning of each cycle the device is reset in the even condition.

At 25, 45, 65, 85 and 105 milliseconds, the condition of the space lead S is examined by a gate G3 and these examination times occur respectively during the five permutable elements of a code combination. The condition of C4 is reversed for each space element so that after the examining pulse at 105 milliseconds, the device stands in the even condition if there were no spaces or two or four spaces, and in the odd condition if there were one, three (or five) spaces.

At 130 milliseconds, the condition of C4 is examined by a pair of gates G-and G10. If C4 stands at odd, G9 opens to fire the output device F3 into the space condition, while if C4 stands at even, G10 opens and F3 is changed to mark, if not already at mark.

Thus the seventh element, inserted at 130 milliseconds indicates whether the five permutable elements of the combination comprised an odd or even number of spaces. Referring now to Fig. 4 which shows the modified receiving side of the system, a space counter C5 is provided, controlled by an examining gate G13. The operation of the last two items is exactly similar to that of C4 and G3 already described in connection with Fig. 3. Thus the space content of each received combination is recorded on C5.

If a received combination contains, for instance, an odd number of spaces, then, the seventh element can be expected to be a space and the pseudo-start element of the succeeding combination should be a mark. Thus, if C5 is standing in the odd condition at the completion of a receiving cycle, as soon as pulses appear on the mark lead, a gate G21 opens and starts the time scale circuit by firing F4 into the start condition.

If on the other hand the preceding combination comprises an even number of spaces, a gate G22 responds to the start transit from mark to space and starts the time scale circuit as before. 7

The presence of an error is detected by a two-condition device F2 having (for example) two discharge gaps one representing the error condition and the other the no error condition. At five milliseconds after the start of each cycle, this device is placed in the no error condition.

If a received combination has been found to have an odd number of spaces, then when the seventh element arrives, the space counter C5 is standing in the odd condition. The seventh element should then be a space. At milliseconds, the condition of the mark lead is examined by a gate G23 and if a mark is present (which should not be the case) gate G23 opens and changes over F2 into the error condition.

If the received combination contains an even number of spaces and the seventh element proves to be (wrongly) a space, then at 130 milliseconds, a gate G24 opens and similarly changes over F2 into the error condition.

The device F2 may, for example, control a contact marking relay so that in the error condition a visual or aural alarm is given. The precise means for giving an indication of error are, however, immaterial to the present invention.

At 131 milliseconds, if an error has been assumed, a gate G18 opens and ensures that the space counter C5 is reset in the even condition before the end of the receiving cycle.

The receiving arrangement of Fig. 4 suffers from the disadvantage that any momentary transition from one line condition to the other will, during the rest condition be interpreted as a pseudo-start element. This renders the receiver vulnerable to stray interference. In order to avoid this, means may be provided to examine the line condition at some interval (say 9 milliseconds) after the receipt of a supposed pseudo-start element and, if the line condition has changed back again, to stop the time scale circuit before any signal is sent out from the receiver. A circuit for achieving this is shown in Fig. 5 which should be considered with Fig. 4.

Let it be assumed that the number of spaces in the last combination was odd, then the space counter C5 is set at odd, the incoming line condition (assuming no error) is space and the receiving cycle will begin as soon as a mark is received. At 9 milliseconds a gate G25 examines the space lead and if the latter is now energised, signifying that the supposed start element was spurious, a pulse is passed to the start-stop device F4 to place it again in the stop condition.

A gate G26 acts in a similar capacity if the start transition is from mark to space and the line has reverted to the mark condition by the time 9 milliseconds has elapsed.

it will be apparent that in addition to providing a simple means of checking errors in reception, the arrangements described in connection with Figs. 3 to 5 provide a certain measure of security since a monitoring teleprinter would only start correctly when the start element was space and would be liable to start prematurely when the stop condition was space. Thus a teleprinter connected to a line between the transmitter and receiver would not be able to receive messages correctly.

While the principles of the invention have been described abo-ve in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What we claim is:

1. A telegraph system comprising means for continuously receiving combinations of elements of two kinds, each of which combinations consists of invariable start and stop elements and a constant number of intelligence elements, which system further comprises means for converting the received combinations into other combinations, each of which consists only of a start element and a constant number of intelligence elements, the start element of any signal combination being always of opposite kind to that of the last intelligence element of the 7 immediately preceding combination, together with means for transmitting the converted combinations.

2. A telegraph system comprising means for continuously receiving combinations of elements of two kinds, each of which consists only of a start element and a constant number of intelligence elements, the start element of any signal combination being always of opposite kind to that of the last intelligence element of the immediately preceding combination, which system further comprises means for converting the received combinations into other combinations each of which consists of invariable start and stop elements and a constant number of intelligence elements, together with means for transmitting the converted combinations.

3. A telegraph system as claimed in claim 1 in which means is provided for converting the stop element of the received combination to an additional intelligence element.

4. A telegraph system as claimed in claim 3 in which the additional intelligence element is used to give a case shift indication.

5. A telegraph system as claimed in claim 3 in which the additional intelligence element is used to indicate whether the total number of the remaining intelligence elements of one kind in the combination is even or odd.

6. A telegraph system as claimed in claim 1 comprising means for registering the last element or" a converted combination and means controlled by the register during the invariable start element of the next received combination for inserting into the corresponding converted combination a start element of opposite kind to that registered.

7. A telegraph system as claimed in claim 2 comprising means for registering the last element of a received COlTr bination and means controlled by the register during the start element ofthe next received combination for initia ing the conversion and transmission of this next received combination.

8. A telegraph system as claimed in claim 6 in which said register means comprises a two-condition device and in which said insertion means comprises a pair of gating devices cross-connected to said two-condition device so that either gating device may only be rendered operative to insert a start element of one kind when said two condition device is in a condition representing an element of the opposite kind.

9. A telegraph system as claimed in claim 7 in which said register means comprises a two-condition device and in which said initiating means comprises a pair of gating devices cross-connected to said two-condition device so that either gating device may only be rendered operative is in a condition representing an element of the opposite" kind;

10. A telegraph system as claimed in claim 5 comprising a two-condition device, means for registering by the concl.ion of said device whether said total number of elements of one kind is even or odd and a pair of gating devices controlled by said two-condition device in such manner that either gating device may only be rendered operative to insert an additional element of a respective kind when said two-condition device is in a respective one of its conditions.

11.. A- telegraph system as claimed in claim 2 in which the last intelligence element of a received combination is used to indicate whether the total number of the remaining intelligence elements is even or odd, comprising means at the receiver for independently determining Whether said total number is even or odd, means for comparing the result of said determination with the last intelligence element as received, and'means for giving an error indication in the event of non-agreement resulting from said comparison.

12; A telegraph system as claimed in claim ll in which the result of said determination is stored on a two-condition device, in which said comparison means comprises a pair of gating devices controlled respectively by said two-condition device in its two-conditions and further controlled by the received signals during said last permutable el ment in such manner that one gating device will be operated if the disagreement is of one kind and the other gating device will be operated if the disagreement is of the other kind and in which said error-indicating device is arranged to be operated by either of said gating devices.

1.3 A telegraph system as claimed in claim 9 comprisinga further pair of gating devices controlled by said two-condition device, means for rendering one or other of said gating devices operative at a given time after the receipt of a start element to check that the start element is still being received, and means operative if the start element has not persisted, to prevent the initiation of the conversion operation.

References Cited in thefile of this patent UNITED STATES PATENTS

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