US2288900A - Method of and means for making coaxial cables - Google Patents

Description

.J. P. GITS July 7, 1942.

METHOD OF AND MEANS FOR MAKING COAXIAL CABLES 2 Sheets-Sheet 1 Original Filed Jan. 15, 1940 AALAAA 'AAAAAA'AAA V V V 14-79" ,4; 17 AA[AAA\/{ /AAAAAAA Patented July 7, 1 942 METHOD or AND MEANS FOR MAKING COAXIAL CABLES Jules P. Gits, Chicago, 1u., assignor to Gits Moldin; Corporation, Chicago, 111., a corporation of Illinois Original application January 15, 1940, Serial No. 313,846. Divided and this application October 17, 1940, Serial No. 361,508

8 Claims.

This invention relates broadly to coaxial cable construction and more particularly to a coaxial cable adapted especially for use as a lead-in of television antennas and the like.

New effects are introduced in the handling of ultra high frequency waves in television transmission and reception. Adequate pick-up at ultra frequencies requires an antenna of a dipole construction having such dimensions as to be tuned to the incoming signals. Fundamentally, the di-pole consists of a rod one-half wave length long. The rod is cut apart at the center, and usually a twisted pair, with one wire joined to each half of the rod, is brought down to the receiving set. Care must be exercised to locate and mount the antenna in order to secure maximum signal pick-up and avoid interference. To illustrate the difiiculties of proper reception, lack of proper signal delivery produces gray and indistinct pictures, while static interference prevents obtaining any picture at all if the antenna is not picking up enough signal. If the signals are weak, enough pick-up might be obtained to form a picture, but the synchronizing impulses may not be strong enough to hold the picture. This will cause drift, no matter how carefully the vertical hold control is adjusted. On the other hand, a slight static impulse might cause each time a slip of one frame of the picture.

One common source of interference is from automobile ignition. The di-pole of the antenna must be located quite often at high locations to reduce or to avoid this interference, and to prevent surrounding high guildings from acting as a shield to theantenna. A long lead-in is therefore required but the signal gain may not offset the added resistance of the lead. To overcome this, since the lead may not be shortened, a

coaxial cable has been suggested for the twisted structed to prevent pick-up and thus avoid in-.

of static interference, or improper insulation be-. tween the conductors ofthe lead-in connecting each section of the di-pole may cause the same trouble or pick up magnetic or radiation dis- I turbances in the vicinity of the receiver.

Broadly, this invention is directed to an improved type of coaxial cable adapted particularly 'for use as the lead-in between a television antenna and receiver, or as the concentric tubes in television transmitting aerials, whereby to overcome the dilficulties heretofore experienced, and to an improved method of making this coaxial cable whereby a very simple and eillcient structure will be provided at minimum cost which method has been disclosed and claimed in my copending application, Serial No. 313,846, filed January 15, 1940, of which this application is a division.

Specifically, the invention relates to a cable structure, and a method of making the same, that includes coaxial or concentric conductors spaced from each other by spaced dielectric members, preferably non-absorptive of moisture, whereby the dielectric members together with the air chambers or pockets formedtherebetween provide an efiicient type of insulation between the coaxial conductors and an eflicient shield against disturbances or pick-ups.

The method herein disclosed novelly includes passing the center conductor through a die block, molding a plurality of spacers thereon and affixing these spacers upon this center conductor by molecular tension resulting from shrinkage or contraction of the thermo-plastic material employed, the spacing of these spacers themselves along the center conductor and the immovable aifixation thereof in this spaced relation being advantageously accomplished preferably by a single molding operation. It will be understood that the outer conductor may be a single tubular or laminated member or a fabricated structure that may be spun or otherwise placed about these spacers. The final layer or coating of insulation may thereafter be formed about the outer conductor. If used in high frequency'transmission, the outer layer may be a lead sheath or like material.

It will be remembered that the method herein disclosed is noted for its simplicity and low cost of operation, and for its ability rapidly to place these spacer members upon the center conductor in a single operation, the forming operation placing these spacer members along the central conductor at predetermined distances and the rapid cooling thereof causing amxation thereof in this spaced relation without additional labor or other expense. The space between these members may form sealed air pockets between is mentioned only as an example.

apart.

any moisture that will break down this insulation. 8

Although the cable herein disclosed is described as being particularly useful as a lead-in between the di-poles of a television antenna and receiver and as the concentric tubes in transmitting aerials, it will be understood that the cable is capable of many uses and is not to be confined to the specific examples given or to a cable necessarily having the outer conductor coaxial with the inner conductor.

Other objects and advantages of the invention will be apparent from the following detail description when taken in connection with the accompanying drawings which forms a part hereof.

In the drawings:

Figure l is an enlarged cross section of a portion of a coaxial or concentric cable embodying the invention;

F 2 is a view at a smaller scale of the central conductor;

Fig. 3 illustrates the method of forming the insulation spacers upon the central conductor; Fig. 4 illustrates the central conductor after.

removed from the die but before the trimming operation;

Fig. 5 is a transverse section through the center of the die block shown in Fig.3;

Fig. 6 is a view similar to Fig. l but illustrating a modification of the structure shown;

Fig. 7 illustrates a further variant embodiment of the invention;

Fig. 8 is a view similar to Fig. 3 and illustrates how the spacing members may be formed by a single operation upon any member of center conductors passing through a die block at one time;

Fig. 9 illustrates a still further variant embodiment of the invention; and

Fig. 10 also illustrates a further embodiment of the invention.

The coaxial cable herein disclosed comprises an inner or central conductor 5, an outer conductor 6 and a plurality of spacing members 1 disposed along the central conductor 5. Spacing members 1 are preferably made of a thermoplastic material eharacterized mainly by its insulation qualities-and ability to be non-absorptive of moisture. I find polystyrene to be an excellent thermo-plastic material for this purpose. It has excellent insulation properties which ap proximate those of air and has a dielectric constant of 2.6 at 60 cycles. For all practical pur poses, this material is considered non-absorptive of moisture. It will be understood, however, that other materials may be used and that polystyrene Spacing members 1 are molded directly upon central conductor 5. They are cooled upon central conductor 5 so that they will contract and thereby be aflixed thereto in a predetermined spaced relation by molecular tension. In other words, the material of these spacing members 1 gripthe central conductor by molecular tension produced by contraction upon molecular tension to produce the aflixation of spacing members 1 upon central conductor 5, as I use it herein, is the result produced, I believe, from injecting the thermoplastic material in material in molten form in die cavities as distinuished from mere heating and then squeezing.

These members 1 thereby become immovably af-- fixed in spaced relation along central conductor 5 cooling; The term central conductor 5 in spaced relation with the without requiring any additional operation or means to keep them spaced at proper distances As disclosed, the method of making the coaxial cable includes passing central conductor 5 through adie 3 comprising a matrix 9- and a patrix in (Fig. 5) having a plurality of recesses or cavities I! cut therein corresponding to the desired shape or configuration of spacing members 1. These recesses II are arranged to communicate by pairs with passages l2 that connect with a main passage l3 communicating with a transverse passage l4 leading to a source of supply. Each passage I2 is divided as indicated at 15 and communicates with its pair of recesses H b opening into these recesses along one of their faces and not at their peripheral edge. Any number of recesses H may be provided in die 8 so that a corresponding numberof spacing members 1 may be formed in one molding operation. The arrangement of passages l2, l3 and I 4 may also be changed, but I consider it advantageous to communicate with each. recess H as shown so that the plastic material may be injected at 'one side and not at the peripheral edge.

Fig. 3 illustrats several central conductors 5 die 8 by a predetermined stepped movement and being rolled upon spool I! with spacing members 1 formed thereon. Fig. 4 illustrates a section of one'pf the central conductors 5 with spacing members 1 formed thereon as removed from die 8 following a molding operation. The thermoplastic material has been cooled and spacing members 1 that have been formed are fixed upon usual tailings attached, these tailings representing the material'that flows into passages l2, I3 and I4 upon each injection. With the material cooled or set, these are readily removed by being broken or severed at the point where they connect to the sides of spacing members 1, it being noted that the points of connection between each side face and the tailing is small in cross section, and

consequently, the material will break at this point without leaving surplus material projecting from the side faces of the spacing members. The cooling of the thermo-plastic material is relatively rapid. Die 8 may be suitably cooled, as by water, so that the material may be sufficiently cool when removed to permit tailings to be severed almost immediately. In this manner, the method is continuous and spacing members may be molded in fixed spaced relation upon their central conductor 5 in one operation without requiring intervmediate spacers between the members 1 or the usual tedious manual operation of threading the.

members 1 upon the central conductor with intermediate spacers interposed or other means employed to hold members 1 properly spaced.

Fig. 3 illustrates how two central conductors may be passed through die 8 at the same'time. This permits spacing members on two conductors to be formed in one injection operation and in practically the same time as would be required for one conductor. Die 8 may be constructed so that any number of conductors may be passed therethrough to have spacing members 1 formed thereon in one injection of the thermo-plastic material,

Spacing members 1 are uniform in shape and are uniformly spaced along conductor 5, and, when inserted in outer conductor 6, their periphery will uniformly contact the inner surface of thisouter conductor so that a plurality of longitudinally spaced air chambers 20, completely closed off from one another, may be formed be- 2,2es,eoo 3 tween these conductors along the entire length of the coaxial cable.

Outer conductor 6 may be a single tubular or laminated member through which central conductor is pulled with spacing members 1 formed thereon, or it may be a fabricated structure that may be spun or otherwise formed about the spacing members 1, to provide the structure shown in Fig. 1. One or more final layers or coatings of insulation 2| may thereafter be formed about outer conductor 6. If used on high frequency transmission, the outer layer may be a lead sheath 22 or like material.

From the foregoing description it will be apparent that the method herein disclosed results in forming any number of spacing members 1 at one time along the inner conductor of a coaxial cable in a fixed spaced relation. This eliminates tedious and expensive assemblies that require additional parts which do not always assure a structure' uniformly made. Moreover, the molecular tension of the thermo-plastic material holding these members I in fixed relation may actually seal these members upon the inner conductor. Air pockets are thereby provided that increase the efliciency of the coaxial cable as a lead-in for a television receiver because it will prevent pick-up of undesirable signal waves and interference disturbances produced from magnetic and radiation effects. It will be also noted that thermo-plastic material has a certain cold flow which may, in time, advantageously form a peripheral seal between the contacting edge of members 1 and outer conductor 6 if this contacting edge should fail to engage the outer conductor tightly. In either event, the contacting engagement will be augmented by the cold flow to assure a tight seal. Hence, moisture will not pass from one air pocket to another, and the pockets will constitute an effective shield against magnetic and radiation disturbances between the di-poles of the antenna and the receiver. The omission of longitudinal spacers between the spacing members 1 increases the efficiency of the cable because the central conductor is thereby exposed to a sealed pocket of air, which acts as a better insulator and shield against the pick-up of undesirable effects along a lead-in between the antenna and receiver.

If the flexibility of central conductor 5 should cause spacing members I to turn or twist when the same is inserted in outer conductor 5 or when outer conductor5 is spun or woven thereabout. edge 24 of one of the die members may be cut away slightly to form a small groove along the groove receiving the conductor. In the ejection operation, this groove will fill with thermoplastic material, so that, when the wire is removed from the die, a longitudinal rib 25 shown in Fig. 6 is formed along conductor 5 between spacing members T. In this manner, conductor 5 is reinforced and the spacing members are prevented from twisting or turning. It will be understood, how

ever, that spacing members 1 may be made of greater dimension along conductor 5, if so desired, to secure a surface engagement larger than shown. 1

The method disclosed is exceedingly simple and inexpensive to practice. The product is likewise simple and inexpensive and may be produced at a fraction of the cost of coaxial cables heretofore constructed.

It will be understood that the method of forming insulated spacing members I is not necessarily limited to a central conductor of a coaxial cable but may be used in other types of cables where it is desirable to space one or more inner conductors within an outer tubular conductor.

However, the cable herein disclosed provides a very efficient cable structure for use as the leadin between a television antenna and receiver. The conductors thereof are effectively insulated from one another to prevent any pick-up of magnetic or radiation disturbances as well as any pick-up of signal waves between the antenna and the receiver.

I wish it to be understood, however, that central conductor5 may be completely surrounded by a layer 26 of insulating material, as shown in Fig. '7, in order more effectively to reinforce spacing members 1 against twisting if there is any tendency for these spacing members totwist when pulled through outer conductor 5 or when this outer conductor 6 is spun or built-up upon center conductor 5 and about the spacing members. I also find this concentric layer 26 'very useful to reinforce center conductor 5 when formed of wire" that is not sufiiciently stiff to hold its shape or is of such a flexible character that it will tend to bend at or adjacent the point where it enters these spacing members, either through normal handling or when outer conductor 5 is placed about the spacing members.

When concentric layer 26 is used, the construction of the die adapted to be used will be somewhat simpler. As shown in Fig. 8, grooves 21 receiving center conductors 5 will be provided with a larger diameter than the diameter of these conductors so that the molding material will flow about the center conductors lying in these grcovesll and into recesses H. Passages l2 and their manner of connecting to the side of recesses H may be eliminated. When a number of center conductors are passed through a single die at one time, as shown in Fig. 8, a single communicating. passage 28 connected to a transverse passage 29 may extend to each central conductor groove 21. No other passage in the die is necessary unless it is desired.

Fig. 9 illustrates another embodiment giving greater rigidity between spacing members 1 near their peripheries, which I find very effectively prevents any twisting of these members I and still permits the use of air as insulation between both conductors 5 and 5. In this connection, spacing members I may be provided with strips 30 that may be preferably formed during the members.

Fig. 10 also illustrates accomplishing substantially the same result by enlarging the area of contact between spacing members 1' and center conductor 5. Although this illustration shows spacing members 1' as being of diamond shape and the preceding illustrations show spacing members I as being of disk shape, it will be understood that other shapes may be used and are contemplated as being within the scope of the invention.

Without further elaboration, the foregoing will so fully explain the gistof my invention that others may, by applying current knowledge, readily adapt the same for use under varying conditions of service, without eliminating certain features, which mayproperly be said to constitute the essential items of novelty involved, which items are intended to be defined and secured to me by the following claims.

I claim:

1. A coaxial cable comprising a central consaid central conductor and being held thereon by the molecular tension of the material out of which said spacing members are formed.

2. A coaxial cable comprising a central conductor, a tubular conductor coaxial with said central conductor, and a plurality of insulation members for axially spacing said conductors,.

said insulation members being of a material having greater shrinkage properties upon cooling than said central conductor, said insulation members being molded upon and spaced apart in fixed relation along said central conductor and immovably heldby molecular tension of the material out of which said members are formed.

3. A coaxial cable comprising a central conductor, a tubular conductor coaxial with said central conductor, aplurality of molded bodies of insulation material having greater shrinkage properties upon cooling than said central conductor, said bodies of insulation material being molded and held by the molecular tension of said material upon, said central conductor at predetermined distances apart to support said cen- 1 tral conductor in insulation relation within said tubular conductor, and a layer of insulation disposed about said tubular conductor.

4. In a coaxial cable, an outer tubular conductor, a central conductor, and a plurality of spacing members in the form' of molded annular bodies of insulation material between said conductors arranged in spaced relation upon said central conductor, said insulation material between adjacent annular spacing bodies extending along and upon said central conductor in integrally molded relation with said annularspacing bodies, both said bodies and said extensions therebetween being immovably affixed to said central conductor by the molecular tension of said molded insulation material.

'5. In a coaxial cable, an outer tubular conductor, a centralconductor, a plurality of spacing members in the form of molded annular bodies of insulation material between said conductors arranged in spaced relation upon said cen- "about their peripheries tral conductor, and an annular sleeve between adjacent annular spacing bodies extending along and upon said central conductor in integrally molded relation with said annular spacing bodies, both said bodies and said sleeves therebetween being immovably aflixed to said central conductor by the molecular tension of said molded insulation material hermetically sealing said central conductor therein.

6. A central conductor for a coaxial cable having a plurality of molded spacing bodies of insulation material having greater shrinkage properties upon cooling than said central conductor, said spacing bodies being molded upon said central conductor and being held thereon by the molecular tension of said molded insulation material out of which said spacing bodies are formed.

7. A coaxial cable formed with a plurality of separate gas containing pockets that are hermetically sealed one from another, which comprises an inner conductor, a plurality of spaced bodies of insulated material hermetically sealed upon said inner conductor in fixed position the g spacing between said bodies of insulation material constituting said pockets, and an outer tubular conductor about said inner said conductor and said bodies 0; insulation material, said bodies of insulation material being hermetically sealed with said outer tubular conductor. a

8. A coaxial cable formed with a plurality of separate gas containing pockets that are hermetically sealed one from another which comprises an inner conductor, a plurality of spaced annular bodies of insulation material hermetically sealed upon said inner conductor in fixed position, an outer tubular conductor about said inner conductor and said bodies .of insulation, said bodies of insulation also being hermetically sealed about their peripheries with said outer tubular conductor to provide thereby hermetically sealed spaces that form said separate gas containing pockets, and means between saidannular bodies of insulation material to reinforce said bodies against a tilting or twisting action that will destroy said hermetical seal between their said peripheries and said outer tubular conductor.

JULES P. GITS.

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