503,765

PATENT SPECIFICATION

Application Date: Oct. 8, 1937. No. 27336/37

Complete Specification Left: Sept. 22, 1938.

Complete Specification Accepted: April 11, 1939.

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PROVISIONAL SPECIFICATION

Improvements in or relating to Electric Cables

I, ALAN DOWER BLUMLEIN, of 37, The Ridings, Ealing, London, W.5, a British subject, do hereby declare the nature of this invention to be as follows:

This invention relates to electric cables.

For the reception of wireless signals it is sometimes desirable to connect a receiving aerial to a radio receiver by a down-lead which has an impedance of about 400 ohms. For example, in some cases it is desirable to employ a lead-in wire and a dummy down-lead which should have such an impedance but difficulties arise in obtaining a cable of the required impedance owing to the fact that the diameter of the conductor which it is then necessary to employ is inconveniently thin and in manipulating the cable during fixing the conductor is frequently broken. The usual type of twin down-lead for a radio receiver consists of an outer sheath of insulating material, such as a rubber, the shape of the insulating sheath being of a substantially dumb-bell shape with a conductor embedded in each of the cylindrical end portions of the insulator. The conductor in the known form of a cable is relatively thick and good results are not obtained in using such a cable in special cases owing to the fact that the impedance of the cable is too low.

The chief object of the present invention is to provide an improved cable which, whilst enabling thin conductors to be employed to afford the necessary high impedance, does not present the difficulty of the conductors fracturing during manipulation.

According to the present invention a cable is provided in which two conductors are arranged side by side in insulating material each conductor being crinkled or deformed at intervals along its length whereby on tensioning the insulating material the crinkled or deformed portions permit extension of the conductors whereby the latter are relieved of any undue tension such as a cause fracture thereof. The conductors can therefore be made of the required thin wire the gauge varying, for example, from 20 to 40 SWG and since the conductors are capable of extension very little danger occurs of the conductors being fractured during installation of the cable.

For the purpose of explaining the invention more in detail reference will be made to the accompanying diagrammatic drawings in which:

Figure 1 is a cross sectional view of one form of cable constructed in accordance with the invention,

Figure 2 is a sectional view along the line 2-2 of Figure 1,

Figure 3 is a cross sectional view of the cable similar to that shown in Figure 1 and according to a modified form of the invention,

Figure 4 is a cross sectional view of a further form of cable in accordance with the invention,

Figure 5 is an enlarged view of a crinkled or deformed conductor suitable for use in the invention, and

Figure 6 illustrates diagrammatically a machine for forming the cable shown in Figure 4.

As shown in Figure 1, the cable comprises a pair of conductors 7 and 8 embedded in a substantially dumb-bell shaped sheath of insulation 9. As shown in Figure 2 the conductors 7 and 8 are crinkled along their lengths so that if the cable is placed under tension of the conductors 7 and 8 can expand whereby no undue tension sufficient to fracture the conductors 7 and 8 can ordinarily be imparted thereto. The sheath 9 in the example shown in Figures 1 and 2 is preferably made of rubber and during manufacture the conductors 7 and 8 may be fed to an extruding press the dies of the press being so shaped that the rubber insulation is extruded in the form shown in Figure 1, the conductors being embedded, as shown, in the cylindrical edges of the sheath. Where the cable is designed to present an impedance of, for example, 400 ohms, the conductors may be of 36 SWG gauge and conveniently formed of an alloy or cadmium and copper such alloy being sometimes referred to as cadmium-bronze. Instead of embedding the conductors 7 and 8 in the sheath 9 the cylindrical edges of the sheath may, as shown in Figure 3, be provided with ducts 10 and 11 in which the conductors 7 and 8 are arranged so that the conductors are in effect air-spaced from the sheath 9 thereby decreasing the average dielectric constant. This decrease of average dielectric constant further increases the impedance and also reduces the power losses.

If desired, instead of forming the sheath 9 of a substantially dumb-bell shape, as shown, the sheath 9 may be of a substantially constant cross section.

Figure 4 of the drawings illustrates an alternative form of the invention in which the insulating sheath is formed of two sections 12 and 13, each section being provided with grooves adjacent its longitudinal edges, as shown, whereby when the sections are assembled as shown in Figure 4, the longitudinal grooves constitute ducts in which the conductors 7 and 8 are arranged. The sections 12 and 13 may conveniently be formed of the material known by the Registered Trade Mark ‘Celastoid’ or other similar material such as paper or fabric treated with a thermoplastic insulating material. The two sections 12 and 13 are suitably secured together after the conductors 7 and 8 are inserted in the ducts.

Figure 5 of the drawing illustrates a crinkled conductor suitable for use in the invention which differs from the conductors shown in Figures 1 to 4 in that instead of the conductors being crinkled continuously, crinkled portions 14 are provided at intervals along the length of the conductor the intermediate portions of the conductor being substantially straight, as shown.

Figure 6 of the drawings illustrates a convenient method of assembling the cables shown in Figure 4. As shown, two lengths of wire 7 and 8 to form the crinkled conductors of the form shown in Figure 2 or 5 are fed between two pairs of crinkled rolls 15 and 16 and after crinkling the two sections 12 and 13 is fed into the path of the conductors 7 and 8 so that the conductors are ultimately fed into the ducts formed by the two sections, the two sections being super imposed as shown in Figure 4. The sections are secured together by passing them through two pairs of heated pressing rolls 17, 18, 19 only one pair of which is shown in Figure 6, the heated rolls serving to soften the thermoplastic material so that the two sections shown adhere to one another. The rolls 18 serve to secure the central portions of the sections together and the rolls 17 and 19 serve to secure the longitudinal edges of the section.

If desired, the sections 12 and 13 may be formed of relatively stiff paper and the two sections gummed or otherwise secured together. The cable shown in Figure 4 and particularly when the sections 12 and 13 are formed of paper may be provided with a suitable weather-proofing compound is necessary.

If desired, instead of the cable being constructed so that a single sheath houses a pair of conductors as described above, a substantially cylindrical or other suitably shaped sheath may be arranged to house only a single conductor of the form described above, or alternatively, a single sheath may be constructed to contain more than two conductors of the form described.

It may in some cases be necessary to apply the invention to relatively large cables for use as high power feeders, in which case similar constructions to those referred to above may be used with thicker conductors up to a gauge, for example, of 10 or 12 SWG.

Dated this 7th day of October, 1937

F. W. Cackett

Chartered Patent Agent

COMPLETE SPECIFICATION

I, ALAN DOWER BLUMLEIN, of 37, The Ridings, Ealing, London, W.5, a British subject, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

This invention relates to electric cables.

For the reception of wireless signals it is sometimes desirable to connect a receiving aerial to a radio receiver by a down-lead which has an impedance of about 400 ohms. For example, in some cases it is desirable to employ a lead-in wire and a dummy down-lead which should have such an impedance but difficulties arise in obtaining a cable of the required impedance owing to the fact that the diameter of the conductor which it is then necessary to employ is inconveniently thin and in manipulating the cable during fixing the conductor is frequently broken. The usual type of twin down-lead for a radio receiver consists of an outer sheath of insulating material, such as a rubber, the shape of the insulating sheath being of a substantially dumb-bell shape with a conductor embedded in each of the cylindrical end portions of the insulator. The conductor in the known form of a cable is relatively thick and good results are not obtained in using such a cable in special cases owing to the fact that the impedance of the cable is too low.

The object of the present invention is to provide an improved flexible cable which, whilst enabling a thin conductor to be employed to afford the necessary high impedance, does not present the difficulty of the conductor fracturing during manipulation.

According to the present invention a flexible cable is provided comprising at least two conductors arranged side by side and maintained in spaced relation and insulated from one another by a common sheath of insulating material, the conductors being crinkled or otherwise deformed along their lengths in such a manner that when the insulating material is tensioned said crinkled or deformed portions permit extension of the conductors whereby the latter are relieved by any undue tension such as would cause fracture thereof. With a cable in accordance with the invention the conductor or conductors can be made of the required thin wire the gauge varying for example from 20 to 40 S.W.G. and since the conductors are capable of extension very little danger occurs of the conductors being fractured during installation of the cable. A high frequency cable has been proposed in the Specification of Patent No. 452,772 in which a pair of wires of 40 S.W.G. deformed along their lengths by bending the wires to a substantially sine wave form, are arranged side by side and maintained in spaced-apart relationship by individual sheaths of insulating material each surrounded by conducting sheaths and with further sheaths of insulating material, the two wires and their individual sheaths being arranged in an insulating binding in turn surrounded by a lead sheath. The present invention mainly distinguishes from this prior Specification in that each conductor is maintained in spaced-apart relationship and insulated from one another by a common sheath of insulating material. Moreover, the provision of the conducting sheath in the prior Specification would render the cable unsuitable for employment in the invention disclosed in the Specification of the co-pending Application.

In order that the said invention may be clearly understood and readily carried into effect the same will now be more fully described with reference to the diagrammatic drawings accompanying the Provisional Specification, in which:-

Figure 1 is a cross sectional view of one form of cable constructed in accordance with the invention,

Figure 2 is a sectional view along the line 2-2 of Figure 1,

Figure 3 is a cross sectional view of the cable similar to that shown in Figure 1 and according to a modified form of the invention,

Figure 4 is a cross sectional view of a further form of cable in accordance with the invention,

Figure 5 is an enlarged view of a crinkled or deformed conductor suitable for use in the invention, and

Figure 6 illustrates diagrammatically a machine for forming the cable shown in Figure 4.

As shown in Figure 1, the cable comprises a pair of conductors 7 and 8 embedded in a substantially dumb-bell shaped sheath of insulation 9. As shown in Figure 2 the conductors 7 and 8 are crinkled along their lengths so that if the cable is placed under tension of the conductors 7 and 8 can expand whereby no undue tension sufficient to fracture the conductors 7 and 8 can ordinarily be imparted thereto. The sheath 9 in the example shown in Figures 1 and 2 is preferably made of rubber and during manufacture the conductors 7 and 8 may be fed to an extruding press the dies of the press being so shaped that the rubber insulation is extruded in the form shown in Figure 1, the conductors being embedded, as shown, in the cylindrical edges of the sheath. Where the cable is designed to present an impedance of, for example, 400 ohms, the conductors may be of 36 SWG gauge and conveniently formed of an alloy or cadmium and copper such alloy being sometimes referred to as cadmium-bronze. Instead of embedding the conductors 7 and 8 in the sheath 9 the cylindrical edges of the sheath may, as shown in Figure 3, be provided with ducts 10 and 11 in which the conductors 7 and 8 are arranged so that the conductors are in effect air-spaced from the sheath 9 thereby decreasing the average dielectric constant. This decrease of average dielectric constant further increases the impedance and also reduces the power losses.

If desired, instead of forming the sheath 9 of a substantially dumb-bell shape, as shown, the sheath 9 may be of a substantially constant cross section.

Figure 4 of the drawings illustrates an alternative form of the invention in which the insulating sheath is formed of two sections 12 and 13, each section being provided with grooves adjacent its longitudinal edges, as shown, whereby when the sections are assembled as shown in Figure 4, the longitudinal grooves constitute ducts in which the conductors 7 and 8 are arranged. The sections 12 and 13 may conveniently be formed of the material known by the Registered Trade Mark ‘Celastoid’ or other similar material such as paper or fabric treated with a thermoplastic insulating material. The two sections 12 and 13 are suitably secured together after the conductors 7 and 8 are inserted in the ducts.

Figure 5 of the drawing illustrates a crinkled conductor suitable for use in the invention which differs from the conductors shown in Figures 1 to 4 in that instead of the conductors being crinkled continuously, crinkled portions 14 are provided at intervals along the length of the conductor the intermediate portions of the conductor being substantially straight, as shown.

Figure 6 of the drawings illustrates a convenient method of assembling the cables shown in Figure 4. As shown, two lengths of wire 7 and 8 to form the crinkled conductors of the form shown in Figure 2 or 5 are fed between two pairs of crinkled rolls 15 and 16 and after crinkling the two sections 12 and 13 is fed into the path of the conductors 7 and 8 so that the conductors are ultimately fed into the ducts formed by the two sections, the two sections being super imposed as shown in Figure 4. The sections are secured together by passing them through two pairs of heated pressing rolls 17, 18, 19 only one pair of which is shown in Figure 6, the heated rolls serving to soften the thermoplastic material so that the two sections shown adhere to one another. The rolls 18 serve to secure the central portions of the sections together and the rolls 17 and 19 serve to secure the longitudinal edges of the section.

If desired, the sections 12 and 13 may be formed of relatively stiff paper and the two sections gummed or otherwise secured together. The cable shown in Figure 4 and particularly when the sections 12 and 13 are formed of paper may be provided with a suitable weather-proofing compound is necessary.

It may in some cases be necessary to apply the invention to relatively large cables for use as high power feeders, in which case similar constructions to those referred to above may be used with thicker conductors up to a gauge, for example, of 10 or 20 SWG.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

  1. An electric flexible cable comprising at least two conductors arranged side by side and maintained in spaced relation and insulated from one another by a common sheath of insulating material, the conductors being crinkled or otherwise deformed along their lengths in such a manner that when the insulating material is tensioned said crinkled or deformed portions permit extension of the conductors whereby the latter are relieved of any undue tension such as would cause fracture thereof.
  2. A cable according to claim 1, where in the sheath is of a substantially dumb-bell shape is cross-section with the conductors arranged in the cylindrical edge of the sheath.
  3. A cable according to claim 1 or 2 wherein the conductors are embedded in said insulating material.
  4. A cable according to claim 1 or 2 wherein the conductors are arranged in ducts in said sheath.
  5. A cable according to claim 1 or2 wherein the sheath is formed of two sections of insulating material each section having grooves along its longitudinal edges so as to provide longitudinal ducts when the sections are assembled together said sections being assembled with the conductors in said ducts, said sections being secured together to maintain the conductors in position.
  6. An electric flexible cable substantially as described with reference to Figures 1 and 2 or Figure 3 or 4 or Figure 5 of the drawings accompanying the Provisional Specification.

Dated this 21st day of September 1938

F. W. Cackett

Chartered Patent Agent