US2102719A - Signal distortion indicating and measuring device - Google Patents

Description

1937. F. s. KINV'EAD 2,7

SIGNAL DISTORTION INDICATING AND MEASURING DEVICE Filed Aug. 4, 1934 4 Shegts-Sheet 1 DELAY REPEA TIER REGENERAUVE REPEA rm v 1 N E Q Q5 9 t s R k \l k I IH 5 WTTTTT lllllllll Q $9 2& $3 fi czfifi 8 u INVENTOR FSJf/N/(EAD ATTORNEY Dec. 21, 1937. Fys. KINKEAD 2,102,719

SIGNAL DISTORTION INDICATING AND MEASURING DEVICE I Eiled Aug. 4, 1954 4 Sheets-Sheet 2 mew! 2w! Sula].

N {w I3 8m w 3 v 2o m .80 k v n R \l [El-[llNl ENTOR F. S. K/N/(EAD ATTORNEY NUE Ewk 4 :w

Dec. '21, 1937. s AD 2,102,719

SIGNAL DISTORTION INDICATING AND MEASURING DEVICE Filed Aug. 4, 1934 4 Sheets- Sheet s s :EjIII-II v FIG. 3.

POLAR/ZED SENDING IIHI RECEIVING M mg? l' 1 N" (5 y 2 INVENTOR 5. K/N/(EAD I A TTORNEY F. s. KINKEAD 2,102,719 SIGNAL DISTOR' IION INDICATING AND MEASURING DEVICE Dec. 21, 1937.

.h. h h h D m l km \vv mE M 1%. NK R w. 9v VM T e N r m ENESQQ I A v% B w Qv Ev Ev vwv Patented Dec. 21, 1937 UNITED STATES SIGNAL DISTORTION INDICATING AND MEASURING DEVICE Fullerton S. Kinkead, Ridgefield Park, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August 4, 1934, Serial No. 738,416

12 Claims.

This invention relates to impulse transmission systems and more particularly to electrical measuring systems wherein means are employed for determining the existence of distortion of received telegraph signals.

An object is to provide a circuit for instantaneously measuring the maximum distortion in signals received over a transmission line in startstop printing telegraph systems.

In transmitting telegraph signals each made up of a plurality of impulses and each impulse having a definitelength, distortion of the impulses and therefore of the signals, may be produced by various causes inherent in the line or in the apparatus connected therewith or both. The distortionwith which this invention is concerned manifests itself in lengthening or shortening the duration of the impulses which constitute the signal transmitted over the line. This lengthen" ing 'or shortening of the duration of the impulses interferes with the proper recording of the signals at any station connected to the line and, consequently, impairs the efilciency of transmission.

According to the present invention, the circuit measures the distortion of the received signal by comparing it with the original signal. The original signals are reproduced at the point of measurement from the received signals by means of the start-stop regenerative repeater. Inasmuch as the repeater causes the regenerated signal to lag the received signal by approximately half a signal dot length, it is necessary to introduce an equivalent delay in the received signal in order that it may be compared with the regenerated signal. The regenerated signals and the delayed received signals are impressed on a circuit which measures a difference in phase each time the line condition changes from marking to spacing or Vice versa. Obviously this method of measuring distortion will fail if the distortion is so great that the regenerative repeater can no longer reproduce the original signal.

The objects and advantages of the invention will be better understood from a consideration of the following description of the operation of a system embodying this invention read in conjunction with the accompanying drawings in distortion exceeds a predetermined amount, provide a visible and an audible indication thereof;

Fig. 3 shows diagrammatically a start-stop regenerative repeater, a delay repeater, and the signal distortion measuring circuit;

Fig. 4 shows an alternative arrangement of the start-stop regenerative repeater, delay repeater and distortion measuring circuit of Fig. 3; and

Fig. 5 indicates the manner in which Figs. 2, 3 and 4 should be arranged.

Referring to Fig. 1, the signal distortion measuring system herein disclosed functions in the general manner hereinafter set forth. The incoming start-stop printing telegraph transmission lines terminate on the banks of a test selector llll. Assume that the brush cf selector llll, under control of circuit means which will later be described in detail, is in contact with the bank terminal to which transmission line Hi2 is connected. The signals incoming over line I02, each signal composed of a plurality of impulses having a definte length, are received over the bank terminal and brush of selector It! and transmitted to ground through the winding of polarized relay H33. In response to the incoming signal impulses, relay H63 operates and releases, which in turn repeats corresponding irnpulses of positive and negative potential to the regenerative repeater circuit I234 and to the delay repeater circuit 185 in parallel. The regenerative repeater lfi i functions, in a manner which will hereinafter be described in detail, and reproduces the original signal over conductor I06, to ground through the winding of polarized relay lfl'l.

Since the signal distortion is measured by comparing the received signal with the regenerated signal, and since the regenerative repeater introduces a lag in the reproduced signal, it is necessary to provide an equivalent lag in the incoming signal. This is accomplished by the delay repeater circuit I05, the detailed operation of which will be set forth hereinafter. The incoming signal impulses, after being delayed, are re peated over conductor M8, to ground through the winding of polarized relay I09.

Relay H0 is normally operated in a circuit from grounded battery, through its winding, over the armatures and the right contacts of relays I91 and I69 to ground. As hereinbefore stated, relay l0! operates and releases in response to the impulses of the regenerated original signals while relay H39 operates and releases in response to the impulses of the delayed received signals. If

perfect signals are received over the circuit under test, in this case over transmission line @552, relays it? and I09 operate and release in unison and the circuit through the winding of slow-release relay H0 is opened for an interval no greater than the travel time of the armatures of relays I01 and I09. This open period is insufficient to cause the release of relay H0. If, however, distortion is present in the received signals, the operation and release of relay I09 will no longer be in synchronism with the operation and release of relay 01 with a resultant lengthening of the open interval in the operating circuit for relay H0. When the distortion in the received signal exceeds a predetermined amount, the circuit through relay l I0 is opened for a period sufiicient to cause this relay to release. Relay H0, in releasing, connects ground over its armature and back contact to grounded battery through signal iii and through lamp H2. Signal Ill and lamp H2 respectively provide audible and visual indications of the distortion condition encountered on the line under test.

Having described thesystem in a general manner, a detailed description of the operation of the circuit elements shown on drawings Figs. 2, 3 and 4 will now beset forth.

Referring to Fig. 2, switch A is of the well known step-by-step type having in this case six brushes paired, such as brushes AA and AB, AC and AD, and AE and AF respectively, mounted on a common shaft (not shown). Each pair of brushes has access to one of three terminal banks (not shown) of switch A. Each terminal bank has pairs of terminals arranged in ten levels, ten pairs of terminals per level. The first bank has ten sets or pairs of terminals TA and TB per level, the second bank ten sets or pairs of TC and TD terminals per level, and third bank ten sets or pairs of TE and TF terminals per level. Brushes AA, AB, AC, AD, AE and AF therefore each have access to one hundred selectable terminals TA, TB, TC, TD, TE and TF respectively. A vertical magnet A1 is provided for advancing the shaft (not shown) and the brushes AA, AB, AC, AD, AE, and AF one step at a time in a vertical direction. A rotary magnet A3 is provided for horizontally rotating the shaft and brushes one step at a time over the terminals of any vertically selected level. A release magnet A4 provides for releasing the shaft and brushes to their normal position. Associated with the shaft and brushes of switch A are the vertical offnormal springs A2 and the tenth rotary step springs As the operation and functions of which will be described fully hereinafter.

Switches B, C, T and U are of the well known single movement rotary type having one or more terminal banks, each bank having ten individual terminals selectable by an individual brush. The switches are provided with rotary magnets B3, C2, T3 and U2 respectively, by which the brush on each switch is advanced progressively, one step at a time, over its associated bank terminals. The respective release magnets B5, Ca, T5 and Us provide for the release of the brushes of their respective switches to their normal positions. Associated with switches B and T are the off-normal springs B4 and T4 respectively, the function of which will be hereinafter set forth in detail;

As previously stated, the banks of switch A are composed of one hundred groups of six terminals each. Each of these groups, corresponding to terminals TA, TB; TC, TD, TE and TF, are accessible to the respective switch brushes AA, AB, AC, AD, AE and AF. Connected to each of the aforementioned six hundred terminals is a mul tiple branch of a start-stop printing telegraph transmission line on which signal distortion measurements may be made.

To start the distortion measurements, key 2! is operated, thereby connecting grounded battery to the right-hand windings of relays 202 and 203, windings of relays 204 and 205, windings of rotary magnets A3, B3, C2, T3 and U2, windings of re lease magnets A4, B5, C3, T5 and U3, to the left winding of relay 202 through resistance 206, and the left winding of relay 203, through resistance 201. Relay'202 operates through its right-hand winding to ground over the normally closed contacts of the off-normal spring B4 and locks through its. left-hand winding from ground on its left .armature and front contact to grounded battery through resistance 206. Relay 203 operates through its right winding to ground over the normally closed contacts of the off-normal springs T4 and looks through its left winding from ground over its left contact and armature to battery through resistance 201. Relay 204 operates from the battery over the contacts of key 20!, through its winding, to ground over the normally closed contacts of the off-normal: springs A2 and looks over its contact and right-hand armature to ground over the right armature and contact of relay 208.

Relay 202, in operating, energizes rotary magnet B3 in a circuit from ground overthe right front contact and armature of relay 202, through magnet B3, to battery over the contacts of key 20L Magnet B3, energized, causes the B switch brushes Bi and B2 to advance onestep and contact the first terminal of their respective banks. The

off-normal springs B4 operate during the first step of switch B and remain in the operated position until the switch is restored to normal. In operating, springs B4 transfer the ground over their armature from the right winding of relay 202 to the left armature of relay 205. Relay 202 remains operated since it is looked through its left winding. With the B1 brush on the first terminal of its associated bank a circuit is completed from the AA brush of switch A, over the bank terminal and brush B1, toconductor 200. With the B2 brush on the first terminal of its associated bank, ground over the B2 brush is connected tothe AL lamp, resistance 206, and the left winding of relay202. This ground shortcircuits the left winding of relay 202 which releases.

Relay 203, operating and looking over previously traced circuits, energizes rotary magnet T3 from ground over its right front contact and armature, winding of magnet T3, to battery at key 20!. In energizing, magnet T3 causes brushes T1 and T2 to advance one step to contact the first terminals of their respective banks. During this first step of switch T the off-normal springs T4 operate, transferring the ground on'their armature from the right winding of relay 203 to the left armature of relay 2E8. The Tl brush 'connects conductor 2!!) to its first associated bank terminal, and the T brush connects ground, over the first terminal of its associated bank, to lamp 0, resistance 20'! and the left winding of relay 203. This ground short-circuits the leftwinding of relay 203 which releases.

Relay 200, operating and locking over previously traced circuits, connects ground over its left front contact and armature, over conductor 2l0, brush T1 and first terminal of associated bank, to the first terminal of the'bank associated with brush C1. The same ground over the left front contact of relay 200 is also connected to the left winding of relay 2!! and also to the armature and back contact of relay 2! I, through the windings of vertical magnet A1 and rotary magnet C2 to battery at key 2M. Vertical magnet A1, in energizing, causes the AA, AB, AC, AD, AE and AF brushes of switch A to advance one vertical step, bringing these brushes into position at the first horizontal rows or levels of TA, TB, TC, TD, TE and TF terminals, respectively, of the A switch banks. The vertical oif-normal springs A2 operate upon the first vertical step of switch A and, in operating, open the operating ground for relay 294 and connect ground to the left front contact of relay 2. Relay 204 does not release at this time since it is locked to ground over the right armature of relay 208. The C2 magnet, in energizing causes the C1 brush to advance one rotary step and contact the first terminal of its associated bank. The operationof magnet A1, in addition to causing a vertical step of the brushes of switch A, also opens the circuit extending from ground over the left con-- tact and armature of relay 204, armature and back contact of magnet A1, resistance M2, to battery at key 20E thereby removing the short circuit from the left winding of relay 2!]. Relay 2 H operates from ground over the left armature of relay 208, left winding of relay 2, resistance M2, to battery at key 2?. In operating, relay 2 opens the circuit to the windings of magnets A1 and 02 causing these magnets to de-energize and release. Magnet A1, in releasing again closes the previously traced short circuit on the left winding of relay 2| i. Relay 2 ll does not release'at this time since, when brush C1 contacted its first associated bank terminal, a circuit was established from battery at key 2M, through the right winding of relay 2H and the winding of relay 2%, brush C1 and first bank terminal, first bank terminal and brush T1, to ground over the left armature and front contact of relay 204. This circuit holds relay 2H and causes relay 208 to operate. Relay 2%, in operating, closes a circuit from ground on its left front contact and armature, over the right armature and back contact of relay 2, through the windings ofrotary magnets A3 and U2, to battery at key 2!. Magnet A3, in energizing, causes brushes AA, AB, AC, AD, AE and AF to make one rotaryor horizontal step and contact the first set of TA, TB, TC, TD, TE and TF terminals of the A switch banks. Magnet U2, in energizing, causes brush U1 of switch U to make one rotary step and contact the first terminal of its associated bank thereby connecting ground to the units lamp l. Relay 208, in operating, also opens the locking circuit for relay 2%. Relay 2B4 releases and opens the circuit from ground over its left front 1 cuit from the windings of vertical magnet A1 and rotary magnet C2 to the left armature ofrelay 2%.

As hereinbefore set forth, switch A has now ad vanced one vertical and one rotary step and switches B, C, T and U have each advanced one rotary step. The brushes of switch A are'in contact with the first of the one hundred'groups of TA, TB, TC, TD, TE and TF terminals of the A Brushes B1, B2, C1, T1, T2'andswitch banks. U1 are in contact with the first terminal of their respective banks. With the switches in the above condition, the first of the six hundred start-stop printing telegraph transmission lines terminating on the bank terminals of switch A is connected to the associated repeaters and distortion measuring circuit over a path which may be traced from the first transmission line (represented by conductor 222) terminal TA, brush AA, first terminal of bank associated with brush B1, brush B1, and over conductor 2% to the circuits of Fig. 3 or Fig. 41 as the case may be.

Upon the connection of a transmission line over conductor 209 of Fig. 2, the delay repeater, regenerative repeater and signal distortion measuring circuits of Figs. 3 or 4 function to measure the signal distortion on that line. The detailed manner in which the circuits of Figs. 3 and 4 operate will be described hereinafter, their operation at this point being covered only to the extent involved in the further functioning of circuits of Fig. 2.

The signal distortion on the first transmission line is measured for a definite interval and, if the distortion does not exceed a predetermined amount, the measuring circuit functions at the end of the measuring interval and returns a ground to conductor 2l3 to cause the circuit of Fig. 2 to advance to the next transmission line'in a. manner shortly to be set forth. Should the signal distortion on the first line exceed a predetermined amount, the distortion measuring circuit returns battery to conductor N4 of Fig. 2 and locks in that condition. Battery on conduct-or 2 I4 completes circuits through the electro magnetic signal 2E5, through the AL lamp to ground over brush B2, and through the tens lamp 0 and the units lamp I over brushes T2 and U1 respectively. Signal 2 I 5 gives an audible alarm and lamps AL, U and i light, indicating that excessive distortion has been encountered on the first transmission line of that group" of lines terminating on the one hundred TA terminals of the A switch bank. This alarm and lamp indication continues until the operation of a releasing key 3% in the associated measuring circuit of Fig. 3 or the cor responding key 484 in Fig. 4 at which time battery.

is removed from conductor 2M and ground is returned to conductor 2! 3 by the measuring circuit.

The ground which is connected to conductor H3, at the conclusion of the distortion measurement on the first line, is extended over the right back contact and armature of relay 202, through the winding of rotary magnet B3 to battery at key 20L Magnet B3 energizes and advances brushes B1 and B2 to the second terminal of their respective banks. The next transmission line (represented by conductor 2%) is now connected over the first TB terminal, brush AB, second bank terminal and brush B1, to the repeaters and distortion measuring circuit over conductor 289. The advance of brush B2 to its second bank terminal transfers the ground over that brush from the AL lamp to the BL lamp so that, in the event of excessive signal distortion, the return of battery to conductor 2M by the measuring circuit causes audible signal 2 l5 to operate and lamps BL, ii and l to light which indicates the condition encountered on the first transmission line of that group of lines which are connected to the one hundred TB terminals of the A switch banks. Atthe termination of the distortion measurement ground is again connected to conductor 2L3 by the measuring circuit. This, and subsequent applications of ground to conductor 213 at the termination of the signal distortion measurement on each succeeding transmission line, cause rotary magnet B3 to energize and advance the B1 and B2 brushes one step at a time. rushes B1 and B2 successively contact the third, fourth, fifth and sixth terminals of their respectively associated banks. The transmission lines connected to the A switch bank terminals TC, TD, TE and TF are connected over brushes AC, AD, AE and AF respectively, and over brush B1 to the repeater and measuring circuits over conductor 209. Brush B2, advancing simultaneously, successively connects ground to lamps CL, DL, EL and FL to prepare the circuit for lighting the particular lamp identifying each group of terminals in the event that battery is returned to conductor 2M due to excessive signal distortion on any line.

On the seventh time that ground is connected to conductor 2I3, magnet B-a again energizes and advances brushes B1 and B2 to the seventh termi- 212.1 of their banks. Ground on brush B2 is connected over its seventh bank terminal, through the winding of relay 205 to battery at key 20I operating relay 235 which looks over its left front contact and armature to ground over the upper contact and armature of the off-normal springs B4. Relay 2535, in operating, connects ground over its right front contact and armature through the winding of the B switch release magnet B5 to battery at key 213i. 7 This ground from relay 205 also connects, over the left back contact and armature of relay 208 and the right armature and back contact of relay 2I'I, through the windings of rotary magnets A3 and U2, to battery at key 20 I Rotary magnet A3 energizes and advances the A switch brushes AA, AB, AC, AD, AE and AF one rotary step to contact the second set of TA, TB, TC, TD, TE and TF terminals. Rotary magnet U2 energizes and advances brush U1 one step thereby removing the ground from the units lamp I and connecting this ground to the units lamp 2'. Re-- lease magnet B5, in energizing as previously stated, causes brushes B1 and B2 to restore to normal in any well known manner, at which time the off-normal springs B4 also restore to their unoperated or normal condition. Springs B4, in restoring, open the locking circuit for relay 205 and again connect ground to the right winding of relay 2i'i2. Relay 2&5 releases, removing the ground from rotary magnets A3 and U2.

With ground connected to its right winding, relay 202 operates through that Winding to battery over key 20!. Relay 202 in operating looks through its left winding and, over its right front contact and armature, connects ground to the winding of rotary magnet B3. Magnet B3 energizes in a circuit to battery over key 20I and advances brushes B1 and B2 to their first respective bank terminals. Upon this first step of switch B the oiT-normal springs B4 operate, opening the cir uit through the right Winding of relay 202 and connecting ground to the left armature of 'relay' 205. Ground on brush B2, over the first bank terminal, short-circuits the left winding of relay 202 which releases, and is also connected to lamp AL. Relay 202, in releasing, removes ground from the winding of magnet B3 and connects this magnet winding to conductor 2I3.

The transmission lines terminating on the second set of TA, TB, TC, TD, TE and TF terminals are now connected over brushes AA, AB, AC, AD, AE and AF respectively to the terminals of the bank associated with brush B1. Since brush B1 is on its first bank terminal the line terminating on terminal TA is connected to the repeater, and measuring circuits over conductor 209.

Subsequent applications of ground to conductor 2I3 advance switch 'B, thereby associating each transmission line connected to the second set of terminals on the first level'of the A switch banks with the repeater and measuring circuits. When switch Breaches its seventh bank ter minals relay 205 again operates and locks. Relay 205, in operating, advances the brushes of switches A and U one rotary step and releases switch B in the same manner as hereinbefore set forth. Switch B again advances under control of ground applications on conductor 2 I3 and the lines connected with the third set of terminals on the first level of the A switch banks are associated with the measuring circuit. This action of switches A, B and U continues until switch A has taken its tenth rotary step at which time the tenth step off-normal springs A5 operate.

With springs A5 operated, the next release of a sequent seventh step of switch B, a circuit is 2 closed from ground over the right contacts of re-" lay 205, through release magnet B5, and over the left back contact and armature of relay 208, right armature and front contact of relay 2!] to battery through the windings of release magnets A4,

C3 and U3, and also over the right back contact and armature of relay 203 to battery through the winding of rotary magnet T3. Magnet T3 energizes and advances brushes T1 and. T2 to the second terminal of their respective banks. nets A4, C3 and Us energize and release switches A, C and U respectively to their normal position. Magnet B5, energized, causes switch B to release which also restores springs B4. With springs B4 normal, relay 205 releases as previously set forth and switch B then advances its first step.

Upon the release of switch A, the ofi-normal springs A2 and A5 restore to their unoperated position thereby respectively opening the locking and the operating circuit for relay 25?, which releases. The A2 springs in normal position close the operating circuit for relay 204 which looks to ground over the right contacts of relay 208. Relay 204, in operating, closes previously traced opcrating circuits for vertical magnet A1 and rotary magnet C2. Magnet A1, in energizing, advances the brushes of switch A one vertical step and, due to the opening of its contacts, opens the short circuit on the left winding of relay 2II which operates over a previously traced circuit. Magnet C2, in energizing, advances brush C1 to contact the first terminal of its bank. The off-normal springs A2, which operate on the first vertical step of switch A, open the operating circuit for relay 204. Relay 2 I I, in operating, opens the circuit through magnets A1 and C2. When magnet A1 de-energizes, it closes its contacts thereby closing the short circuit around the left winding of relay 2 which releases. Relay 2, in releasing, again closes the operating circuits for magnets A1 and C2 and the brushes of switch A take a second vertical step and brush C1 advances to the second terminal of its bank. The A1 magnet, in energizing, opens its contacts which removes the short circuit from the left winding of relay 2 I I. Relay 2 I operates and opens the circuits through magnets A1 and C2 which de-energize. When the contacts of magnet A1 close, the left winding of relay 2 is short-circuited but relay 2 remains operated through its right winding, winding of relay 208 which operates, brush C1 and its second bank terminal, second bank terminal and brush T1, to ground over the left contacts of relay 204. Relay 208, in operating, opens the locking circuit for relay 204 which releases, and closes the circuit from ground over its left front contact, right armature and back contact of relay 2H, to battery through rotary magnet A3. Magnet A3 energizes and advances the brushes of switch A to contactthe first set of terminals of the second level of the A switch banks. Relay 204, in releasing, opens the circuit through the windings of relays 2i i and 208. Relays 2H and 208 release, relay 200 opening the A2 magnet circuit and closing the locking circuit for relay 204, and relay 2H closing, in part, the A1 and C2 magnet circuits.

The transmission lines which terminate on the first set of terminals of the second level of the banks of switch A are now connected to the B switch, bank terminals associated with brush B1. As the associated signal distortion measuring circuit continues to function, ground applications to conductor 2l3 cause the advance ofv switch B which progressively associates each transmission line with the repeaters and measuring circuits over conductor 209.

. In a manner similar to that hereinbeforeset forth, the continued applications of ground to conductor 2 l3 cause switches A, B, C, T and U to function until the brushes of switch A have contacted each of the one hundred sets of TA, TB,

TC, TD, TE and TF terminals and switch B has associated each of the six hundred transmission lines connected to the aforementioned terminals with the repeater and, distortion measuring circuits. Brushes C1 and T1 control the number of vertical steps that the brushes of switch A take following the release of switch A after its brushes have contacted the ten sets of terminals in any particular bank level, since switch T advances one step for each operation of release magnet A4 and since vertical magnet A1 and rotary magnet C2 mustenergize and release for the number of times corresponding to the number of the bank terminal in contact with brush T1 at that time.

During each step of the foregoing operations, brushes B2, T2 and U1 prepare the proper circuits for the group, tens and units lamps, respectively, so that the application of battery to conductor 2! by the measuring circuit, at any time, will cause signal 2l5 to sound, and the lamps associatecl with'the particular line upon which excessive signal distortion has been encountered to light.

When brush T1 reaches the tenth terminal of its associated bank, it closes the circuit from battery through the right winding of relay M to the left armature of relay 204 which is unoperated at that time. Upon the operation of relay 204 for the advance of the A switch brushes to the tenth levels of the A switch banks, relay 21 8 operates and looks through its left winding to ground over the operated contacts of the off-normal springs T4. Relay 2l8, in operating, closes a circuit from battery at key 21, through the winding of release magnet T5, right armature and contact of relay 218 to the sixth terminal of the bank associated with brush B2.

After the brushes of switch A have advanced to the tenth sets of terminals of the tenth levels of the A switch banks, and after the B switch has subsequently advanced brushes B1 and B2 to their sixth bank terminals, the ground over brush B2 energizes the release magnet T5. Magnet T5, energized, causes the T switch to restore to its normal position at which time the ofi-normal springs T4 also restore to normal. When springs T4 restore, the locking circuit for relay M8 is opened and that relay. releases. In addition, ground over the normally closed contacts of springs Ti operates relay 283 through its right winding. The release of relay M8 opens the circuit through release magnet T5. Relay 203, in operating, locks through its left Winding and closes the circuit through magnet T3 which causes brushes T1 and T2 to be advanced to the first terminal of their respective banks. Ground over brush T2 short-circuits the left Winding of relay 288 which releases since the circuit through its right winding was opened by the operation of offnormal springs T4 upon the first step of switch T.

When magnet A3 releases after the tenth rotary step on the tenth bank levels of switch A, relay 2!! operates over the now operated tenth ofinormal springs A5. Relay 2 l I, in operating, locks to ground under control of the operated A2 springs and prepares the circuit for release magnet A4. When ground is returned to conductor 2 l 3 at the termination of the distortion measurement of the six hundredth transmission line, rotary magnet B3 is energized advancing switch B to the seventh step. Relay 205 operates from ground over brush B2 and the seventh bank ter- I minal. Relay 205,'in operating, locks under control of theoperated B4 springs, and closes the energizing circuits for release magnets A4, B5, C3 and U3. Switches A,'B, C and U restore to normal, in turn restoring off-normal springs A2, A5 and B4 to normal. Springs A5, restoring to normal, open the operating circuit for relay 2H. Springs A2, restoring to normal, open the locking circuit for relay 211 which releases, and also close the circuit through the winding of relay 204 which 0perates. Springs B4, restoring to normal, release relay 205 by opening its locking circuit, and also operate relay 202 through its right winding.

From this point on, the circuit functions in the same manner as hereinbefore set forth from the beginning of the detailed description of the operation of Fig. 2, with the exception that relay 203 has already operated and released, switch T having taken its first step immediately upon its return to normal as previously noted,

The transmission lines, beginning with those terminating on the first terminals of the first level of the A switch banks, will be successively connected to the repeater and distortion measuring circuits, as previously set forth, the circuit of Fig. 2 functioning as long as key 253i remains operated.

-Referring now to Fig. 3, this figure comprises the delay and regenerative repeater circuits and the signal distortion measuring circuits. The delay repeater circuit consists essentially of relays 303, 304 and 305, resistances 306 and 357, and condenser 308. The regenerative repeater consists essentially of the start-stop distributor D and relays 300 and M0. The distributor D is composed of a receiving ring and receiving segments 3| I, a sending ring and sending segments 3i2, a set of brushes 3|3 associated with the receiving ring and segments 3! i, and a set of brushes 3M associated with the sending ring and segments 3I2. A clutch 3l5, upon being released by latch 3H5, causes brushes 3l3 and M4 to make one complete revolution over their associated rings and segments in a manner well known in the art. The signal distortion measuring circuit consists essentially of relays 3!'!, 3|8, 3l9 and 320.

The interval during which signal distortion measurements are made on any transmission line is controlled by interrupter 32!. This interrupter is arranged to close its contacts for approximately one second once each minute, the contacts being open during the remaining 59 seconds of the minute interval. Signal distortion measurements or any line are made during the 59 second open interval of the interrupter and, if no excessive distortion is encountered over that period, the

following one second closure of interrupter 32! causes the measuring circuit and the associated circuit of Fig. 2 to function and pass on to the succeeding transmission line. Should excessive distortion be encountered during a measuring interval, the measuring circuit functions to look in an indication of this condition, and the further operations of interrupter 32'! are ineffective until the measuring circuit is manually released. The manner in which the foregoing operations take place will be subsequentlyset forth in detail.

For the purpose of illustrating the complete functioning of the circuitsof Fig. 3, let it be assumed that a signal distortion measurement has just been made on a transmission line connected to these circuits over conductor 209 of Fig. 2, and that no excessive signal distortion was encountered on the signal impulses received over that line.

When the contacts of interrupter 32! now close at the end of the 59 secondmeasuring interval, ground over the interrupter contacts operates relay 325 in an obvious circuit. Relay 325, in operating, connects ground over its front contact to battery through the left winding of relay 326, and also connects this same ground, over the right back contact of relay 320, to conductor 2 !3. Relay 326 operates through its left winding, and the ground on conductor 2 !3 of Fig. 2 causes the circuit of Fig. 2 to function, as hereinbefore set forth, and connect the next transmission line to conductor 209 of Fig. 2. Relay 325, by its operation, also opens the circuit from ground over its back contact, back contacts of relay 326, to battery through the left winding of relay 33! (previously operated as willlater be described) and relay 33! releases. Relay 33!, in releasing, connects negative battery, through resistance 328, over its right back contact to the winding of relay 330, and also connects negative battery, through resistance 329, over its left back contact, through the right winding of relay 326, to the armature of relay 302. Relay 33!, in releasing, also opens the circuit tothe armature of.

The particular transmission'line on which signal distortion measurements are about to be made has now, by the functioning of the circuit of Fig. 2 in a manner previously described, been connected to conductor 209, and over this conductor to ground through the Winding of polarized relay 302. Relay 326, at this time, is being held operated through its left winding. At the end of the one second closure, the contacts of interrupter 325 open and'release relay 325. Relay 325, in releasing, opens the circuit through the left winding of relay 326, but relay 326 does not release immediately since it is of the slow-to-release type.

Relay 302, being polarized, operates its armaw ture to contact its right or left contacts in uniover the printing telegraph transmission line connected to conductor 209 from Fig. 2. At all times when no signals are being transmitted, a marking current is applied to the line. The polarity of this marking currentis such that the armature of relay 302 is held against the right contact of the relay. Each transmitted character is composed of a series of six impulses of which the first impulse (known as the start pulse) is always spacing. An impulse of spacing current causes the armature of relay 302 to make contact with its left contact. The polarity and arrangement of the remaining five impulses following the start pulse is dependent upon the particular character being transmitted. The armature of relay 302 will, therefore, be on the. right contact'of the relay for all marking impulses and during the interval between transmitted charactera'and will be on its left contact for all spacing impulses.

Relay 302, on its right contact in response to marking current or impulses, connects grounded negative battery through resistance 335, over three parallel paths, namely, to the right winding of relay 326, to ground through resistances 306 and 30'! and the lower winding of relay 303, and to the receiving ring 322 of. distributor D. When on its left contact, in response to spacing impulses, relay 302 connects grounded positive battery through resistance 334 over the same parallel paths to the aforementioned points.

The series of impulses incoming over the line, representing successive characters, may be transmitted in rapid succession under control of a tape transmitter or a continuously operated keyboard, or they may be transmitted slowly from a keyboard in which instance a considerable interval of marking current separates eachimpulse series.

As stated hereinbefore, upon the release of relay 325 the circuit through the left winding of relay 326 is opened but, since relay 326 is slowto-release, the relay remains operated for an interval. Also, the previous release of relay 33! connected grounded negative battery through resistance 329 and through the right winding of relay 326 to the armature of relay 302. Relay 302, therefore, in response to series of incoming impulses in rapid succession, contacts the grounded positive battery on its left contact with sufficient frequency to hold relay 325 energized through the right windingof that relay. Relay 326, remaining operated, prevents the operation of relay 33! upcn'the release of relay 325. The operation of the circuit under this condition will be set foith in detail later.

Assume that the series .of impulses, corresponding to characters, are being transmittedslowly' from a manually operated keyboard; Relay 302, in following the incoming impulses, will, therefore, be off its left contact for a sufficient interval (in response to the marking current between characters) to allow relay 326 to release. Relay 326, in releasing, causes relay 33! to operate in a circuit from grounded battery through the left winding of relay 33!, normally closed con tacts of relay 326, to ground overthe back con tact and armature of relay 325. Relay 33!, in operating, removes the'battery from the right winding of relay 326, removes the battery from the winding of relay 330, and connects the ground from the armature and back contact of relay 325 to the armature of relay 3!9, through the contacts of key 318.

Upon the first incoming impulse, which is the start pulse, relay 302 operates to its left contact thereby connecting grounded positive battery,

through resistance 334, to conductor .333. This positive potential operates the clutch release magnet 324 in a circuit over conductor 333, receiving ring 322, brush 3|3, start receiving segment 323, to negative potential through the winding of magnet 324 to grounded negative battery. Magnet 324, in energizing, disengages latch 3 !6 from clutch 3l5 and the distributor brushes 3!3 and 3M now make one revolution over their associated rings and segments. The speed at which the brushes revolve is uniform and the speed of the driving motor (not shown) of distributor D as well as the speed of the driving motor of the distributor at the distant transmitter is held to within approximately ':1 per cent by a centrifu gal governor associated with each motor.

As soon as brush 3l3 passes off segment 323, the circuit through magnet 324 is opened. Magnet 324 de-energizes and latch 3I6 restores to normal in which position, at the conclusion of a complete revolution of the brushes, it re-engages clutch 3 5 to hold the brushes until the next start pulse is received.

The receiving segments 34! to 346, inclusive, are so placed with respect to the stop position of brush 3!3 that the brush is in contact with any receiving segment only during the middle portion of the received impulse. The sending segments 35! to 3565, inclusive, are so arranged with respect to brush 354 that this brush does not contact a particular sending segment until receiving brush M3 is just leaving or has just left the corresponding receiving segment. With respect to the received impulses, therefore, the signals to be regenerated by sending brush 3! and'its associated ring and segments will be delayed'by approximately one-half of the time required to transmit one signal element.

When brush 3!3 reaches the first receiving segment 34! a circuit is completed from the armature of relay 302, over receiving ring 322, brush 3I3, receiving segment 34!, to ground through the upper winding of polarized relay 309 and through resistance 336. Relay 309, at this time, is locked in the position of its last previous operation in a circuit from ground through resistance 350, lower windings, armature and left or right contact of relay 309, to grounded positive or grounded negative battery through resistance 33! or 333 respectively. If the polarity of the current in the aforementioned circuit through the upper winding of relay 309 is in the direction opposite to the last previous current flow through that winding, relay 309 will unlock and move its armature to its opposite contact and will again look through its lower winding in that position. If the polarity of the current through the upper winding is the same as the last previous current flow through that winding, relay 309 remains locked with its armature on the contact to which it last moved. The armature of relay 309, therefore, follows the operation of the armature of relay 302 for each alternate impulse and connects, depending upon its position, positive or negative battery, through resistances 331 and 338 respectively, over its left or right contact and armature, to sending segments 35!, 353 and 355. Brush 3H5, at this time, is in contact with sending segment 35'! which is connected to grounded positive battery which will operate polarized relay 3! to its left hand contact to repeat the start pulse. As receiving brush 3I3 is leaving segment 34!, sending brush 3l4 contacts the first sending segment 35! thereby completing a circuit from positive or negative battery on the armature of relay 309, over the first sending segment 35!, brush 3l4, sending ring 339, to ground through the winding of relay 3H3. Depending on the polarity of the current through its winding, relay 3l8operates its armature to its opposite contact or keeps its armature on the contact already made.

As the distributor brushes 3!3 and 3E4 continue to advance, brush 3i3 contacts the second receiving segment 342, this closure corresponding in time to the middle portion of the second incoming impulse following the start pulse. Grounded positive or grounded negative battery, depending upon the position of the armature of relay 302 in response to the incoming impulse, is connected over the contact and armature of relay 302, conductor 333, receiving ring 322, brush 3l3, receiving segment 342, to ground through the upper winding of relay 3m and through resistance 340. In a manner similar to that described for relay 359, relay 350 will either remain locked or will move its armature to the opposite contact and then look, depending upon the polarity of the current through its upper winding. The locking circuit for relay 3!0 may be traced from ground through resistance 349 and the lower winding, armature and left or right contact of the relay, to either grounded positive or grounded negative battery through resistance 34! or 348 respectively. The armature of relay 3l0 follows the operation of the armature of relay 302 for the impulses incoming over receiving segments 342, 344 and 345. Relay 3), depending upon the position of its armature, connects grounded positive or grounded negative battery, through resistances 34'! and 308 respectively, over its left or right contact and armature, to sending segments 352,354 and 356.

As receiving brush 3!3 leaves receiving segment 342, sending brush 3l4 leaves sending segment 35! and moves on, contacting the second sending segment 352 which corresponds to receiving segment 342. The positive or negative potential from the armature of relay 3w is now applied to the circuit extending over segment 352, brush 3l4, sending ring 339, to ground through the winding of polarized relay 3l8. Relay 3IB, as in the case of the preceding impulse, will either keep its armature stationary or will move it to the opposite contact, depending upon the current polarity and on the position assumed by the armature during the previous impulse.

In a manner similar to that hereinbefore described, the three remaining impulses of the series which compose the particular character being transmitted, plus a sixth impulse known as the stop pulse, are regeneratively repeated through the winding of relay 3l8; receiving brush 3'!3 alternately associating the armature of relay 302, over receiving segments 343, 344, 345 and 346, with the upper windings of relays 309 and M0, and sending brush 3I4 alternately associating the armatures of relays 309 and SW, over sending segments 353, 354, 355 and 355, with the winding of relay 3!8.

Since sending segments 35! to 356, inclusive, are of uniform length and uniformly spaced, it will be obvious that the regenerated impulses produced in the winding of relay 3l8 correspond tothe original undistorted impulses being transmitted from the distant end of the transmission line. As previously stated, however, the regenerated signals lag the incoming signals by approximately one-half an impulse length, since the sending brush 3!4 does not contact a par ticular sending segment until the receiving brush N3 is leaving or has just left the corresponding.

receiving segment, the receiving segment at that time carrying the middle portion of the particular impulse. Due to this lag in the regenerated signal, it is necessary to introduce a corresponding lag in the incoming signals which are to be compared with the undistorted regenerated signals during the signal distortion measuring interval. This lag in the incoming signals is produced by the delay repeater circuit which functions in the manner hereinafter set forth.

The delay repeater circuit operates simultaneously with the regenerative repeater circuit, both circuits functioning from the same impulses of positive and negative potential supplied over conductor 333 when relay 302 responds to the signal impulses incoming over conductor-209.

Assume that the last prior operation of relay 302 was in response to marking current. The armature of relay 302, therefore, moved from its left to its right contact thereby reversing the polarity of the current in the circuit through resistances 306 and 30'! and the lower winding of relay 303. In response to this change in polarity, relay 303, after an interval obtained in a manner subsequently explained, unlocked and moved its armature from its left to its right contact. Relay 303 then looked in that position in a circuit from ground through resistance 35!, upper winding, armature and right contact of relay .303, to grounded negative battery through resistance 353. The operation of relay 303 removed the positive battery, through resistance 358, from. conductor 364 and connected negative battery, through resistance 359, and over its right contact and armature, to conductor 364. This changed the polarity of current in the circuit through resistance 360 and through the winding of polarized relay 3H, and caused relay 311 .to move its armature from its left contact to its right contact. change in the potential polarity on conductor 364 also'caused a surge through condenser 362, in a circuit throughresistance 363 and the windings of biased polarized relays 305 and 304 to ground. Relays 304 and 305 are oppositely poled with respect to their series circuit, and

the aforementioned surge was in a direction which caused relay 304 to momentarily move its armature to contact its left contact. Condenser 308 had started to charge from the grounded negative battery over the right contact and armature of relay 302 and through resistance 305 to ground on the other plate of the condenser. The momentary closure of the left contact of relay 304 caused the complete charging of condenser 308 from grounded negative battery through resistance 355 and over the left contact and armature of relay 304 to the upper condenser plate, the lower plate being grounded.

As has just been set forth, therefore, prior to the first incoming impulse of the signal impulses about to be delayed, the armatures of relays 302, 303 and 311 are contacting their respective right contacts, and condenser 30B is completely charged, with the negative charge on its upper plate connecting to the junction of resistances 306 and 301. 7

When relay 302 now operates its armature from its right to its left contact, in response to the first or start impulse (which is always spacing), the potential on conductor 333 is changed from negative to positive. Since the junction point of resistances 306 and 30'! is at negative potential at this time, due to the existing charge The on condenser 308, the application of positive potential to conductor 333 and through resistance 306 does'not immediately cause current to flow in the positive direction through the lower winding of relay 303." Condenser 308 first discharges in a circuit through resistance 305, armature and left contact of relay 302, to grounded positive battery through resistance 334 and, when discharged, again starts charging to this positive potential which is the reverse, in polarity, of the preceding charging potential. After condenser 308 has recharged to a certain point, the junction of resistances 305 and 30? becomes sufficiently positive with respect to ground that the currentflow in the lower winding of relay 303, in the positive direction, is suflicient to overcome the effect of locking current in the upper Winding of that relay, and relay-303 will operate its arma-- ture away from its right contact and move to its left contact.

When relay '303 transfers its armature from right to left, it reverses the polarity of the potential on conductor 364, operating relay 3H to its left contact, and causing a surge through condenser 362,'resistance 363 and the windings of polarized relays 305 and 304. This surge is in the direction which causes the momentary operation of relay 305. Relay 305 momentarily completes the circuit from grounded positive battery through resistance 366, left contact and armature of relay 305, to the upper plate of condenser. 308 thereby completing the charging of that con denser. Relay 303, in operating to its left contact,;locks in that position in a circuit from grounded positive battery, through resistance 353, left contact, armature and uppper Winding of relay 303, to ground through resistance 36!. 1

The function of relays. 304 and 305 is to provide for the rapid and complete charging of condenser 308 to either polarity of charge upon each operation of relay 303 and prior to the subsequent operation of relay 302, thereby insuring a uniform delay interval for each impulse.

Succeeding impulses repeated to the delay re peater circuit by relay 352 cause relays 303, 304, 305 and 3|! to function in a manner similar to that just previously described for the first impulse. Marking impulses, which operate relay 302 to its right contact, cause relay 3 03 to operate to its right contact after condenser 308 discharges and partially recharges, and relay 303, after this delay interval, causes relay 3 l i to operate to its right contact and also momentarily operates relay 304 to complete the charging of condenser 308. Spacing impulses cause the circult to function in a manner identical with that described forthe first or start impulse, which was spacing.

In the foregoing manner, relay 3H follows the incoming impulses in agreement with the operation of relay 302 but delayed by the interval required to discharge condenser 358 and recharge that condenser, in the opposite polarity, to a point where the current through the lower Winding of relay 303'is effective in unlocking that relay and operating it to its opposite contact. This delay cult, while relay 311 is operating from the incoming signals Which have been delayed to compensate for the lag present in the regenerated signals. If no distortion is .present in the incoming signals, relay 311 will operate in unison with relay 318, and the ground fromthe armature of relay 318 will be removed from the armature of relay 311 only during the interval required for the transfer of the armatures'of relays 311 and 318 from the left to the right contacts and vice versa. If distortion is present in the incoming signal im pulses, the operation of relay 311 will no longer be in synchronism with the operation of relay 318. This results in prolonging the interval dur ing which the ground over the armature of relay 318 is removed from the armature of relay 3E1.

The ground suppliedover the arm-a'tures and contacts of relays 311 and 313, when both of these relays are in their same respective positions, connects to one side of condenser 399, thereby shortcircuiting that condenser. This same ground is also connected to grounded negative battery through the upper winding of polarized relay 319 and resistance 331, causing a current flow through the upper winding of relay 319 in a direction which holds the armature of that relay on its right contact. When the ground is removed from the armature of relay 311, during the transfer time of the armatures of relays 311 and 313 as they are operating in synchronism, the short circuit is removed from condenser 369. The current in the upper winding of relay 319, however, does not immediately fall to zero since condenser 369 charges from the grounded negative battery through that winding and temporarily maintains the current flow. Before the charging current flow ceases, due to the complete charging of condenser 339, relays 311 and 318 will have again closed the circuit to ground over their armatures and contacts to short-circuit condenser 339 and reestablish the current flow through the upper winding of relay 319.

Assume now that distortion is present in the incoming signal impulses. Relay 311 will, therefore, due to the distortion, get out of step with relay 318 as these two relays are repeating the signal impulses. This prolongs the interval during which the ground is removed from condenser 369 and from the upper winding of relay 319. If this interval is of sufficient duration, condenser 339 completely charges before the energizing circuit for the upper winding of relay 319 is reestablished and the current through that winding, therefore, falls to zero.

The next-to-upper winding of relay 359 is permanently energized in a circuit from ground through the winding and through resistance 368 to grounded negative battery, and this winding is so wound that its effect on relay 319 opposes that of the upper winding of that relay. When the upper winding current, therefore, falls to zero, as stated above, the next-to-upper Winding of relay 3E9 becomes effective and moves the armature of the relay off its right contact. Prior to this time the left winding of transformer 312 has been energized in a circuit from grounded negative battery, left winding of the transformer, right contact and armature of relay 319, contacts of key 313, middle left armature and front contact of the operated relay 33!, and back contact and armature of the unoperated relay 325, to ground. When relay 3E9 therefore opens its right contact, the circuit through the left winding of transformer 312 is opened thereby inducing a; surge of current through the lower winding of relay 319 over the secondary winding of transformer 312. This surge is in the proper direction to immediately operate the armature of relay 319 to the left contact of that relay. 7

When the armature of relay 319 closes to its left contact, a circuit is completed from the previously traced ground on that armature, over the left contact of relay 319 to grounded battery through the contacts of key 319 and the winding of relay 3213. This ground is also connected over the normally closed right cont-acts of relay 320,

and through resistance 311 and the next-to-lowermost winding of relay 319 to groundednegative battery thereby providing a locking circuit for relay 319 until the complete operation of relay 323 has been effected.

Relay 329, in operating, looks over its right front contact and armature to ground over the upper armature and back contact of key 313 and opens the locking circuit for relay 319. In addition, the operation of relay 323 connects battery over its left armature and front contact to conductor 214 of Fig. 2, thereby causing an audible alarm and a visual indication of the sign-a1 distortion encountered, in the manner hereinbeforedescribed under the detailed operation of Fig. 2. Relay 329, in operating, also opens the circuit from conductor 213, over its outer right armature and back contact, to the front contact of relay 325, thereby rendering the operation of relay 325,

under control of interrupter 321 at the conclusion of the measuring interval, ineffective in advancing the circuits of Fig. 2 to the succeeding transmission line. The alarm indications remain locked-in under control of key 313. i

The length of the interval during which the ground over the arm-atures and contacts of relays 311 and 318 can be removed from the upper winding of relay 319, before causing that relay to function and cause an alarm to be given as hereinbefore set forth, is controlled by the charging time of condenser 369. This interval may be varied by changing the capacity of condenser 369 which is variable. Condenser 369 may therefore be set at a value of capacitance such that any predetermined corresponding amount of signal distortion causes the measuring circuit to function and cause an excessive distortion alarm to sound. It will be obvious that the alarm indicates that the distortion encountered on the transmission line under observation is equal to or exceeds the amount of distortion predetermined by the adjustment of condenser 369.

If it is now desired to quantitatively measure the distortion present in the incoming signals, key 318 is operated. Key 318, in being operated, transfers the conductor on the armature of relay 319 from the left middle armature of relay 331, to ground over the upper front contact of key 318. The conductor from the left contact of relay 319 is transferred, by the operation of key 318, from the winding of relay 329 to grounded battery through lamp 319."Relay 320 does not release since it is locked in its operated position under control of key 313.

As the armature of relay 319 now moves to its left contact in response to the excessive signal distortion, lamp 319 lights from the ground on the armature of relay 319. By changing the capacity of the variable condenser 369 to a point where lamp 319 no longer lights, a measurement of the maximum distortion present in the incoming signal is obtained. Condenser 369 may be provided with an indicator calibrated to give the approximate percentage of signal distortion.

relay 33!.

At the conclusion of the particular excessive distortion measurement, key 318 is restored to the normal position. Key 318, in releasing, opens the circuit to lamp 319, reconnects the conductor from the left contact of relay 3I9 to the winding of relay 320, disconnects the direct ground from ,the armature of relay3l9, and again connects the armature of relay 3l9 to the left middle armature of relay 33!. Key 313 is now momentarily operated. The operation of key 313 opens the locking circuit for relay 320 which releases, thereby removing grounded battery from conductor 2| 4 of Fig. 2 which silences the audible alarm and extinguishes the visual signal of Fig. 2. The operation of key 313 also connects ground to conductor 2l3 of Fig. 2, causing the circuits of Fig. 2 to function as previously described and connect the succeeding transmission lineto conductor 20 9.

Assuming that no excessive signal distortion is encountered on the transmission line under observation, relays 3H and 318 operate in unison during the measuring interval and remain in synchronism suflficiently to prevent the complete charging of condenser 369. Relay 3 l9, therefore, does not move its armature 01f its right contact. At the conclusion of the 59-second open interval of interrupter 32l the interrupter contacts close and operate relay 325. Relay 325, in operating,

removes the ground from the armature of relay 319, and connects ground over its armature and front contact to battery through the left winding of relay 326, and to conductor 2l3 over the right back contact and armature of relay 320. The ground over conductor 2I3 of Fig. 2, causes Fig. 2 to function as previously described and connect the next transmission line to conductor 209 of Fig. 2. From this point on, the operation of the circuit is identical to that hereinbefore set forth, from the corresponding point of the grounding of conductor 2|3 at the outset of the description of the detailed operation of Fig. 3.

' In the foregoing description of the operation of Fig. 3 it was assumed that the series of incoming impulses, corresponding to characters, were being transmitted slowly from a distant manually operated keyboard. Under that condition the armature of relay .302, in following the incoming impulses, was therefore off its left contact for a period suflicient to allow relay 326 to release. When relay 326 released it operated Relay 33| in turn opened the circuit from battery through the right winding of relay 326 and thereby prevented the further operation of relay 326 at that time.

7 Assume now, instead, that the incoming series of impulses are being transmitted in rapid succession from the distant end of the line under control of a continuously operated keyboard or under control of a tape transmitter. As previously set forth, under this condition, upon the opening of the contacts of interrupter 32l at the beginning of the measuring interval, the release of relay 325 opens the circuit through the left winding of relay 326 but relay 326 does not release since the armature of relay 362 is on its left contact for intervals of sufiicient length to hold relay 326 energized through its right winding. Relay 326, remaining operated, prevents the operation of relay 33! upon the release of relay 325 at the beginning of the measuring interval.

With relay 33l released, the circuit to the armature of relay 3l9'is open and grounded negative battery, through resistance 328 is connected to the winding of relay 336 over the right armature and back contact of relay 33l.

The first incoming impulse over the transmission line, which is the start pulse, causes relay 392 to operate to its left contact and complete the circuit from grounded positive battery through resistance 334, left contact and armature of relay 302, conductor 333, distributor re ceiving ring 322, brush M3 and receiving segment 323, to grounded negativeibattery through the winding of clutch release magnet 324 and also to grounded negative battery through the winding of relay 330. Relay 330, in'operating, closes the circuit from ground on the armature and over the back contact of relay 325, operated contacts of relay 326, contact and armature of'relay 330, to grounded battery through rotary magnet 315. e

Magnet 315, in energizing,'causes brush 7316 of switch S to step'to the first terminal of its associated bank at which time the oif-normal springs 332 operate and prepare the circuit from grounded battery through the winding of release magnet 31! to the inner armature of relay 33!.

Since the start pulse operated the clutch release magnet 324, the brushes of distributor D revolve through one revolution and regeneratively repeat the incoming impulses to relay 3i8 in the manner previously described. Simultaneously, relays 303, 304 and 305 function as hereinbefore set forth, and cause relay 3|! to follow the delayed incoming impulses. The distortion measuring circuit is ineffective, however, since there is no ground on the armature of relay 3L9 due to the non-operated position of relay 33!.

When brush 313 moved off segment 323' it opened the circuit through thewindings of clutch release magnet 324 and relay 333. Clutch release magnet 324, released, causes the distributor brushes to come torest at the conclusion of one revolution. Relay 336, in releasing, opens the circuit through the rotary magnet 375 of switch S.

The start pulse of the second series of incoming pulses causes the distributor brushes to make another revolution and also again operates relay 333 which, in turn, energizes rotary magnet 3'25 thereby causing the brush 315 of switch S to move to the second terminal of its associated bank.

The foregoing cycle of operations will continue, each operation of relay 33!! causing brush 316 to advance to the next terminal of its bank, until brush 313 contacts its tenth bank terminal at which time ground over brush 3'13 and the tenth terminal is connect-ed to grounded battery through the right winding of relay 33L Relay 33!, in operating through its right Winding, opens the circuit to the winding of relay 333 to prevent further operations of that relay, removes the negative potential from theright winding of relay 326 which permits relay 323 to release, and connects ground from over the armature and back contact of relay 325, over the left middle armature and front contact of relay 33! 'to the armature of relay 3|9.

Relay 326, in releasing, closes the circuit from ground over the armature and back contact of relay 325, over its normal contacts to grounded battery through the left winding of relay 33! and over the inner right front contact and armature of relay 33L over the operated off-normal springs 332, to grounded battery through the winding of the release magnet 31''. of switch S.

Release magnet 3'", in energizing, causes in any well known manner, brush 313 to restore to its normal position at which time the off-normal iii 209.. ofaFig. 4 and. after distortion measurements springs 332. also restore to their normal, non-operated position. As brush 316 leaves the tenth bank terminal, in restoring to normal, the circuit through the right winding of relay 331 is opened. Relay 331 does not release however since it is being held operated through its left winding over the previously traced circuit established upon the release of relay 326.

Since ground is now connected to the armature of relay 319, the distortion measuring circuit is effective and subsequent series of impulses incoming over the transmission line under observation cause the regenerative repeater, delay repeater and signal distortion measuring circuits to function in a manner identical with that hereinbefore set forth for the functioning of these circuits in response to slowly transmitted impulse series.

The purpose of delaying the start of the signal distortion measurements when the incoming series of signal impulses are being transmitted in rapid succession is to prevent the false operation of relay 320 upon the transfer of the measuring circuit from one transmission line to another. Assume, for example, that a transmission line is connected to conductor 209 during the middle of a series of impulses incoming over that line, and that the first impulse effective in operating relay 302 is a marking impulse. Since a start pulse and a spacing impulse are identical, the regenerative repeater will not start to function immediately but will await the first spacing impulse, after which the operations of relays 311 and 318 may be out of synchronism with respect to complete series of impulses. This condition would result in the possibility of a false excessive signal distortion indication, even though no excessive distortion was actually present in the incoming signals, were it not for the ineffectiveness of the measuring circuit at this time due to the absence of ground from. the armature of relay 3l9. The interval introduced by the stepping of switch S from its first to its tenth bank terminal (corresponding to ten revolutions of the brushes of distributor D) provides ample time for distributor D to come into step with the incoming signal. In the foregoing manner the possibility of false excessive signal distortion indications is guarded against.

Referring now to Fig. 4, this figure comprises a delay repeater circuit, a regenerative repeater circuit, and a signal distortion measuring circuit which function in the samegeneral manner as the corresponding circuits of Fig. 3. The points of difference between Fig. 4 and Fig. 3 are in the delay repeater and signal distortion measuring circuits, which in the case of Fig. 4- employ vacuum tubes.

The regenerative repeater circuit of Fig. 4 functions in the same manner as that hereinbefore set forth for the regenerative repeater of Fig. 3. The start-stop distributor D1 is identical with distributor D of Fig. 3, and the manner in which the incoming signals are regeneratively repeated from the contacts of relay to the winding of relay 3&8 is the same in both cases. The individually numbered circuit elements 409, 410, 4| I, 412, 413.

414, M5, 496, 411, M3, 420, 421,422, 423, 424, 425, 426, 423, 423, 430, 43!, 433, 434, 435, 431, 438, 439, 441, 442, 443, 444, 445, 445, 441, 448, 449, 450, 45!, 452, 453, 454, 455, 456 and 451 function in a manner identical with the corre spondingly numbered elements 309, 3lli, etc., of the regenerative repeater circuit of Fig. 3.

The transmission lines are connected to conductor 203 of Fig. 2 which conductor is, for the purpose of describing Fig. 4, part of conductor have. been. made, a ground is connected to conductor 213 of. Fig. 2 either by the operation of relay 425 or bythe operation of key 413. Con-- ductor 2.5.3 of Fig. 2 is, for the purpose of describing Fig. 4, part of conductor 213 of Fig. 4. The ground on conductor 213' causes the circuits of Fig.2 to advance to the succeeding transmission line. as hereinbefore set forth in the description of Fig. 2.. If excessive distortion is encountered, grounded battery is connected over conductor 2 I4 to conductor 2 94 of Fig. 2 to give an audible alarm and a visual indication of the condition as outlined under Fig. 2.

The operations andfunctions of interrupter 421, relays 420, 425, 426, 430 and 43f, resistances 428 and 429, and key 413, in controlling the distortion measuring period and in connecting ground to conductor 213' and battery to conductor 214', are identical with the operations and functions of the correspondingly numbered interrupter 32 I, relays 320, 325, etc., of Fig. 3.

Themanner in which relays 426 and 431, and

\magnets 41.5 and 411, brush 416 and off-normal springs 432 of switch S1 function, in delaying the start of signal distortionmeasurements when the transmitted impulse series are incoming in rapid succession, is identical with that set forth for the correspondingly numbered relays, magnets, brush and springs. of Fig. 3.

Relays 402and 403 operate in series under control of the impulses incoming over conductors 2'39 and 209'.

In response to the incoming signal impulses,

thearmatures of relays 402 and403 contact their respective right or left contacts, the left contacts for spacing and the right contacts for marking. Impulseso-f positive and negative polarities over the contacts and armature of relay 402 cause the distributor D1 and relays 409 and M0 to function and regeneratively repeat corresponding. undistorted impulses through the winding of relay 4.18 in the manner hereinbefore described.

Simultaneously with the regeneration of the undistorted signal impulses through relay 4I8,

the received incoming signal impulses are retube 401 is normally energized in a local circuit.

The negative potential on the grid of the tube at this time is sufliciently large to prevent any flow of current in the anode circuit of the tube. The negative battery over the contacts and armatures of relays 403 and 404 is also connected to one side of rheostat 460 and to one plate of condenser 459 and this condenser is completely charged in a circuit extending to grounded positive battery on its opposite plate;

When the. armature of relay 493. now moves to its left contact in'response to the first spacing impulse, the negative potential source is disconnected from the grid of tube 401 and from the upper plate of condenser 459. Condenser 453 starts discharging through rheostat 460 thereby continuously diminishing the negative potential a on the grid of tube 401. Condenser 459 completely discharges and its upper plate and the grid of tube 401 finally assume the positive potential of the battery connected to the lower plate of condenser 459. Current now flows from ground on the cathode and over the cathode-anode circult of tube 401, through the middle winding of relay 406 to grounded positive battery over the left contact and armature of relay 405. Relay 496, prior to this flow of current through its middle winding, was locked with its armature on its right cont-act in a circuit from grounded negative battery through resistance 462, right contact, armature and upper winding of relay 406, to ground through resistance 480. The flow of current through the middle winding of relay 406 is of sufficient amount and in the proper direction to counteract the effect of the locking current through the upper winding, and the armature of relay 496 now moves from its right toits left contact. Relay 406 looks in this position in a circuit from grounded positive battery through resistance 46I, left contact, armature and upper winding of relay 406, to ground through resistance 48%).

When the armature of relay 406 moves from its right to its left contact it changes the potential on conductor 43! from negative to positive there-,

by reversing the direction of the current flow in the circuit extending through the windings of relays 404, 405 and M1 to ground through resistance 466. Due to this current fiow reversal, the armature of relays 404 and 4|! move from their right to their left contacts and the armature of relay 405 moves from its left to its right contact. 1

With the armature of relay 404 on its left contact, grounded negative battery is again connected over the armature and left contact of that relay, over the left contact and armature of relay 403, to both the upper plate of condenser 459 and the grid of tube 401 through resistance 458. Condenser 459 charges, its upper plate becoming negative, and the current over'the cathode-anode circuit of tube 40! falls to zero due to the negative potential on the grid of the tube.

Relay 406 remains with its armature on the left contact however, since the relay is locked in that position by the previously traced flow of current through its upper winding.

With the armature of relay 405 on its right contact, the circuit through the middle winding of relay 406 is open and positive potential is connected through the lowermost winding of relay 455 to the anode of tube 401. The middle and the lowermost winding of relay 405 are connected in circuit in opposite directions with respect to their effect on the armature of the relay. A flow of current through the lowermost winding of the relay, as will subsequently take place, will therefore cause the armature to move in the direction opposite to that caused by the flow of current through the middle winding of the'relay.

As previously stated, the reversal of the polarity of the potential on conductor 48| causes the armature of relay 4 l! to move from its right to its left contact which brings the position of that armature into agreement with the position to which the armature of relay 402 moved in response to the first incoming impulse.

Assuming now that the second incoming impulse is marking, the armatures of relays 402 and 493 move from their left to their right contacts in response to that impulse. Relay 402, in operating, reverses the polarity of the potential on conductor 433 and causes the second impulse to be regeneratively repeated to the winding of relay M8 as previously set forth; Relay 463, in operating, disconnects the source of negative potential from condenser 459 and from the grid of tube 401. Condenser'459 discharges and, after an interval, the upper plate of the condenser and the grid of. tube 40'! become positive, as hereinbefore described, and current flows from ground over the cathode-anode circuit of tube 401, through'the lowermost winding of relay 406, to grounded positive battery over the right contact and armature of relay 455. The current in the lowermost, winding of relay 406 opposes and overcomes the locking current flowing in the uppermost winding of the relay, and the armature of relay 495 therefore moves from its left to its right contact. Relay 406 looks from grounded negative battery through resistance 462, over the right contact, armature and upper winding, to ground through resistance 480. Re-- lay 496, in operating in the opposite direction, reverses the polarity of the potential on conductor 48| which, in turn, reverses the current flow through the windings of relays 404, 405 and 4H. Relay 404, in operating, again impresses the negative potential on condenser 459 and onto the grid of tube 46'! thereby causing the current in thecathode-anode circuit of the tube to cease flowing. Relay 405, in operating, transfers the anode circuit of tube 401 from the lowermost winding of relay 406 to the middle winding of that relay. Relay M1, in operating, moves its armature to its right contact in agreement with the position of the armature of relay 402 in response to the marking impulse.

Succeeding incoming impulses cause relays 493, .404, 405, 406 and 4H, and tube 401 and condenser 459 to function inthe same manner the potential supplied over the armature of relay 403. Since this interval is dependent upon the discharge time of condenser 459 which controls the grid potential of tube 401, its length is determined by the capacity of condenser 459 and the resistance value of rheostat 460. The

, values of condenser 459 and rheostat 460 are so chosen that the impulses repeated through the winding of relay 4|"! are delayed sufficiently to compensate for the lag introduced by the regenerative repeater into the undistorted impulses which are simultaneously being repeated through the Winding of relay 4|8.

The potential on the grid of tube 40'! upon each discharge of condenser 459 is of such a value that the anode current flowing through either the lowermost or middle winding of relay 406 is greatly in excess of that required to overcome the effect of the opposing locking current and just operate the relay in the opposite direction.

' The purpose of this excess in operating current will be subsequently set forth. The function of resistance 458 is to prevent excessive grid currents on tube 401 upon the discharge of condenser 459.

When condenser 459 is charged, with its upper plate at negative potential, the negative potential Kit on the grid of tube 401115 greater than that required to just reduce the anode current of the tube tozero thereby preventing any ilow of. current in the operating windings of relay 496 during a considerable portion of the discharge time of condenser 459. Therefore, when condenser 459 discharges, there is first a comparatively long period of no current through either operating winding of relay 496 followed by a rapid rise in anode current to a large ultimate amount. This rapid build-up of operating current through either operating winding of relay 466, to a point in excess of the amount required to just unlock and oppositely reoperate the relay, minimizes the effects of any inequality in the voltages of the positive and negative locking potentials for relay 406 and also minimizes any difference which may --exist in the magnetic effectiveness of the middle and lowermost operating windings of the relay. This insures a uniform. delay interval upon each change of the positions of the armatures'of relays-403 and M1 in response toa change from spacing to marking '01 vice versa.

With relay- 4!1 following the-delayed received incoming signal impulses and relay 418 followingthe undistorted regenerated signal impulses, excessive signal distort-ion measurements are made in the manner hereinafter set forth.

The filaments or cathodes of tubes 410 and 418 are energized in local circuits. The circuit of tube 410 and transformer 412' is so connected that it will oscillate-when certain voltage condi-' tions are obtained on the grid of tube 410. Normally, with the'armatures of relays4l1' and. 418 on their same respective contacts resistance 468 and condenser 469 areshcrt-circuited in a cir-' cuit over the armatures and contacts of those relays. A negative potential, from the'negative terminal of the battery connected to potentiometer 436, is applied to the grid return cjonductor of tube 419. Under this condition no oscillations take place in the circuit consisting of tube 410- and transformer412.

When relays 41 1 and 418 operate in synchronism, that is, when the receivedllne signals are perfect and the lag through-the "delay repeater equals that introduced bythereg-enera'tive repeater', the short circuit on resistance 4'68 and, condenser 469 will be open only during the interval required for the armature of relays:4l1 and M8, to travel from their respective right contacts to the left contacts or vice versa. During this interval the negative potential on the grid of tubej410 will decrease due to the fact that condenser 469 will start to charge from the positive potential connected to its upper plate through resistance 461. This rate of negative potential decrease on. the grid of tube 416 is controlled. by the values of resistances 461. and. 468, the capacity of condenser 469, and on the voltage of the positive potential connected to, resistance 461. These values are so chosen that, the. Point to which the grid potential of tube 410 is reduced during, the travel time of, the armatures of relays 4l1 and- H8 is well downjon the lower portion of the grid voltage-anode current characteristic curve of tube 419. Rheostat 483 is adjusted to a. value such that tube .410 will not. oscillate in response to the aforementioned grid potential reduction.

When relays M1 and 4"! again close their armatures to either their respective left or ri ht contacts, the :potential on the grid'of tube "416' again returns to its "full-initial"negative-va1ue as determined by the value of resistance 482 and by thesetting of potentiometer 436'which at this time is on its zero position.

If no excessive'distortion is present inthe incoming signal, relays M1 and 4!!! continue to operate in response to the incoming impulses until the contacts of interrupter 42! close and cause relay 425 to operate. Relay 425, in operating, removes the ground from the armature of relay H9, operates relay 426 through the left winding of that relay, and connectsground over its armature and front contact, over the back contact and outer right armature of relay 429 and over conductor 2 53' to conductor 2|3 of Fig. 2. This ground causes thecircuits-of Fig. 2 to function, in the manner hereinbefore described, and advance tothe next transmission line, connecting that lineto conductor 209' of Fig. 4 in place of-the-lineu-pon which signal distortion measurements haveijust been completed.

Assume now that distortion is present the incoming signal impulses ancl that relays M1 and H8 therefore no longer operate in synchronism. Since the operations of relays M1 and 41 8 are now out of step, the period during which the short circuit aroundresistance 468 and condenser 469 is open is lengthened by an amount proportionate to the amount of di'stortign present in the signals.

As hereinbefore set forth, when the short circuit around resistance 468 and condenser 469 is opened, the negative potential on the grid of tube Nit-starts decreasing since condenser 469 starts to charge in a circuit frompositive potential through resistance 461 to the upper plate of the condenser, to negative potential on*'- the lower plate of the condenser through potentiometer 436.

Should asufficient interval elapse before the succeeding closure of the short circuit around resistance 463 and condenser 469, the negative potential on the grid of tube 416 decreases to the point where the circuit consisting of tube 410 and transformer 412 will-break into oscillation. Normally, the negative potential applied to the grid of tube 418 through the right winding of transformer "449 is just sufficient to'prevent any flow of current in the anode circuit of that tube. However, when tube 416 goes into'oscillation, these oscillationsare impressed on the grid of tube 418through the windings of transformer 449' and the potential on the grid of tube 418 changes and causes current to flow through the cathode-anode circuit of the; tube and through the-uppermost winding of polarized relay4l9.

The armature of relay M9 is normally on the right contact of the relay due to a flow ofcurrent.

in the circuit from ground, through themiddle winding of the relay, and throughresistance 453 to grounded negative battery. I'heflow of current in the uppermost winding of relay 4!9,'

ground over the armature and back contact of relay 425, over the front contact and left middle.

armature of relay 43!, normally closed upper inner contacts of key'484, armature andleft contact of relay 4+9, to battery: through the winding. of relay .426; Until. relay-420 has completely 'opera ted, relay4'l9 locks in a circuit from grounded negative battery through its lower winding, through resistance 464, over the normal contacts of relay 423, to' the previously traced ground over the left contact and armature of relay 4l9.

Relay 426, in operating, looks over its front.

contact and inner right armature to ground over the upper armature and back contact of release key 473. Relay 426, in operating, also connects battery over its front contact and left armature, over conductor 2 I4, toconductor 2 I4 of Fig. 2 to cause the circuits of Fig. 2 to function and give an audible and' a visual indication of the excessive signal distortion condition encountered. Relay 426, in operating opens its right normal contacts and thereby opens the locking circuit of relay 420 to battery through lamp 485. Relay 426 remains operated since it is locked to ground Y cludes tube 476 does not oscillate on the longest over the upper contacts of key 413. The upper armature of key 484 transfers the conductor which connects to the armature'of relay 4!!! from the middle left armature of relay 43| to ground over the upper outer contact of the key.

As the armature of relay '4I9 nowlcontacts the left contact of the relay in response to the excessive signal distortion, lamp 485 lights from the ground on the armature of relay M9. The arm of potentiometer 436 is now moved from its zero position toward the left portion of the potentiometer; thereby increasing the normal negative potentialon the grid of tube 410. When the adjustment of potentiometer 436 is such thatthe negative potential onthe grid of the tube 410 is increased to a value where the'circuit which ininterval during which the short circuit on re- 7 sistance 468 and condenser 469 is opened by the operations of relays 4| 1 and M8, relay 4| 9 will no longer respond to the excessive distortion and lamp 465 will therefore be extinguished as an indication that the maximum distortion has been reached. Potentiometer 436 may be provided with an indicator calibrated to show the approximate percentage of signal distortion measured in the foregoing manner. a

At the conclusion of the measurement, key 484 is restored to its normal position. The restoring of key 484 opens the circuit to lamp 485, removes the ground from the armature of relay 4!!! and closes the circuit from that armature'to the middle' left armature of relay 43l, and closes the circuit from the left contact of relay US through the normally closed inner upper contacts of key 484, to the winding of'relay 420. Key 413 is now "momentarily operated which opens the locking 7 moves the battery from conductor 2M and con-,

circuit for relay 426. Relay 420 releases and reductor 2l4 of Fig. 2 which silences the audible alarm and extinguishes the visual signal of Fig. 2. The momentary operation of key 413 also connects a ground to conductor H3 and conductor 2|3 of Fig. 2 to cause the circuits of Fig. 2 to function as previously set forth and connect the succeeding transmission line to conductor 209.

I Since the r'egenerative'repeater circuits of Figs. 3 and 4 function under control of the middle portion of each signal'i'mpulse, it is obvious that these repeater circuits'cannot reproduce incoming signals on which the distortion is so great that the changes in potential polarity on the distributor receiving rings 322 and 422, under the respec tive control of the operations of relays 362 and 462 in response to the incoming signal impulses, occur after the receiving brushes 3l3 and M3 have passed the active receiving segments 34I to 346, and MI to 446 inclusive, respectively. As the receiving brush 3E3 or 4l3 passes over its associated active receiving segments, relay 3I8 or 418, as the case may be, will operate in response to the polarity conditions existing on these receiving segments. These polarity conditions depend upon the positions in which relays 309 and 3H! or relays 469 and 4H respectively, were locked toalarm and indicating signal will be given in themanner hereinbefore set forth, 'but no maximum distortion measurement can bemade since any change in the adjustment of .condenser 369 of Fig. 3 or in the adjustment of potentiometer 436 of Fig, 4 is ineffective for that purpose due to the fact that relay 3|8, or relay'4l8, while operating, is entirely out of control of the incoming impulses.

What is claimed is:

1. A signal distortion measuring-device comprising electromagnetic means responsive to periodic signals of marking and spacing character, a regenerative repeater circuit anda delay circuit connected in parallel to said means, and measuring means connected in common to said circuits whereby'the outputs of said circuits are impressed on said measuring means to measure difference in phase each time the line signal changes from marking to spacing and vice versa.

2. In combination, a source of periodic marking and'spacing signals, a signal distortion measuring device comprising electromagnetic means, a regenerative repeater circuit including rotary starta stop means, a delay circuit including means for delaying the received signals sufiiciently to match the lag of the regenerative repeater circuit, and

measuring means connected in common to said circuits whereby the outputs of said circuits are impressed on said measuring means to measure their difference in phase each time the'line signal changes from marking to spacing and vice versa.

3. A signal distortion measuring device according to claim 1, wherein the delay circuit comprises a continuously operatingmeans for selecting the interval during which the signal distortion meas urements are made, and means operative when the distortion exceeds a'predetermined amount for rendering the said continuously operated means ineffective. V V V 4. In a signaling system comprising a station,

a plurality of "signal transmission .circuits ar ranged in groups and terminating at said station,

a signal distortion indicating and measuring device including a continuously rotating timing element, switching means controlled by said timing element for selecting, first, said groups separately and in sequence and, secondly, the circuits of each of said groups separately and in sequence for testing purposes, receiving relay means responsive to the signals received from each of said circuits, parallel paths connected to said receiving relay means, a regenerative repeater circuit and a delay circuit respectively connected in said paths, a plurality of relays synchronously operable when no distortion is present in the received signals, but asynchronously operable when distortion is present, connected in common to said paths and respectively responsive to said repeater circuit and said delay circuit, an operable element controlled by said plurality of relays and arranged to be maintained non-operated at times when no excessive distortion is present in the signals received over each of said plurality of circuits but operated when excessive distortion is present in the signals received over each of said plurality of circuits, and indicating means responsive to said element in an operated condition for determining the circuit over which ex cessively distorted signals are being received.

5. In a signaling system according to claim 4 wherein the signal distortion indicating and measuring device also comprises locking means for automatically maintaining the selecting, or switching, means stationary in an operated position when excessive distortion is present in the signals received over the circuit being tested, to thereby maintain the indicating means operated and manually operated switching means for releasing said locking means when desired to advance said selecting, or switching means.

6. In a signaling system according to claim 4 wherein the signal distortion indicating and measuring device also comprises quantitative means for indicating the amount of distortion present in the signals received over each of said plurality of circuits.

'7. In a signaling system according to claim 4 wherein the signal distortion indicating and measuring device also comprises a rotary stepping device for causing said regenerative repeater circuit to properly receive the signals received over each of said circuits.

8. A signal distortion measuring device comprising a plurality of circuits'arranged in groups for transmitting polar signals, a continuously rotating timing cam, switching means controlled by said timing cam for selecting said groups separately and in sequence and said circuits in each group separately and in sequence only at such times when there is no distortion present in signals received over said circuits, a relay responsive to polar signalsreceived over said circuits, a regenerative repeater circuit and a delay circuit connected in parallel to said relay, distortion measuring means connected in common to said repeater and said delay circuit for measuring any difierence in duration of corresponding impulses in the output of said repeater and said delay circuit, a pair of relays included in said measuring means respectivelyresponsive to the output of said repeater and said delay circuit and arranged to operate simultaneously at times only when the signals incoming over said transmission circuit are distortionless another relay arranged to be maintained in one position by the simultaneous operation of said pair of relays, and an impedance element connected to one of said pair of relays and said other relay for delaying the operation of said other relay for a predetermined interval after either one of said pair of relays release.

9. In a signaling system, a device for measuring distortion present in incoming signals comprising a source of signaling current impulses, relaying means for regenerating said impulses, a circuit for transmitting said regenerated impulses, parallel paths including said circuit, distributing means connected in one of said paths for reproducing the current impulses as originally transmitted from said source, distortion introducing means in another of said paths for delaying the transmission of said regenerated impulses for a predetermined interval, and indicating means common to said parallel paths for indicating and measuring the difierence in time between each of said regenerated impulses and its corresponding reproduced impulse.

10. In a signaling system, a device according to claim 9, wherein the distortion introducing means includes a network and an arrangement of electromagnetic relays cooperating therewith to bring 'a variable element of said network to a steady state between said regenerated impulses.

11. In a signaling system, a device according to claim 9, wherein the distortion introducing means includes two interconnected impedance elements, another impedance element connected to a point between said interconnected. elements, a source of potential for maintaining between said regenerated impulses a steady potential of either polarity on said other element, relaying means responsive to the signaling impulses from said.- source for slowly reversing the polarity of the potential on said other element, other relaying means effective to operate and repeat a signal impulse each time the potential is reduced to zero value, a pair of electromagnetic relays oppositely polarized and responsive to said repeated impulses'of opposite polarities, respectively, for expediting the increase of potential of either polarity to its maximum value on said other impedance element.

12. A device for measuring distortion of signal impulses incoming over a plurality of transmission lines arranged in groups, comprising electromagnetic means responsive to periodic signal impulses incoming over said lines, a selective mechanism for automatically connecting in a regular sequence each of said lines to said electromagnetic means, a regenerative repeater circuit including rotary start-stop means, a delay circuit including means for delaying the incoming signal impulses sufficiently to match the lag of the signal impulses repeated by said regenerative circuit, measuring means connected in common to said circuits whereby the outputs of said circuits are impressed on said measuring means to measure the difference in phase of the beginning and ending of corresponding signal impulses, indicating means, and other selective mechanism operated simultaneously with the first mentioned se lective mechanism for operating said indicating means each time a difierence in phase occurs in corresponding signal impulses.

FULLERTON S. KINKEAD.

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