US2307237A - Telegraph signal distortion measuring apparatus and system - Google Patents

Description

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W, R ETAL 2,3@?,23? TELEGRAPH SIGNAL DISTORTION MEASURING APPARATUS AND SYSTEM Filed March 29, 1941 2 Sheets-Sheet l W 2" REfl JRW/LM'RSON ATTORNEY Jan. 5, 1943. w. T. REA HAL 2,307,237

TELEGRAPH SIGNAL DISTORTI ON MEASURING APPARATUS AND SYSTEM Filed March 29, 1941 2 Sheets-Sheet 2 /66 /.67\ v f 7 SPAC/NG\\ v MARKWG /N N RS W $R A y JRWILKERSON QMM' ATTQRMEV alenled .lan.

one arrnaa'rps SYSTEM Wilton T. Rea, Wayside, and .lleflerson R. Wilkerson, New York, N. l(., assignors to Bell Telephone Laboratories, Incorporated, N ew York, N. in, a corporation oi New York Application March 29, 1941, Serial No. 385,802

22 Claims.

This invention relates to telegraph testing equipment and, more particularly, to telegraph testing apparatus employing a cathode ray tube for indicating both the type and the amount of bias and distortion present in telegraph signals.

It is an object of this invention to provide a telegraph system with an indicating device which may be easily connected directly into a telegraph system while it is in service for indicating, Without disturbing the transmission of signals, both the type and the amount of bias and distortion present in telegraph signals transmitted over the system.

It is also an object of the invention to provide a telegraph distortion indicator with a cathode ray tube for readily indicating both the type and the amount of bias and distortion possessed by each impulse of a telegraph permutation code signal combination, each impulse being assigned a different indicating area on the screen of the cathode ray tube.

Another object of the invention is to provide the telegraph distortion indicator with means for preventing the production of parasitic spots on the screen of the cathode ray tube that might otherwise be caused by the chattering of the armature of the receiving relay.

These and other objects of the invention are accomplished by providing the cathode ray tube of the distortion indicator-with a damped sinusoidal oscillatory sweep circuit having two voltages 90 degrees in quadrature and designed to cause the cathode ray beam to follow a logarithmic spiral path at the rate of one revolution per pulse of the incoming signal and to make six and one-half revolutions for each five unit telegraph permutation code signal combination and an additional revolution for each additional unit of the code. side the top edge of the tubes screen and move in a logarithmic spiral path curving in toward the center of the screen. Due to the decrement of the oscillatory circuit, the electron beam enters the indicating area of the screen approximately half way through the start pulse. The decrement, or damping, of the oscillatory circuit is controlled by a vacuum tube and'the circuits are tuned to cause the beam to make a complete revolution in the time allotted to each impulse of the permutation code signal combination. This also controls the spacing between the adjacent turns of the spiral. Since the path of these revolutions ultimately approaches the center of the screen of the tube, means are provided for These revolutions start outquickly returning the beam to its initial starting position at the outer edge of the tube for making another series of convolutions.

The potential applied to the intensity control electrode of the tube is made sufficiently negative so that ordinarily the beam is invisible. In response to each transition of the line current, a short positive impulse is applied to the intensity control electrode of the tube to produce a momentarily visible spot of light on the screen. In the case of an undistorted signal, there would be a row of visible spots, or flashes, along a radius of the screen. Distortion of the signals will cause displacement of the flashes from this line, the angular displacement being proportional to the amount of the bias and distortion. Consequently, the amount of bias and distortion may be read in terms of the percent oi the displacement on a radial scale in which per cent is equal to 360 degrees of arc. The type of bias and distortion is indicated by the position of the flash in respect to the normal radial line; that is, whether the flash is in advance of the radial line or behind it.' A half wave copper-oxide rectifier, or varistor, is included in the intensity control circuit to prevent the production of parasitic spots on the screen that might otherwise be caused by the chattering of the contacts of the receiving relay.

These and other features of the invention will be described in detail in connection with the description of the drawings, in which:

Fig. 1 is a circuit diagram 01' the distortion indicator;

Fig. 2 is a graphical representation of the voltages applied to the electron beam deflecting electrode of the cathode ray tube;

Fig. 3 is a graphical representation of a startstop permutation code signal combination; and,

Fig. 4 is a diagrammatic view showing the path of impingement of the electron beam upon the screen of the cathode ray tube.

Referring now to Fig. 1, the reference numeral ll designates a signal responsive polarized relay. Across the operating winding of relay ll input jack I2 is connected so that telegraph signals may be applied across the operating winding 01' the relay in the direction to oppose and overcome the effect of the biasing winding of the relay. The" biasing winding is connected through resistor I! to battery conductor I, over which current is supplied from grounded battery I6. The armature of relay II is connected to ground and is operable between the contacts I! and It.

For convenience in describing the system, the

armature is shown engaging the contact I1, and all other circuit conditions correspond-thereto. This is the condition of relay when responding to a marking impulse and although a source of telegraph signals has not been shown applied to jack |2, it is to be assumed that relay H is responding to a marking impulse. Relay contact I1 is connected to one end of the operating winding of a polarized relay l3, the other end of which is connected through resistor 2| and battery conductor l3 to grounded battery l3. The operating winding of polarized relay l3 thus is energized to oppose and overcome the biasing winding, one end of which is connected through resistor 23 to battery conductor 3 and the other end of which is connected through resistor 22 to ground.

The armature of polarized relay I3 is connected to battery conductor l3 and thus to battery l6 and is operable between contacts 23 and 23. The contact 23 which the armature of relay l3 engages when the operating winding of the relay is energized is connected through resistor 23 to one side of an oscillatory circuit which consists essentially of the inductance 21 and condenser 23 in parallel. The branch of the oscillatory circuit which contains the inductance 21 includes in series with the inductance the secondary winding of a feedback transformer 23 and resistors 3| and 32. potential d vider resistors 33 and 33 in series across the condenser 23. The terminal of condenser 23 which is connected to the resistors 32 and 33 is connected to ground, whereby two paths for current through the armature of relay l3 and resistor 23 are provided. one extending through inductance 21, the secondary of transformer 23, resistors 3| and 32 to ground, and the other extending through resistors 33 and 33 to ground. Current through this network causes condenser 23 to become charged to the potential difierence across the resistors 33 and 33 in series. The point of interconnection of the secondary of transformer 23 and the resistor 3| is connected to grid 33 and the point of interconnection of resistors 33 and 33 is connected to grid 31 of a twin triode amplifier-tube 33 which is provided with the usual indirectly heated catho e 39.

The resistors 33 and 33 are of such value that when the receipt of a start signal permits the circuit to oscillate, the total resistance across said resistors causes the condenser voltage to be in quadrature with the voltage developed across resistors 3| and 32. That part of the voltage across condenser 23 which is represented by the potential diflerence across resistor 33 is applied to grid 31 of tube 38 and the potential difference across resistors 3| and 32 is applied to grid 33 of the tube. Thus the voltages of grids 36 and 31 are in quadrature.

Plate 3| of tube 33 which is controlled by grid 33 is connected to the vertical deflecting plate 32 of a cathode ray tube 33 and plate 33 of the tube 33, which is controlled by grid 31 is connected to the horizontal deflecting plate 33 of cathode ray tube 33. Plate potential for the plates 3| and 33 of tube 38 is obtained from high voltage conductor 31 of full wav rectifier tube 33 through potentiometers 39 and 5|, respectively, at the high potential end of a voltage divider which consists of the paralleled potentiometers 33 and 3| in series with resistors 52, 33, 33 and 33, the latter of which represents the low potential end of the potential divider and has its free end connected to ground. High potential conductor 31 The oscillatory circuit also includes 01 the rectifier includes a filter consisting of the inductance 31 and condensers 33 and 33. Positive potential is applied from potentlometers 33 and 3| to plates 3| and 33, respectively, through the load resistors 3| and 32, respectively.

The contact 23 of polarized relay I9 is connected through resistors 33 and 33 to ground. One end of the biasing winding of a polarized relay 31 is connected through resistor 63 to ground and the other end is connected through resistor 66 to battery conductor I3. The operating winding of polarized relay 31 has one end connected to battery conductor I3 through reslstor 38 and the other end of the winding is connected to back contact 69 of relay 61 and to one side of condenser 1| the other side of which is connected through resistor 12 to ground. The armature of relay 61, which is operable between contact 69 and a front contact 13 is connected to ground. From this it will be apparent that the operating winding of relay 31 may become energized through its armature and contact 13 or through a charging current for condenser 1|.

The contact 13 of relay 31 is connected directly to the ground side of the biasing winding of relay l9. When the armature of relay 61 engages contact 13, the ground connection for the biasing winding of relay I9 supplied through resistor 22 is short-circuited and the biasing winding of relay IQ is connected directly to ground, whereby the current through that winding is increased. The increase is sufficient to give the biasing winding sole control over relay l3 so that its armature will be maintained in engagement with the contact 23 and will not be moved during subsequent energization of the operating winding of relay l9.

As previously stated, the voltages applied to grids 33 and 31 of amplifier tube 33 by the oscillatory circuit, the principal components of which are the condenser 23 and inductance 21, are in quadrature. The resistors associated with the oscillatory circuit are so proportioned that the voltages in quadrature phase are equal in amplitude. These voltages are amplified by the tube 33 and are applied to one each of the horizontal and vertical deflecting plates 36 and 32, respectively, of cathode ray tube 33. Other capacitances such as the condensers 13, 15 and 16, may be connected in parallel with the condenser 23 selectively by means of the keys 11, 18 and 19, respectively, to change the frequency of oscillation of the oscillatory circuit.

The resistor 3| previously identified as being in the circuit of grid 33 of amplifier tube 29, is in the form of a potentiometer and its slider 3| is connected to the grid 33 of a feedback amplifier tube 86 which may be a triode tube having an indirectly heated cathode 31. The plate 33 of tube 36 is connected to one end of the primary winding of transformer 29, the other end of which is connected by conductor 92 to the plate voltage conductor 31. A condenser 93 is connected across the primary winding of feedback transformer 23, and the function of the condenser 93 is to adjust the phase of the current in the feedback circuit which includes the plate of tube 33, so that it will be in phase with the current in the oscillatory circuit comprising the inductance 21 and the condensers 28, 13, 15

and 16 or whatever number of those condensers are connected in a parallel, so that the current fed back into the oscillatory circuit will be in phase with the current locally generated in the oscillatory circuit. The secondary of feedback transformer 21 being in series with inductance 21 in the oscillatory circuit, the currents traversing the primary winding of feedback transformer 29 are impressed upon the oscillatory circuit which feeds the grids 98 and 91 of amplifier tube 99.

In addition to the electrodes 92 and 99 the cathode ray tube 93 has two other electrodes 99 and 98 for controlling the deflection oi' the electron beam and the electrodes 99 and 99 are connected to the low potential side of a half wave rectifier which includes tube 97. The cathode ray tube also has an electrode I99 by which the intensity of "the electron beam is controlled. This electrode is connected through conductor I98 and blocking condenser Illi to one side of condenser Iii and to one end of resistor I99, the other end of which is connected to ground. The other side of condenser III is connected to one end of the winding of a retardation coil H2. The other end of the winding of retardation coil H2 is connected to one terminal of a half wave copperoxide rectifier H9 and the other terminal oi'the rectifier is connected to the right-hand stationary springs H9 and H9 or single and double keys iii and H9, respectively. The halfw ave rectifier II 9 is sometimes called a varistor due to the fact that it readily passes direct current in one direction and greatly retards passage of direct current in the other direction. Thus it may be considered as having the characteristics of a variable resistor offering low resistance to the passage of current in one direction and extremely high resistance to the passage of current in the other direction.

The key III is a single-pole double-throw key. the swinger I I9 of which is biased to engage the left-hand stationary spring I2I. Swinger M9 is connected to the contact I9 of polarized relay II through resistor I22 and the left-hand stationary spring MI is connected through resistor I29 to battery conductor I9. Stationary spring I is also connected to the left-hand swinger spring I26 of key M9 which is a double-throw key. The stationary spring I29 with which swinger I129 cooperates and into engagement with which the swinger I29 is normally biased, is connected to swinger H9 01' key Ill and thus through resistor I22 to contact iii of polarized relay II. The right-hand swinger spring I29 of key H8 is connected to the point of interconnection of the operating winding of relay i9 and the resistor 2 I.

A power supply for the cathode ray tube 99 comprises a transformer ml, the primary winding of which is connected to a source of alternating current 992, the rectifier tube 91 connected across the high voltage secondary winding of transformer I9I as a half wave rectifier, potentiometers 993 and I39 connected between the plates of rectifier tube 99 and the high voltagewinding of transformer II9I for supplying the proper biasing voltages to the intensity control electrode I199 and focussing electrode of the cathode ray tube, and filter condensers I36 for filtering out the alternating components of the output of rectifier tube 91. The transformer I9I also supplies current for operating the rectifier 99 and the cathode heaters of amplifier tubes 99 and 89 of cathode ray tube 99.

The control exercised over the cathode ray tube 99 by the system hereinbefore described affects the intensity of the beam of electrons and the deflection of that beam. The intensity of the beam is controlled by the control grid I". The

deflection of the beam is controlled jointly by the pair of horizontal deflecting plates 46 and 98 and the pair of vertical deflecting plates 42 and 99. For the purposes of the description of the operation of the system, it will first be assumed that a rest impulse which is a steady marking condition is applied through the Jack I2 to the operating winding of polarized relay II.- It will also be assumed that neither of the keys Ill and H8 is operated and therefore that they remain in the condition shown in Fig. 1.

With operating winding of polarized relay II energized, the effect of the biasing winding is overcome and the armature of the relay is held in engagement with the back contact I'I. Thus ground is connected through contact I1 and through the operating winding of polarized relay I9, through resistor 2| to grounded battery I9, whereby the operating winding of polarized relay I9 overcomes the effect of the biasing winding and the armature is held in engagement with back contact 22. Since battery It is connected to the armature of polarized relay I9, positive battery is connected to the armature and through contact 23 and resistor 26 to the oscillatory circuit consisting essentially of the inductance 21 and as many of the condensers 28, I9, I5 and I9 as are connected into the circuit by having their keys I1, 18 and 79 closed. The flow of current is from grounded battery It through the armature of polarized relay I9, contact 22, resistors 29, 99 and 39 to ground, and through inductance 27, secondary of transformer 29, and resistors 9i and 32 to ground. Theflow of current main tains a charge on the condensers at least one of which, having the reference numeral 28, is permanently connected in the oscillatory circuit. The potential difierence across the resistor 39 due to the flow of current therethrough provides a biasing voltage for the grid 31 of amplifier tube 99, and the flow of plate current through load resistor 62 of plate 99 provides a steady potential of low value across the horizontal deflecting plates 99 and 96 of cathode ray tube 93 with plate 96 slightly negative with respect to plate 99. Since current also flows through inductance 21, secondary of transformer 29, and resistors 3i and 92 to ground, the potential difference across resistors 3| and 32 establishes a biasing potential for the grid 36 of amplifier tube 98 at a certain level above ground and this bias is preferably of a relatively high value so' that considerable plate current flows through the load resistor iii of 'plate 9i and aii'ords a high negative potential upon the vertical deflector plate 92 of cathode ray tube 99 with reference to the potential of deflector plate 99 which is connected to the junction of resistors 52 and 53. In actual practice. the potential difference between horizontal deflecting plates 96 and 99 is very low so as to defleet the electron beam in the cathode ray tube 99 horizontally only to an insignificant extent and the potential difference between vertical deflecting plates 92 and 99 is suificiently high to deflect the beam beyond the limits of the screen of the cathode ray tube. Thus the beam is defiected almost vertically and its point of impingement is outside the limits of the screen.

The polarized relay 91 has its operating winding energized by current from grounded battery It through resistor 68, operating winding of relay 91, back contact 69 of the relay and armature to ground. The biasing winding of polarized relay 91 is also energized from battery I6 through resistor 86, biasing winding of the relay and resistor (it to ground, and the biasing winding overcomes operating winding and holds the armature on contact 69.

Upon the transmission of a start-stop permutation code signal combination through jack l2, the start impulse, which is of spacing nature, cuts off the current through the operating winding of relay I i, in the case of current-no-current signals, or reverses the current through that winding, in the case of polar signals. When polar signals are received, the biasing winding is left open and is not used. In either case the armature of polarized relay Ii moves out of engagement with contact I! and into engagement with contact i8. Thus the circuit of the operating winding of polarized relay I9 is interrupted and the armature of that relay moves out of engagement with contact 23 and into engagement with contact 2 3. Battery is thus removed from the oscillatory circuit and is connected through contact 26 and through resistor 63 and resistor M to ground. The resistor 63 is thus placed in parallel with the resistor 66 and the biasing winding of relay 67 between grounded battery l6 and resistor 66. The resistance value of resistor 63 is relativel low as compared with the combined resistance of resistor 66 and biasing winding of relay iii in series, so that a part of the current through resistor 66 is diverted through resistor 63 and the current through the biasing winding of relay 61 is materially reduced. The operating winding of relay 6'! thus assumes control of the armature and moves the armature into engagement with the front contact 13. As the armature moves out of engagement with contact 69, ground is disconnected from the operating winding of relay 6? but that winding continues to be energized for an interval, due to a charging current for condenser H flowing from grounded battery l6 through resistor 68, operating winding of polarized relay B1, condenser H and resistor 12 to ground. When the armature of polarized relay 6! has moved into engagement with the front contact 13, ground is connected through the armature and contact 13 directly to the biasing winding of polarized relay i9, shortcircuiting the resistor 22 through which the biasing winding of relay i9 previously received energizing current. The current through the biasing winding of relay I9 is thus increased to such a value that the operating winding of relay l9 cannot move the armature of that relay into engagement with contact 23 as long as the armature of relay 6'! remains in engagement with contact l3.

The removal of battery from the oscillatory circuit due to movement of the armature of polarized relay i9 out of engagement with contact 23 permits inductance 21 and the condenser or condensers included in the oscillatory circuit to set up oscillations. Since the grids 35 and 31 of amplifier tube 38 are connected respectively to the inductive and capacitative branches of the oscillatory circuit, biasing voltages are applied to the grids in accordance with the oscillatory current. The plates 4| and M controlled respectively by the grids 36 and 31 of amplifier tube 38 are connected to the vertical and horizontal beam deflecting plates, respectively, of cathode ray tube 43 so that potentials are applied to the plates 42 and 46 corresponding to the oscillatory current. The combination of resistors in the oscillatory circuit is such as to apply to the vertical deflecting plate, a voltage which is in quadrature with and equal in magnitude to the potential 'tinues.

applied to the horizontal deflecting plate. The constants of the oscillatory circuit are such that the circuit oscillates at an integral nurber of cycles, one or more, per impulse of the incoming permutation code signal. As long asthe armature of polarized relay i9 remains out of engagement with the contact 23, no energy from battery H5 is put into the oscillatory circuit and therefore the energy within the circuit decreases steadily and logarithmically as oscillation con- The result of these conditions of the oscillatory circuit is that the electron beam traces on the screen of the cathode ray tube 63 a logarithmic spiral at the rate of one or more complete revolutions per impulse of the incoming signal.

Since the potentiometer resistor 3i and the secondary of feedback transformer 29 are connected in the oscillatory circuit, oscillatory current flows in this circuit. The slider iii of potentiometer resistor 3i takes oil a part of the voltage through the potentiometer 3i and applies it to the grid of amplifier tube 86. Plate current results in the plate circuit of amplifier tube 96 and this current is oscillatory in accordance with the oscillating potential derived by the slider ill of potentiometer 3i. Since the primary of feedback transformer 29 is included in the plate circuit of amplifier tube 86, the transformer feeds oscillatory energy into its secondary winding and thus into the oscillatory circuit through the resistors 3| and 32 and through the inductance 21. The condenser 93 which shunts the primary winding of feedback transformer 9i adjusts the phase of the oscillatory current fed into the secondary circuit of transformer 29 so that the current delivered to the oscillatory circuit by amplifier tube 86 is in phase with the original oscillatory current in the oscillatory circuit. Thus the feedback circuit acts as a negative resistance and lowers the decrement of the oscillatory circuit. In practice the gain of the feedback circuit is so adjusted as to compensate for the differenc between the direct current resistance of the inductive branch of the oscillatory circuit and its resistive component at the frequency of oscillation.

In Fig. 2 the solid line represents the oscillatory voltage applied between the vertical deflecting plates 42 and Mi and the broken line represents the oscillatory voltage applied between the horizontal deflecting plates 46 and 96. It will be noted that as previously stated, the voltage which controls horizontal deflection of the electron beam leads the voltage which controls vertical deflection of the beam by 90 degrees. It will also be noted that the magnitude of the oscillatory voltages diminishes logarithmically throughout the interval allotted to a complete start-stop permutation code signal combinatlon.

In Fig. 4 the broken line indicates the path of the electron beam produced by the voltages derived from the sweep circuit, which includes the oscillatory circuit, the deflection voltage amplifier and the feedback amplifier. As previously stated the electron beam path, which is indicated by-the broken line, is in the form of a logarithmic spiral, each convolution of which is completed in the interval allotted to one impulse of a permutation code combination. It will be noted that there are six full convolutions and a fraction of a seventh, which represent the start impulse, the five code impulses and the stop impulse. The starting point of the beam is located outside the screen of the tube. in order that the transition from marking condition of the stop impulse to armature in that position, decreases to the value oi the current through the biasing winding of the relay by the time the middle of the stop impulse of the received permutation code signal has been reached. Further decrease of the charging current for condenser Iii decreases the control of the operating winding of the relay over its armature and permits the biasing winding to assume control, whereupon the armature is returned to engagement with contact 88. At this time the armature of polarized relay M, which has been following the permutation code signal to control the intensity of the electron beam in a manner which will be described later, has returned to engagement with contact H as a result of the energlzatlon of the operating winding of relay .II by the'stop impulse. The restoration of the armature of polarized relay $1. to engagement with contact 8% results in the reduction of current in the biasing winding of polarized relay I9 due to removal of the shunt around resistor 22 and the energized operating winding of relay I9 restores its armature to engagement with contact 2%. Thus battery is applied to the oscillatory circuit, battery current again flows through resistors it, 32, t3 and at, the inductance 21 and the transformer winding, and the condenser 28 and any others of the condensers It, I5 and i6 that are connected in parallel with condenser 28 are restored to fully charged condition. Oscillation in the oscillatory circuit is thus terminated and the resistor 26 is of such value that the currents and voltages of the oscillatory circuit are caused to return to their steady state in a critically damped manner so that the system will be restored rapidly to the initial condition, applying to the horizontal and vertical electron beam defleeting plates t8 and t2, the potentials which they had at the beginning of the signal, whereby the electron beam is restored to its initial position at the top and outside limits of the screen of the cathode ray tube, which is represented by the solid line circuit in Fig. 4:. The damping is such that the beam will be restored to initial position in one impulse interval, whereas the discharging time during which the beam is rotated is as long as a full code combination interval.

It will be apparent from the foregoing description that the path traversed by the electron beam of the cathode ray tube t3 is the same for all signal combinations received and is entirely independent of the combinations of marking and spacing impulses which make up the signal. The tracing of the path by the electron beam is initiated by the start impulse of a received permutation code signal combination and thereafter the path is derived solely from the operation of the oscillatory circuit. The composition of the signals is utilized for controlling the intensity of the electron beam and it is the control of the intensity of the beam that causes it to become visible upon the screen of the cathode ray tube 63. Normally the control grid I06 is biased negatively to a sufflcient extent that the beam would not be cludes the resistor 2|.

visible upon the screen even if tracing a path within the area of the screen, it being remembered that when the polarized relay II is responsive to a steady marking condition not representing a group of impulses of a start-stop code signal combination, the beam is deflected outside the limits of the screenl The point of impingement of the electron beam upon the screen is rendered visible by making the control grid I05 more positive and is restored to invisibility by reducing the potential on the control grid.

Potentials for rendering the control grid I06 more positive and therefore rendering the point of impingement of the electron beam upon the screen of cathode ray tube t3 visible are applied through the contacts H t or I I8 of the keys II! and H8, respectively, and through half wave rectifier H8, retardation coil H2 and condensers III' and IN. The positive impulses for rendering the point of impingement of the electron beam visible are produced in response to transitions from marking to spacing or spacing to marking con dition of the polarized receiving relay II, and the key H8 is arranged to permit observation of spring I26 out of engagement with spring I21,

and that key II'I remains unoperated. With the armature of polarized relay II in engagement with contact il in response to a marking signal, current will flow through the previously described energizing circuit of polarized relay I9 which in- The resistance value of the operating winding of relay I9 is a small fraction of the resistance value of resistor 2| so that the potential diiference across the operating winding of relay It causes the spring I28 of key H8 to be at a potential slightly above ground potential. This potential is supplied through half waverectifier H3 and inductance II2 to condenser III, and is not sumcient to raise the potential of control grid I06 of the cathode ray tube to a value that will render the electron beam visible. When polarized relay II responds to a spacing signal and the armature of the relay is moved out of engagement with contact II, the circuit of the operating winding of relay I9 is interrupted and therefore current ceases to flow through resistor 2i. When the armature of relay i I engages contact I8, current flows from battery I8 through battery conductor It, resistor l23, springs l2l and H9 of key I", resistor I22, contact I8 of relay II and armature of that relay to ground. The resistance value of resistor I23 is the same as that of resistor 2I and the resistance value of resistor I22 is the same as that of the operating winding of relay I9, so that a steady drain on battery I8 is maintained regardless of which or the contacts I I and I8 the armature of relay II engages. The flow of current through the substitute resistors I22 and I23 has no present efiect other than to maintain a steady potential difference "across battery I6 regardless of whether the receiving relay II is responding to a marking or spacing condition. The interruption of the circuit of the operating winding of relay I9 and resulting cessation of current through resistor 2I reduces to or near zero the potential difference across this resistor. Accord in y, the full potential of the battery is applied through springs I28 and H6 of key H8 and through half wave rectifier H2 and retardation coil II2 to condenser III. Condenser ill thus becomes charged, the charging current returning to ground through resistor I00, and the positive potential is applied to the control grid I66 of the cathode ray tube 63 through condenser I01 to increase the intensity of the electron beam to a value which will render its point of impingement, upon the-screen of the tube visible. The relative values of the retardation coil I I2, condenser I II and resistor I06 are so chosen that the circuit is verynearly critically dammd. The potential therefore rises very rapidly, becomes nearly constant for a short interval and falls to zero with rapidity almost equal to the rise, thus producing a sharply defined spot on the screen. This pulse is in the direction in which the half wave rectifier H6 is connected to accommodate a flow of current and hence the rectifier presents low impedance to the charging current for the condenser III.

When the receiving relay II again responds to a marking impulse and moves its armature into engagement with contact I'I, current flows through the operating winding of relay I6 and through resistor 2|, and the potential applied to the upper terminal of the half wave rectifier I I3, drops to the former value only slightly above ground. The potential across condenser III at this instant is considerably in excess of the potential applied to the upper terminal of the half wave rectifier and accordingly the condenser seeks to discharge. The discharging current is in the reverse direction and therefore a negative potential is again applied to the control grid I06 02 the cathode ray tube 03 to render the point of impingement of the electron beam upon the screen of the tube invisible. The half wave rectifier H3 offers high impedance to the fiow oi the discharge current in the opposite direction and therefore the fiow of discharging current is prolonged over an extended interval as compared with the interval during which condenser III became charged. The prolongation of the discharging interval prevents chattering of the contacts of polarized relay I I, which might occur incident to movement of the armature into engagement with the contact I1, from recharging condenser Ill during the discharging interval and thus prevents the production of unwanted visible spots upon the screen of the cathode ray tube. From the foregoing it will be apparent that with key IIO operated, a visible spot will appear on the screen of the cathode ray tube 66 in response to each transition from marking to spacing condition as the electron beam traces its invisible spiral path and that no visible spot will be produced in response to transitions from spacing to marking condition.

When it is desired to observe transitions from spacing to marking condition, key H6 is restored to unoperated condition and key H1 is operated, thus bringing its movable spring I I9 into engagement with its stationary spring [I6 to connect the right-hand end of resistor I22, the left-hand end of which is connected to contact I8 to the upper terminal of the half wave rectifier H6.

Upon the restoration of key -I B to normal, the upper end of resistor I23 is connected to the right-hand end of resistor I22 through springs I26 and I21. With this circuit arrangement, when the armature of relay II moves from contact II to contact I8, and interrupts the energizing circuit of the operating winding of relay I6,

asoasv I22 whereby current flows through those re sisters and since the resistance value of resistor I22 is a small fraction of that of resistor I26, the potential applied to the upper terminal of the half wave rectifier H3 through springs H9 and H6 of key II! is only slightly above ground and the charging current for condenser I II is insufllcient to raise the potential of control grid I66 of the cathode ray tube to a value which will render the electron beam visible upon the screen. However, when a spacing signal causes the armature of relay II to move out of engagement with contact I6 and into engagement with contact I'I, current will cease to flow through resistors I26 and I22 and the potential applied to the upper terminal of the half wave rectifier will be that of the positive end of battery I6 since there is no potential diflerence across resistor I26. Char ing current for condenser III will therefore flow and the potential of control grid I06 will be raised to cause the point of impingement of the electron beam upon the screen of the tube to become visible. When, in response to the next spacing signal, the armature of relay II again engages contact I6, the potential of the upper terminal of the half wave rectifier will be reduced to a value near ground potential and condenser III will discharge slowly to reduce the potential of control grid I06 and render the beam invisible upon the screen of tube 30 regardless of subsequent chattering oi the armature of relay II on contact I6.

It is possible to observe transitions from marking to spacing condition and from spacing to marking condition by placing both of the keys Ill and H6 in the operated condition. With this circuit arrangement the operating winding of polarized relay I0 and its companion resistor I22 are both connected to the upper terminal of the half wave rectifier N3, the former through the springs H6 and I26 of key H6 and the latter through springs H6 and H9 of key Ill. Under these circumstances upon movement of the armature of relay II out of engagement with contact Ill, the full potential of battery I6 is applied to the half wave rectifier through resistance 2|. Charging current flows through condenser III and the potential of control grid I06 is momentarily raised to cause a visible spot on the screen of the tube. As soon as the armature of relay I l engages contact I6, a circuit is completed from grounded battery I6 through battery conductor I0, resistor 2|, springs I26 and H6 of key H6, springs H6 and N9 of key II'I, resistor I22, armature of relay II to ground. From this it will be apparent that the charging of condenser III take place only during the transition of the armature of relay II from contact I! to contact I0 and that as soon as the armature engages contact I6, the upper terminal of the half wave rectifier is brought substantially to ground potential over the conductive path from grounded armature of relay II through resistor I22 and springs H0 and H6 of key In.

The armature of relay II, now being in engagement with contact I6, will be moved to engage contact H in response to the next marking impulse. As the armature leaves contact I6. current ceases to fiow through resistor I22 and the full potential 01. battery I6 is again applied to the upper terminal of the half wave rectifier H0 through resistor 2I and through springs I28 and II6 ofkey H6. Condenser III again becomes charged and the control grid I06 of the cathode it completes the circuit through resistors I26 and i6 ray tube is momentarily rendered positive to cause a islble spot to appear on the screen of the tube. When armature of relay it engages contact ill, the energizing circuit for the operating winding of relay it is completed and the potential on the upper terminal of the half wave rectifier Ht applied through springs I28 and tilt of key lit is reduced due to the fiow of current through resistor ti and the operating winding of relay it.- As in the case of the transition from marking to spacing, the charging of condenser Mi occurs only duringthe transit time of the armature, and during the reception of the impulse which caused the transit of the armature the condenser iii discharges.

Due to the decrement of the oscillatory circuit, the electronbeam enters the screen of the tube approximately half way through the start pulse. Thereafter each positive impulse on the intensity control electrode causes a spot of light to become visible on the screen of the cathode ray tube, the spot being simultaneous with a transition of the relay ii. If the signals are without bias or distortion, the visible spots representing transitions of the relay ill will appear at the same relative point in each convolution of the sweep circuit spiral and the visible points will be aligned radially of the spiral at the point of zero bias or distortion, The alignment will be radial because the sweep circuit is so adjusted that the electron beam describes exactly one convolution of the spiral for each impulse of the code combination;

The dots 5%, MY, EM, MW and l5l in Fig. 4 reprev sent the transitions of an unbiased and undistorted signal having the characteristics of the signal shown in Fig. 3 and observed for transitions. from marking to spacing and spacing to marking. It will be observed that there is no visible point between the points Hit and ltd to represent a transition to the fourth impulse of the code combination, since there is no transition in the code combination shown in Fig. 3, the third and fourth impulses being of marking nature.

Bias or distortion suffered by telegraph signals usually results from adverse lineconditions and is evidenced by lengthening or shortening of certain or all of the impulses of a code combination. lengthening of marking impulses is accompanied by shortening of spacing impulses and conversely lengthening of spacing impulses is accompanied by shortening of marking impulses of a code combination. Any such distortion of telegraph signals will cause the visible point representing a transition from one type of impulse to the other to deviate from a radial line on the screen of the cathode ray tube. If all marking impulses of a signal combination are equally distorted as in biased signals, the transitions from marking to spacing will be aligned along one radius and the transitions from spacing to marking will be aligned along another radius. If only one impulse of a code combination is distorted, a visible point representing its transition will be out of radial alignment with points representing the transitions of the remainder of the signal.

The 360 degrees of angle from the zero position represents the extent to which an impulse may be During the reception of telegraph signaling impulses aflected by fortuitous distortion, the spots appear to jump or wander over substantial areas of the screen of the cathode ray tube. As an aid in observing maximum deviation or displacement of a spot from the reference position, a semicircular mask may be put over the screen in such manner that it obscures substantially all of the spots. The mask may then be adjusted so that only the spot having the farthest deviation from the reference point is visible at its edge. This enables the deviation of this particular spot to be readily observed on the scale.

In Fig. 3 the reference line I66 indicates the interval relative to the start-stop permutation code signal represented in Fig. 3 during which the armature of polarized relay I9 is held in engagement with the front contact 26, due to the application to the biasing winding of that relay of direct ground connection through the armature and contact 73 of polarized relay 61, rather than through the resistor 22, Reference line I61 indicates the interval during which the armature of relay I9 engages the back contact 23 and in this interval the relay I9 is responsive to control by the receiving relay ii.

In Fig, 4 the portion I68 of the broken line representing the trace of the electron beam of the cathode ray tube 3 3 indicates the path of the beam returning to normal or initial position following the reengagement of the armature of relay IS with its left-hand contact 23, which occurs during but not in response to reception of the stop impulse at the end of the signal combination. In Fig. 2 the sharply rising solid line at the right of that figure and descending broken line represent the voltages applied to the vertical and horizontal deflecting plates, respectively of the cathode ray tube which cause the beam to trace the portion I68 at the end of its spiral path.

Instead of providing for travel of the beam in a path as indicated in Fig. 4, with the beginning of the path outside the limits of the screen and the terminus of the path near the center of the screen of the tube, the beginning of the path may be brought inside the screen by reducing the gain of the triodes comprising the tube 38 and the pitch of the spiral may be reduced to zero by so adjusting the potentiometer arm 8| as to increase the feedback obtained from the tube 86 through transformer 29. Then the path of the beam will be circular and the visible points produced by undistorted signals will appear at a single point rather than along a radius of the screen.

If the frequency of the oscillatory circuit is so adjusted that the electron beam makes two revolutions during each received impulse, the 360 degrees of thescreen will represent 50 per cent of a, pulse length. In this manner, by causing the beam to rotate two or more times during each received impulse, the scale representing small values of distortion may be greatly magnified.

Although a specific embodiment of the invention has been disclosed in the drawings and described in the foregoing specification, it is to be understood that the invention is not limited to such specific embodiment but is capable of modification, rearrangement and substitution of parts and elements without departing from the spirit of the invention and within the scope of the appended claims;

What is claimed is:

1. A start-stop telegraph signal distortion indicator having in combination a source of startstop ermutation code signals composed of impulse transitions, means for receiving said signals, a cathode ray tube, oscillator means activated once per received permutation code combination of signals for causing the ray oi said tube to travel in an arcuate path, means for normally maintaining the intensity of said ray at a level to render it invisible on the screen of said tube, and means for transiently increasing the intensity of said ray in response to the reception of an impulse transition to render said ray visible on the screen of the tube.

2. A start-stop telegraph signal distortion indicator having in combination a source of startstop permutation code signals composed of impulse trarisitions, means for receiving said signals, a cathode ray tube, means activated once per received code combination of signals for causing the ray of said tube to travel unidirectionally in an arcuate path, means operable independently of received signals for terminating the travel of said ray at the end of a received signal combination, means for normally maintaining the intensity of said ray at a level to render it invisible on the screen of the tube, and means for transiently increasing the intensity of said ray in response to the reception of an impulse transition to render said ray visible on the screen of the tube.

3..In a telegraph signal distortion indicator, means for receiving telegraph signals composed of current transitions, a cathode ray tube, an wcillator circuit for applying to said cathode ray tube electron beam deflecting voltages of equal magnitude and in quadrature, means for connecting across said oscillator circuit a source of steady potential to produce a predetermined initial deflection of said electron beam, means controlled by said signal receiving means for disconnecting said source of potential from said oscillator circuit to permit said circuit to oscillate and apply decreasing oscillatory voltages to said cathode ray tube whereby to deflect said electron beam in a spiral path, and means controlled by said signal receiving means for increasing the intensity of said electron beam in response to signaling current transitions.

4. In a telegraph signal distortion indicator, means for receiving telegraph signals composed of current transitions, a cathode ray tube, a damped oscillatory circuit for applying to said tube diminishing voltages in quadrature and equal in magnitude for causing the electron beam in said tube to be deflected in a spiral path, means controlled by said signal receiving means for initiating oscillation of said oscillatory circuit, and means also controlled by the signal receiving means for increasing the intensity of said electron beam in response to signaling current transitions.

5. In a telegraph signal distortion indicator, means for receiving telegraph signals composed of current transitions, a cathode ray tube, a damped oscillatory circuit connected to said tube for applying thereto diminishing oscillatory voltages in quadrature and equal in magnitude for causing the electron beam in said tube to be said tube, and means controlled by said signal aacaaar receiving means for increasing the intensity of said beam in response to signaling current transitions to render said beam visible on said screen.

6. In a telegraph signal distortion indicator, means for receiving telegraph signals composed of current transitions, a cathode ray tube, a damped oscillatory circuit connected to said tube for applying thereto diminishing oscillatory voltages in quadrature and equal in magnitude at the rate of an integral number of cycles per normal telegraph signal impulse interval for causing the electron beam in said tube to be deflected in a spiral path, means controlled by said signal receivingmeans for initiating oscillation of said circuit, means operable independently of said signal receiving means for limiting oscillation of said circuit to an interval equalto that allotted to a telegraph signal code combination, means for normally maintaining the intensity of the electron beam of said tube at a level to render it invisible on the screen of said tube, and means controlled by said signal receiving means for transiently increasing the intensity of said beam in response to signaling current transitions to render said beam visible on said screen.

7. In a telegraph signal distortion indicator. means for receiving equal length permutation code telegraph signals composed of current transitions, a cathode ray tube, a damped oscillatory circuit connected to said tube for applying thereto diminishing oscillatory voltages in quadrature and equal in magnitude at the rate of one cycle per normal impulse of said code for causing the electron beam in said tube to be deflected in a spiral path, means controlled by said signal receiving means for initiating oscillation of said circuit, means operable during reception of a code combination but independently of said signal receiving means for limiting oscillation of said circuit to an interval equal to that allotted to a permutation code signal, means for normally maintaining the intensity of the electron beam at a level to render its point of impingement on the screen of the tube invisible, and means controlled by said signal receiving means for transiently increasing the intensity of said beam in response to signaling current transitions to render points of impingement of said beam with said screen visible at corresponding points in the convolutions of said spiral path for undistorted signaling impulses.

8. In a telegraph signal distortion indicator, means for receiving telegraph signals composed of current transitions, a cathode ray tube including electrical potential responsive means for controlling the intensity of the electron beam of said tube, means for normally ap lying a predetermined potential to said intensity controlling means, means controlled by said signal responsive means for increasing the potential applied to said intensity controlling means, and means connected between said potential increasing means and said intensity controlling means for nullifying the effect upon said intensity controlling means of chattering of said signal responsive means.

9. In a telegraph signal distortion indicator, means for receiving telegraph signals composed of current transitions, a cathode ray tube including electrical potential responsive means for controlling the intensity of the electron beam of said tube, means for normally applying a predetermined potential to said intensity controlling means, means controlled by said signal responsive means for increasing the potential applied to said intensity controlling means, and means offering ass-was? low resistance to the flow of electrical current in one direction and high resistance to the flow of electrical current in the opposite direction contube, means for normally applying a predetermined potential to said intensity controlling means, means including electrical energy storing means controlled by said signal responsive means for increasing the potential applied to said intensity controlling means in response to signaling current transitions, and means associated with said electrical energy storing means for retarding the discharging of energy by said storing means to nullify the efiect upon said intensity controlling means of chattering of said signal responsive means.

11. In a telegraph signal distortion indicator, means for receiving telegraph signals composed of current transitions, a cathode ray tube including electrical potential responsive means for controlling the intensity of the electron beam of said 3- tube, means for normally applying a predetermined potential to' said intensity controlling means, means including electrical energy storing means controlled by said signal responsive means for increasing the potential applied to said intensity controlling means, and half wave rectifier means connected in series with said electrical energy storing means for readily accommodating the flow of current to charge said energy storing means and for retarding the flow of current to discharge said energy storing means to nullify the effect upon said intensity controlling means of chattering of said signal responsive means.

12. In a telegraph signal distortion indicator, means for receiving signals composed of current transitions, including an element movable between two positions in response to current transitions, a cathode ray tube including electrical potential responsive means for controlling the intensity of the electron beam of said tube, means for normally applying a predetermined potential to said intensity controlling means, means for applying an increased potential to said intensity controlling means, means for causing. said increased potential to be applied to said intensity .2

controlling means upon movement of said element from one position to the other, and means for causing said increased potential to be applied to said intensity controlling means upon movement of said element from said other position to said one position.

13. In a telegraph signal distortion indicator, means including an element movable between two positions for receiving telegraph signals composed of current transitions, a cathode ray tube having means for controlling the intensity of the electron beam of said tube, a circuit for controlling said intensity controlling means, means controlled by said element for energizing said circuit,

selectively operable means for causing said circult to be energized from said energizing means upon transition of said element in one direction and to be cleenergized upon the next transition oi! said element, and selectively operable means for causing said circuit to be energized from said energizing means upon transition of said element in the other direction and to be deenergized upon the next transition of said element.

14. In a telegraph signal distortion indicator, means for receiving permutation code telegraph signals composed of impulse transitions, a cathode ray tube, means for imparting to the ray of said tube a predetermined initial deflection, means activated once per received code combination of signals for causing the ray of said tube to travel unidirectionally in an arcuate path, means operable independently of received signals for terminating the travel of said ray at the end of a received signal combination, and means for critically damping said travel causing means to energization, whereby to cause said ray to be restored to said initial position in an interval equal to a small fraction of the interval of reception of a code combination.

15. In a telegraph signal distortion indicator, means for receiving permutation code telegraph signals composed of impulse transitions, a cathode ray tube, means for causing the ray of said tube to be deflected to a predetermined initial position, oscillator means activated once per received code combination of signals for causing the ray of said tube to travel unidirectionally in an arcuate path, means operable independently of received signals for terminating the travel of said ray at the end of received signal combination, and means for critically damping said oscillator means to energization, whereby to cause said ray to be restored to said initial position in an interval less than an impulse interval of a permutation code combination.

16. In a telegraph signal distortion indicator, means for receiving permutation code telegraph signals composed of impulse transitions, a cathode ray tube, means for causing the ray of said tube to be deflected to a predetermined initial position, oscillator means activated on per received code combination of signals for causing the ray of said tube to travel unidirectionally in an arcuate path, means operable independently of received signals for terminating the travel of said ray at the end of a received signal-combination, and a resistor included in the energizing circult of said oscillator means proportioned to damp said oscillator means critically to energization, whereby to cause said ray to be restored to said initial position in an interval less than an impulse interval of a permutation code signal combination.

17. In a telegraph signal distortion indicator, means for receiving permutation code telegraph signals composed of impulse transitions, a cathode ray tube, oscillator means activated once per received code combination of signals for causing the ray of said tube to travel unidirectionally in an arcuate path, means for damping said oscillator means critically to energizing current whereby to bring said ray to, an initial position in an interval less than an impulse interval of a permutation code combination, means for prolonging the discharging of said oscillatory means foran interval longer than the interval occupied by a permutation code signal combination, and means for terminating the travel of said ray at the end of a received signal combination.

18. In a device for receiving equal length permutation code signals, a signal responsive relay, a second relay responsive to operation of said signal responsive relay, normally inactive oscillator means set in operation by said second relay and adjusted to oscillate at an integral number of cycles per impulse interval oi said mgnals, means controlled Jointly by said signal responsive relay and said oscillator means for displaying signaling impulse transitions, a third relay operable under the control oi said second relay for rendering said second relay unresponsive to said signal responsive relay, and means for limiting the operation of said third relay substantially to a permutation code signal interval.

19. In a device for receiving equal length permutation code signals, a signal responsive relay, a second relay responsive-to operation of said signal responsive relay, normally inactive oscillator means set in operation by said second relay and adjusted to oscillate at an integral number of cycles per impulse interval of said signals. means controlled jointly by said signal responsive relay and said oscillator means for displaying signaling impulse transitions, a third relay operable under the control of said second relay for rendering said second relay unresponsive to said signal responsive relay, and means including a condenser to be charged by energizing current for said third relay for limiting the operation of said third relay substantially to a permutation code signal interval.

20. In a telegraph signal receiving device, a signal responsive relay. 9, second relay operable by said signal responsive relay, a third relay operable bysaid second relay for maintaining said second relay operated independently of control by said signal responsive relay, a normally inactive oscillator rendered active by said second relay, means associated with said third relay for predeterminedly limiting the interval during which said third relay remains operated, and a cathode ray tube controlled Jointly by said oscillator and said signal responsive relay for registering signal responsive operation or said signal responsive 7 ssorssr ii. m a wav a t receiving device. a signal resiwnmve relay, a second relay operable by said signal rmponsive relay, a third relay operable by said second relay for maintaining said second relay operated independently of control by said signal responsive relay. said third relay having alternative energizing paths one oi which normally short-circuits the other, means operated by said third relay for interrupting said one path whereby said other path becomes edective, means contained in said other path for predeterminedly limiting the interval during which said other path remains eflective to maintain said third relay operated, and a cathode ray tube controlled Jointly by said second relay and said signal responsive relay for registering signal responsive operation of said signal responsive relay.

22. In a telegraph signal receiving device, a signal responsive relay, a second relay operable by said signal responsive relay. a third relay operable by said second relay for maintaining said second relay operated independently of control by said signal responsive relay, said third relay having alternative energizing paths one of which normally short-circuits the other, means operated by said third relay for interrupting said one path whereby said other path becomes effective to maintain said third relay operated, a condenser contained in said other path for prolonging the operation of said third relay for a predetermined interval following the interruption oi said one path, and a cathode ray tube controlled Jointly by said second relay and said signal responsive relay for registering signal responsive operation of said signal responsive relay.

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