US2691698A - Security telephone cable with jammer and alarm - Google Patents

Description

Oct. 12, 1954 K. H. SCHMIDT SECURITY TELEPHONE CABLE WITH JAMMER AND ALARM Filed Oct. 26, 1950 Patented Oct. 12, 1954 SECURITY TELEPHONE CABLE WITH JAMMER AND ALARM Kenneth H. Schmidt, Danbury, Conm, assignor to Research Products, Incorporated, Danbury, Conn., a corporation of Connecticut Application October 26, 1950, Serial No. 192,241

8 Claims. 1

This invention relates to a telephone system including a security cable in combination with a jammer and an alarm.

The main object of the invention is to provide a tamper-proof telephone system, particularly for private telephone and inter-ofiice communications.

It comprises a specially designed cable and an alarm unit which in combination provide a tamper-proof cable and telephone installation.

Standard telephone cable is liable to tampering or tapping by use of induction coils, cutting across the lines, and many other devices.

It is therefore another object to provide a system which sets off an alarm if anyone attempts to cut or tap onto the cable itself.

A further object is to provide a continuous multiple frequency tone signal radiated through the cable which will render ineffective the use of induction coils or other means of sound detection that are not directly hooked into the line, and will completely block any pick-up of the voice messages being relayed through the telephone cable.

Although primarily for private telephone and interofiice communications, this cable and system are not limited thereto, but can also be used for outdoor cable installations from one building to another or over any distance desired; the only change would be the outside covering of the cable would be weatherproofed.

With the foregoing and other objects in view, I have devised the construction illustrated in the accompanying drawing forming a part of this specification. It is, however, to be understood the invention is not limited to the specific details of construction and arrangement shown, but may embody various changes and modifications within the scope of the invention.

In this drawing, the figure is a side elevation of the cable with parts broken away to more clearly show the construction. and showing it connected in the alarm and protection system.

The base of the cable is a standard telephone cable comprising numerous twisted pairs of wires I depending upon the number of stations to be installed, and they are covered with an insulating covering, such. for example, as a paper wrap 2. This wrap is covered with a suitable metal foil, preferably aluminum foil 3 comprising a strip of the foil wrapped spirally around the cable, shown in the drawing in a counterclockwise direction. The adjacent coils or convolutions could be spaced if desired. but preferably are either abutting or in contact at their edges or overlapping,

so that the entire cable is covered with the foil for shielding purposes and to ofiset an induction coil. This layer of foil is covered with a second insulating and protective Wrap 4 which is preferably polyethylene or similar plastic to reduce capacity effects between layers of foil. Another wrapping of metal foil, preferably aluminum foil 5, is added. This wrap runs in the opposite direction to that of the foil 3, in this case clockwise. This wrap is applied in a manner that the laps or adjacent convolutions are suitably spaced so that they do not touch or overlap, a satisfactory distance being approximately a quarter-inch between turns. The strips of the wrap may be of different widths, but they are preferably about three-quarters of an inch wide. The outer covering 6 of the cable will be a protective insulating jacket of some suitable material, for indoor use such as extruded plastic. For a cable to be installed outdoors, an additional armored covering (not shown) such, for example, as lead, will be used to provide weatherproofing and protection.

An alarm or indicator unit is used in conjunction with this cable and accomplishes two purposes in respect thereto. This comprises an alarm or indicator 1 connected to a circuit 8 with a pair of differential relays EI and ID, the alarm or indicator circuit being provided with current from the battery I I, while the relay circuit is provided with current from a battery I2 and is grounded at I3. This circuit may be controlled by a suitable variable resistance I4. This relay circuit is connected to the outer layer of foil 5 at one end of the cable, as indicated at I5, and the adjacent end of the inner foil is grounded, as indicated at IS. A continuous current of, say, threequarters ma., is fed through one of the differentials, as 9, causing that relay to close and open the alarm or indicator circuit 8, as shown in the drawing. The second relay Ill is in series with the first relay and requires a greater current, say 1 ma., to close it, and therefore remains open, as shown in the drawing. The circuit as indicated continues through the outer wrapping of foil 5 through the entire length of the cable where at the other end there is connected in the circuit a resistance and capacity unit I! in a connection between the outer wrapping 5 and the inner wrapping 3, the connections to the respective wrappings being indicated at IB and I9. From there the circuit returns through the inner wrapping of foil 3 to the alarm through the ground I6.

Accompanying the constant current circuit through the layers of foil on the cable is a constant oscillator tone. This tone is produced by a tone-generator which generates a multi-frequency sawtooth wave form at approximately 1000 cycles. This generator is coupled across the inner foil layer 3 and outer layer of foil 5 by the ground 2| and connection 22 so that the outer wrapping will produce a magnetic field around the outside of the cable.

It will be understood from the above that the alarm and protective unit is coupled directly to the two layers of foi1 3 and 5 on the cable. If the outer wrapping of foil 5 is cut in any Way. breaking or changing the continuous coil circuit, an open circuit condition will exist, cutting off the constant, say three-quarter ma., current required to keep the first relay 9 closed. I'his relay will then open, and as it opens it closes the alarm or indicator circuit 8, causing the alarm to sound and give warning that someone is tampering with the cable.

In like manner, if in attempting to cut into the cable the outer foil 5 is shorted against the inner foil 3, which would happen in an attempt to tap directly into the wires I, a short circuit is caused, throwing additional current into the circuit, say 1 ma, which is enough to close the second relay In. When this relay closes, it closes the alarm circuit 8, causing the alarm to sound.

It will be understood the cable when used in a telephone system will be terminated in various terminal boxes or terminal cabinets (steel cabinets), not shown. Each box or cabinet will be equipped with a microswitch (also not shown) controlling an alarm circuit, so that if anyone tries to open the box or cabinet, or the microswitch is disturbed in any way, it will operate to sound or operate an alarm or indicator.

There may also be used in conjunction with this circuit a zone-indicating meter (not shown) which could be used to determine and localize the point of tampering. Each phone station and/or a certain portion of the connecting cable would represent a zone. Penetration into the cable or tampering at the phone itself could be observed at the zone-indicating meter by the change in current through the meter. Different values of current for each zone to be applied to the meter are produced by the appropriate selection of resistances and allied switching arrangements.

The intensity of the oscillator tone from its tone generator 2n that is generated through the foil layers is of such amplitude that it will create a serious interference with an induction coil or other pickup device that might be used to pick up conversation in any of the twisted pairs of wires I of the cable. The amplitude of this signal is held to such limits that it will not create an interference on the twisted pairs of wires or a telephone cable runnin parallel to the cable in question.

It will be seen from the above that this cable in combination with the alarm and protector provides a tamper-or tap-proof telephone system, and one which will prevent tapping of the telephone wires by the use of induction coil or other means of sound detection, that is not directly hooked into the line, and will also give a signal or alarm if any attempt is made to tamper with or tap any of the lines by cutting into the cable and connecting directly to the circuit wires.

Having thus set forth the nature of my invention, I claim:

1. A telephone system comprising a cable including a plurality of pairs of telephone circuit conductors, a pair of electrical conducting foil wrappings about said conductors one over the other and insulated from each other, one of said wrappings comprising a narrow strip of foil wound spirally about the cable in spaced convolutions, a tone generator, an electric circuit connecting the output from said generator to the foil wrappings at one end of the cable, and means electrically connecting the foil wrappings at the other end of the cable.

2. A telephone system comprising a cable including a plurality of pairs of telephone circuit wires, a wrapping of insulating material about said wires, a conducting foil wrapping on said insulating material comprising a narrow strip of metal foil wound in a spiral with adjacent coils in contact, a second wrapping of insulating material about said foil, a second conductinf foil wrapping on said second insulating wrapping comprising a fiat strip of metal foil wound in a spiral with the adjacent coils spaced from each other, an insulating covering for the second foil Wrapping, a tone generator, an electric circuit connecting the output from said generator to the foil wrappings at one end of the cable, and means electrically connecting the foil wrappings at the other end of the cable.

3. A telephone system comprising a cable including conductors of telephone circuits, a wrapping of electrical conducting foil around said conductors, a second wrapping of electrical conducting foil over the first wrapping and insulated therefrom, one of said wrappings comprising a narrow strip of foil wound spirally about the cable in spaced coils, a pair of differential relays connected in series with each other and operable on different current densities, a source of current connected in series with said relays and said wrappings at one end of the cable, a circuit including a plurality of switch means controlled one by each of said relays, one of said switch means being arranged and operable by one of the relays with a given current density to open said circuit and the other of said switch means arranged and operable by the other relay on a different current density to close said circuit, and means electrically connecting the wrappings at the other end of the cable.

4. A telephone system comprising a cable including a plurality of pairs of telephone circuit conductors, a pair of electrical conducting foil wrappings about said conductors one over the other and insulated from each other, one of said wrappings comprising a narrow strip of foil wound spirally about the cable in spaced convolutions, an electric circuit, a second electric circuit connected to said foil wrappings at one end of the cable, a pair of differential relays in said latter circuit each operating on a different current density from the other, switch means operated by each relay controlling the first circuit. and means electrically connecting the wrappings at the other end of the cable.

5. A telephone system comprising a cable including a plurality of pairs of telephone circuit wires, a wrapping of insulating material about said wires, an electrical conducting foil wrapping on said insulating material comprising a narrow strip of metal foil wound in a spiral with adjacent coils in contact, a second wrapping of insulating material about said foil, a second electrical conducting foil wrapping on said second insulating wrapping comprising a flat strip of metal foil wound in a spiral with the adjacent coils spaced from each other, an insulating covering for the second foil wrapping, an electric circuit, a second electric circuit connected to said foil wrappings at one end of the cable, a pair of differential relays in said latter circuit each operating on a different current density from the other, switch means operated by each relay controlling the first circuit, and means electrically connecting the wrappings at the other end of the cable.

6. A telephone system comprising a cable including a plurality of pairs of telephone circuit wires, a wrapping of insulating material about said wires, an electrical conducting foil wrapping on said insulating material comprising a narrow strip of metal foil wound in a spiral with adjacent coils in contact, a second wrapping of insulating material about said foil, a second electrical conducting foil wrapping on said second insulating wrapping comprising a flat strip of metal foil wound in a spiral with the adjacent coils spaced from each other, an insulating covering for the second foil wrapping, an electric circuit, a relay circuit connected to the foil wrappings at one end of the cable, a pair of differential relays connected in series in the latter circuit and each operating on a different current density from the other, switch means operated by each relay controlling the first mentioned circuit, and means electrically connecting the wrappings at the other end of the cable.

7. A telephone system comprising a cable including a plurality of pairs of telephone circuit conductors, a pair of electrical conducting foil wrappings about said conductors one over the other and insulated from each other, one of said Wrappings comprising a narrow strip of foil wound spirally about the cable in spaced convolutions, an electric circuit, a second electric circuit connected to said foil wrappings at one end of the cable, a pair of diiferential relays in said latter circuit each operating on a different current density from the other, switch means operated by each relay controlling the first circuit, a tone generator, an electric circuit connecting the output from said generator to the foil wrappings at said end of the cable, and means electrically connecting the foil wrappings at the other end of the cable.

8. A telephone system comprising a cable including a plurality of pairs of telephone circuit wires, a wrapping of insulating material about said wires, an electrical conducting foil wrapping on said insulating material comprising a narrow strip of metal foil wound in a spiral with adjacent coils in contact, a second wrapping of insulating material about said foil, a second electrical conducting foil wrapping on said second insulating wrapping comprising a fiat strip of metal foil Wound in a spiral with the adjacent coils spaced from each other, an insulating covering for the second foil wrapping, an electric circuit, a relay circuit connected to the foil wrappings at one end of the cable, a pair of differential relays connected in series in the latter circuit and each operating on a difierent current density from the other, switch means operated by each relay controlling the first circuit, a tone generator, an electric circuit connecting the output from said generator to the foil wrappings at said end of the cable, and means electrically connecting the foil wrappings at the other end of the cable.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 961,827 Williams June 21, 1910 1,578,980 Gasser Mar. 30, 1926 1,705,949 Williams Mar. 19, 1929 1,840,637 Reid Jan. 12, 1932 2,027,222 Baughman Jan. 7, 1936 2,047,271 Kennedy July 14, 1936 2,056,085 Alles Sept. 29, 1936 2,132,259 Emanueli Oct. 4, 1938 2,180,731 Dickinson Nov. 21, 1939 2,423,537 Wheeler July 8, 1947 2,581,213 Spooner Jan. 1, 1952

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