US1559641A - Signaling with phase reversals - Google Patents

Description

H. NYQUIST SIGNALING WITH PHASE REVERSALS Nov. 3, 1925.

Filed Aug. 28, 1923 4 Sheets-Shbet 3 T0 limo/"jig Transnulssiwa IN VEN TOR l/jywls't iii/pa 'ATTORNEY Nov. 3 1 I v H NYQUIST SIGNALING WITH PHASE REVERSALS FiledAug. 1923 Film J1 orning Darwm t.

IN VE TOR Z fiQTTORNEY 4 Sheets-Sheet Patented Nov. 3, 1925.

HARRY NTYQUIST, OFiELMHURST, NEW YORK, ASSIGNOR. TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK. v

SIGNALING WITH PHASE BEVE'BSALS.

Application filed August 28, 1923. Serial 1T0. 659,754..

To all whom it may concern:

Be it known that I, HARRY NYQUIST, residin at Elmhurst, in the county of Queens and tate of New York, have invented certain Improvements in Signaling with Phase the same circuit, the channels being so arranged that by the transmission of an alternating current of given magnitude, a sigdi nal response of greater amplitude will be produced. Another object of the invention is to provide a circuit of the type above described, in which the efiect of foreign interference will be reduced. Another object of the invention is to provide a multiplex telegraph system so arran ed that the mutual interference between I will be a minimum. A still further. object of the invention is to provide a tele' aph system in which the biasing efiec't of t e .received 'si als caused by variations in the transmisslon equivalent of the circuit will 80 be ractically eliminated.

hese objects, together with other objects of the invention, are accomplished by transmitting an alternating current of constant frequency and amplitudeand by reversmg the phase of the transmitted current in response to the marking and spacing signals. At the receiving station, the transmitted current will be combined with another cur rent of equal amplitude and of the same f uency but with its phase constant. While, in general, this controlling current may be either generated at the transmitting station and transmitted to the receiving station, or generated at the receiving station under the control of the current source at the transmitting station, the specific embodiment of the invention herein disclosed illustrates only the former of these methods. The i'nventlon may now be more fully understood from the following detailed description thereon. when read n connection with the accompanying drawlng, Figure 1 of which illustrates a number of curves showing the form of wave transmitted in 'flerent channels accordance with the present invention; 'Fig. 2 of which shows a schematic circuit vdiagram embodying the transmitting apparatus of the present invention; Figs. 3 and 4 of which illustrate two different types of recelving arrangements to be employed in connection with the present invention; Figs. 5 and 6 of which illustrate two different cir cuit arrangements for producing phase reversals; Fig. 7 of which illustrates a piece of apfparatus adapted to reduce the effect of lnter erence at thereceiving station; and Fig. 8 of which illustrates curves showing the o eration of the apparatus of Fig. 7

Re erring to Fig. 1, the curve designated a illustrates the current condition in the line of an alternating current telegraph system spacing signal corresponds to the no-current condition of the line, the particular signal illustrated being the letter I. Curve 6 represents the same letter when current in I the line corresponds to the marking condition. The curve designated 0 represents the same letter formed in accordance with the present invention by sim ly reversin the phase without altering t e magnitu e of the current. It will be seen that if a signaling wave such as is illustrated by the curve a is combined at the receiving end with the simple sine wave of the same frequency and constant amplitude as shown b the curve marked 1, the resultant wave wi 1 be identical either with curve a or b, depending upon whether the constant sine wave be made to correspond in phase to the marking condition or the spacing condition of the si al wave. Inasmuch as the received signa is the result of two waves 0 and d, the signal will havean amplitude twice as great as the signal produced by waves such as shown' A signal wave such as that illu'strated at 0 will be advantageous (provided a wavesimilar to d can be supplied at the re-' at a or b.

ceiving end) either from the standpoint of producing a stronger signal at the receiving station, or from the point of view of obtaining as strong a signal as can be at resent attained, but with a line current only alf as great'as that required for signaling methods of the prior art.

Fig. 2 illustrates the apparatus necessary at a transmitting station where the present invention is applied to a multiplex carrier telegraph system. For purposes of illustration, two signaling linesL and L are provided, each having four channels transmitting thereover at different carrier frequencies. The number of channels transmitting over each line may, of course. be made either greater or less in number than that illustrated. The carrier currents for the four lines may be supplied, for example, from four sources of 500, 700, 900 and 1100 -cycles, respectively, and the several sources may supply as many signaling lines as are necessary to carry the desired trafiic. Gommon to each of the signaling lines is a control line L the purpose of the latter being to transmit the control frequencies corresponding to each of the channels ofeach signal line. Where, for example, four carrier channels are provided for each signal line, there will be four different signaling frequencies transmitted over each of the lines and four constant amplitude, constant phase and constant frequency currents will be transmitted over the control circuit L But one control circuit will be necessary, regardless of the number of signaling lines in-, volved in the system, and consequently, the provision of the control circuit will, in general, represent but a small additional expense over and above that of the transmis sion lines themselves when the important advantages in operation are taken into consideration.

Each of the carrier frequency sources, as, for example, the 500 cycle source, is connected to common bus-bars as illustrated at 10, and from the bus-bars connections lead through suitable filters or other selecting devices F F and F, to the control circuit L and the various transmitting lines such as L and L. Each of the other sources will be connected; to the control circuit L. and the various transmission lines such as L and L'- through similar groups of filters as illustrated. A phase correcting or controlling device of well-known character is illustrated at 14 in connection with the control circuit for the purpose of adjusting the phase of the control frequency to the desired relation with the signaling current, as will be described later, one of these phase controllers being provided in connection with each carrier source.

. For the purpose of simplicity of illustration, the signaling mechanism for producing the current reversals in the signaling frequencies applied to the circuits L and L are shown as being simple pole changers such as 18, 18, etc. Simple pole changers of this type are not, however, well adapted .for producing the phase reversals in practice for the reason that a certain amount of time must elapse for the armature of the pole changer to pass from one contact Accordingly, it is preferred that some arrangement such as is illustrated in Fig. 5 be utilized for producing the phase reversals. Fig. 5 illustrates a bridge arrangement comprising three arms, each of resistance R, and a fourth arm including the contact of a relay 22, whereby when the contact is closed, the resistance of the fourth arm will be zero, and when it is opened, the resistance will be infinite. Circuit connections extend from two opposite corners of the bridge to the carrier supply source (not illustrated) and circuit connections from the other two corners of the bridge extend through suit-able apparatus (not illustrated in Fig. 5) to the signaling line. Preferably, the impedance looking towards the source and looking towards the signaling line should have the same value R as the arms of the bridge. It will be obvious fromthis circuit arran ement that if the key K controlling the cmcuit of the relay 22 is closed, so that the fourth arm of the bridge is of zero resistance, the bridge will be unbalanced to transmit current of a definite amplitude to the line, while if the key is opened, so that the the opposite sense, thereby causing a current of equal amplitude to flow in the opposite direction. In the case of an alternating current supply, it will be obvious that this will produce a change in phase of 180 in current supplied to the line. Since this change in the phase. is instantaneous upon the making or breaking of the contact, there will be no hiatus between reversals.

A modified arrangement is illustrated in Fig. 6. In this figure, a balancing arrangement comprising a hybrid coil 23 and a balancing resistance or network 24 and a circuit 25 is provided. The current supply may heconnected, for example, to the midpoints of the windings of the hybrid coil, the circuit to be supplied being in turn connected to the secondary of the hybrid coil, although the circuit will work equally well if the current source is connected to the secondary and the circuit to be supplied be connected to the midpoints of the hybrid coil. It the impedenoe of the circuit 25 be made just equal to that of the network 24, it will be apparent that no current will be. transmit-tedfrom the source to the circuit to be supplied. lhe circuit 25, however, contains the contact of a relay 22 and when the contact of the relay is closed, the circuit 25 has zero resistance, while with the contact open, the circuit 25 has infinite resistance. In the one case, the circuit will be unbalanced in one direction, and in the other case, the circuit will be unbalanced in the opposite direction, so that by manipulating e key K to open and close the contact of the relay 22, reversals in phase of the alternating current supplied will occur, and these reversals will occur instantly upon the making or breaking of thecircuit.

Itwill be noted in connection withjthe circuit'of Fig. 2 thatinasmuch as the controlled currents transmitted over the line L5 come from the same source as the signaling currents transmitted over the lines L, L, etc., they will be of the'same frequenc as the signaling currents themselves. Furt ermore, inasmuch as the controlled currents pass over a circuit substantiallythe same as the signaling circuits, they wlll be subject to the same phase changes and hence suitable for combination in proper" phase relation with the signaling currents received at the receiving station. In connection with the phase relation, it will be noticed that the phase relation of the arriving currents at the receivingstation may .be adjusted by means of the phase correction device connected in series with each source supplying the control circuit, and once the phase is fixed for each frequency, it will remain properly adjusted without further attention. It will further be observed that apart from the addition of the control circuit, the arrangement shown at the transmitting station involves substantially the same units of apparatus as are provided for ordinary multlplex carrier telegraph systems except that the transmitter conslsts of a reversingarrangement instead of the usual device for opening and shorting the circuit. The

wavesof each frequency resulting from the operationof the transmitting key will correspond in form to the wave shown at c in fii 3 illustrates one arrangement whereby t e signals may be received. The signaling lines such as L and L terminate at the-receiving station in hybrid coils such as 26 and 26', the opposite terminals of the hybrid coils bein connected to common bus bars leading to t e incoming control circuit ,L It is, of course, desirable thatthe control currents supplied to the terminals of the hybrid coil be equal in amplitude to the signaling currents supplied to the opposite terminals. Since, however, the current transmitted over the, control circuit L, supplies a plurality of receiving circuits and will, in general, be substantiall no greater in amplitude during transmisslon over the line than the current transmitted over each signaling circuit, it is necessary to su ply amplifying arrangements such as A an A between the terminals of each hybrid coil and the bus-bars of the control circuit. By

a suitable adjustment of the amplifiers (which may of any type well known in the art), the control current sup lied to the hybrid coil may be made equa in amplitude to the signaling current.

The secondary winding ofeach hybrid I coil is connected to bus-bars such as .27 and 27 to which the individual receiving channels are connected. -The signaling channels corresponding vto the signaling line L include filters such as RF,, RF RF, and RF each selective of the particular carrier frequency assigned to the channel, each receiving channel also including a detector such as 1),, D etc. Thedetectors may be of any well-known type, such as ordinaryvacuum tube detectors, and as isusually the practice in carrier telegraph circuits, the receiving element associated with the detector comorises a polar relay havingone winding in the plate circuit and another winding in an auxiliary circuit including a resistance properly proportioned with respect to the plate resistance of the tube, the latter circuit being also supplicdwith current from the plate source. The circuitof the detectin tube is so adjusted that when no signal is eing received, nocurrent flows through i the upper winding and the current in the lower winding produces a pull tending to shift the armature of the relay in one direction with a given force. When a normal signaling current is being received, however,

sufiicient current flows in the plate circuit to energize the upper winding of-the polar relay to produce a force substantially twice as great, tending to shift the armature in the opposite direction.- This results in a properly unbiased polar 'rela action for a received signal of given amp itude.

Returning to the hybrid-coil 26, it will be observed that balancing resistances or networks 28 and 28', are'associated with the hybrid coils. portioned with respect to the impedance 901G112 into the receiving channels that the circuits leading to the signaling line and the control circuit are con ugate with respect to each other. By means of this arrangement, the incoming signal wave of the form shown in curve 0 of Fig. 1 is su erposed upon the control wave of the form s own by the curved to produce in the secondary circuit of the hybrid coil a wave of either the type illustrated by curve a or the type illustrated bycurve 6, depending upon the phase relation of the control wave to the signal wave. At the same time, a complementary wave will .be produced in the network 28 or 28, as the case maybe. That is to say, if the wave in the secondary assumes the form of curve a, the wave in the network will assume the form of curve, b, and vice versa.

This may be readily understood by con.- sidering that if the wave 0, during the marking inter-val, is transmitted through the lhese networks are so profrom the signal.

lower windings of the hybrid coil to the terminals of the network in opposite phase relation to the wave at transmitted through the upper windings of the coil, a wave such as I), having twice the amplitude of the signal wave, will be produced in the network during the marking period but no wave will be induced in the secondary of the hybrid coil because the waves oppose each other. During the spacing period, the signal wave and the control wave will be series-aiding in the hybrid coil and will consequently produce a wave of double amplitude in the receiving circuit. No current will, however, be transmitted to the network during the spacing period. On the other hand, if the phase of the control wave be changed 180, the opposite effect will be produced, no current being transmitted to the network during the marking and a double marking current being transmitted to the receiving terminal. During the spacing period, no current will be transmitted to the receiving terminal but a double current willbe transmitted to the network. In short, the operationgof the hybridhcoil arrangement is'such that the signaling wave such as 0, transmitted 'over a signal line, will be transformed at the receiving terminals into a wave either of type a or of type b, having twice the amplitude of the transmitted signaling wave. As the received wave is of the ordinary type, it is consequently detected after being selected into the proper receiving channel by a detector of ,the ordinary type. Consequently, the only additional feature required by the receiving circuit over and above the apparatus used in ordinary carrier telegraph systems is the hybrid coil for translating the signal current from a wave of type 0 to a wave of type a or b, as the case may be.

It will be observed that the signals received by means of the arrangements shown in Fig. 3 vary in amplitude as the transmission equivalent of the circuit varies. This introduces a bias into the received si nals due to the fact that the detected signal ing current flowing through the upper winding of the polar relay will not necessarily be twice as great as'normal current flowing in the lower winding. Since it is not, in general, practicable to vary the biasing current in the lower winding to correspond to the change in the amplitude of the detected signaling current, it follows that the arran e ment of Fig. 3 from the standpoint of has is no better than an ordinary carrier tele graph circuit of the usual type. The operation in this respect, however, may be greatly improved by supplying the biasing current v For example, it will be obvious that if marking currents are transmitted through the filters illustrated to the detectors to operate the upper winding of the polar relay, the spacing currents which are transmitted to the network might be selected similar filters and transmitted through similar detector tubes to energize the lower winding of the polar relay, thereby avoiding any biasing effect due to change in the transmission equivalent. As this is not a very practicable method owing to the duplication of filters and detectors, it is preferred to use an arrangement such as shown in Fig. 4 for accomplishing the same result.

In accordance with Fig. 4, duplex balanced vacuum tube detectors are employed instead of single vacuum tube detectors such as shown in 'Fig. 3. The signaling current having the form of wave 0 is led through filters such as RF RF etc., in the various receiving channels to the input circuits of the detectors as indicated, in such a manner as to produce opposite potentials upon the grids of the tubes. The several control frequencies are selected by receiving filters such as RF, RF etc., and transmitted over a circuit inductively connected to the common conductor of the input circuits of each duplex detector. As a consequenceof this connection, the'control wave potential will be added to the signal wave potential upon the one grid, While the two waves will oppose each other upon. the other grid. Depending upon the phase of the control wave, it is possible by a proper adjustment of the detecting tu es to impress only marking currents upon the upper tube, for example, and only spacing currents upon the lower tube. The detected component of the marking current will then energize the upper winding of the polar relay to shift the armature in the one direction, while the detected component of the spacing current will energize the lower winding to shift the armature in the opposite direction. No biasing efi'ect will take place with this arrangement, because the current in each winding of the polar relay depends to the same extent upon the transmission equivalent of the signaling and control circuits.

While the methods of signaling above discussed result in doubling the amplitude of the received signal, it should be noted that with the system disclosed we will have foreign interference from two sources, namelythe foreign interference which is introduced through the signaling circuit, and also the foreign interference which is introduced in,

the control circuit. While at first thought it might se'e'mthat these two interfering currents would tend to combine in the same manner as the signal currents to produce a greater interference in the receiver, it will be found upon closer analysis that such is not the case. Owin to-the fact that the signaling and contro currents are controllable in phase, the phase relations of these two currents will be fixed to produce the maximum amplitude of the signal. The

two interfering components obtained from the control and signaling circuits, respectively, continually Vary in phase with respect to each other and will, on the averagg, tend to neutralize each other in art. For example, if We consider two interfering Waves received in the control circuit and a signaling circuit, it will be apparent that the relative phases of the two components will vary from zero to 180 and that, on

interference which is introduced in the control circuit. The arrangement consists of a vacuum tube distorting device 40 having a high rsistance 41 in its input circuit and a sharply tuned circuit or filter 42 in its output circuit. If we consider a simple sine wave applied to the input circuit of the vacuum tube, the effect is to cut off the top and bottom of the wave, thereby tending to roduce in the output circuit a more or ess square-topped wave. (See curve Y of Fig; 8.) The square-topped wave, as is well-understood, is equivalent to a wave of the original frequency having superposed thereon various harmonics of the original frequency. The tuned circuit or filter 42 will then have the effect of selecting the fundamental frequency and eliminating the harmonics, so that the wave finally transmitted will be substantially a pure sine wave. Suppose now the sine wave. impressed upon the input circuit is subjected to interference of such a nature as to var the form of the wave to that illustrated by the curve X of Fig. 8. Obviously, any interference suchas that shown at n, o and p, which tends to increase or decrease the amplitude of the wave, will be to alarge extent eliminated by passing it through the distortin tube, since the interference will be out 0 when the to and bottom of the wave are cut off by t e distorting circuit. Interference such as that shown at m, tending to slightly widen the wave, will, however, result in a slight widening of the' square-topped wave so that in this particular pulse there will be a slight distortion as indicated. Even this distortion, howlever, to a large extent disappears upon passing the square-top ed wave through the filter and substantial a pure sine wave will be transmitted as indicated by the curve Z.

In the arrangement of Fig. 4, it is, of

course, necessary to provide in each channel leading from the control circuit an amplifier such as A A A etc., for the purposeof making the controlcurrent equal in amplitude to the received signaling current. While this amplifier may be a simple vacuum tube amplifier of the ordinary type, it is preferred to modify the circuit as illustrated .in Fig, 7 to produce a distorting effect upon the applied wave at the same time that it is amplified, thereby to a large extent eliminating the interference components from the control wave and producing as the effective control wave a wave such as is shown by thecurve Z of Fig. 8.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departin from thespirit of the invention as define in the following claims.

What is claimed is:

1. The method of signaling, which consists in transmitting a waveof constant amplitude and frequency but reversed in phase at intervals to indicate signals, and combining at the receiving station with the wave thus transmitted, a wave of substantially the same amplitude and frequency but unreversed in phase.

2. The method of signalin which consists in transmitting a wave 0% constant amplitude and frequency but reversed in phase at intervals to indicate signals, transmitting to the receiving station a similar wave except that it is unreversed in phase, and combining the two waves at the receiving station.

3. The method of signaling, which consists in generating a wave of constant amplitude and frequency, applying a portion of the energy of said wave to each of two circuits, reversing the phase of the wave ap plied'to one circuit at intervals, and combiny mg the wave reversed in phase with'the unreversed wave at the receiving station.

4. The method of signaling, which consists in generating a wave of constant amplitude and frequency, applying a ortion of v the energy of said wave to each 0 a plurality of circuits, transmitting the wave over one of said circuits without phase reversals, producing phase reversals corresponding to signals in the components of said wave transmitted over others of said circuits, and separately combining the unreversed wave at the receiving station with each of the waves transmitted over the other circuits to produce signals corresponding to each circuit.

5. In a signalin system, means for transmitting a wave 0 constant amplitude and frequency, means for producing phase reversals in said wave in accordance with signals, means at the receiving station to comquencybut unreversed in phase.

6. n a signaling system, means for trans- 'mitting a Wave of constant amplitude and frequency, means to produce phase reversals in said wave in accordance with signals, means to transmit to the receiving station a wave of substantially the same amplitude and frequency but unreversed in phase, and means to combine the two waves at the receiving station.

7. In a signaling system, means for generating a wave of constant amplitudeand frequency, means to apply a portion of the energy of said wave to each of two circuits, means to reverse the phase of the wave applied to one circuit in accordance with signals, and means at the receiving station to combine the wave reversed in phase with the unreversed wave.

'8. In a signaling system, a plurality of signaling circuits and a control circuit, means for generating a wave of constant amplitude and frequency, means to apply a portion of the energy of said wave to each of the signaling circuits, meansto produce phase reversals in the wave applied to each signaling circuit, means to apply a portion of the energy of said wave to said control circuit, and means at the receiving station to separately combine the wave transmitted over said control circuit with the waves transmitted over the signaling circuits.

9. In'a signaling system, a plurality of signaling circuits and a control circuit, means to generate a plurality of constant amplitude Waves of diflerent frequencies, means to apply a portion of the ener of each of said waves to said control clrcuit without phase reversals, means to apply a portion of the energy of all,of said waves to each of said signaling circuits, means associated with each signaling circuit for producingsphase reversals in each of the waves applied thereto inaccordance with separate signals, means at a receiving station to select from each signaling circuit the individual waves with their phase reversals, and means to combine with each selected wave of each circuit a corresponding wave received from the control circuit which is unreversed in phase.

10. In a signaling system, means to transmit to a receiving station a wave of constant amplitude and frequency reversed in phase at intervals in accordance with signals, means to transmit to said receiving station a wave of similar amplitude and frequency but unreversed in' phase, means to separate interference components from the latter wave comprising a distorting device for rendering the wave substantially square-topped, selective means for selecting a wave of sine form from the distorted wave, and means to combine the selected wave with the wave which is reversed in phase to produce a signal.

11. In a signaling system, a transmitting device comprising a balanced type of circuit, a single source of current supply for said circuit and a contact in said circuit so arranged that when the contact is opened the .circuit will be unbalanced in one sense with respect to said source and when the contact is closed the circuit will be unbalanced in the 0p osite sense with respect to said source.

12. n a signaling system, a transmitting arrangement comprlsing a .single source of current, a circuit to which current from said will be transmitted to said first mentioned source in opposite phase relation.

13. In a signaling system, a transmitting arrangement comprising a source of alternat' ing current, a circuit-to be supplied with current from said source, a balanced type of circuit associated with said first mentioned circuit, connections from said source to neutral points of said balanced type of circuit, and a. contact in said balanced type of circuit so arranged that when the. contact is opened the circuit will be unbalanced in one direction andwhen it is closed it will be unbalanced in the opposite direction.

14. In a signaling system, means to transmit an alternating signaling current of, constant amplitude and frequency. in which marking and spacing intervals are differentiated by reversals in the phase of the current, a detecting device comprising .two detecting elements, means to-actuate one element with currents of one phase and means to actuate the other element with currents of the opposite phase.

15. In a signaling system, means to transmit an alternating signaling current of constant amplitude and frequency in which marking and spacing intervals arefldifl'erentiated by reversals in the phase of the current, a detecting arrangement-comprising a pair of detecting elementsga polar relay having a winding in circuit with eachv detecting element, means to transmit a detected current through one winding of said relay in response to currents of one phase, and means to transmit a detected current through the other winding of said relay in response to currents of the opposite phase.

16. In a signaling system, means to transmit a signaling current of constant amplitude and frequency in which marking and spacing intervals are differentiated by reversals in the phase of the current, means to combine said current/with a current of substantially the same amplitude and frequency but Without phase reversals to produce resultant current components, one of which has constant amplitude current during a marking interval and no current during the spacing interval and the other of which has no current during the marking interval and constant amplitude current during the spac- -ing interval a pair of detecting devices, 10

means to impress one of said components upon one detecting device and means to impress the other component upon the other detecting device.

In testimony whereof, I have signed my 1 name to this specification this 27th day of August, 1923. y

- HARRY NYQUIST.

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