US2193017A

US2193017A - Lead-in conductor

Info

Publication number: US2193017A
Application number: US126352A
Authority: US
Inventors: Jr Rex Earl Bassett
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-02-18
Filing date: 1937-02-18
Publication date: 1940-03-12
Anticipated expiration: 1957-03-12

Description

Mam}! 1940- R. E. BASSETT. JR 7 2,193,017

LEAD-IN CONDUCTOR Original Filed Feb. 18, 1937 2 Sheets-Sheet ,1

iNVENTOR I Rex or/ 50888:: L/n BY m ATTORNEY March 12, 1940.

R. E. BAssETT. JR

LEAD-IN CONDUCTOR originai Filed Feb. 18, 1937 2 Sheets-Sheet 2 INVENTQR or/ Bassetzf L//- ATTORNEY Patented Mar. 12, 1940 UNITED STATES PATENT OFFICE Application February 18, 1937, Serial No. 126,352

Renewed August 8, 1939 3 Claims.

The present invention relates to radio aerials and particularly to improvements in transmission lines and couplings used in the construction thereof. This application discloses an improvement upon the apparatus described in application Serial No. 99,571 filed in the name of Rex Earl Bassett, Jr., on September 5, 1936, and is a continuation in part of application Serial No. 99,571.

In order to improve both the transmission and reception of radio signals, it has been found desirable to erect the antenna Where it is as free as possible from local interference. Accordingly, transmission lines have been utilized to transmit the signal energy to the antenna from the transmitter and from the antenna to the receiver. Transmission lines have been used extensively with antennae of the doublet type, which have been found very suitable for the reception of both short wave and the regular broadcast range frequencie Heretofore, a concentric transmission line has usually consisted of a hollow tube of conducting material with a conductor suspended axially thereof by suitable insulators. Lines of this type not only are expensive to manufacture, but require a considerable outlay for upkeep. Usually they are filled with dry nitrogen gas under pressure, to prevent dielectric failure due to con densation of moisture inside the line.

Recently, transmission lines of the above type have been largely displaced by the twisted pair line, consisting merely of two insulated wires twisted together. The insulation most often used has been rubber, but because of the susceptibility of rubber to atmospheric conditions the average life of the line is not very great. Collection of moisture between conductors causes it to function unsatisfactorily.

The principal object of the invention is to provide a new and improved flexible transmission line that may be easily and efliciently secured to antennae.

Further objects and advantages of the invention are apparent from the description, in which reference is had to the accompanying drawings illustrating preferred embodiments of the invention.

Fig. I of the drawings is a vertical section, showing a preferred form of the invention;

Fig. II is a fragmentary enlarged horizontal section taken on the line 2-2 of Fig. I;

Fig.,III is a vertical section, showing a modifled form of the invention; and

Fig. IV is an elevation, partly in section, showing the manner in which the terminal end of the device of Fig. III may be connected to the antenna.

These specific drawings and the specific description that follows are to disclose and illustrate the invention, and limitations upon the claims.

The preferred form of transmission line comprises a central conductor surrounded by a layer of a flexible dielectric that is impervious to water, which is in turn surrounded by a flexible tubular conductor.

This construction enables the line to be connected to the antenna in a simple yet secure and highly effective fashion. The central conductor may be extended and partly uncovered to form a connecting portion for attachment to one of the terminals of the antenna, and the outer conductor may be suitably secured, as by soldering, to another connecting portion for attachment to the other terminal. It is not necessary to cover the junction of these connecting portions of the transmission line with moisture proof material because of the layer of impervious dielectric between the conductors, but a body of rubber may be molded thereabout to add strength to the connecting portions and to guard further against any interference with the operation of the line through deposition of moisture.

Even though moisture penetrates the outer conductor so that the outer conductor becomes thoroughly wet, the impervious dielectric substantially prevents the moisture from getting into the dielectric field between the conductors, and there is no interference with the operation of the line. No expensive waterproof outer coating is necessary, and leaks in the outer coating are not to be feared. In addition, the layer of impervious dielectric is thick enough that it obviates interference from deposition of moisture in the crotch where the conductors lead outward to opposite branches of the antenna.

In Fig. I, a length of untinned No. 12 B and S gauge copper wire I is spirally or longitudinally wrapped with a layer of paper I! impregnated with varnish or Wax, to prevent the sulphation that is caused by sulphur present in the rubber. Surrounding the paper is a relatively thick coating of rubber insulation it which is preferably good grade rubber having a low dielectric constant.

The rubber is covered by a flexible tube or sleeve 13 closely braided from No. 30 tinned copper wire. This tube or sleeve constitutes the outer conductor of the concentric transmission line.

The tinning of the wire in the braided outer conductor l3 does not increase appreciably the resistance of this portion of the transmission line because of the relatively large diameter of the tube, but prevents sulphation, like the layer of paper around the inner conductor, as well known to those skilled in the art. The central conductor i0 is untinned, because tinning makes are not to impose the radio frequency resistance of that conductor too high.

The thickness of the rubber layer 12 may be varied as desired in order to obtain a transmission line having a surge impedance matching that of the antenna. If rubber having a dielectric constant of 2.8, a central conductor of No. 12 solid soft-drawn wire, and a braid of No. 30 wire are used the thickness of the dielectric must be .21 inch for an impedance of 62.5 ohms. The amount of power to be transmitted through the line of course determines the diameter of the inner conductor.

When the dielectric constant of the rubber is 2.8, the relationship of the surge impedance Z, the inside diameter D of the outer conductor, and the outside diameter d of the inner conductor is as follows:

2:79 Log At the antenna end of the cable a central rubber covered conductor, which may be formed by removing a length of the outer conductor l3, extends outward for several inches, and is bent at an angle of approximately 45 to the axis of the cable. Soldered to the end of the braided tube 13 is a piece of No. 12 copper wire 14, several inches long, which diverges from the axis of the cable in the opposite direction, likewise at an angle of about 45. Conductor M may be covered with a layer of waxed paper l I and a protecting sheath of rubber 12.

In the modified form of transmission line shown in Fig. III, the central conductor i is surrounded by the layers of wax impregnated paper II and rubber compound 12. The rubber layer is surrounded by an anti-sulphation sheath of soft waxed cotton braid l5. Then the outer conductor l3 may be braided over the cotton braid l5, and untinned copper wire may be used therefor.

To protect the copper braid, an outer covering 16 may be employed, which need not be waterproof, but may be composed of soft waxed cotton braid.

The terminal end of the line is made substantially weatherproof by extending conductor ID as in the previous modification, and providing a divergingconductor M, with a sheath l2 of rubber. A substantial length of the diverging portions of these conductors is surrounded by a body of rubber compound I! that entirely prevents accumulation of water therebetween. The described construction provides an integral rubber body at the terminal end of the line that not only efiectively prevents the aforesaid accumulation of moisture, but also acts to strengthen the coupling. Exposed portions of the copper conductors to which the rubber is to be applied may be tinned.

The types of apparatus described immediately above are chiefly used with the half Wave doublet antenna, which consists of two oppositely extending conductors supported a predetermined distance above the ground and parallel thereto. A preferred mode of making the connection to the antenna is illustrated in Fig. IV, in which the transmission line of Fig. III is shown coupled to a doublet antenna comprising conductors I8 and 19 secured to a cylindrical ceramic insulator 20. Insulator 20 is provided with transverse holes 2| adjacent its ends to facilitate the securing of the conductors.

The transmission line is supported in the central cup-shaped depression 22 adapted to receive the molded portion ll of the line, the cup-shaped depression 22 being provided with a central aperture through which the transmission line extends. The conductors l0 and M are secured to the antenna portions l8 and I9, as by soldering.

The concentric. transmission line described above is quite flexible and may be handled rough- 1y without fear of injury thereto. It may be shipped like other flexible cable and out to desired lengths. It retains its concentricity and its electrical constants remain unchanged even after repeated flexure.

The line is very easily attached to antennae already in position or to antennae installed with the line. It may be submerged in water or buried in the earth, and its characteristics are not materially afiected by the presence of moisture on its exterior, as the moisture cannot enter the dielectric field.

Changes in the illustrated embodiments may be made and other embodiments of the substance of the invention may be devised to meet various requirements.

Having described my invention, I claim:

I. In an apparatus of the class described, a lead-in connection comprising a support, flexible central conducting means for connection with one portion of an aerial, a layer of rubber surrounding the central conducting means, a tubular conductor enclosing the rubber layer, a branch conductor for connecting the tubular conductor with another portion of the aerial, and a body of rubber molded about the connection between the tubular conductor and the branch conductor for sealing the connection against moisture and retaining the central conductor on said support.

2. In an apparatus of the class described, a lead-in connection comprising an insulation support having a substantially cone-shaped transverse opening, flexible central conducting means for connection with one portion of an aerial extending upwardly and outwardly through said opening, a layer of moisture-impervious solid dielectric surrounding the central conducting means, a tubular conductor surrounding the dielectric layer, a branch conductor for connecting the tubular conductor with another portion of the aerial, said connection being substantially within the transverse opening and a body of dielectric of substantial size molded about the connection between the tubular conductor and the branch conductor.

8. In an apparatus of the class described, a support having a transverse opening, a central copper conductor passing through said opening for connection with one portion of an aerial, a layer of rubber of a thickness predetermined in accordance with its dielectric constant surrounding the central conductor, a braided tubular copper conductor enclosing the rubber layer, a branch conductor for connecting the tubular conductor with another portion of the aerial, a body of rubber of substantial size molded about the connection between the tubular conductor and the branch conductor and arranged to support said central conductor in said transverse opening, and anti-sulphation layers substantially separatin the rubber from the copper surfaces.

REX EARL BASSETT, JR.