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Publication numberUS2094132 A
Publication typeGrant
Publication dateSep 28, 1937
Filing dateJul 15, 1935
Priority dateJul 15, 1935
Publication numberUS 2094132 A, US 2094132A, US-A-2094132, US2094132 A, US2094132A
InventorsMiller Merton R
Original AssigneeAssociated Electric Lab Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Telephone system
US 2094132 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Sept. 28 1937. R 2,094,132



Patented Sept. 28, 1937 UNITED STA'I ES TELEPHONE SYSTEM Merton R. Miller, Evanston, Ill., asslgnor, by

mesne assignments, to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware,

Application July 15, 1935, Serial No. 31,398

a 11 Claims. (01. 179-15) ing equipment is located at the subscriber's premises, thereby eliminating the possibility of surreptitio'us listening by employees at a public telephone exchang'e through which connections are set up. I

The invention will be described hereinafter with reference to the accompanying drawing, which shows diagrammatically the apparatus and circuits involved. The invention is applicable to numerous situations, but for convenience it will be assumed to be in use for providing secret communication between two oflices of some organization having confidential business that has to be discussed by telephone. These omces may be in the same or in different cities. Each oflice may be equipped with a private branch exchange telephone system, or P. B. X., having local telephones and trunk lines to the nearest exchange of the public telephone system. 7

Referring now to the drawing, the equipment there shown is located at the P. B. X. switchboard at one of the oflic'es of. the organization. There is a duplicate equipment at the P. B. X. switchboard in the other ofiice.

The four jacks J to J inclusive, are outgoing trunk jacks at the P. B. X. switchboard and give access to four outgoing trunks extending to the nearest public exchange. There may be more than the four trunk lines shown. The four plugs P to P inclusive, are associated with the secret service equipment and are used to connect such equipment up to four of the regular outgoing trunk lines such as those terminating in jacks J to J Jacks J to J5, inclusive, are jacks of the secret system and give access to four secret channels for conversation. These latter jacks appear on the P. B. X. switchboard as special Jacks, and the same is true of the plugs P to P The P. B. X. operator is also provided with four 50 sets of coding keys A, B, c, and D, and with a distributor DR. The keys should be mounted in conveniently accessible manner. The distributor and driving means may be located in rear of the face panel of. the switchboard if room is available;

otherwise it may be mounted in a small cabinet tributor motor 52.

set on top of the switchboard or on a table alongside of it. If a separate cabinet is used for the distributor thekey sets A to D may be included in it also.

The distributor DR comprises a face plate 5 having conducting rings and segments as shown and is rotatably mounted on a hub 8. Connections to the rings and segments of the distributor are made by means of flexible leads which permit rotation of the face plate 5 through about 360. 10 The face plate 5 has a toothed rim cooperating with a worm 6 which is turned by a hand wheel or dial 1. The dial I is accessible to the operator. The brushes of the distributor are attached to an arm Ill, mounted on a shaft 9. The shaft 8 is 5 rotated at a speed of about two to four times a second by a motor i2 through a reduction gear box ii. The motor i2 is a constant speed motor, preferably a synchronous motor.

The reference character S indicates a switch 20 for connecting up a source of current to operate the distributor motor. Current for operating the tone buzzer i3 is also supplied through the switch S.

Proceeding now with the explanation of the 25 operation of the system, the equipment may be connected up at both ends simultaneously by the P. B. X. operators according to pre-arrangement, or either operator may initiate the connec tion. Assuming the operator having the equip- 30 ment shown in the drawing desires to set up the secret system, she will first actuate the No. 2 key in each of her key sets A to D, inclusive, and will then throw the switch S to start thedis- The operator then plugs into 35 the first secret jack J with one of her regular cord circuits and inserts the first plug P into an idle outgoing trunk jack such as J. If common battery signalling is used on the trunk lines the act of plugging into the outgoing trunk, 40 which puts a bridge across the trunk conductors, will signal the operatorat the public exchange; otherwise the P. B. X. operator will ring on the trunk line in the usual manner, the repeating coils of the secret equipment being adapted to pass ringing current as well as voice currents.

Upon obtaining a response from the operator at the public exchange, the P. B. X. operator will order up a connection in the usual manner to the distant ofiice of. the firm, where the call will come in on a trunk jack similar to Jacks J --J .The signalling and supervisory equipment is not shown, but may be of the usual character. The distant P. B. X. operator answers the call with one of her regular cord circuits and upon learn- I elusive, and throws her switch 8, the same as was done at the originating P. B. X. ThedistantP. B. X. operator then transfers her cord circuit to the flrst jack such as J of her secret equipment and inserts the plug corresponding to plug P in the trunk line over which the call was received. The two operators may then converse to check the continuity of the talking circuit through the secret equipment at both ends. These circuits will be more fully explained later, but it may be stated that with the same keys operated in all key sets only a straight non-secret conversation over the single channel so far set up is involved. I

The originating P. B. X. operator will now proceed to set up three more calls to thedistant P. B. X. in the same manner, using successively the jacks J. J", and J which are connected up to outgoing trunk lines by inserting plugs P to P into outgoing trunk jacks such as J to J As the calls are received at the distant P. B. X. the operator answers by inserting plugs which correspond to plugs P to Pin the trunk Jacks over.

which thecalls are received, care being taken that corresponding plugs such as P at the two I P. B. X. switchboards are used for the same con.-

nection- When the four connections are finally established there will be four separate telephone channels interconnecting the two P. B. X. switch- I boards.

I number. Assuming that the number is 2431, the

operator at the originating P. 3.3:. will operate the'No. 2 key in key set A, or rather will leave this key in operated position, and will operate the:No. 4 key in key set B, the N0. 3 key in key set C, and the N0. 1 key in key set D. The operator 'atthe distant exchange will do likewise.

One of the secret channels may be used as an order wire, although a regular connection could be put through and used for that purpose as soon as the system is properly synchronized. It will be assumed, therefore, that the originating operator leaves up her cord circuit in jack J and stays on the line with her headset. At the distant P. B. X. the operator will plug into the corresponding jack and will then proceed to synchronize her distributor with the distributor at the originating P. B. X. In order to accomplish this the operator will rotate the face plate of her distributor by means of her dial such as 1 until the channel becomes clear and she can converse with the originating operator. Either operator could, of course, perform this operation as both distributorsare adjustable.

Assuming now that the originating operator has a call for a secret channel to the distant ofilce of the firm, she will connect the calling party with a secret service jack such as J by means of one of her regular cord circuits, and will transmit the number of the channel used and also the name or number of the called party to the distant P. B. X. operator over the channel being used as the order wire. The distant operator will therefore connect 'up the called party to the channel terminating in her jack J, and the calling and called parties can then converse as desired.

Other secret connections can also be set up over the remaining channels. Either operator may, of course, originate calls, transmitting the necessary fully understood. Considering a connection set up by way of jack J at the originating P. B. X. and the corresponding jack at the distant P. B. X., it

will be observed that with the connection estab-' lished the talking circuit from the local party in the originating P. B. X. will be extended through springs of Jack J to the repeating coil R With the distributor arm ID in the position shown in the drawing the right-hand winding of repeating coil R is connected over conductor 20, key No.3 of key set C, conductor 29k brush set 46, and conductor 25 to the left-hand winding of repeating coil R The right-hand windings of repeating, coils, R -R and the left hand windings of .repeating coils R -R* are connected to a common conductor 48, or to ground, and consequentlythe right-hand winding of repeating coil R winding of repeating coil RF. the talking I circuit will extend from jack J by way of repeating coil R key set C. distributor DR in position shown, repeating coil R, plug P", and'jack J to the second inter-exchange telephone channel, which is now set up over jack J At the distant P. B. X. this telephone channel continues by way oi a plug similar to P repeating coil correspondingv to R distributor such as DR (now running I will be connected in series with the left-hand insynchronism with distributor DR), a key set I such as C to a jack such as J terminating the other end of the secret channel in use.

As the. distributor arm 'lll moves around it 1 shortly enters the quadrant associated with key set B, whereupon the right-hand winding of repeating coil R will be connectedwith the lefthand winding of repeating coil R over conductor ,20, key No. 4 of key set B, conductor 34,

brush set 45, and conductor 26. The talking circuit then extends from jack J by way of repeating coil R key set B, distributor DR, repeating been substituted for the second.

When the distributor arm l0 passes into the quadrant associated with key set A, the righthand winding of repeating coil R will be connected with the left-hand winding oi. repeating coil R over conductor 20, key No. 2 in key set A, conductor 36, brush set 41, and conductor 24. The talking circuit now extends from jack J by way of repeating coils 1'1. and R plug P and jack J to the first telephone channel, 1. e., the first telephone channel is substituted for the third. The same substitution is made by the distributor at the distant P. B. X. and the talking circuit is maintained.

When the distributor arm 10 passes into the quadrant associated with key set D, the righthand winding of repeating coil R will be connected withthe left-handwinding of repeating coil R over conductor 20, key No. 1 of key set D, conductor .3, brush set 44, and conductor 21, whereupon the fourth telephone channel over jack J will be substituted for the first channel over Jack J The same substitution is made by the distrib- 75 the talking circuit has been maintained intact throughout one complete revolution of the distributors notwithstanding that it hasincluded successively the second, third, first, and fourth telephone channels. v

The distributors keep on rotating and the same cycle of substitutions as described above is repeated over and over again as long as the conversation keeps on. When the parties finish the P. B. X. operators are notified in the usual way by their local supervisory signals and will pull down the connection.

So far the explanation has dealt only with the secret channel terminating in jack J? but it will be clear that the other three secret channels planation a table has been prepared showing all the connections between the secret jacks J --J and the outgoing trunk jacks J J throughout a complete rotation of the distributor. .25

In-compiling thistable it was assumed'that plugs P -P are inserted in jacks J -J respectively, and that the code number 2431 has been the key sets AD.

Quadrant C' Jack J connected to jack J Jack J 5 connected to jack J 1 Jack J 7 connected to jack J Jack J a connected to jack J Quadmnt B Quadrant A Jack J connected to jack J Jack J connected to jack J Jack J 7 connected to jack J Jack J connected to jack J Quadrant D Jack J 5 connected to jack J Jack J connected to jack J Jack J" connected to jack J Jack J connected to jack J 'or by tapping a telephone line outside the premises' of the P. B. X. subscriber, will be unable to hear anything intelligible, even with the-equipment as thus far described. The listener would hear one fourth of each secret conversation going on, as each secret channel would use the tapped line for one fourth of the time, but the part of each conversation thus picked up would be chopped up into fragments interspersed between frag- The speed of the distributors is high enough so that no complete words appear with the result that the voice currents picked up make a hopeless jumble of sound.

However, with only one secret channel in use the conversation could be picked up by means of set up on g mit listening in on all fourtelephone channels simultaneously. -In order to defeat the success of such a scheme each secret channel is normally connected at the springs of the associated jack such as J with a source of tone current. Thus.

the drawing shows the left-hand winding of repeating coil R connected by way of normally closed contacts of jack J and conductors 50 and 5| with the buzzer l3, which is in operation continuously while the switch S is closed. The otherthree secret channels are connected to the buzzer l3 in the same way. At the other P. B. X. there is a buzzer similar to H, which is connected up the same way. The distant buzzer I3 may be of a different frequency than the buzzer l3, but both preferably generate complex tone currents which are within the voice frequency range.

Thus it will be seen that each secret'channel carries tone currents when not connected up for conversation, and that these tone currents are switched from one telephone channel toanother the same as voice currents, whereby any conversation over 'a secret channel is effectually mixed either with tones or other conversations, or both, so as to prevent interception by listening in on any number of the telephone channels.

The successfuloperation of the system, of

course depends on maintaining the two distrib-.

utors in fairly close synchronism. If the synchronous motors driving the distributors are supplied from the same inter-connected power system, there will be no trouble at all on this account,

' and the two distributors after once being adjusted will stay together for along time. If themotors are supplied from different power. systems, as

channel all the time, except when answering other calls, and will at once detect any departure from synchronism and correct it.

In order to prevent the interception of conversations by the use at some intermediatepoint of equipment such as is shown, which might readily be built by anyone knowing the principle employed, the P. B. X. operators I are preferably instructed to change the codes at frequent intervals. In order to avoid the necessity of transmitting code numbers by telephone, the operators may be each provided with a'list of code numbers, which are to be used successively. With this plan it is only'necessary for one operator to tell the v other operator to changecodes, whereupon both be secured by providing live or six key sets instead of four, and by changing the distributor segments to correspond.- q

The use of one wire or grounded circuits through the secret equipment simplifies the keys and the distributor and since these circuitsare entirely local and very short there will ordinarily be no trouble irom noise or cross-talk. However.

1: desired, additional springs may be added the keys and additional segments to the distributor so as to carry through both sides of each secret channel and provide full metallic circuits through- The invention having been described; that which is believed to be new and for which the protection of Letters Patent is desired will be pointed out in the appendedclaims.

What is claimed is: I

1. In a. secret communication system, two telephone stations, a plurality of telephone channels extending between said stations, automatic means at each station for connecting a telephone to said channels successively, and coding means at each station for predetermining the order in which said channels are used, each coding means comprising a'plurality of selectively operable switching devices operable at will to change the order of use.

2. In a secret communication system, two tele-' phone stations, a plurality of telephone channels extending between said stations, automatic means at each station for connecting a telephone to said channels successively, a source of tone current, and nieans for connecting said tone source to each channel at times when said telephones are not connected thereto.

3. In a secret communication system, a plurality of telephone channels, a transmitting circuit, means for breaking a conversation occurring on said circuit into sections, means for distributing said sections to'said channels in predetermined order, and coding means comprising a set of keys for changingthe order atwill.

4. In a secret communication system, a plurality of secret channels, a plurality of telephone channels, means for switching each secret channel from one telephone channel to another periodically, whereby the speech currents on any telephone channel'will be a mixture of speech currents from said secret. channels, and means operable at will while said switching means is operating to cancel the effect thereof, whereby each secret channel can be maintained in connecticn with a particular telephone channel.

5. In a secret communication system, a plurality of secret channels, means for mixing speech currents from channels in use before transmitting such speech currents, and means for maintaining tone currents of audible frequency on channels not in use so that the full number of audible frequency currents will always'be available for mixing purposes whether all channels are in use for conversation or not.

6. In a secret communication system, a transmitting circuit, a telephone channel, means for breaking a conversation occurring on said circuit into sections and for transmitting non-contiguous sections over said channel, a source of tone current,'and means for transmitting tone current over said channel in the intervals between the transmission of sections oi. conversation.

phone circuit, a plurality of other'circuits, a ro- .tary distributor for connecting said first circuit to said other circuits successively, said distributor comprising a plurality of angularly p ced sections, and coding means for predetermining the order in which said other circuits are connected to, said coding means comprising a plurality of groups of keys, one said sections.

8. In a secret communication system, two tele-' phone circuits, a plurality of intermediate ci1-' distributor connections at will to cause each secret channel to be switched periodically to a difierent telephone channel.

10. In a P. B. x. switchboard including answering jacks, outgoing trunk jacks and cords for connecting them, secret service arrangements comprising secret service Jacks to which said answering jacks may be connected by said cords, secret service plugs adapted to cooperate with said trunk jacks, speaking connections between 'said secret service jacks and secret service plugs,

and means including a distributor for continuously changing said connections so that each secret service Jack is repeatedly connected to said secret service plugs in succession one at a time.

11. A switchboard as set forth in claim 10, characterized by'the provision of speaking connections each including a single wire passing throughthe distributor and a common ground return conductor, and repeating coils for converting such single wire grounded circuits to metallic circuits at each secret service-jack and plus.


7. In a secret communication system, a tele-- group for each of I

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2472705 *Jul 17, 1944Jun 7, 1949Homrighous John HTime division carrier multiplex telephone system
US2482039 *Sep 6, 1945Sep 13, 1949Nea Service IncSecret communication employing signal sequence switching
US2513335 *Sep 1, 1945Jul 4, 1950Standard Telephones Cables LtdDemodulator system
US2517365 *Apr 14, 1947Aug 1, 1950Patelhold PatentverwertungMultiplex communication system with channels of different band widths
US2586475 *Jan 27, 1947Feb 19, 1952Patelhold PatentverwertungSecrecy system wherein frequency bands of messages are intermixed during multiplexing
US2707208 *Mar 31, 1945Apr 26, 1955Rca CorpSecrecy facsimile system
US3012099 *Apr 24, 1943Dec 5, 1961Bell Telephone Labor IncMessage transmission with privacy
US3012100 *Apr 24, 1943Dec 5, 1961Bell Telephone Labor IncTelephone privacy system
US4802220 *Mar 20, 1985Jan 31, 1989American Telephone And Telegraph Company, At&T Bell LaboratoriesMethod and apparatus for multi-channel communication security
U.S. Classification380/33
International ClassificationH04K1/00
Cooperative ClassificationH04K1/00
European ClassificationH04K1/00