US2080082A - Commutating balanced multiplex telephony - Google Patents

Commutating balanced multiplex telephony Download PDF

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US2080082A
US2080082A US757580A US75758034A US2080082A US 2080082 A US2080082 A US 2080082A US 757580 A US757580 A US 757580A US 75758034 A US75758034 A US 75758034A US 2080082 A US2080082 A US 2080082A
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tubes
circuit
frequency
subscribers
tube
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Loth William Arthur
Givelet Joseph Armand
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00—Secret communication
    • H04K1/02—Secret communication by adding a second signal to make the desired signal unintelligible

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  • the present invention concerns improvements in and relating to this system so as to permit on the one hand its practical application and on the other torender telephony (ortelegraphy) secret.
  • the external windings of the plate and grid transformers. are connected in series with the line leading. from: the subscriber.
  • the separation of the conversations is improved by placing complementary rectifiers, preferably of the copper oxide type, at suitable points in the circuits, and the high resistance connected to the neutral point. is. replaced by rectifiers or valves which have a definite finite resistance in one direction and. an. infinite resistance in. the other direction. For currents in the latter direction, the conversation which is not to be heard is completely suppressed.
  • a simplification consists in using a singletransformer for each subscribers line, the said. transformer having three windings, one for the subscriher, one for the plate and one for the grid.
  • An electrostatic screen is provided between the winding of the subscriber and the other windto prevent the high frequency from passing to the subscriber and to thus eliminate all interference from that source.
  • the dead intervals of interruption or commutation are filled with a low audio frequency designed to produce garbling, the receiving apparatus being arranged to allow only the conversations to'pass and to block the interfering garbling frequency.
  • the interferingfrequency or garbling should be: preferably different from that of the voice. It should be suificiently low so as not to interfere with the normal operation of the system and if it produces a background noise by spreading over into the conversation intervals, this will be eliminated or greatly moderated by a filter or an anti-resonant circuit which allows the voice frequencies to pass but blocks the garbling frequency.
  • Av tunable oscillating circuit can also be used at each station, comprising a variable inductance coil and a variable capacity to tune this circuit to the frequency of the commutating heterodyne.
  • the above mentioned resistance device could be thus omitted.
  • Fig. 1 shows a telephone line according to our invention connected simultaneously with two subscribers stations at each terminus.
  • Fig. 2 shows a modification of the circuit with one tube connected to copper oxide rectifiers.
  • Fig. 3 shows a modification employing transformers with three windings.
  • Fig; 4 shows an application of the combined circuits to obtain an additional channel.
  • Fig. 5 shows a secrecy system with an interpolated garbling frequency using a garbling frequency source at one station and a filter at the other station to eliminate the background noise, filling one cyclic group of intervals with a garbling frequency.
  • Fig. 6 shows an arrangement with tuned oscil- Eating circuits and plug connecting blocks.
  • the output of heterodyne oscillator l is inductively coupled by a winding 2 to a tapped secondary winding having two parts 3, 4, with symmetrical tap point 5.
  • Rheostats 6 and 6 permit the adjustment so that tap point- 5 is truly neutral or at zero potential.
  • To this tap point 5 are connected the filaments of tubes 1 and 8, which are in push-pull.
  • tubes 1 and 8 which are in push-pull.
  • a transformer 9 has one winding which is its plate winding connected to the plate and another transformer if) has one of its windings which is its grid winding connected to the grid of tube '1, and corresponding windings of transformers H and 52 are connected to the plate and grid of tube 8.
  • fhe other or subscribers circuit windings of the transformers 9 and 50 are connected in series to the subscribers line from the subscriber A, and the other or subscribers circuit windings of transformers H and i2 are connected in series to subscribers line B.
  • Each subscriber station has its microphone l3 and I1, its local talking battery l4 and 18, its microphone transformer l5 and I9, and its telephone receivers l6 and 20. The devices for calling, the switches, etc., have not been shown.
  • transformer I5 When the subscriber A speaks into his microphone IS, the secondary winding of transformer I5 delivers the modulation to the two subscribers circuit windings of transformers 9 and Hi.
  • the transformer iii modulates the grid of tube 1' and causes the transmission of speech on the line.
  • the transformer 9 therefore allows the speaker tohear himself speaking, which fact presents no difhculty.
  • and 22 terminate in two tubes 7 and 8' connected in a similar manner and communicating with two respective subscribers stations A and B, but here there is no principal control oscillator at the receiver corresponding to l at the transmitter because it is unnecessary.
  • supplementary rectifiers are connected, preferably of the copper oxide type, at suitable points in the circuit and in the appropriate sense to permit the current to flow in the desired direction.
  • a group of primary rectifiers 23 and 24 connected in parallel with the windings 3 and 4.
  • Rectifiers 25 and 25 are also connected between the plates of tubes 1 and 8 and the line 21 and 22.
  • Other rectifiers 26a and 21a are connected between the tap point 5 and the cathodes of tubes 7 and 8. The same arrangement is provided for the tubes 1' and 8' at the other terminus.
  • a common battery applies a suitable potential to the anodes. As shown in Fig.
  • this common battery 5a is connected to apply to the plates of tubes 7 and 8 a potential negative with respect to their filaments, the negative terminal of the common battery 5a being connected to the mid-point 5 of the transformer secondary winding between its two halves 3 and 4.
  • the voltage of battery 5a is necessarily less than the peak voltage applied to windings 3 and 4 by heterodyne oscillator i.
  • Tubes I and 8 are respectively operative only when their plates are positive, and hence only during that portion of the cycle of the heterodyne oscillator when the instantaneous alternating voltage in windings 3 or 4 exceeds the voltage of battery 5a.
  • neither tube 1 nor 8 is operative at the instant when the potential of heterodyne oscillator l passes through zero, nor for an interval before and after that instant, the length of this inactive interval depending on the voltage of battery 5a. There is therefore an appreciable time interval between cessation of the operation of one tube and the commencement of the operation of the other tube, which fact avoids interference between the outputs of the two tubes.
  • Fig. 2 shows a simplified diagram with the tubes 7, 8 and l, 8, each connected with a rectifier 28, 29 and 28', 29', connected in the desired sense to ensure the blocking of the undesired one of the simultaneous conversations.
  • the described arrangements are also applicable to telegraphy, the microphones being replaced by keys and the receivers by any appropriate telegraphic receiving apparatus.
  • the control heterodyne oscillator l is then not necessarily of an ultra-audible frequency.
  • Fig. 3 shows the connection between the office 0 which has two subscribcrs stations I and III and the office C which has two subscribers stations II and IV.
  • This is a balanced system in which the neutral points are at 30 and 30' and the series of valves or copper oxide rectifiers at 3!, 32, 3!, 32.
  • the transformers 33, 3t, 33, 36' across whose plate windings are shunted a condenser 35, 36, 35, 36', and these transformers also have a third winding connected with the corresponding subscribers station.
  • the assembly is simpler and the required space much less.
  • An electrostatic screen such as a thin metal band, tin foil or similar conducting plate, between the circuit winding of the subscriber and the other windings, is connected with the filament battery and thence with the ground, which screen is not shown. This prevents all passage of high-frequency currents to the subscriber, through capacity coupling between the windings, and therefore suppresses all interference from that source.
  • Fig. 4 the devices are applied to a system of combined balanced circuits D and E, each of which is equipped with our system for multiple transmission as shown in Fig. 1.
  • one-to-one auto-transformers such as 31, 38, 3 38, are connected with respect to one of the talking circuits, the two windings of each of these autotransformers are in series, in such a manner that the ampere-turns are added, and that their selfinductance prevents the mixing of conversations transmitted by each of the. windings.
  • These windings act as choke coils as to the high-frequency currents as well as to the telephone frequency currents circulating in the circuits.
  • each of the wires of the circuit D functions in parallel with the other wire of the same circuit.
  • the two wires of the circuit E which also function as two wires in parallel as to stations F and F.
  • the other subscribers stations connected in multiple as in the arrangement of Fig. 1, are shown at A, B, A, B, and A1, B1, A1, B1, and they are not interfered with by the conversations of F and F because the points of connection respectively of the distributing switchboards 39, 40, 39', 49, with the wires of the circuits D and E, have respectively balancing resistances 4
  • the sources of control oscillations 45, 46 supply the switchboards of the circuits D and E and this can be arranged by having the principal single control oscillator i (Fig. l) to have, in addition to its primary winding which serves to maintain oscillations, two secondary windings, one for the distributing swtchboard of the first circuit and the other for that of the second circuit.
  • Fig. 5 shows a system wherein the voice current is periodically interrupted at a super-audible frequency for intervals forming an appreciable part of the period of such voice current frequency, and such intervals of interruption are filled with a low audible frequency from an auxiliary source, to produce garbling, and means is provided in reception to eliminate the garbling frequency.
  • the voice current is periodically interrupted at a super-audible frequency for intervals forming an appreciable part of the period of such voice current frequency, and such intervals of interruption are filled with a low audible frequency from an auxiliary source, to produce garbling, and means is provided in reception to eliminate the garbling frequency.
  • Fig. 5 there are two tubes 41 and 48 con nected in push-pull between the wires 2! and 22.
  • the tube 41 has its plate connected with the wire 2
  • is connected with the common filament heating battery and it is applied to the grid of tube 4? through the transformer 52.
  • An oscillator 55 of musical audio frequency is applied to the grid of tube 48 with energy at a suitable level through the transformer 54.
  • the balancing of the two circuits is ensured by the adjustable resistances 56 and 51', which circuits can be considered as arms 01' a bridge.
  • a tube 58 is provided on a single bridge arm between the wire 2! and a neutral point 59 which is the common point of the two resistances 60 and BI.
  • These resistances can be advantageously replaced by detectors, and preferably by copper oxide rectifiers in the circuit arrangement shown in Fig. 1.
  • the tube 58 is connected similarly to the tube 41 with head receivers 49- shunted by the capacity 50, microphone 5i, microphone transformer 52, and the filament battery supplying the microphone.
  • a filter 62 formed by suitable resistances and capacities is inserted ahead of the telephone receivers.
  • the plates of tubes 41 and 58 are also positive.
  • the conversation is heard in the receivers 49 and vice-versa in receivers 4s when speaking into microphone 5
  • the noise of the. garbling frequency passes into the line when the terminal 64 is positive, therefore when terminal 63 is negative, hence at the moment when the conversation between the two stations cannot pass on account of the negative voltage on the terminal 63, andthe plate of tube 41.
  • the garbling frequency cannot pass because at that instant there is a negative voltage on terminals e 64 and the plate of tube 48. It is known that these interruptions at ultra-audible frequency of the heterodyne for chopping are not perceptible to the ear.
  • the filter 62 which is connected, if necessary, to each transmitting tube. If the garbling frequency is 60 cycles, the smoothing circuit 62 will reduce in the same proportion the 60 cycle frequency component of the voice, which fact olfers no difliculty, because the important part of the voice frequencies are close to 800. For this reason, it is recommended to employ a garbling oscillation of very low frequency.
  • a further improvement consists in having the tube such as 41 or 48 or 58 of Fig. 5 connected to each station in shunt with a tuned circuit having a variable capacity and a variable inductance coil, whose mid-point is a neutral point connected with the filament battery through balancing resistances.
  • the secrecy is even better assured than with the previously described arrangements, for if the tuned oscillating circuit is not tuned to the corresponding transmitting station, it is impossible to hear the conversation, or to transmit.
  • Fig. 6 a combination of this kind is shown with the use of plug connecting blocks (called Bavarian commutators) for connecting in the different values of capacity and inductance of the tuned oscillating circuit.
  • Fixed condensers 65, 66, 61, etc. are connected in parallel, each connected with a split connecting block 68, 69,
  • Tube 76 of Fig. 6 corresponds to tube 58 of Fig. 5.
  • the tubes 41 and 58 perform corresponding functions. These arrangements for tuning are in addition to the chopping and garbling method described for Fig. 5.
  • the resistance 19 serves as balance and the resistances and BI likewise, and these moderate also a too sharp tuning. If the connecting blocks are numbered, a numerical combination can be arranged and the tuning in of two stations together will only be possible if the agreed combination is realized With the plugs at each station, which increases further the security of secrecy.
  • the connecting blocks with plugs can also be connected at desired places to interrupt the current when the plug is removed or to short circuit an element when the plug is inserted, the system only operating with an arranged and secret combination or code.
  • oscillation generating circuits With the arrangement of oscillation generating circuits, one can have several stations, of any desired number, tuned in two by two on different wave lengths and thus obtain multiple telephony in secrecy.
  • a two-conductor telephone transmission line a terminal oflice at each end of said line, each of said offices comprising a pair of telephone subscribers stations and a pair of subscribers lines respectively connected thereto, a pair of electron tubes at each of said offices connected in push-pull balanced relationship with their cathodes interconnected and their plates connected respectively to the conductors of said transmission line, a unilaterally conducting resistance connected between the plate and cathode of each of said tubes, a source of alternating voltage of superaudible frequency, and means for applying said super-audible voltage to the plate circuits of said tubes symmetrically about the cathodes of said tubes, each of said subscribers lines being coupled to the plate circuit and grid circuit of a corresponding one of said tubes respectively.
  • a two-conductor telephone transmission line comprising a pair of telephone subscribers stations and a pair of subscribers lines respectively connected thereto, a pair of electron tubes at each of said offices connected in push-pull balanced relationship with their cathodes interconnected and their plates connected respectively to the conductors of said transmission line, a unilaterally conducting resistance connected between the plate and cathode of each of said tubes, a source of alternating voltage of superaudible frequency, means for applying said super-audible voltage to the plate circuits of said tubes symmetrically about the cathodes of said tubes, and an individual subscribers transformer respectively for each of said subscribers stations, each of said transformers comprising three windings, one of said windings being connected to a corresponding subscribers line, and said other windings being connected respectively to the plate circuit and grid circuit of a corresponding one of said tubes.
  • a pair of similar multiplex telephone systems as set forth in claim 1 connected between the same two offices, a pair of one-to-one autotransformers respectively connected across the conductors of the line of each of said systems, a superposed additional subscribers station at each of said offices connected between the common points of said auto-transformers at each of said ofiices respectively, and variable rheostat means connected between said lines and said push-pull circuits of said tubes for varying the potential relationships between said tubes and said lines.
  • a two-conductor telephone transmission line comprising a microphone and telephone receiver, a pair of electron tubes at a first one of said offices connected in push-pull balanced relationship with their f cathodes interconnected, said microphone and receiver at said first office being respectively connected in the input and output circuits of a first one of said tubes at said first oiiice, a source of alternating current of audible frequency (1011- nected to the input circuit of a second one of said tubes at said first oifice, the plates of said tubes at said first ofilce being respectively connected to said conductors of said transmission line, a source of alternating voltage of superaudible frequency, means for applying said superaudible voltage to the plate circuits of said tubes symmetrically about the cathodes of said tubes, one-to-one voltage dividing means connected across said conductors of said transmission line at a second one of said ofiices, an electron tube at said second ofiice
  • variable rheostat means connected between the plate of each of said tubes and the corresponding conductor of said transmission line for varying the voltage relations therebetween, and a controllably variable tuned circuit at each of said offices connected between said conductors of said transmission line symmetrically, said tuned circuit comprising an inductance coil whose mid-point is connected to the cathode of the tube at the corresponding office.
  • each of said ofiices comprising a telephone subscribers station and a subscribers line connected thereto, a pair of mutually polarly opposed balanced unilaterally conducting resistances connected in series balanced relation between the conductors of said transmission line at each of said ofiices, a subscribers circuit electron tube at each of said offices having its plate and cathode connected between a first conductor of said transmission line and the common point of said opposed resistances connected in series, means for applying a speech input current from said subscribers station to the input terminals of each of said subscribers circuit tubes at each of said offices, complementary means at a first one of said offices connected across the other of said resistances of said office for applying an audio-modulated carrier frequency between the second conductor of said transmission line and the common point of said resistances at said oifice connected in series, said complementary means comprising a complementary electron tube having its plate and cathode connected between said second conductor and said common point in pushpull relation to
  • a two-conductor telephone transmission line a terminal ofiice at each end of said line, each comprising a pair of sources of audio-frequency signal and a pair of signal lines respectively connected thereto, a pair of electron tubes at a first one of said offices connected in push-pull balanced relationship with their cathodes interconnected, said signal lines at said first oflice being respectively in electrical relation with the input circuits of said tubes at said first oilice, the plates of said tubes at said first office being respectively connected to said conductors of said transmission line, a source of alternating voltage of super-audible frequency, means for applying said super-audible voltage to the plate circuits of said tubes symmetrically about the cathodes of said tubes at said first office, one-to-one voltage dividing means connected across said conductors of said transmission line at a second one of said oifices, a pair of electron tubes at the second of said offices having their output circuits respectively connected between each of said transmission lines and the mid-point of said voltage
  • a two-conductor telephone transmission line a terminal office at each end of said line each comprising a pair of sources of audio-frequency signal and a pair of signal lines respectively connected thereto, a pair of mutually polarly opposed balanced uni-laterally conducting resistances connected in series balanced relation between the conductors of said transmission line at each of said ofiices, a pair of electron tubes at each of said ofiices connected in push-pull balanced relationship with their cathodes connected together to the common point of said resistances at said respective office, said signal lines at each of said offices being respectively in electrical relation with the input circuits of said tubes at said office, the plates of said tubes at each of said ofiices being respectively connected to said conductors of said transmission line, a source of alternating voltage of super-audible frequency, means for applying said super-audible voltage to the plate circuits of said tubes symmetrically about the cathodes of said tubes at a first one of said offices, and individual electrical sound reproducing means respectively connected to the output
  • a two-conductor telephone transmission line a terminal ofiice at each end of said line comprising a microphone and a telephone receiver, a pair of mutually polarly opposed balanced unilaterally conducting resist ances connected in series balanced relation be tween the conductors of said transmission line at each of said ofilces, a pair of electron tubes at a first one of said offices connected in pushpull balanced relationship with their cathodes connected together to the common point of said resistances at said first office, said microphone and receiver at said first oflice being respectively connected to the input and output circuits of a first one of said tubes at said first ofrlce, a source of alternating current of audible frequency connected to the input circuit of a second one of said tubes at said first ofiice, the plates of said tubes at said first office being respectively connected to said conductors of said transmission line, a source of alternating voltage of superaudible frequency, means for applying said superaudible voltage to the plate circuits of said tubes at said first office symmetrically

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US757580A 1933-12-21 1934-12-14 Commutating balanced multiplex telephony Expired - Lifetime US2080082A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2541399A (en) * 1945-11-19 1951-02-13 Blake Kenneth Electronic switch
US2936338A (en) * 1957-12-11 1960-05-10 Bell Telephone Labor Inc Switching circuit

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2541399A (en) * 1945-11-19 1951-02-13 Blake Kenneth Electronic switch
US2936338A (en) * 1957-12-11 1960-05-10 Bell Telephone Labor Inc Switching circuit

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