US2328789A - Submarine cable signaling system - Google Patents

Description

Sept. 7,y l943. a. s. DIAMOND 2,328,789

SUBMARINE CABLE SIGNALING SYSTEM Filed July l0, 1941 3 SheetS-Sheet l Sept. 7, 1943- B. s. DIAMOND SUBMARINE CABLE SIGNALING SYSTEM vFiled July 1o, 41941 3 Sheets-Sheet 2 Sept. 7, 1943. B. s. DIAMOND SUBMARINE CABLE SIGNALING SYSTEM Filed July l0, 1941 3 Sheets-Sheet 3 h. wai@ k.

A TTORNEY Patented Sept. 7, 1943 UNITED srrxrEs rasTENTV oFFlcE s l 2,328,7s9mY l SUBMARINE' CABLE lSIGALING Bertram S. Diamond, St. Johns, Newfoundland,`

assigner to Commercial Cable Company, New1 York, N. Y., a` corporation of New York application July 1o, 1941, serial No. 401,807

8 Claims.

This invention relates to submarine cable signaling systems. y Y

It is known that the attenuation of sinusoidal alternating lcurrents transmitted over an ocean cable varies with the frequency of the current. The phase of the received current with respect to that at the sending end .also varies ,with the frequency of the current. i

As cable Morse signal currents contain alternating currents of many frequencies, the effect of the attenuation `and phase shift of these components is .to cause a great distortion of the received signaling currents.

`This distortion is partially overcome by the use of shaping networks at the sending end and atthe receiving end of the cable circuit in a mannerwell known in the art of cable operation.

It has been `found very difficult, however, to carry this correction beyond a certain point by means of available electrical ,networks and the remaining distortion"is the principal cause in limiting the speed of operation of cable circuits. Certain of the shorter signal combinationsare amongthe most important as regards the application ofV pre-distortion to iurtherreduce distortion at the receiving end. Amongthese are the vcombinations for A, N, D, G, W, U, and a succession of alternate Es and Ts.

Y ASignals received over a long cable may beconsidered as being'formed by a'number of sinusoidal components. For convenience, definite sequences of these signal combinations may be studied which, being then periodic, can be analyzed by Fouriers Theorem. The analysis sh'oWs that each ofthe various wave forms for the sigf nal combinations listed above has two essential components, namely, a fundamental frequency and a harmonic, and that signal distortion is` largelydue to partialsuppression and phase shift ofV harmonics, particularly such harmonics as Zit/3, 37b/4, 3yr/5, tn/l, 5n/1, etc., where n is the rate of speed in signaling elements.

The object of the present invention is directed towards making a further improvement in correcting distortion by pre-distorting the signal currents at the sending end in a sense opposite to that which is caused by their transmission over the cable. Thus, if the currents of various essential`frequencies, listed above, which form the cable signals when combined, were transmitted with their` respective amplitudes such that each would have approximately the same amplitude on the receiving instrument as ,at the sending end and, at the same time, a phase correction was applied to each component that i' would counteract the `phase ,displacement vvthat occurs in transmission, the received signals would lbe free from distortion. l

The `invention will'now be described with the aid of the accompanying drawings., of which,

Figi. 1 Yis a schematic showing offthe circuits of `one embodiment of the invention.

. Fig. 2 shows the circuit arrangement for a modification of the invention.

FigQS 'is a group 4of curves illustrating signals received from a circuit according to the present invention;` Y

Fig. Llis a group of signal curves from an ordinary transmitting circuit.

Fig. 5 shows the effect of transients on a wave form, while Fig. 6 shows the same wave form as received from a transmitter circuit according to thepresent invention. y

Fig. shows curves of groups of three reversals and the curbing impulses transmitted therewith.

Referring now to Fig. 1 of the drawings.

The :contacts of a tape controlled transmitter i are shown schematically in the drawings. The mechanical detailseoi the transmitter being well known areomitted, g but it is to be understood that the mechanism is of the type, in the present embodiment which sends block signals, rather than beat signals, that is to say, that instead ofsending out four beat impulses for the letter H, one block impulse is sent of a duration equal to the time of sending the four beat signals. The transmitter has a dot contact lever 2 and a dash Contact levert cooperating with Xed `contacts 6 and 5 respectively. The operation ofvthese contacts is lcontrolled by a tape and tape feeding mechanism and cooperating pocker rods attached to said contact levers which sense perforations in a tape. This'mechanism is well known and not shown. An adjustable cam 6 turning in xed relation to a member, not shown, for reciprocating the pocker rods, engages cam arm I and closes contacts 8 and 9 once each revolution.

lWhenthe dot pocker rod enters a perforation in the tape, contacts 2 and Il close, and positive potential from sources ie and il ows through a Winding l2 of dot locking relay M and I3` of dot pulse transmitting relay l5 back to negativo' potential on the pecker contacts.`

25 and 2@ of the dot and dash lockingrelays and 2l and 133 of therespective pulse transmitting relays are constantly energized by a light potential suicientto return the armatures to the left or spacing side whenever the other windings arc deenergized. i i

When eithendot locking relay Ill. or` dash locking relay 2l is operated, the tongue thereof moves rposed of dot, dash and'zero elements.

from the left or spacing contact; S to the right or marking contact M where it remains until the current is cut oiA by the opening of the corresponding pecker contact. The spacing Contact of the dot relay is connected through winding 28' thereof and through winding 29 of a dot signa-l transmitting relay 3b. Marking contact M is connected through winding 32 in-series with Winding 23 of dot signal transmitting relay 30. CamV contact 8 is connected to both of tlfie'circuits-just described at junction point 34.

The windings of relays 2| `and 3| are interconnected in a similar manner. Dash locking relay 2| has its contact S connected through winding 3l and winding 38 of relay 3| to the tongue of relay ifi. Marking contact M of relay 2| is lconnected through winding -llthereo'f 'and winding 4| of relay 3| to the tongue o-f` dot locking relay Ut. toa source of positive potential. 'Marking contacts M of signal transmitting relays 3|) and 3| are connected through suitable resistances R5- and R8 to the positive pole of a source'of potential 45, While the corresponding spacing contacts are similarly connected to the negative pole thereof through resistances R5 and R1.

Tongue 45 of dot signal transmitting relay is connected to ground and also through condenser 48 to the apex 5| of aconventicnal cable bridge duplex. Tongue Mis connected through Winding l t9 of transformer 56 to apex 5 I.

One terminal of winding 52 of transformer 5U is connected through variable condenser 53 to tongue 5d Aof relay l5, while the opposite terminal is connected through variable resistance 575, for f locking relayglli, dash lockingrelay 2|', signal v transmitting relays 3l! and 3| up to and including the actual cable circuit, with the exception of the Thetongue of relay 2| is connected transformer circuit,` is well known and operates in the usual manner. Closing of a dot or dash transmitter Contact 'operates either the-dot or dash locking relay. The subsequent closing of cam contacts S and 9 operates acorresponding signal transmitting relay overa circuit prepared by the operation of leither dot or dash locking relays.

until the cam contacts 8 and 9 again close, and from their tongues are seni-l the various three element signal combinations of cable Morse, co-m- When a zer-o signal follows a dot or dash signal the lock` ing relays are not operated, their tongues having both been restored to their spacing contacts-by the weak current through the windings 25 and 25,

and the closing of cam contacts 8 and 9 causes the previously operated dot or dash signal transmitting relay tongue to return to its spacing contact and thus send a zero signal to the cable.

The signal transmitting relays being polarized remain in their last operated position The secondary t9 of transformer however,

is included in the output circuit from the signal transmitting relays and theprimary 52`thereof is energized by current from potential source 51 as pulse transmitting relays l5 and 22 are operated.

It'will' benoted that these relays operate' atthe f sameitime as dot andfdash locking'relay'sA [4T and operation of thefdot pulse transmitting relay l5.

which was operatedvdirectly from the same closing of the dot contacts 2 and l! of the cable transmitter. As previously stated, the transmitter sendsv outblock signals, and relay l5 will remain on its marking contact until dot transmitter contacts 2 and 4 again open.

Condenser 53 is inserted in the transformer in,- put'c'ircuit, so that this circuit may be tunedwto any desired range of frequenciesand resistance 55 is inserted in orderfto control the amplitude and the sharpness of the tuning. With proper Values ofv inductance in the transformer pri'- mary and secondary respectively, and with the proper' ratio 'o-f the effective E. M. F. developed across the transformer secondary to that of the signaling battery on the signal` transmitting relays, the amplitude of the higher frequencies may be greatly increased in relation to that of the lower frequencies with'tlie result that signal shape at high speed constantsis considerably irn-r proved at the receiving end and higher rates of speed are` thus made possible. pre-distortion bythe use of the circuits of Fig. 1 is shown by the signals of Fig, 3. should' be compared with those of' Fig. 4 which Were sent without pre-distortion.

The insertionA of inductance in the transmis-v sion mesh has the effect of changing the phase relationships between the various frequency components and the 'signals' tending to retard .the vhigher frequencies relatively. To compensate forthis, the signal transmitting relays should bev retarded in order to lobtain the best results at high speed constants, the actual phase difference between the pulse transmitting relays and the signal transmittingY relays which will give b'est'results depend on the various circuit constants'. The retardation of the signal transmitting relays may be accomplished by any Well known method, for example, the adjustable cam and contact arrangement shown in the present embodiment, and/or the insertion of a relay in the cam contact circuit'.

Condenser 48 is for the purpose of by-passing Athose higher harmonics which are imperceptible at the receiving end and play no part in the formation of signals but are troublesome in ob-r V4three components, a transient, a periodic, and a: second transient, the first" transient being of the same polarityv asthe first element in the trainand the second transient being of the same polarity Aas-'the last element of the train. The relative amplitudes of ltransient and periodic Vmovements before entering the receiving network will vary according tothe rate of speed, KRlJf the:cable,and` nature of the sending Ilet- Wor f The effect of' this y These signals Fig. shows the effect of transients on trains of reversals, each of four cycles, as received at a high speed constant from a standard transmission network. It will be observed that the rst and last elements are thicker and have greater amplitude than the inside elements.

Fig. 6 shows trains of reversals at the same speed and with the same receiving conditions but With the transmitting circuit of Fig. 1. This circuit as well as the modification thereof described below provides shorter pulses of opposite polarity to that of the signaling element at the beginning and ending respectively of each group of signaling elements, when the transformer secondary is connected so that it sends a pulse in the proper sense with respect to the signal from the Signal transmitting relays. These short impulses, which may be termed curbing impulses, -curb the transients, and reduce considerably distortion rom this cause. This is shownin Fig. 7 which represents the sending end pulsesr of a train of reversals. The train of reversals in this case is one of three complete cycles.

Another embodiment of the invention is shown in Fig. 2 in which two tuned transmitting units are used in addition to the normal signal transmitting relays. same manner as the corresponding relays of Fig. 1 but in this case two pairs of pulse transmitting relays are employed, the operating windings thereof (not shown) being controlled directly from the transmitter contacts. In this case the primary of one transformer 66 or 6l may be tuned to the band of frequencies between, say, 371,/ 5 and 511,/ t, while the primary of the other transformer may be tuned to the band of frequencies between, say, 211./'5 and 571/1. Or one may be broadly tuned to the higher frequency band while the other may be tuned as narrowly as may be found practicable on the band between, say 311/5 and 5ft/.

While the present invention has been described in connection with cable terminal equipment it will be understood that the invention may be applied at intermediate transmitting points, i. e., cable repeaters, particularly of the regenerative type, where according to well known practice transmission is effected from rotary distributors. Furthermore it will be understood that the invention may be used for the transmission of signals other than cable Morse signals, for eX- ample, signals of the kind used in the printing telegraph art.

What is claimed is:

1. In a cable system, a signaling device, a transmitter for transmitting signals under the control thereof, an output circuit for said transmitter, means for keeping said output circuit in the rhythm of said signals, means for deriving a predetermined band of harmonics of a vfundamental frequency at which said signaling device is operated, and means for impressing said harmonies upon said output circuit whereby said signals and said harmonics are combined in said output circuit.

2. In A a cable system, a .signaling device, a transmitter for transmitting signals under the control thereof, an output circuit for said trans'- mitter, means for keying said output circuit in the rhythm of said signals, means for deriving a predetermined band of harmonics of a fundamental frequency at which said signaling device is operated, and means for impressing said harmonies upon said output circuit in a predetermined phase relationship with respect to said signals in said output circuit whereby retardation The relays `are operated in the of the high frequency characteristics of the composite signal by the cable is compensated.

3. In a cable system, a signaling device, a transmitter for transmitting signals under the control thereof, an output circuit for said transmitter, means for keying said output circuit in the rhythm of said signals, a tuned circuit controlled by said signaling device for generating a predetermined band of harmonics of a fundamental frequency at which said signaling vdevice is operated, and a transformer having one winding in said output circuit and another 'winding in said tuned circuit.

4. A cable system according to claim 3, wherein a variable resistance is provided in said tuned circuit for controlling the amplitude of the harling device is operated, contacts controlled by said V'gpulse transmitting relay for opening and closing said tuned circuit in the rhythm of the transmitted signals, and a transformer having one winding in said signal transmitting circuit and another winding in said tuned circuit.

7. In a cable signaling system for transmitting block signals, a keying device comprising dot and dashcontacts, dot and dash locking relays, dot and dash signal transmitting relays,

Yand d-ot and dash pulse transmitting relays, cir-I cuits controlled by said dot and dash contactsV for operating said `locking relays and said pulse Y transmitting relays, circuits controlled by contacts of said locking relays for operating said signal transmitting relays, a signal transmitting circuit, a source of potential contacts associated with `said signal transmitting relays for applying negative, positive, and zero potential conditions to said signal transmitting circuit, a circuit tuned to a band of harmonics of a' fundamental frequency of the keying signals, contacts controlled by saidpulse transmitting relays for connecting a source of potential to said tuned circuit, and a transformer having one winding connectedY in said tuned circuit and another winding connected in said signal transmitting circuit.

8. In a cable system, a signalingl device, a transmitter for transmitting signals under the control thereof, an output circuit for said transmitter, a tuned circuit controlled by said signaling device for generating a predetermined band of harmonics of a fundamental frequency at and another winding in said second-mentioned tuned circuit.

BERTRAM S. DIAMOND.

, CERTIFICATE OF CORRECTION. Patent No. 2,528,789. September- Y, 19li5.

BERTRAM S. DIAMOND.

It is hereinr certified that error appears in the printed specification of the above numbered patent requiring, Correction as follows: Page 5, first column, line 56, claiml, for "keeping" read --keying--g and'that the said Letters Patent shouldfbe read with this correction therein that the same may conform to the record of the case in thePatent Office. Signed and sealed this rZth day of December, A. D. 19lp5.

.Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

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