US2281035A - Repeatered transmission system - Google Patents

Description

April 28, 1942.

E. L-GREEN REPEATERED TRANSMISSIN SYSTEM Filed May 31, 1941 3 Sheets-Sheet 1 April 28, 1942. 1.1 GREEN 2,281,035

REPEATERED TRANSMISSION SYSTEM` Filed May 3l, 1941 3 Sheets-Sheet 2 /N I/E N TOR ATTORNEY April 28, 1942.

Filed May 31, 1941 Sheets-Sheet 3 ql ["n Pr Pr 9/ fr i, FIG-3 lscr Rrcr 6/ aff 2 2 ../6 VVVAV VVV 23 l 76) 8) a 1 L, 3 /03 Moo HPF Amo LPr D l- 7l) E mM/s. (3L TEMI. 'l'

.von Pr ,van pr /N VEN TOR E l. GREEN BV ATTORNEY Patented Apr. 2.8, 1942 UNITED STATE REPEATERED TRANSMISSION SYSTEM Estin I. Green, Multum, N. J., assignmto Ben Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 31, 1941, Serial No. 396,148

rc1. 17a-44) 10 Claims.

This invention relates to long distance elec# tric signaling systems in which duplicate transmission facilities are provided to insure continuity of service.

It has been proposed heretofore to separate along distance signaling system having duplicate transmission facilities into a multiplicity of sections or links so that if in any link the regular or working transmission facility becomes impaired, it may be replacedby the spare or idle facility in that link. Where provision is made for effecting the substitution automatically under the control of currents transmitted with the signals, asin the wire line system disclosed in I. G. Wilson Patent No. 2,229,158, January 21, 1941, for example, it is found that under some conditions encountered in practice there is a possibility that unless special precautions are taken the occurrence of a necessary substitution in one link may give rise to unnecessary substitutions in other links or that the automatic replacement of an impaired facility in one link may occasion repeated linterchange of the two facilities in a distant link. y

A principal object of the present invention is to provide an improved system of the kind described and more particularly to eliminate unnecessary or false operation or to reduce substantially the likelihood of its occurrence.

The embodiments of this phase of the present invention that are hereinafter described in detail are specifically adapted for a wire line transmission system of a type such as the coaxial system employing two one-way transmission lines each of which is provided with signal repeaters having automatic gain regulation under the control of a pilot wave transmitted with the signals. The system is divided into a plurality of links for switching purposes and it is so arranged that at the input or sending end of each link both lines receive the signals and pilot waves from whichever of the two lines in the preceding link happens to be the working line. At the output or receiving end of each link automatic switching means are provided which operate in the event that transmission over the regular line is impaired to connect the idle line in that link to the input end of the next linkY and to disconnect the regular or working line therefrom. Transmission, in a given link is deemed to be impaired if the pilot wave received at the output end of the working line fails or if otherwise the intensity of the received pilot departs .from a preassigned normal value by more than a certain amount. In response to such failure or abnormal departure of the pilot, the switching mechanism is automatically' set into operation.

Gain regulated repeaters at the receiving end of each switching link normally operate in the two lines to maintain the pilot output intensity in each line approximately at a predetermined constant value, which is the same for both the working line and the spare line. If the two intensities are exactly alike and there is then an abrupt failure of the pilot on the working line, quickly followed by substitution of the idle line, the repeaters at all subsequent switching points experience only a momentary effect inasmuch as the pilot received by Way of the substituted line is of the same intensity. as the pilot previously received by way of the regular line.

Under some conditions, however, the pilot may not fail abruptly at a given switching point but its intensity may gradually drift in one direction or the other. beyond prescribed normal limits. Substitution of the idle line will take place in the affected link as before when the prescribed limit is passed but with this this difference. pilot drifts from its normal value, to a lower value, for example, the gain regulated repeaters in the following section of Working line will continually accommodate themselves to the changing pilot intensity thus maintaining, at the next 'switching station a constant pilot output. When the drifting pilot passes through the prescribed limiting value and the substitution of lines is made in the affected link, there appears at that next switching point a sudden increase in the pilot intensity equal to the vdifference in the intensities of the two pilots at the receiving end of the affected link. This sudden increase in pilot intensity is communicated almost instantly to all subsequent switching points, inasmuch as the various regulators do not operate instantaneously, and if at any such subsequent point the pilot output intensity happens to be at the moment of the switching somewhat higher` than the prescribed normal value although within the prescribed limits, the increase in pilot intensity incidental to switching will raise the total pilot intensity at that point above the upper normal limit and cause a switch to occur. This switch is obviously unnecessary for in a few moments the regulators would have reduced the pilot intensity to a value within the normal range and transmission would have been quite normal.

So also if the pilot output intensityv in the idle line of the affected link happenedto be below its normal value at the moment of switching', the comparatively large change in pilot intensity As the switching points.

If the circuitfis so arranged that a manual adjustment is required after a switch occurs before` the switching mechanism is in condition to make another switch, only one false switch can ,take place at any one point. The circuit, however, may be fully automatic so that it will switch back and forth between regular and spare lines whenever the pilot level on the working line departs from'its normal range. In such a fully automatic system it is theoretically possible to have as many successive false switches at a distant switching point as there are switching points between'it and the initial switching point.

In general, false switching may occur under either of two circumstances, (1) when there is a drift of vthe pilot level on the working line beyond the normal limits while the pilot level or. the idle line remains within the normal range, and (2) whenthere has been a drift of the pilot level on the idle line in ,one link, the level on the working line in a following link having varied from normal in the same direction, and the working line of the rst-mentioned link, being normal, becoming subject to a sudden failure.

In accordance with this phase of the present invention as embodied in two systems illustrated in the drawings, the objective of reducing or eliminating false switching is attained by automati-l cally adjusting the relative pilot levels on the two lines at each switching point so that so long as they remain Within `the prescribed normal y the I. G. Wilson patent supra, such a system may provide for a phase displacement of 120 degrees between the currents transmitted through the two facilities and a vector addition of the two currents at a receiving point. If the two vectors so combined are of equal amplitude, thevector resultant at the receiving point will be of the same amplitude as either component alone, hence 7,

if one facility is suddenly disabled .there will be little or no change in the amplitude of the received current and service can continue substantially unimpaired.

' Another object of the present invention is to obvate the false operation of marginally operative devices in a system of the kind last described that might occur if the two current vectors were not exactly equal. Even though the two facilities be provided with automatic transmission regulators these would ordinarily permit a limited range of relative amplitude variation such that the vector resultant at a given point might be sensibly different than either vector alone. More particularly the difference, in respect of the amplitude of pilot or control currents transmitted through the system, might be sufcient that in the event of sudden failure of one facility, various marginally operative devices responsive to the control current would be subject to false operation. These devicesmay be for example alarm circuits and switching devices adapted to disconnect impaired facilities.

In accordance with a feature of the present invention provision is made for accurate equalization of the transmission levels in the two facilities at points where vector combination of the respective transmitted cur'. ents is effected. In accordance with another feature, the duplicate facilities are divided into a multiplicity of links with vector combination of the currents at the junctions' thereof and preservation of the 120-degree relation at the input end of each link.

The nature of the present invention and its various features, objects and advantages will appear more fully from a consideration of the following description of the embodiments illustrated in the accompanying drawings. In the drawlngs: i

Fig. 1 illustrates an embodiment of the invention comprising duplicate, alternatively operative Atransmission lines in which the pilot output of the working line varies the pilot output on the idle line in the same direction and degree;

.-Fig. 2 illustrates a modification of Fig. l in which the pilot outputs of the two lines are at each switching point continuously and automatically adjusted to equality;

Fig. 3 illustrates an embodiment of the invention comprising duplicate, simultaneously operative transmission lines in which the transmission levels on the two lines are accurately equalized in the manner of Fig. 2: and

Fig. 4 further illustrates the Fig. 3 system.

Referring more particularly now to Fig. 1, there is illustrated a system of the kind described com prising two transmission 1ines,` LI and L2, arranged for transmission in the same direction betweena pair of terminal stations not shown. For switching purposesthe line system is divided into a multiplicity of tandem links with a hybrid coil at each junction adapted to receive signals from one or the other of the lines in the preceding link and to apply them to the transmit ends of both of the lines in the following link. At the output or receiving end of each link there are provided switching means which. operate under the control of pilot currents transmitted through the system along with the signals to connect one or the other of the lines throughv the hybrid coil to the input end of the next link. Thus in each link both lines are normally continuously ener` gized with signal and pilot throughout their lengths but only one is effectively connected at its output end for through transmission.

Repeaters 2 are interposed at intervals in each line and there may be a plurality of them in each link in addition to those at the junction or switching points, viz., repeater 3 in line LI and repeater 23 in line L2. All of these repeaters are of a type adapted for automatic gain regulation under the control of pilot current transmitted with the signal, and they normally operate toy maintain the transmission levels at their respective outputs within xed limits despite fluctuations in the attenuation of the transmission line and other effects tending to change the transmission equivalent of the system. The pilot currents that con trol the switching means may serve also for the `amplifier for the diverted pilot current and 'a repeater gain control mechanism -5 that is autoi of pilot output intensity, and the gain control mechanism comprises a silver sulphide element or other thermistor. connected in gain-controlling relation in the repeater-amplifier circuit.

The switching mechanism includes a relay 1 Y that is associated with the output end of line LI and a corresponding relay 21 associated similarly with line L2. These relays may, if desired, be of a type consisting of two magnetic reeds surrounded by a glass envelope containing a sultable gas such as helium, the contact between the reeds being actuated by an external magnetic field, all as disclosed in the pending application of L. R. Schreiner, Serial No. 342,635, iiled June 27, 1940. This construction permits the outer conductor of a coaxial circuit to be carried continuously through the relay. In one condition of the system, neither of the relays 1 and 21 is operated, in which case line LI is connected b'y relay 1 to the input terminal of the hybrid coil 5I in the next section and line L2 is connected by relay 21 to a terminating resistor 28. `In an'alternative condition of the system both of these relays are operated and in this case line LI is disconnected from hybrid coil 5l and terminated i by resistor 8 while line L2 is disconnected from terminating resistor 28 and connected to the input Iterminals of hybrid coil 5I.

-As previously intimated, the system may be arranged for semiautomatic operation, that is,

for a single automatic transfer from the' regular the latter becomes impaired, and, without the intervention of an attendant, a switch may be made in the reverse direction if the substituted line then becomes impaired and the other line has in the meantime been restored to normal. First to be described is the semiautomatic arrangement. This requires that the resetting or restore key Il be closed and that a circuit shunting the key be brok'en at the point a-a.

Treating line LI as the regular line and line L2 as the spare, Vand assuming that the circuit is arranged for semiautomatic operation. relays 1 and 21 are then normally in the unoperated condition and line LI is connected for through transmission. To effect a switch to line L2 in the event of impairment of line Ll, means are provided. responsive to an abnormal change in the pilot level at the output of repeater 3, to operate relays 1 and 21. The operating means comprises a detector 9 that is connected to receive the diverted pilot from the output of repeater 3 and that is so constructed, as by incorporating a pair of differently biased relays. that if the intensity of the pilot applied to it departs from a preassigned range a relay l0 in its output circuit is immediately operated. If'as suggested the pilot intensity at the output of repeater 3 is normally held by the gain regulating system to a range of plus or minus three decibels, the operating margin of detector 5 can be arranged to coincide,

orit may be otherwise so arranged as to operate when predetermined limits are exceeded.

Associated with the' output of repeater 23-and controlled by pilot current diverted therefrom is a detector 29 and a relay 30 which respectively correspond with detector 9 and relay l. As long as the pilot intensity at the output o repeater 23 is within the normal range, or in other words as long as line L2 is unimpaired and in condition tobe used for replacing line Lil, relay Mi is unn operated and its upper break contact is closed. Then on operation of relay l@ in response to a fault on line Ll, an operating battery circuit for relays 1 and 21 is closed through the upper and lower make contacts of relay i@ in series and the upper break contact of relay 33t). Thereupon relays 1 and `21 operate and line L2 is thereby substituted for line L! for through transmission. At the same time an operating battery circuit for a lock-up relay d2 is closed through the upper make contact of relay l@ and the upper break contact of relay 39. The consequent operation of relay t2 closes a holding circuit through one of its make contacts and key di. With relay t2 in its locked position, a holding circuit for relays 1 and 21 is completed through one of its make contacts. A lamp 44 in series with the operating winding of relay 42 lights Whenever this relay is in its operatedcondition, or in'v other words as long as the spare line is in use.l

It will be noted that on manually opening restore key 4|, the'operating circuit of lock-up relay 42 will be broken, andif line LI is unim paired at the time so that relay I0 is in its unergized, thereby released, and cause line Ll to be 'substituted for line L2.

For fully automatic operation of the switching system key 4I is held open, or removed, and the shunting circuit is completed through a-a. The lower break contact of relay 30 now serves ir. lieu of the key Il. In normal operation over line LI, the last-mentioned break contact is closed, sothat when occasion arises a switch can be made to line L2. If on that occasion line L2 is impaired, and relay 30 is therefore in its operated condition, both contacts of that relay are open and a switch is precluded.

After a switch is made to line L2, lock-up relay 42 holds switching relays 1 and 21 in their operated condition even though line Li is restored to normal and relay I0 is thereby released. If now line L2 becomes impaired and relay 30 therefore operates, the opening of the lower contact of relay 30 breaks the operating circuit of lock-uprelay 42 thereby releasing relays 1 and 21 and restoring the system to. its original condition, that is, lwith line LI in service. Thelast-described switch is precluded, however, if line Ll is still impaired and relay l0 is therefore still operated.

The Fig. `1 switching arrangement as above described, whether conditioned for semiautomatic or fully automatic operation, is such that a normal or necessary interchange of lines in one link may give rise to false switching in other links under certain conditions hereinbefore described in detail. These conditions, it will be recalled, involve the fact that whereas the various pilot levels in both lines at all switching points may lie within the normal range just prior to the occurrence of a fault, these levels may have drifted from the center or mean value of their respective ranges in such relative directions that the sudden change in level ordinarily to be expected on substituting one line for another may be enough that the normal range is momentarily exceeded at various switching points. In accordance with a feature of the invention provision is made in Fig. 1 to reduce the likelihood of such false switches occurring.

More particularly, provision is made in Fig. 1v

for varying the transmission equivalent oi' the idle line in synchronism with the variations.v in the pilot output level on the working line so that at the instant before switching the pilot output levels on both idle and Working lines are at least approximately equalized. For thisfpurpose an auxiliary amplifier 6 of .adjustable gain is interposed in line LI following repeater 3 and a similar auxiliary amplifier 26 is likewise disposed at the output of repeater 23. The gain adjusting mechanism of each auxiliary amplifier is illustrated as comprising an indirectly heated thermistor, viz., thermistor element I I and heater I2 for amplifier 6 and thermistor element 3| and heater 32'for amplifier 26.

Heating current for 'each of the thermistors is derived from a -constant current source when the line with which it is associated is the working line, and from the pilot current on the other line when the line with which it is associated is the idle line. Thus a rectifier I3 connected in parallel with the input of detector 3 supplies amplified, rectified pilot current for .heater 32 through a break contact on relay 42 that is closed as long as line LI is the working line, while heater I2 is supplied through another break contact on relay 42 with constantcurrent from a source 45. When relay 42 is operated, incidental to substitution of line L2 for line LI, heater 32 is supplied with current from a constant current source 'through a make contact of relay42 and heater I2 is supplied with current through another Amake conthe reference value, zero decibels, when the in-V tensity of the pilot in the opposite line is exactly at its mean value, that is at the center of its normal operating range. The circuit parameters can be and are further so selected that any change in the intensity of the heating current derived from the pilot in one line givesrise to an equal change in the same sense in the gain of the auxiliary amplifier in the other line.

If for example, then, line LI is the working line and the pilot intensities at the output of-repeaters 3 and 23l arel at their respective mean values, the gain of auxiliary amplifier 6 is held at zero value by the heating current supplied from source 45 and the auxiliary amplifier 26 is likewise maintained vat 'zero gain under the control of the `pilot current derived from line LI. Now if the pilot level on line LI beginsvto` change, the gainof auxiliary amplifier 26 in line L2 changes indirect proportion so that the pilot level on line L2 at the output of amplifier 26 is maintained exactly equal to that on line LI. It will be apparent that if there should be a sudden failure of line LI under these conditions, there would be only a momen- .tary change of pilot level experienced at-subsequent switching points and false switching would not occur.

' In general it may be said that the Fig. 1 ar-- rangement operates at each switching point to restrict the differential between the pilot level on the two lines to a value not exceeding half the normal range of either pilot. In the embodiment of the invention illustrated in Fig. 2, on the otherhand, the differential may be further reduced and in fact eliminated so that a switching operation atanygiven switching point Y gives rise to no sensible change inpilot intensity tact on the same relay from the output of a rec- 4 l.

at .subsequent switching points.

In Fig. 2 the'switching mechanism is essentially the same as that shown in Fig. 1 and corresponding elements are assigned the same refer. encecharacters. A principal difference that will be noted is the shifting of the auxiliary amplifiers 6 and 26 to a position preceding the point at which pilot currents are diverted for control of the switching mechanism and the provision of separate pilot filters for the automatic gain regulators of repeaters 3 and 23. As in Fig. 1 the pilot intensity at the respective outputs of repeaters 3 and 23 is maintained within prede-v termined limits of plus or minus 3 decibels for example; the gain of theauxiliary amplifier in the working line is maintained at a constant reference value of zero decibels, for example; and the` gain of the auxiliary amplifier in the idle line is continuously adjusted in accordance with the pilot intensity on the working line. In Fig. 2, however, the adjustment of the gain of' the auxiliary amplifier in the idle line proceeds automatically until the lpilot level at its output is equal to the pilot level at the output of the other auxiliary amplifier. The pilot equalizing equipment in Fig. 2 comprises a differential relay 41', the opposing windings of which are supplied with operating current from the rectifiers I3 and 33. Relay 41 is connected through contacts on relay 42 to control the operation of reversible motor 43 which drives a rheostat 50. lIfhe adjustment of the latter controls the amount of battery current that is supplied to thermistor heater 32 through a break contact lon relay 42 when line LI is in use, and it also controls the amount of battery current supplied to the heater I2 through a make contact on the same relay when line L2 is in use. 'I'he circuit elements are so proportioned that when the outputs of rectiiiers I3 and 33 are equal, the armature of dierential relay 41 stands in its neutral position.

Assume that line Lil is the working line and that the pilot intensity at .the output of auxiliary amplifier 6, initially equal to that at the output of auxiliary amplifier 26, begins to drift, for example, to decrease. Thereupon the armature of differential relay 41 is moved to its lower contact and motor 49 together with the wiper arm of -rheostat 50 are thereby causedto rotate. This changes the heating current to 'heater 32 and in such sense as to decrease the gain of auxiliary amplifier 26.

Operations continue until the gain is so reduced that the intensities of the two pilots are equal, whereupon the armature of differential relay 4l assumes its neutral position and stops the motor 43. Similarly if thev pilot intensity on working line'LI relatively increases, the armature of differential relay 41 is moved to its upper contact and motor 43 is driven in the opposite direction to raise the sain of amplifier 26. When line L2-is the working line, the gain of auxiliary amplifier 6 in line LI is controlled in the same manner. It will be noted, however, that in this case movement of the armaturev of diierential relay 41 to either of its contacts requires that motor 49 be driven and rheostat 50 so that under all conditions the wiper arm of rheostat D is precluded from leaving its associated resistor.

In Fig. 3 the invention is shown embodied in another form in a system comprising duplicate transmission facilities that normally are.both connected for concurrent through transmission. In this case it is assumed that the two lines are energized with the same signal and pilot currents but displaced in phase relative to each other by' 120 degrees throughout the frequency range of interest.v At the end of each link the currents in one of the lines, say L2, are reversed in phase and the currents from the two lines are then applied to respective terminals of a hybrid coil 6|. These terminals are in conjugate relation with each other but are in transfer relation with the output terminalsof the hybrid coil, the latter` being connected to Vtransmit the vector sum ofthe applied currents to the outgoing line LI. The other line L2 of the next link receivesl the current of reversed phase from line L2 in the preceding link through a level adjusting pad 62. Further details of the over-all system will be described with reference to Fig. 4.

As previously indicated the regulated amplifiers 3 and 23 at the end o f the transmission link shown in Fig. 3 operate to maintain the intensity of the currents in the two lines approximately equal, whereas for optimum performance of the system and freedom from false operation of various elements therein, the two intensities should be held to a higher degree of equality. In accordance with the present invention, the relative level equalizing means oi' Fig. 2 is utilized tion from a terminal station at the left through the duplicate transmission lines Ll and L2 which are subject to the same changes in attenuation and which for specific example may be coaxial conductor pairs within the same cable. The signals'to be transmitted may comprise a multiplex of telephone channels or television signals, ranging in either case from 64 to 2064 kilocycles per second for specific example. Whatever their character, the signals from the signal source 1l are' applied to. thetwo lines LI and L2 with equal amplitudes in the two lines but displaced in phase relative to each other by 120 degrees throughout the signal frequency range.

The phase displacement is effected by applying the signals from source 'll to the respective with certain simplifications for this purpose. As

shown in Fig. 3, only one auxiliary amplifier of adjustable gain need be used, just as only one auxiliary amplier is variably controlled in Fig. 2 while the other line is in service. If auxiliary amplifier 26 is the one retained as indicated in Fig. 3, its gain is continuallyadjusted by meansA of reversible motor 49 and rheostat 50 as before so that the gain adjustment proceeds until the current level at the output of amplifier 26 is the same as that at the output of repeater amplifier 3. For the equalizing function detectors 9 and 29 need not be used and rectiiiers I3 and 33 may be connected directly to the control windings of relay 4l. The two detectors, however, may be used for other purposes as for example for sound-` ing an alarm or for disconnecting one of the lines if it becomes impaired. As inFig. 2, the gain control for auxiliary amplifier 26 may be so adjusted that the gain is zero when the control pilot level on line LI is at its mean value.

The transmitting terminal station for the Fig. 3 system and the combining circuits at successive llink junctions are shown in Fig. 4 with the level modulators 12 and 'i3 which are supplied with carrier current from a source 15. The frequency of the latter may be, for example, 8 megacycles per second. A phase shifter 'I4 is interposed in the lead from carrier source 15 to one of the modulators 'i3 and it is designed to introduce a carrier phase shift of 120 degrees. Of the two principal second order side-bands produced by a modulators 12 and 13, either the two upper sidebands or the two lower side-bands `are to be suppressed, and it may besupposed, for example, that high-pass filters 16 and 'Il are adapted to pass only the upper side-bands. The latter are then applied to the respective modulators 18 and 19 which are respectively supplied with carrier currents in like phase from source 15. The two lower side-bands resulting from this operation are selected by respective low-pass filters and 8|, individually amplified and applied to the respective lines Ll and L2. It can readily be demonstrated that the two side-bands thus applied to the line are identical with the original signals from source 'H but displaced in phase from each other by degrees. Pilot currents to be transmitted through 4the system may be 'derived from the transmittingterminal 'il consignals and pilotsin the two lines can be com- Y bined andthe vector resultant will be equal in magnitude to either of the component vectors alone. Thus, if the two vectors are maintained exactly equal in amplitude, as bymeans of the Fig. 3 level equalizer, and one line shouldfall, transmission would continue through the other without any abrupt change in amplitude or other effect except a phase shift of 60 degrees. The latterphase shift is small enough that carrier telegraph signals which might be present on the line would be transmitted satisfactorily.

Once the currents from the two lines are combined, some such means as that provided at the transmitting terminal station would ordinarily be required toproduce another set of phasedisplaced currents for transmission through the next link of the system. In Fig. 4, however, this necessity is avoided and other advantages secured by providing, at the output end of each link, means for reversing the phase of the signals-in one of the two lines and means for applying'to the outgoing section of the other line the vector resultant of the incoming signals in that line and the phase-reversed signals from the other line.

More specifically, as shown in Fig. 4, the rehybrid. coil is applied to line L2.

. maintaining the intensities of said pilot currents applied directly to the next section of line L2 through a pad 85 which compensates for the loss occurring in hybrid coil 6I. Brief consideration will disclose that the two sets of currents thus delivered to the next section of the transmission system are again in 1Z0-degree phase relation with respect to each other. The repeater station at the end of the next link is the same as the f first except that the phase-reversing amplier IBB is disposed in line LI and the resultant of the vectorial addition of the two signals in the Alternate Junctions in the system are alike in the respects described.

` Although the present invention has been described largely in terms of illustrative embodiments, it will be understood that the invention is susceptible of embodiment in various other 'forms within the spirit and scope of the appended claims.

What is claimed is:

1. A long distance signaling system with duplicate transmission facilities comprising two repeatered transmission lines interconnecting the same points, a plurality of switching stations separating said system into a multiplicity of tandem links each having an input and yan output'end, means for applying pilot waves and signals concurrently to both of said lines at the input end of each of said links, switching means at the.

output end of each of said links for connecting said lines alternatively to the input end of the next link, said switching means being controlled by the intensity of pilot waves received from` the line that is so connected to the next link and operative to effect the alternative connection when said intensity'departs from anormal limited range, automatic transmission regulating means normally maintaining the pilot intensities in both of said lines at the output end of each link within said limited range, and means constricting the differential between said last-mentioned intensities to a value substantially less than said limited range. I

2. A long `distance signaling system comprising regular and spare facilities in a multiplicity of 2,281,035 .peater station at the' end of the first link comity of long ydistance transmission links each having an input end and an output end, means for maintaining pilot current on both of said facilities in each of said links, transmission regulating means respective to the two facilities normally within a predetermined range at the output end of each of said links, means at each of said links responsive to a departure of the regulated pilot intensities from said predetermined range for disconnecting the affected facility, and means at each of said links fornormally restricting the differential between said regulated pilot intensities.

4. A long distance transmission system 'comprising duplicate transmission facilities separated into a multiplicity of links for the concurrent transmission of the same signals, means for maintaining a 1Z0-degree vector relationship between the respective signals applied to the two facilities, 4means at each junction of said links for reversing. the phase of the signals received from one of the facilities of the preceding link relative to the phase of the signals received from the other, means for applying the signals of reversed phase to one of the facilities of the next link, means for vectorially combining said signals of reversed phase with said signals from said other facility and means for applying the vectorially combined signals to the other facility in v the said next link.

5. A combination in accordance with claim 4 in which alternate links of the one facility receive said vectorially combined signals and in which the intermediate links of said one 'facility receive l said signals of reversed phase.

6. A signaling system comprising duplicate transmission facilitiesseparated into a multiplicity of long distance transmission links, means for applying signals and pilot waves to the two transmission facilities in each of said links,

vmately constant, and means at the junction of said links operative under the control of said pilot waves for equalizing the transmission levels in the two facilities irrespective of'variations in relative level permitted by said regulating means.

7. A system comprising two long distance transmission lines each including repeaters intersuccessive transmission links, means for transthe operating margin thereof, and means asso- 4cated with each of said switching means for reducing the intensity differential between the control-'currents in the two facilities.

3. In a signaling system comprising duplicate transmission. facilities separated into a multiplicposed in tandem therein, means for transmitting control currents through both of said lines in the i the said control currents in the two lines,

8. A combination in accordance with claim 7 comprising means at said-one repeater substanti ally equalizing said intensities independently of said regulating means.

9. In4 combination, two long distance transmission lines extending over the same route,

.means for transmitting control current through each of said lines, transmission regulating means normally maintaining said control current within a limited range at a plurality of points along said lines, means at one of said points for automatically replacing the control current in one of said lines with the control current from the other of said lines for transmission to another of said points, means at said other point marginally operative by the control current in one of said lines. and means at said one point continually restricting the intensity differential of said control current at said one point to a value substantially less than the operating margin of said device.A

10. 'A system comprising a pair" of duplicate long distance signal transmission facilities separated into a multiplicity of links, each with a plurality of amplifying repeaters therein, interlink coupling means Asupplying signal and control currents from the output end of each link tothe input ends of both facilities of the next following link, transmission regulating means normally maintaining the said control current in both of said facilities within-a limited intensity range at the output end of each of said links. means marginally operable by said regulated control current transmitted through said system, said coupling means being adapted to supply signal and control currents as aforesaid from the output end of either facility alone in a given link in the event of failure of the other facility in that link, and /rneans inhibiting false operation of said marginally operable means incidental to failure of one facility in a preceding link, comprising means substantially equalizing the intensity of the regulated control current in the two facilities at the output end of each of said links.

ESTILL I. GREEN.

Images