US2135171A - Wave demodulating means - Google Patents

Description

H. CHIREIX WAVE DEMODULAT ING MEANS Filed Feb. l2, 1955 5 Sheets-Sheet l l Eg Il 4400044 750 WAVE /0 l afrfcrof? R m oE Mm T mm Nv NHOR EC O w ...n l In A N E H7 Y B lNOV. 1, 1938. H, CHlRElX 2,135,171

WAVE DEMODULATING MEANS Filed Feb. -12, 1935 3 sheets-sheet 25 INVENTOR HEHI CHIBEIX BY? am .l E

ATTORNEY WAVE DEMODULATING MEANS Filed Feb. l2, 1935 5 Sheets-Sheet 5 l El:g 6

INVENTOR HENRI CHIREIX ATTORNEY Patented Nov. 1, 19138 PATE 2,135,171 WAVE DEMODULATTNG MEANS Henri Chireix, Paris, France, assigner to Compagnie Generale de Telegraphie Sans Fil, a corporation of France Application February 12, 1935, Serial No. 6,137 In France February 15, 1934 6 Claims.

The present invention consists in novel devices adapted to be used in signal reception which in addition are suited to insure a system of secret transmission useful for communications over telephone wires or cables, telegraphy through ground, and telegraphy by Hertzian waves.

Independently of-the usual means consisting in the use of a code, secrecy is assured according to the present invention by the particular method of transmission and reception.

It is known that one of the most widely used signalling methods consists in the transmission of musical or tonal, audio frequency currents, these currents being interrupted or chopped by a key in accordance with a certain code, say, the Morse code.

It is also known that it is possible to key by causing a current known as the working current to iiow on a certain frequency, and another current known as the rest or spacing current to iiow on another frequency.

It is also known that it is possible to combine in one and the same frequency the working and the spacing transmissions by causing by the key certain variations of phase in the modulator current.

The invention is concerned with this latter mode of signalling, and it discloses new means of receiving signals transmitted in this way.

As a matter of fact, according to the prior art it has been necessary to provide at the receiving station a current being absolutely in synchronism with the outgoing current so as to bring out and make noticeable the variations in phase. Indeed, the maintenance of synchronism necessitated the transmission of synchronizing signals, and this is liable to involve serious inconvenience from the viewpoint of synchronism and of insuring secrecy of the method that is employed.

Now, the present invention dispenses with the necessity of strict synchronism and therefore of the sending of synchronizing signals or the continuation of transmission outside the actual operating periods.

It discloses more particularly two practical embodiments, these two embodiments being predicated upon the use of one and the same basic invention which is as follows:

The transmission of current being insured by means of a current generated by the aid of a tuning fork, for instance, and suitably amplified, this current, at the receiving end, is caused to beat with polyphase currents produced, for instance, by another tuning fork and, according to wellknown methods of heterodyne reception, the said (Cl. Z50-8) receiving tuning fork vibrates with very close approximation at the same frequency (say, within one-thousandth). What results beyond the detectors is a polyphase current having the very low frequency of the beat. With polyphase current there is produced a rotating field by ways and means generally known in the art.

This eld will turn in either sense according to the sense of the asynchronism, or else will not rotate at all during the intervals of time where isochronism is attained.

Keying is effected by means of Variations of phase, that is to say, by advancing an angle 9 to characterize a working transmission and retarding it a similar angle for spacing.

The rotating field just referred to will be shifted forward or caused to la-g the same angle no matter what the position of its axes at the instant in question. For a working transmission or signalling it may turn, for instance, in the sense of the clock, while for spacing it will turn anticlockwise.

'I'hese rotations are used for decoding the transmitted text by means of one from among two arrangements hereinafter described by way of example. In describing these arrangements reference will be made to the drawings in which Figures 1 and 2 are circuit diagrams including the essential elements of my phase rotation analyzing circuits, While Figures 3, 4, 5 and 6 show details of recording or indicating devices which may be used to record or indicate the output of Figure 2.

l and 2 represent in Fig. 1 the tubes of a twin symmetric or push-pull system.. Each system may comprise two triodes or tubes of a more improved type comprising, for instance, tubes having two control grids. For the sake of simplicity there is shown for each system one tube equivalent to two separate triodes. The four grids are biased at the initiation of the plate current by the source 3 and excited in parallel by the modulation to be received by means of transformer They are moreover excited by pairs in opposition by the twol phases of a two-phase alternator 5 whose frequency is very closely the same as the frequency of the currents to be received'. There is thus insured detection by virtue of the lower knee in the plate characteristic. 50

rEhe circuits of the plates are 'constituted by the resistances E being preferably equal and shunted by condensers l and inserted between the anodes and the high-Voltage source connected at 8. The plates are moreover connected with the four deflector plates 9 of a cathode-ray tube. The part and purpose of the condensers l being to short-circuit the alternating current components of high frequencies of the plate current, there is obtained between the two deecting plates of a system of plates an electrostatic alternating eld of Very low frequency due to the beats between the modulation to be received and the local generator. The cathode pencil subjected to two alternating elds of this kind will thus turn very slowly, and the spot upon the fluorescent screen will describe, for instance, very slowly a circle if the amplitudes are alike. Indeed, if isochronism is present or attained during a more or less long period the spot will be reduced to a fixed point upon this circle, and the spot will be shifted in one sense or the other as soon as isochronism ceases. If the currents received by the transformer i are modulated in phase as has been stated, the modulation being translated in a phase displacement of 20, then the spot will shift very rapidly, for instance, the clockwise sense at the instant a signal is sent and will return in the opposite sense at the instant spacing begins. Owing to the visual persistence of the retina, keying will be seen in the form of lines of like lengths, but succeeding one another at unequal intervals according to whether short dots or long dashes are involved.

It will be noted that if the transmitter is stopped the spot naturally will come to be located in the center of the screen. From the instant of start, with the vkey in the beginning being blocked for spacing, the spot will appear at any point at all of the circle and at the rst signal it will describe in a predetermined sense a rotation 29.

Hence, there exists no ambiguity, and the reading of the message may begin at once.

The second embodiment here disclosed involves a receiver apparatus which is more practical in actual use and allows of actuating a relay so as to be able to record the transmitted text in the usual way. There is employed a specialrelay conceived in a way as indicated in Fig. 3 and fed from an electromagnetic rotating eld as soon as a state of asynchronism is established. This rotating field could be produced in accordance with the scheme shown in Fig. 2V where 5 represents a local two-phaseY generator comprising phases a and b, lll detectors of the copper oxide type, for instance; Il resistances, Ma and lllb windings wound V-fashion, for instance, corresponding to the phases a and b resulting in the rotary field, l5 capacities shunting these windings, and finally the source'of modulated waves connected with the input terminals. It will be seen that a detector element such as l!! is Vsubject to the potential resulting from a phase of the local generator 5 and the reception. One of the windings, for instance Ma, will thus be traversed by a maximum current of definite direction when the incoming energy has the phase of a while the current will b-e of Zerovalue when the phases are in quadrature since the potentials are then geometrically equal at the terminals of the two detectors in the phase. The current inV lila will then again be of maximum value, but will be opposite in direction compared with the preceding one, when there lis phase opposition between the incoming energy and phase a.

Hence, the current in 14a Varies in accordance with a sine law, according to the phase of the incoming energy compared with the phase a. The same situation holds true regarding the curat 2t).

rent in llb except that the current will beef zero value in Elib when it is at its crest value in Ma because of the fact that the law of variation is here of sinuous form shifted an angle of degrees because the incoming energy is combined here with the phase b being in quadrature with the phase a. The currents in Ma and Mb are therefore endowed with all of the qualities required ,to feed a rotating field system such as the relay which is represented in Figs. 3, 4, and 5 as shall hereinafter be described. 'I'hese figures are: Fig. 3 a perspective view, Fig. 4 a plan View, and Fig. 5 a section taken on line A-B.

Referring to the drawings, l denotes the windings Ma and Mb connected V-fashion of the rotating eld system, Fig. 2. These windings are accommodated in the slots of a rotor l2, the current being fed by way of rings I3.

The rotor turns in the interior of a stator constituted by two sets of curved magnets I6 having polarities of the same nature N and S placed opposite each other, and pole pieces such as indicated at il forming between themselves an airgap.

In the air-gap of these pole-pieces is disposed a magnetized needle i3 presenting poles such as 11. and s. This needle is pivoted directly at I9 on the peak of the rotor l2, it constitutes the keeper of a polarized relay; its stroke is limited either way by stops on contacts such as indicated 2l denotes finally regulating springsof the keeper I8 in the air-gaps of pole-pieces l'l. The assembly is mounted on the frame such as 22. The operation of the system is as follows:

Assoon as a transmission takes place, a field is set up in the windings I4 and the rotor l2 will become oriented in such a way that there will be coincidence between the line of the poles of the rotor and the line of the poles of the magnets i6. When the position of equilibrium has been reached, the needle I8 is positioned on a line of symmetry of the flux. As long as the state 0f isochronism is maintained the rotor will not move; but as soon as `the said state ceases to exist the rotor will turn slowly in either sense. If keying then takes` place by virtue of variation of the phase by an amount i0 compared with the mean phase the rotor will not be driven because of its high (relative) inertia, but the far lighter needle will respond to the keying.

From the instantaneous viewpoint, as a matter of fact, the rotor field will be phase-displaced by i0 degrees. Under these conditions the ux of the rotor will be closed by the magnets Il by traversing the air-gaps formed between the polepieces il and the needle I8 will be shifted under the action of this uX.Y

' It could also be said that the instantaneous displacement of the eld creates in the opposite pole-pieces Il supplementary poles n and s, or s and n which destroy the symmetry of the lines of force. It is evident that if the keying is irregular the line of the poles n and s will not be positioned exactly in the center of the arc amounting to 26;but this is immaterial, in fact, one could'even stay on a continuous dash or a space provided that the angle 0 is not chosen too large (0 90 degrees). VIf, for instance, there is chosen 26:;-90 degrees and'stayng'on space, the instantaneous torque will be of maximum value at the instant work is started, because the polar line will then be caused to turn suddenly an angle of 90 degrees, and since the entire flux of the rotor will become closed in the air-gaps of the pole'pieces l1, If one keys thereafter in a regular manner, the rotor will be displaced 45 degrees approximately and present a position as indicated in Fig. 4. If the state. of isochronism is not exact, the rotor will be shifted more accord.- ing to the slip frequency which, however, is always very small. It will be understood that it is desirable to make the rotor relatively heavy in -order that it may not be driven along. The

springs 2l, 2l, moreover should be so regulated in order that in the absence of transmission the needle may be in equilibrium (unstable) in the air-gaps of the pole-pieces I'I.`

It will evidently be possible to have recourse to the contacts of the relays to Operate a recorder with, tape or simply for closing the circuit of a telephone fed from the local oscillator. In this latter instance there is thus preserved the advantage of reception by ear.

It will be noticed that the circuit arrangements hereinbefore disclosed are directly useful with high frequency and may be employed under particularly favorable conditions in telegraphic communication on long waves. It is Very likely, indeed, that by the aid of tuning forks frequencies that are stable to within $409,000 may be obtained, in other words, that on waves greater than 3000 meters it is possible to insure an asynchronism whose frequency will not be over two beats each second. By using circuit arrangements as hereinbefore disclosed together with apparatus of a kind as described, it will be feasible to handle traflic under conditions far better than under present day conditions. As a matter of fact, it is well known that from the viewpoint of disturbances, atmospherics and jamming, keying and signalling predicated upon phase shifting insures a maximum degree of immunity.

Although in the exemplified embodiments hereinbefore illustrated recourse is had to twophase fields, it is evident that the invention is equally applicable to any other multiphase fields.

It will be evident, on the other hand, that other dispositions predicated upon the same basic idea could be considered. More particularly speaking, in the second solution it could be conceived that the light needle designed to respond to and follow the keying is subjected to a turning field independent of the former, though connected with it mechanically.

For instance, the rotor could be made heavier and the stator could be divided into two parts, one constituted by magnets such as I whose purpose, as above pointed out, is to orientate the rotor flux, and another consisting of non-magnetized magnetic pieces supporting the poles I1 and designed to collect the flux of the rotor when the lines of the poles are displaced under the action of keying. This arrangement has the advantage over the preceding one of shifting the mobile needle i3 in an air-gap not permanently magnetized.

This modification is illustrated in Fig. 6. The rotor I2 of the relay comprises slots or grooves in which are placed windings I4 of the rotary-field system, the current being fed by way of the rings I3.

Upon the casing 22 of the stator are mounted, on the one hand, the magneticpieces I'I, and these are of the same form as the pieces IS-II in Figs. 3 to 5. They enclose between themselves an interferric space in which is mounted a needle or pointer I8 pivotal on the end I9 of the rotor. The latter is sufficiently heavy so that its flux will embrace the pieces I6 and I1. The mechanism of the contacts. between which the'needle moves is the same as in Figs. 3 to. 5.

I claim:

l. In al system for demodulating a carrier wave modulated in phase, meansL for producing two 5 phase displaced waves, a pair of rectiiiers, circuits for applying saidy phase displaced waves separately to said rectii-'lei-s, a circuit havingtwo reactive branches connected with said rectifying means for producing a rotary field, an indicator 10 responsive to said rotary field, and a circuit for` applying said carrier wave to be demodulatecl to said reactive branches.

2. In a system for demodulfating a carrier wave the phase of which is altered at signal frequency, l5 a pair of thermionic systems each having a cathode, and a pair of control grids, symmetrically arranged relative to said cathode and a pair of anodes, a source of alternating current, a phase displacing circuit connecting said source to the control grids in both of said thermionic devices,

a circuit for applying said modulated waves in phase to the control grids of each thermionic system, the phase of the modulations applied to the control grids of the different devices being different, means energized by the anode currents of said thermionic system for producing a rotary field, and an indicating device connected with the anodes of said thermionic systems and responsive to said rotary field.

3. In a system for demodulating a carrier wave the phase of which is altered at signal frequency, a pair of thermionic systems each having symmetrical control grids, a cathode and symmetrical anodes, a source of alternating current, a phase displacing device connected with said source to derive therefrom waves of displaced phase relation, a circuit connected with said device foi` applying waves of one phase to the control grids in one of said thermionic devices, a second circuit connected to said device for applying waves of a different phase to the control grids in the other of said thermionic systems, a circuit for applying modulated waves in phase to the control grids of each thermionic system the phase of the modulations applied to the control grids of the different thermionic Isystems being diiferent, means energized by the anode currents of said thermionic systems for producing a rotary field, and an indicating device connected with the anodes of said thermionic systems, kand responsive to said rotary field.

4. In a system for demodulating a carrier Wave the phase of which is altered at signal frequency, a pair of thermionic tubes each having a pair of symmetrical control grids, a cathode and a pair of symmetrical anodes, a source of a frequency of the order of the frequency of the carrier wave, phase displacing circuits connected with said source to derive therefrom waves of displaced phase relation, a circuit connected with said phase displacing circuit for applying waves of one phase in phase opposition to the control grids in one of said thermionic tubes, a circuit for applying waves of a different phase in phase opposition to the control grids in the other of said thermionic tubes, a circuit for applying modulated waves in phase to the control grids of each tube the phase of the modulations applied to the control grids of the different tubes being diiferent, impedances connecting the anodes of each tube in push-pull relation, means comprising connections between said impedances for producing a rotary eld, and an indicating device connected with the anodes of said tubes, and responsive to said rotary field.

5. A communication method in which the signals transmitted are represented by an alter- `nating current Whose phase is varied in accordance with the message which includes the steps of, beating said alternating current with locally generated multi-phase alternating current of substantially the same frequency as said phase 1r, Varied current to produce a multi-phase alternating current the phases of which are of substantially the same beat frequency, producing by means of said last named multi-phase alternating current a rotary field, and utilizing said rotary field to actuate indicating means.

6. In a system for producing indications of phase modulations on alternating current Waves, a source of multi-phase alternating current of a frequency of the order of the frequency of the phase modulated current,'means for combining said phase modulated current with said multiphase current to produce beat notes which are characteristic of the phase Variations on said rst named alternating current, a cathode ray tube having a plurality of pairs of deflecting plates adjacent the path of its ray, and means for impressing each of said produced beat notes on a diierent pair of said plates.

HENRI CHIREIX.

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