US1791579A - Telegraph signaling system - Google Patents

Description

Fab W, 1931. F. J. SINGER LZQLS'ZQ TELEGRAPH SIGNALING SYSTEM Filed March 20. 1929 2 Sheets-Sheet l k U E E b INVENTOR ATTORNEY Feb. w, 1931. F. J. SINGER 397939579 TELEGRAPH SIGNALING SYSTEM Filed March 20, 1929 2 Sheets-Sheet 2 Zmyim. 2 Wa 0e Zecellved 629ml 4% 4% Maiulazed Cal/Tier Patented Feb. 10, 1931 UNITED STATES PATENT OFFICE FRED J. SINGER, F ROCKVILLE CENTER, NEW YORK, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK TELEGRAPH SIGNALING SYSTEM Application filed March 20, 1929. Serial No. 348,500.

This invention relates to signaling systems generally, and particularly to signaling systems employing carrier Waves of very low frequencies. More particularly, this invention relates to receiving systems suitable for receiving pulses of alternating current representing signals characteristic of carrier telegraphy, the alternating pulses being derived from waves of low frequency.

In this application, a carrier telegraph system is disclosed, in which the carrier wave or waves employed are of a frequency only several times the dot frequency of the transmitted signals. Pulses of low frequency current are produced in accordance with the signals. These pulses are transmitted over a wire circuit and subsequently converted into direct current pulses, each pulse of direct current corresponding to each received alternating current pulse.

One of the objects of this invention is to provide a telegraph system for signaling with carrier waves of very low frequency with small ornegligible distortion.

Another of the objects of this invention is to provide an arrangement for producing alternating current pulses from direct current pulses representing signals, and for converting these alternating current pulses into 0 the corresponding direct current pulses, with small or negligible distortion, in which the lengths of the direct current pulses derived from the alternating current pulses correspond closely to the lengths of the direct current pulses employed at the sending end in producing the alternating current pulses.

Another of the objects of this invention is to provide an arrangement for interconnecting a line circuit over which alternating cur to rent of some definite frequency or frequencies between the limits of a predetermined band may flow and a direct current relay so that the direct current relay may be continuously operated throughout the period during which current of the proper frequency or frequencies is resent in the line circuit.

And it is a furt er object of this invention to interconnect a line circuit over which alternating current may flow and a direct current relay through a pair of three-element vacuum tube rectifying devices which, respectively, rectify the opposite halves of each alternating current cycle and provide the current necessary to operate the direct current relay.

While this invention will be pointed out with particularity in the appended claims, the invention itself, both as to its. further objects and features, will be better understood from the detailed description hereinafter following, when read in connection with the accompanying drawing in which Figure 1 represents a telegraph system employing a threeelectrode vacuum tube rectifying element for half-wave rectification; Fig. 2 represents a modification of the receiving system shown in Fig. 1, providing two three-electrode vacuum tube rectifying elements for fullwave rectification; Fig. 3 represents a receiving system suitable to replace the receiving system shown in Fig. 1, this receiving system including means for receiving two alternating current pulses or bands of signals, and Figs. 4a, 4b, 4c, 4d, 46 and 4f representing curves disclosing certain of the features of the invention.

Referring to Fig. 1 of the drawing, the transmitting end of a telegraph system is shown at the left, and the receiving end at the right, both connected by a wire circuit. At the transmitting end, there is a transmitting relay R having two windings W and andan armature which ma vibrate between contacts designated 1 and 2. lVinding V, is connected in series with a resistance Z and another resistance Z, a battery B and ground. The right hand terminal of the winding W is also connected in series with resistance Z battery B and ground, the lefthand terminal of this winding being connected in series with a variable resistance Z a key K, the winding of a sounder R resistance Z. battery B and ground.

An oscillator 0 provides current of the carrier frequency to be employed throughout the system. This oscillator may be of any wellknown type, preferably one capable of producing alternating current of comparatively low frequency. This oscillator transmits signaling current to bus-bars E through a pair of resistances, one designated Z con- I nected in shunt with the oscillator, and the other designated Z in series with the oscil lator and through a band filter F \Vhen key K is opened, current will flo w from battery B 1 through winding W causing the armature of relay R to close contact 23nd oscillator C will be rendered practically ineffective. When key K is closed, current will flow from batteries B; and 13 through the winding of the sounder R and through the winding W of the transmitting relay R The current through winding W may be controlled in its magnitude by adjustment of the resistance Z and, ordinarily, the current through winding W may be approximately twice as great as that through winding W Consequently, the armature of relay R will close contact 1, and current will then flow from oscillator C over resistance Z and through the band filter F to the bus-bars E Thus, by operating key K, current derived from oscillator C will be modulated and transmitted to bus-bars E in accordance with signals.

Current impressed upon bus-bars E will ordinarily be more than just a simple alternating current wave. The current derived from oscillator 0 may include all frequencies within the spectrum, and the band filter F is provided for the purpose of limiting the width of the band impressed upon bus-bars E Thus, if oscillator 0 produces current of a frequency of, for example, 255 cycles, the band filter F may transmit only those frequencies lying between the limits of, for example, 170 cycles and 340 cycles.

It is to be clearly understood that a transmitting set similar to the one just described may also be connected to the line L in order to impress upon bus-bars E another band of frequencies representing another set of signals. It is to be understood that still other transmitting sets similar to the one described may be added, as required, within the scope (itl of this invention. For the sake of clarity, however, the description of the arrangement shown in Fig. 1 will be limited to the transmission of that band of frequencies derived from oscillator O and filter F Current flowing over bus-bars E is transmitted through a transformer T an amplifier A. another transformer T to bus-bars E The amplifier A may be of any wellknown type, preferably one employing vacuum tubes.

Pulses received by bus-bars E represent marking and spacing signals characteristic of telegraphy. As already stated hereinabove, these pulses are composed of a plurality of frequencies constituting a band, and it will be clearly understood that these frequencies may be on either side of the carrier produced by the oscillator O. The band filter F may be of the same general type as filter F freely transmitting the component freqnencies lying between the same redetermined limits as those of filter F an substantially suppressing all other frequencies.

The output of the filter F is impressed, through a potentiometer Pkupon a. vacuum tube system including a three-element vacuum tube V The potentiometer is employed for the purpose of controlling the magnitude of the voltage of the current to be impressed upon the input circuit of vacuum tube V The output circuit of vacuum tube V is coupled by means of a transformer T to the input circuit of another vacuum tube system including a three-element vacuum vtube V employed as a rectifying element.

While the vacuum tube V is employed herein merely for the purpose of amplifying the band of frequencies transmitted by filter F through potentiometer P, it will be understood that any other amplifying device or means may equally well be employed instead thereof, within the scope of this invention. Moreover, if the current transmitted by filter F through potentiometer P has considerable energy, the vacuum tube amplifying system may perhaps be omitted, in which event the potentiometer P may be terminated by the primary winding of transformer T The grid electrode of vacuum tube V is maintained suitably negative with respect to its filament electrode. The plate electrode is connected to the filament electrode through a condenser C of large capacity in order that alternating current components in the output circuit of the vacuum tube maybe freely shunted thereby and so that the variations in the amplitude of the current flowing through winding W of relay R may be reduced to a minimum. The direct current relay R hasthree coupled windings W Wu and W12, This relay also includes an armature which may vibrate between contacts designated 1 and 2. The axis of rotation of the armature ofthis relay is connected in series with a winding of a sounder R a resistance Z and ground. WVinding W of relay R is connected in series relationship with resistance Z 1, battery B and ground. The plate electrode of vacuum tube V is connected to ground through the primary winding of a transformer T winding W of relay R resistance Z and battery B lVinding VV of relay R is connected in a local circuit with the secondary winding of the transformer T lVinding W1 is permanently connected in a. local circuit with resistance Z and battery B and is employed to normally bias the armature of relay R, against contact 2. It will be understood that a similar biasing effect may be obtained by connecting the armature to a spring, not shown, or by placing the armature nearer one pole than the other, not shown, or by any other means.

a When a pulse of alternating current, such ,as may be produced by oscillator O, is impressed upon the input circuit of vacuum tube V the positive half of each of the various cycles in the pulse will be etfective in 5 substantially diminishing the negativity of the grid electrode with respect to the filament electrode, so that substantial current may tlow from battery B through resistance Z winding lV the primary winding of transformer T and the plate and filament electrodes of vacuum tube V and ground. During the negative half of each of the various cycles, however, the negativity of the grid electrode will be substantially increased so that the impedance to the flow of current from battery B through the circuit ust described will be. greatly increased, and practically no current will then flow throughv the plate circuit of vacuum tube V There will be a current flow through winding W however, because a charging current will flow from battery B into condenser C Accordingly, the armature of relay R will move toward contact 1 a short time after the beginning of the pulse and will remain on contact 1 until a short time after the end of the pulse, when it will return to contact 2, under the influence of current through winding VV Reference character T designates a socalled kick transformer. Since the secondary winding of this transformer is serially connected with winding W of'relay R this transformer tends to further couple windings l/V and W Accordingly, when current increasing at a rapid rate, as at the beginning of a pulse, flows through winding W and the primary winding of transformer T the transformer will act to build up a substantial electromagnetic effect about winding 7 to cause the armature of relay It to move to contact 1 more quickly. On the other hand, at the termination of an alternating current or pulse, this transformer will tend to set up a current in its secondary which will cause winding 7 to assist winding l/V in retracting the armature of relay R In effect, then, this transformer causes the direct current relay R to becomemore accurately responsive to thecurrent transmitted to the input circuit of vacuum tube V It is apparent that the rectifying system shown in Fig. 1 rectifies only one-half of each alternating current wave. During the positive half of each cycle, current will be rectified, and during the negative half of each cycle, there will be no rectification. With currents of exceedingly low frequencies, this will cause distortion, as will be apparent from the description hereinafter following. To overcome this distortion, it is necessary to provide a receiving system which is suitable for rectifying both halves of each cycle.

A full-wave rectifying system is shown 1n bus-bars E Fig. 2, and this system may be employed to replace the one shown in Fig. 1 which 1s connected to the bus-bars E In Fig. 2, the reference character L designates the pair of conductors connected to the The band filter F potentiometer P and vacuum tube V may be similar in all respects to those elements shown in Fig. 1 anddesignated by the same reference characters.

The output circuit of vacuum tube V is coupled, through transformer T to the input circuits of two three-clement vacuum tubes V and V employed to act as rectifying devices. The grid electrodes of these devices are maintained at suitable negative potentials with respect to the corresponding filament electrodes by means of a common battery B this battery being connected to the grid electrodes through the upper. and lower halves of the secondary winding of transformer T The plate electrodes of these devices are tied together, and, as such, are connected to the corresponding filament electrodes through a stabilizing condenser G which is of comparatively large capacity. Battery B is grounded at its negative terminal and its positive terminal is connected to the plate electrodes of devices V and V through a resistance Z winding VV of relay R and the primary winding of transformer T Winding W of relay R is connected in series with another resistance Z battery B and ground.

A line which is suitable for transmitting direct current pulses characteristic of telegraphy is designated L and this line is directly connected to the axis of rotation of the armature of relay R The contacts 1 and 2, between which the armature of relay R may vibrate, are serially connected with resistances Z and Z and batteries B and B respectively, the point common to these batteries being grounded; WVhen the armature of relay R closes contact 1, current flows from battery B through resistance Z and over lineL Later, when this armature closes Contact 2, current flows from battery B through resistance Z and also over line impede the electronic emissions between the corresponding plate and filament electrodes. Accordingly, no current, or a practically negligible current, will be derived from battery B I The armatureof relay R will be held against contact 2 by the current flowing from battery 13 through resistance Z and winding W and current will flow from battery B over line L Moreover, condenser (1 will become charged to the voltage of battery B10.

When a pulse of alternating current of the proper frequency is impressed upon line L or, in general, when current of any frequency or frequencies between the predetermined limits of filter F are transmitted over the line L,,, that current will be impressed upon the input circuit of vacuum tube V through potentiometer P and the potentiometer may be manipulated to adjust the voltage of the impressed current. Vacuum tube V will amplify the transmitted current and impress that current through transformer T upon the input circuits of the three-element rectifying devices V3 and V During the positive half of each alternating current cycle, the grid electrode of one of the vacuum tubes, for example, V will be rendered less negative with respect to its filament electrode, while the grid electrode of the other of the vacuum tubes V; will be rendered more negative with respect to its fila-v ment electrode. Accordingly, direct current will flow from battery B over the circuit which includes resistance Z winding W1 of relay R primary winding of transformer T the plate and filament electrodes of vacuum tube V, and ground. Since the grid electrode of the vacuumtube V is rendered more negative with respect to its filament electrode, practically no current will flow in the circuit which includes the plate and filament electrodes of that tube.

During the negative half of each alternating current cycle, the voltages impressed upon the in ut circuits of vacuum tubes V and V, will e in the opposite direction, and therefore the grid electrode of vacuum tube V will be rendered more negative with respect to its filament electrode than is normally the case, and the grid electrode of vacuum tube V, will be rendered less negative with respect to its filament electrode. Consequently, direct current will flow from battery B through the circuit which includes resistance Z15, Winding W 11 of relay R the primary winding of transformer T the plate and filament electrodes of vacuum tube V, and ground. Since the grid electrode of vacuum tube V is rendered highly negative with respect to its filament electrode, practically no current will flow in the circuit which includes the plate and filament electrodes of the latter tube.

It is to be particularly noted that during the impression of current of proper frequency upon the grid electrodes of the rectifying devices v and V pulsating current flows through the winding W of relay R and that this current is uni-directional. Thus, during the positive half cycle of each alternatin current, current flows through the plate nlamentcircuit of vacuum tube V and during the negative half ofeach cycle throu h the plate filament circuit of vacuum tube '5 Shortly after the beginning of an alternating current pulse, the current through winding W is substantially greater than the continuous current through winding W and therefore the armature of relay R is moved away from contact 2 and toward contact 1. After contact 1 is closed, current will flow from battery B through resistance Z and over line L.,. Likewise, shortly after the end of an alternatin current pulse, the current through windin 11 will be reduced to zero and therefore t e armature of relay R is moved away from contact 2 toward contact 1 under the influence of current through windin W After contact 2 is closed, current wi a ain flow from battery B through resistance and over line L The action of condensers C as well as that of kick transformer T tends to stabilize the current through winding W and to prevent the current from falling to zero when the current which is impressed upon the grid electrodes of devices V and V, passes through a zero value.

When no current is impressed upon the grid electrodes of vacuum tubes V3 and V condenser C is charged to the voltage of battery B However, when proper current is impressed upon the grid electrodes of vacuum tubes V8 and V current will flow through a circuit which includes the plate and filament electrodes of one of these tubes, for example, the plate and filament electrodes of vacuum tube V whereupon condenser C will partly discharge through a local circuit which includes the plate and filament electrodes of vacuum tube V The discharge of condenser C will be a maximum when the impressed wave reaches the point of maximum amplitude in its cycle. Thereafter,

condenser C will become almost fully recharged to the voltage of batttery B It will be apparent that when current flows through the plate and filament electrodes of the other vacuum tube, i. e., tube V,, condenser 0 will again partly discharge in a local circuit which includes the plate and filament electrodes of tube V the discharge reaching its maximum value at a point in the cycle where the current is a maximum, this condenser thereafter becoming recharged to the voltage of battery B As in the case of the half-wave rectifying circuit described hereinabove, the kick transformer T accelerates the movement of the armature of relay R from contact 2 to contact 1 at the beginning of a pulse, and accelerates the movement of the armature back to contact 2 at the end of a pulse.

Fig. 3 shows line L connected to bus-bars E Band filters F and F are connected in parallel to bus-bars E each of these filters freely transmitting current of a definite frequency oraband having predetermined limits.

The filter F may, for example, transmit currents having frequencies between zero and 170 cycles, and filter F may transmit other currents having frequencies between the limits of 170 and 340 cycles. These currents are transmitted through potentiometers P and P transformers T and T threeelectrode amplifying devices V and V transformers T and T to the input circuits of the three-electrode vacuum tube rectifying devices V and V and V and V respectively.

Battery B is employed for heating the filament electrodes of all of the vacuum tubes just referred to, this battery being connected in a circuit which includes resistance Z resistances Z and Z and the filament electrodes of vacuum tubes V and V in parallel, the filament electrodes of Vacuum tubes V7 and V 8 in parallel, resistance Z the filament electrodesof vacuum tubes V and V in parallel and ground. The current which flows through resistances Z and Z causes the production of voltages suflicient to render the grid electrodes of vacuum tubes V and V suitably negative with respect to the filament electrodes of the respective tubes.

Battery B is connected in parallel to the primary windings of transformers T and T and with the plate electrodes of vacuum tubes V and V this battery providing the proper operating positive potential for these plate electrodes. A battery B is connected through a resistance Z and the secondary windings of transformer T to the grid electrodes of vacuum tubes V and V Part of the voltage of battery B is applied through resistance Z and the secondary windings of transformer T to the grid electrodes of vacuum tubes V and V It is to be noted that only part of the voltage of battery B is necessary to properly render the grid electrodes of vacuum tubes V and V negative with respect to the corresponding filament electrodes because the filament electrodes of vacuum tubes V and V are at comparatively higher potentials than the filament electrodes of vacuum tubes V and V Battery B is connected to the plate electrodes of vacuum tubes V and V through winding W of relay R the primary winding of. transformer T and a meter M and resistance Z in parallel. A battery B is connected to the plate electrodes of vacuum tubes V and V through winding W of relay R the primary winding of transformer T and meter M and resistance Z in parallel. The battery B supplies continuous current to windings \V and W of relays R and R respectively, through resistances Z and Z in parallel and ground. Condenser C is connected between the plate electrodes of vacuum tubes V and V and the corresponding filament electrodes, and a condenser C is connected between the plate elec paths provided by the arrangement of Fig- 3 are each similar in many respects to the receiving path shown in Fig. 2 and each dperates in a similar manner. Further description of the arrangements of Fig. 3 seems unnecessary.

Fig. 4a shoWs a progression of signal pulses over a circuit of the type shown in Fig. 1. The marking and spacing pulses correspond to those produced by key-K in modulating the current flowing from batteries B and B The modulated carrier represents the Wave produced by oscillator O. For simplicity in explanation, it is to be noted that the changes from a marking signalto a spacing signal are assumed in this figure to occur exactly at the time when the carrier passes through zero. It is to be further noted in this and in Figs. 4b, 4c, 4d, 46 and 4 that no account is taken of the effect of filters, etc., in changing the envelope of the modulated carrier.

While these effects are present, their introduction into Fig. 4 would complicate the exfplanations of half-wave and full-wave recti cation. The reduction in distortion by using full-wave rectification rather than half-Wave rectification, will still be obtained, however, even though the envelo e of the modulated carrier may be changed y the filter and line networks between the oscillator at the transmitting station, and the rectifiers at the receiving station. It will also be apparent in this figure that the stabilizing effect of condensers C C and C shown in Figs. '1, 2 and 3, are not shown for simplicity. In Fig. 4a, only one-half of the received wave is rectified, and the received signal is almost a duplicate of the transmitted signal. It is to be understood that the carrier wave has a frequency somewhat higher than contemplated for the arrangements shown in Figs. 2 and 3, and still it seems that each received marking pulse is somewhat shorter than the corresponding marking pulse transmitted to theextent of one-half of an alternating current cycle. I

Fig. 4b shows the corresponding progression when the changes from marking to spacing and back again to spacing occur exactly at the point where the carrier passes through its maximum value. Here, the received signal, though derived from a halfwave rectifier, more closely resembles the transmitted signal. It is to be noted from Figs. eta and 4?) that in the general case where the carrier pulse does not necessarily begin nor end at the zero or the maximum point in a particular cycle, it is possible to have the received signal shorter than the transmitted signal by as much as one-half cycle of carrier current for each marking pulse due to the employment of half wave rectification.

Since'the carrier frequency may be considered high with respect to the signal dot frequency in Figs. 4a and 4?), (one ratio may be 425 cycles to 24 dots), the marking slgnal at the receiving end is shortened only an inappreciable amount and the distortion is not very great.

If half-wave rectification is employed and the signals are modulated on a carrier wave of considerably lower frequency, then the progression of signal pulses is shown in Fig. dc. Here changes from a spacing signal to a marking signal and back again to a spacing signal are shown for illustration to occur exactly as the carrier passes through zero. In Fig. 4d, a similar progression of pulses is shown, but in this case the changes from a marking signal to a spacing signal, and so on, are selected to occur exactly as the carrier passes through its maximum value. In the case shown by Fig. 4d, the received signal wave is not shortened nor distorted very much, whereas in the arrangement having the characteristics shown by Fig. 40 the received signal wave is considerably shorter than the transmitted signal. From these illustrations,

it will be apparent in the general case that the likelihood of obtaining a large distortion, as is disclosed in Fig. 4c, is as great as the likelihood of obtaining only a small or inappreeiable distortion, as is shown in Fig. 4d and the most probable value may still be objectionably large.

To overcome the eiiects tending to produce distortion, as is illustrated by Figs. 4c and 4d, a full-wave rectification circuit is necessary, and such a rectification circuit is shown in Figs. 2 and 3. It will be apparent that a fullwave rectification circuit will not introduce the distortion resulting from the loss of part of a cycle of the carrier during rectification. The advantages of full-wave rectification are shown by the curves of Figs. 4c and 4 During rectification, both the positive and negative halves of each cycle are acted upon with the result that a pulsating current is produced which changes from zero to a maximum and back again to zero throughout each halfcycle in the alternating current pulse. When the stabilizing condensers are connected, as shown, the magnitude of the pulsations are considerably reduced, with the result that a fairly constant rectified current flows through the corresponding winding of relay B Inasmuch as time is required to overcome the biasing current of each receiving relay, it will be apparent that the received signal, as produced by the receiving relay, begins somewhat after the beginning of the transmitted signal and ends a corresponding interval of time after the end of the transmitted signal.

While this invention has been disclosed in certain particular embodiments, merely for the purpose of illustration, it will be under stood that the general principles of this invention maybe disclosed in other and widely varied organizations without departing from the spirit of the invention and the scopeof the appended claims.

WVhat is claimed is:

1. An arrangement for operating a direct current relay when current is present having a frequency lying within the limits of a predetermined band, comprising a pair of vacuum tube rectifying elements the plate,

electrodes of which are directly tied together and the filament electrodes of which are similarly tied together, and a source of elec troinotive force, said source of electromotive force being connected in a series circuit between a point common to said plate electrodes and a point common to said filament electrodes, said series circuit including the winding of the direct current relay.

2. A full Wave rectifying system for receiving signals transmitted as alternating current pulses, including two three-element vacuum tube rectifiers, means to bias the grid electrodes of said rectifiers negatively with respect to the corresponding filament electrodes, means for alternately operating said rectifiers during each transmitted pulse of alternating current, and a relay the winding of which is connected between a point common to both plate electrodes of said rectifiers and a point common to the corresponding filament electrodes and through which current may continuously flow unidirectionally as obtained alternately from'the rectifiers.

'3. In a carrier telegraph system, the combination of two rectifier-s each having an electron discharge path, said paths being arranged in parallel relationship, an electromagnetic winding, means for coupling said rectifiers with said winding, and means for alternately and periodically establishing electronic discharges in said paths in order to continuously transmit current unidirectionally through said winding.

4;. In a carrier telegraph system in which pulses of alternating current represent signals. the combination of two electron dis,-

charge circuits in parallel relationship, a

direct current relay, a source of direct current potentlal connected to said circuits through the winding of said direct current tinuously with unidirectional current during the impression of each pulse of alternating current.

5. The combination of two electron discharge paths, a condenser of large capacity,

an electro-magnetic winding connected in series with said condenser,'means for coupling said discharge paths in parallel relationship with said condenser, and means for alternately energizing said discharge paths in order to continuously energize the electromagnetic winding.

6. The combination of two vacuum tube rectifying devices each including a plate electrode and a filament electrode, the plate electrodes being tied together, and the filament electrodes being similarly tied together, a relay, a source of direct current potential connected between both filament electrodes and both plate electrodes through the winding of said relay, and a condenser of large capacity connected between both filament electrodes and both plate electrodes.

7. In a carrier telegraph system in which pulses of alternating current represent signals, the combination of a direct current relay, two space discharge paths, said paths being connected in parallel with each other and in series with the winding of said relay, means to alternately provide electronic discharges through said paths continuously during the impression of each pulse of alternating current, and means for continuously energizing the winding of said relay in accordance with the integrated effect provided by the discharges through said paths.

8. In a carrier telegraph system, the combination of a source of current having a frequency which-may vary between the limits of a band of definite width, two thermionic devices, means whereby said devices may alternately respond to and rectify the current of said source, an element coupled to said thermionic devices and supplied with unidirectional current derived alternately from said thermionic devices, and means for rendering the current flow throughsaid element substantially constant.

9. The combination of two thermionic devices, means to alternately and periodically operate said devices as rectifiers, an element coupled to said devices and continuously supplied with unidirectional current as a result of rectification, and a condenser of large capacity the electrical charge of which varies so as to equalize the flow of current through said element.

10. In a carrier telegraph system, means for producing pulses of alternating current in accordance with signals, means for independently and alternately rectifying the opposite halves of each alternating current cycle, and a direct current relay coupled to the rectifying means and continuously energized during each pulse by the current derived from said rectifying means.

11. In a carrier telegraph system, means for producing pulses of alternating current corresponding to signals, a full-wave rectifier for completely rectifying each alternating current cycle, a direct current relay continuously operated by the rectified current throughout the duration of each pulse, and

mgans forstabilizing the operation of said re ay.

12. In a telegraph system, the method of signaling with a very low frequency wave. which consists in producing a pulse of low frequency current in accordance with a marking signal and omitting such a pulse in accordance with a spacing signal, independently rectifying the positive and negative halves of each transmitted cycle, and combining the independently rectified currents so as to form a continuous current.

13. The method of signaling, which consists in generating a very low frequency wave, independently and alternately rectifying opposite halves of each cycle, and integrating the rectified waves so as to form a unidirectional wave of substantial amplitude.

In testimony whereof, I have signed my name to this specification this 18th day of March, 1929.

FRED J. SINGER.

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