Multiplex telephony and telegraphy.

Application filed November S, 1810. Serial No. 590,804.

(DEDICATED TO THE PUBLIC.)

To all whom it may concern:

Be it known that I, Georue Owen Squier, major in the Signal Corps, U. S. Army, a citizen of the United States, and residing 5 at Washington, District of Columbia, (whose post-office address is War Department, Washington, District of Columbia,) have , invented certain new and useful Improve ments in Multiplex Telephony and Teleg10 raphy, of which the following is a specification.

This application is made under the act of March 3, 1883, chapter 143, (Us S. Statute -XXII, p. 625,) and the invention herein de•15 scribed and claimed' may' be used by the Government of the United States or any of its officers or employees in the prosecution of work for the United States or by any person in the United States without the pav: 20. ment of any royalty thereon.

This invention relates to multiplex telephony and telegraphy and. has as its object the simultaneous transmission of a plurality of telephonic and telegraphic messages over ' 25 a single circuit.

A further object of the invention is to make use of grounded or earthed connections in combination with the usual metallic cir-.. cuit.

A further object is to render such a system as the above silent to external disturbances and in such manner as to eliminate all crosstalk or harmful effects of one message upon ’ . another.

A further object is to apply electric waves of such frequencies as to make possible the selection and complete independence of the various messages.

A further object is to superimpose upon a standard battery telephone circuit, as now commercially in use, one or more, telephonic and telegraphic circuits without any interference of the various messages.

In accomplishing the above results, use is made of electromagnetic waves, or oscillations, of high frequency, propagated’by means of wires, and. where use is made in this application of the term high frequency, _JO it is ..understood to mean any ultra-souiid three co-pending applications, .-serial isuu 50 ..frequency or frequencies above the limit of bers 590,801.590,802, and 590.803. filed Ν' audition. vember 5, 1.910. ......

Reference is here made to my co-pending applications, Serial Numbers 590,801 and 590,802, filed November 5, 1910, in which I have discussed at length the advantages and limitations Of the use of electromagnetic waves of various frequencies in such systems as described there and here. In accomplishing the desired results, I have found it necessary and sufficient to combine the engineering practice of wireless telegraphy and telephony with the engineering practice of wire telegraphy and telephony. I have, also found it necessary, in order to obtain satisfactory results, to make use of such detectors as are commonly found in the wireless telegraphic art. Attempts have been made at multiplex telephony, but I have found these inoperative for the- reason, among others,· that-no detector or equivalent device has been used. These detectors are not used because of any greater inherent sensitiveness to electrical energy than resides in the telephone receiver itself, but because the energy being in the form of rapid oscillations cannot affect the telephone or other communicating device; These rapid oscillations can not sensibly affect the telephone, because the diaphragm in its motion must reverse with the reversal of the current and the deflecting impulse if applied directly to the telephone receiver will be first in one direction and then in the- other with a frequency so high that the diaphragm cannot sensibly follow or respond. Furthermore, if the diaphragm should respond with this frequency the effect would not be audible. Also in the case of the ordinary telephone, on account of the large self-inductance of the instrument, the high frequency E. M. F. generated by the waves would produce in the telephone receiver only extremely weak currents. I have found it necessary therefore, and consider it an important part of my invention, to make use of some form of integrating detector to transform the rapid oscillations into effects which can be manifested by the indicating instrument.

This application is closely related to my s. Serial Num-----------,------ίο-, In each of these, nse is :

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030,360 made of high frequency waves as a vehicle for the^: telephone or telegraph messages which are impressed upon the same line as carries the telephonic currents from anordi6 nary local battery telephone set. In my co-pending application, Serial Number 590,803, I have shown a specific manner of connecting a plurality of high .frequency circuits in parallel between the 10 : ordinary battery line and the earth. In this application I shall describe a manner of connecting a plurality of such high frequency circuits in series relation, making use of the telephone circuit and ground connections.

In the drawings forming a part of this specification, several· modifications for circuit connections ' are shown, and in said drawings, Figure 1 illustrates a circuit in which a plurality of transmitting or receiv20 ing circuits is connected in series in a ci^r . cuit between the earth and the ordinary telephone line. Figs. 2, 3 and 4 illustrate a ' modification of Fig. 1.

Referring to these figures in detail, Fig.

1 shows a common metallic circuit A—A' for ordinary telephony, across which, are bridged the telephone sets B B'. These telephone sets include, the usual apparatus in present use in local battery circuits, there 30 being shown a transmitter 1 of any suitable form such as a microphone transmitter with its local battery 2 and the- primary of the transformer 3. Also there are shown connected in the usual way the ringing circuit

4, the switchhook 5 ana the receiver 6. The secondary of the transformer 3 is bridged directly across the line when the receiver is off the hook. The invention is not in any way connected with the details of this tele40 phone connection, any ftf the usual circuifg being suitable, and the one described being given merely as an illustration. Connected to the line wire A', at or near its connection to the telephone set B, I have shown a cir45 cuit connection to the earth at E, this circuit including the variable inductance I, the secondary coil S, the primary coil P, and the variable condenser C, these .all being connected directly in series. Inductively con50 nected to the secondary S is a primary coil P which is in circuit with the high frequency generator G, this-circuit also including a variable condenser C, and a microphone M. Inductively connected to the primary P, 55 is a secondary coil S„ including in its circuit a variable condenser C and a variable inductance L·'. Shunted around the ’condenser «.is the detector D, and operatively associated with the detector D is the tele60 phone set F, with a battery jf desired. At or near the station B' is a similar earth connection, including the inductance I', the primary P/, the secondary S' and the con denser C', these being all variable and connected in series in the same manner as shown β.^Γ> at the station B. Inductively connected to the primary' P/ is a receiver circuit R', similar in every respect to the receiver R at the station B. Inductively connected to the secondary S' is a transmitter circuit Τ', 7 0 similar in .every respect to the transmitter circuit T at the station B. The receiver !{' is tuned to the frequency of the oscillations given off by the transmitter T and the receiver circuit R is tuned to the frequency 75 developed by the transmitter Τ', these frequencies being sufficiently different to afford effective, selective tuning. The tuning elements throughout the circuit which comprise the various condensers and inductances are 80 all variable in order to permit of ready and effective tuning of each and any circuit. The high frequency transformers are all so constructed as to give variable coupling, either by sliding the one coil within the 85 other, or having one coil swing within the other, or by any other suitable method well known in the wireless art.

The operation of the system is as follows: Ordinary telephonic communications may be 90 carried on between the stations B and B' by the telephone sets. Simultaneously therewith high frequency oscillations may be impressed on the line A' by the transmitter circuits T and Τ'; both of these operating at 95 the same time, if desired. These high frequency oscillations are modified in accordance with-speech by the microphone M, and oscillations transmitted by T are picked up by the receiver R' and are rectified or trans- IOC formed by the detector D in such a way as to give a reproduction of speech in-. the telephone F, all of these being well known in the art. So also oscillations modified by the microphone M at the transmitter circuit T' 105 will be. translated into speech at the station R. All of these messages may exist on the same line at the same time without any crosstalk or interference whatsoever. If desired, one or more of the microphones M may be 100 replaced by suitable telegraphic keys in order that communication by telegraphy may be carried on. Obviously this change will not affect the -principle of the operation in any way whatsoever. The telegraphic sig- 115 nals may be produced by the ordinary key placed directly in the generator circuit or by such an arrangement as is shown in Fig. 3 of my co-pending-application, Serial Number 590.801. It is to be noted in this circuit 120 that I have connected a metallic circuit to earth at both ends, and I have done this without experiencing any difficulty in consequence of external disturbances. I am able to accomplish this by means of the condensers 125

I C and C', which, in addition to acting as

080,359 tuning elements, also act as a check to any earth disturbances in the vicinitv. This is possible only because the condensers <’ and C here used are of very small electrical di5 -inensions, being measured in some thousandths of a microfarad, whereas the condensers now in ordinary use in telephone practice have a capacity'measured in microfarads. Such large condensers offer very ) small inijwdance to the passage of external disturbances of such frequencies as are within the audible limit, but. with my very small condensers and sharp tuning in the ground circuit to a frequency entirely above audition, these low frequency audible disturbances are. entirely shut, out, .giving me what I choose to call a “silent ground connection”. In view of the fact that heretofore single line telephone circuits which include a ground return, or a '2-wire telephone circuit which is grounded at either end,.are subject to many and strange noises, the causes of which are not entirely understood; I consider that my present invention, whereby I am enabled to use it ground connection on a single telephone circuit with no such disturbances, a very important and essential part of iny invention. I have found-the above circuits entirely successful on a standard telephone line circuit consisting of a pair of twisted copper conductors, paper insulated, which pair constitutes but one out. of a large number inclosed in a lead sheath used in ordinary city- traffic. This lead sheath surrounding the pair of wires brings the earth connection very close indeed to the line circuit all along its length, but in spite of this, my selective circuits are so effective as Io give no trace whatsoever of any crosstab or influence due to external disturbances. It is apparent that any number of transmitter or receiver circuits inay be connected m series in addition to the two shown m lig. 1.

Fill- '2 shows a modification of Fig. 1, in which a. plurality of earth branches are connected in parallel, each single branch connected to earth being similar in every respect to (he earth branches shown in Fig. 1, and each including two or more circuits which may! be transmitter or receiver circuits, these circuits being indicated only diagrammatically and designated by the reference characters T and R throughout. The 65 connections of. the battery sets B and B' are shown only diagrammatically, it being understood that the connections are similar to those shown in Fig. 1. Each transmitter has a different frequency always being of CO ultra-sound frequency,' and £ach’ transmitter has a corresponding receiver circuit at the ether end_:of the line tuned to its frequence I may also use condensers K and IC bridged across the lines A A' which serve the purpose of placing the two lines A and A' in 65 pundk-J for the high frequency currents. Ί his capacity, however, is made so small as to give practically insuperable impedance to the telephone currents of ordinary frequencies as given by the telephone sets B and 70 B . It is also obvious, as shown in Fig. 2, that high frequency currents may be connected to the line wire A as shown at T^,zand R, these circuits having connected in them a plurality of transmitter or receiver 75 circuits in any suitable arrangement.

Eig. 3 shows a further modification, which is a combination of the systems shown in rigs. 1 and 2 and the systems shown in my co-pending application. Serial Number 80 590,802. In this figure, a plurality of branches connected to the earth is shown, each circuit including a plurality of transmitter or receiver circuits’, as shown in Fig. 2. In addition to this high frequency trans- 85 nutter circuits are inductively connected by means of transformers connected directly in the line circuit in series with the battery . sets B and B' in the manner described in my appending application, Serial Number .590,802, cited above. In this case, the condensers K and K' are necessary, in order to give a free path for the high frequency oscillations of the series connected transmitter and receiver sets Τ'and R'.

fig- 4 shows a further modification in which the battery sets B and B' and one of the line wires such as A, are entirely eliminated, in which case I have multiplex telephony by a single wire using earth return As is apparent from this Fig. 4, I have shown a plurality of ground branches, each including a plurality of telephone or receiver sets, each transmitter having a different frequency and having a receiver set at the other end of the line tuned to its periodicity. Also in series with the line, I have connected other transmitter and- receiver Sets, as shown diagrammatically at Τ' and R^z. In this case I am able to carry on multiplex telephony by the single wire con-nected to earth at various points without, any cross-talk or disturbances from external causes,, and I consider this an .essential part of my invention. In connection with Fig. I, 115 ; I have shown means whereby Morse teleg- i raphy. may .be carried on in the usual way j h nd this without any cross interference of the messages. In case way stations are used | on the line, each of such stations will be ¹²⁰ ' ' shunted by a small condenser or a coni denser and inductance tuned to the frei fluency of the high frequency oscillations.

i Thus it is apparent that my invention may : be superimposed directly on the present ¹²5 !

Morse telegraph systems. Other forms of.

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high frequency transmitter and receiver circuits may be used in place of those shown, and various suitable modifications are shown' and described in detail in my co-pending ap5 plication, Serial Number 590,801 cited above.

Although several modifications have been described in detail in this specification, it is obvious that many changes may be made without departing from the spirit of the in10 vention, and I therefore do not wish to be limited to the exact connections shown, but