US2520991A - Method of making low-loss delay lines - Google Patents

Description

Sept. 5, 1950 J. YoLLEs ETHOD 0F HAKING LOW LOSS DELAY LINES Filed Sept. 6', 1944 INVENTUR. l Jia? ,Va/f5 Patented Sept. 5, 1950 METHOD F MAKING LOW-LOSS DELAY LINES Jack Yolles, Dayton, Ohio i Application September 6, 1944, Serial No. 552,857

2 Claims. (Cl. 154-228) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

The invention to be hereinafter described relates to radio low loss delay lines and method of making same.

It is a recognized fact that radio waves travel at the rate of about 1000 feet per microsecond. It is frequently and for -many purposes desired to delay radio messages. A well known delay practice is that of simply lengthening the path of travel and a recognized way of doing this is to Wind the inner conductor of a coaxial line spirally so that the message, following the conductor, will have a correspondingly longer or greater path to travel, relative to the length of the spiral. A serious difficulty in this spiral winding is lack of uniform spacing of the helices, resulting in reilections and corresponding objections. This difficulty is increased by application of an outer dielectric layer because during that application the helices are more or less disturbed with resulting alteration of the spacing.

The main objects of the present invention are to overcome the above and other objections and provide a simple, eilicient, compact, flexible, low attenuation, high delay coaxial line.

In order to more clearly disclose the construction, operation and use of the invention reference should be had to the accompanying drawings forming part of the present application.

Throughout the several gures of the drawings, like reference characters designate the same parts in the diilerent views.

In the drawings:

Fig. 1 is a side elevation, showing the several parts successively, partly stripped back;

Fig. 2 is an enlarged central longitudinal section of Fig. 1; and

Fig. 3 is an enlarged lateral crossx section of Fig. 2.

As illustrated in the drawings, a single centrally disposed copper conductor in the form of a rod or wire is used. This may or may not be used according to particular circumstances, as

As one example of one line embodying the present invention the following will serve to illustrate. About a 1A diameter dielectric core l of a polystyrene derivative is spirally wound a No. 22 bare uninsulated copper wire 2 at the rate of approximately 16 helices to the inch all uniformly spaced. In winding, the wire is slightly embedded in the plastic so that the successive helices become denitely seated and anchored in place thereby maintaining their uniformity of spacing. Over this spirally wound conductor is extruded a polyethylene layer s to a thickness of 312. Polyethylene is suiiciently lower in melting point than the polystyrene derivative to permit the required temperature for practical extrusion without risking softening of the polystyrene derivative at time and point of contact between the two. Thus, the polyethylene cuter dielectric layer is thoroughly and completely molded about, between, around and over the helices, the seating or anchorage of the helices remaining undisturbed and the uniform spacing being maintained. As the polyethylene layer solidies, the helices will be completely embedded, mostly within it, and partly within the polystyrene, the uniu form spacing being permanently maintained. By extruding the outer dielectric on the conductor wound spirally on the inner dielectric, the di-v electrics become thoroughly molded about the Wire minimizing or completely eliminating all air gaps and all physical discontinuities. About this polyethylene layer is disposed a tightly woven copper braid d as the cuter conductor. About this entire assembly is disposed a chemically inert weather tight jacket 5.

While certain plastic dielectrics have been specifically mentioned, such mention is purely by way of example and with no thought of limitation. Many other plastic dielectric materials are thoroughly practical and could be used either substantially equally well, or, at least with ample satisfaction. An essential characteristic of the dielectric is that it shall show relatively low loss in use with ultra high frequencies. It should also be ilexible. Where extrudable material is used for the outer dielectric, its melting point must be appreciably lower than that of the inner dielectric material to avoid softening of the inner dielectric material when the two contact and consequent disarrangement of the conductor helices.

While the outer dielectric may be applied in other ways than by extrusion, application by extrusion is a simple, eflicient, practical, relatively quick and highly satisfactory way for the specic dielectric named as Well as for others.

Extrusion application also has the advantage of minimizing or completely eliminating all air gaps and all physical discontinuities. While No. 22 wire has been referred to and 16 helices to the inch about a 1A" core stated as an example, it will be well understood that various other sizes of wire and core and various other pitches of helices are within the eld of the invention according to the particular circumstances. Likewise, as to the thickness of the layer oi the second dielectric.

A coaxial conductor or line made in accordance with the above method is ilexible and has both low attenuation with ultra high frequencies and high delay.

It is believed that the construction, operation and use of the invention and method involved therein will be clear from the preceding detailed description.

Many changes may be made in the construction, arrangement and disposition of the parts of the invention and in the steps of the method involved therein, within the scope of the appended claims, Without departing from the eld of the invention and it is meant to include all such within this application wherein only one preferred form of the invention has been illustrated purely by way of example and with no thought or intention to, in any degree, limit the invention thereby.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A method of making an electrical cable including the steps o! forming a smooth surfaced cylindrical core of dielectric material, helically winding an electrical conductor tightly around said core so that the turns of said helix are uniformly spaced and are slightly embedded into the surface of said core, extruding a tubular layer of dielectric material having a lower melting point than that of the core about said core and said conductor so as to completely surround all exposed portions of said conductor and secure said conductor against movement relative to said core and layer, said extruded layer of dielectric 4 material being applied at a temperature high enough so that it will completely ll said exposed 4 portions, but low enough so that said\.cylindrical core oi' dielectric material will not soften, and forming a tubular outer conductor about said layer.

2. A method of making a flexible high-trequency delay line comprising the steps of forming a ilexible cylindrical' core of highmelting point dielectric material, winding an electrcal conductor around said core to form a uniformly spaced highly inductive helix embedded in the surface of said core, applying a ilexible tubular layer of lower melting point thermoplastic dielectric material about said core and conductor at sumcient heat and pressure to cause only said thermoplastic material to now and completely surround and contact all exposed portions of said conductor and said core thereby further securing said conductor against movement relative to said core. said thermoplastic dielectric material being applied at a temperature high enough so that all of said exposed portions are completely surrounded, but low enough so that said cylindrical core will not soften, and surrounding said tubular layer with a close itting outer tubular` conductor to form with said helix a concentric-high-frequency delay line.

JACK YOLLES.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,442,648 Carter Jan, 16, 1923 1,707,700 Wodtke Apr. 2, 1929 2,090,510 Bower Aug. 17, 1937 2,163,235 Chatham June 20, 1939 2,218,979 Arutunoilf Oct. 22, 1940 2,294,919 Lunsford Sept. 8, 1942 2,387,783 Tawney Oct. 30, 1945 FOREIGN PATENTS Number Country Date 21,377 Great Britain Oct. 14, 1893 of 1892 383,528 Great Britain of 1932

Images