US3488759A

US3488759A - Coax connector unit

Info

Publication number: US3488759A
Application number: US546819A
Authority: US
Inventors: John R Winegard
Original assignee: Winegard Co
Current assignee: Winegard Co
Priority date: 1966-05-02
Filing date: 1966-05-02
Publication date: 1970-01-06
Anticipated expiration: 1987-01-06

Description

6, 1970 J. R. WIN E GARD 3,488,759

' COAX CONNECTOR UNIT Filed May 2, 1966 2 Sheets-Sheet 1 34b r inventor I ID 3o I J hn-R.wine akd w B5, @wm &

Jam 1970 I J. R. ,WINEGARD 3,488,75

' I COAX CONNECTOR UNIT Filed May 2., less" 2 Sheets-Sheet 2 v Inverztcr v J n- R, winegard United States Patent 3,488,759 COAX CONNECTOR UNIT John R. Winegard, Burlington, Iowa, assignor to The Winegard Company, Burlington, Iowa, a corporation of Iowa Filed May 2, 1966, Ser. No. 546,819 Int. Cl. H03h 5/00 US. Cl. 333-26 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a coax connector unit with an embedded balancing transformer suitable for attachment directly to the antenna input terminals of a television receiver or to the supply terminals of a television antenna.

While conventional 300 ohm twinlead transmission line is useful for most television antenna connections, there are occasions when it is desirable, indeed essential, to employ shielded coaxial cable. Such cable is characterized by the fact that it is shielded and therefore can be used under circumstances where losses and stray signal pickup associated with the 300 ohm twin-lead line are not accept able. Typically, such cable has a characteristic impedance of approximately 72 ohms and is used, for example, to feed ratio frequency signals to a plurality of television receivers from a common signal source. However, the nominal impedance for television receivers, and to a large extent the associated antennas as well, is approximately 300 ohms balanced-to-ground.

It is not acceptible from an efficiency standpoint to connect the receiver or antenna directly to such feed cable because of the 72 ohm to 300 ohm mismatch and because the 72 ohm cable is unbalanced. It is therefore expedient to provide a balancing means between the 72 ohm coaxial cable and the television receiver input terminals or between the cable and the antenna supply terminals.

Until now the balancing arrangement has usually been provided by transformers and connections which are mounted in housings and which must be mounted behind the television receiver or otherwise placed wherever convenient. These devices are expensive due to their mechanical design and associated coaxial connector fittings. Further, they are unsightly, bulky, and often can be accidentally dislodged or disconnected when the back of the receiver is dusted or cleaned. If placed at the antenna location such devices are subject to deterioration due to the environmental extremes of the weather.

In accordance with one embodiment of the present invention, the balancing and impedance matching apparatus for interposition between the coaxial transmission line and the input terminals of a television receiver is constructed as a single, compact unit integral with the end of the coaxial cable. The unit may include a suitable coax fitting interposed for convenient separation from the associated coaxial cable if so desired. The balancing and impedance matching apparatus includes a sub-miniaturized balun transformer wound on a ferrite core and embedded in a mold of resilient but weather-resistant material, e.g., soft or medium-soft rubber. A pair of terminals or prongs extend from the mold casing for connection to input screw terminals. In this embodiment, the prongs are preferably formed from rigid, suitably tempered steel wire and include S-shaped convolutions toward the outboard ends which provide a camming guide action to facilitate connection to the television terminals. In another embodiment, however, the prongs are constructed from straight wire stock, but of a malleable material having a degree of flexibility, such as copper-tinned conductor, so as to conveniently accommodate the various screw terminal configurations encountered in different television antennas.

In fabrication, a molding or encapsulation process is employed which ensures the balun transformer and associated component parts are positioned in a substantially centered relation to the mold sides. The process contemplates a mold cavity wherein the component parts of the coax connector unit are suspended from opposite ends and wherein inclined, opposing entry or gating ports are provided in the sides of the cavity mold through Which the encapsulation material is forced into the cavity under a predetermined pressure. The mold material entering the mold cavity selectively fills the interior in a manner to force the balun transformer and component parts to the centered position within the cavity.

With the connector unit as thus described, a coaxial cable may be connected to a television antenna or receiver which provides an effective impedance match and balancing circuitry with no more objectionable appearance, difficulty of connection, or opportunity for accidental breakage than is associated with the connection of an ordinary appliance cord. Another important feature of this construction resides in the fact that while relatively intense high-frequency fields are involved in the action of the transformer embedded in the end of the cable, the losses are slight because the fields generated are essentially confined to the associated ferrite core.

It is therefore an object of the present invention to provide an improved coax connector unit, constructed as an integral part of a coaxial transmission line cable and which can be connected directly to the terminals of television antennas and receivers.

Another object of the present invention is to provide a device of the foregoing type wherein signals from the unbalanced coaxial transmission line cable are efliciently fed to the balanced input terminals of a television receiver and wherein the respective impedances of the cable and receiver are substantially matched.

Still another object of the present invention is to provide a device of the foregoing type wherein signals are received from balanced output terminals of a television antenna and efficiently fed to an unbalanced coaxial transmission line cable without prejudice to the performance of the attenna and wherein the respective impedances of the cable and antenna are substantially matched.

Yet another object of the present invention is to provide a device of the foregoing type wherein the component parts of the coax connector unit are encapsulated in a protective molded casing of weather-resistant, shockabsorbent material integral with the coaxial transmission line cable and wherein such component parts are posi tioned and maintained in a substantially centered position with respect to the mold sides during the encapsulation process.

A further object of the present invention is to provide a device of the foregoing type wherein the connectingwire terminals or prongs extending from the molded casing of the unit for connection to the input terminals of the television receiver include formed convolutions at the outboard ends to facilitate such connection through a camming guide action.

An additional object of the present invention is to provide a device of the foregoing type that is small, attractive in appearance, self-contained, electrically efficient, and conveniently and inexpensively manufactured and sold, to the end that the device has a wide range of practical usefulness and commercial application.

The novel features which are believed to be characteristic of the present invention are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof, will best be understood by reference to the following description taken in conjunction with the drawings, in which:

FIGURE 1 is a view in perspective of one embodiment of the coax connector unit constructed in accordance with the present invention;

FIGURE 1a is a fragmentary view in perspective of another embodiment of the invention in which the connecting prongs have a straight wire configuration;

FIGURE 2 is a top plan view of the coax connector unit of FIGURE 1 with internal components visible;

FIGURE 3 is a fragmentary view in cross-section of the ferrite core showing the coil winding detail;

FIGURE 4 is an enlarged view in cross-section of the coax fitting as shown in FIGURES 1 and 2;

FIGURE 5 illustrates another embodiment of the coax connector unit wherein the coax fitting is not employed;

FIGURE 6- is a fragmentary view showing a detail of the terminal prongs of FIGURE 1;

FIGURE 6a is a fragmentary view showing a detail of the terminal prongs of FIGURE la;

FIGURE 7 is a schematic diagram of the balun transformer and coaxial cable;

FIGURE 8 is a view in perspective of the two-piece mold with the formed cavity and entry ports shown in dotted line;

FIGURE 9 is a cross-section in elevation of the mold of FIGURE 8 taken generally along the lines 8-8;

FIGURE 10 is a fragmentary plan view showing one manner of connecting the prongs of the unit of FIGURE 1 to input screw terminals; and

FIGURE 10a is a fragmentary plan view showing another manner of connecting the prongs of the unit of FIGURE 1 to input screw terminals.

Referring now to the drawings, a coax connector unit 10 is shown in FIGURE 1 which has been constructed in accordance with the present invention. The unit 10 consists of an elongated, ovalular shaped casing or pod 12 from which a pair of connecting prongs 14 extend at one end and terminate in S-shaped convolutions at their outboard ends. The prongs 14 in FIGURE 1 are intended for connection to the screw terminals which form the input to a television receiver. FIGURE 1a shows another embodiment for the coaxial connector unit 10 wherein the terminal prongs 14' are provided as essentially straight-line conductors. The significance of the particular configurations for the connecting prongs in FIGURES 1 and la will be subsequently described.

The pod 12 of FIGURES 1 and la is formed of a molded, weather-resistant and shock-absorbent material having a degree of resiliency, such as soft rubber or the like. This construction provides sufficient protection for the embedded internal parts from the environmental extremes as well as being capable of absorbing shocks and rough treatment, which might otherwise be detrimental to the embedded internal component parts.

As shown in FIGURES 2 and 7, the coax connector unit 10 includes a network 20 consisting of a balancing and impedance transformation device, such as the balun transformer 21, to effect transfer of signals between balanced and unbalanced circuits while at the same time effecting a substantially close impedance match between nominal 300 ohm and 75 ohm terminal impedances. The balun device 21 includes a pair of transformers 2g and 24 wound on a common ferrite core 26. Each of the

transformers

22 and 24 consist of a pair of windings, i.e., 22a-22b, and 24a-24b, respectively. The core preferably is of a generally rectangular configuration formed of a suitable compressed ferrite material. In the form shown, the dimensions of the core 26 are approximately /2 long by A" thick. The core 26 has a pair of non-intersecting cylindrical bores of approximately /s" in diameter extending therethrough along the longitudinal axis so as to form two separate winding compartments for winding the transformers 22 and 24 (best seen in FIG- URE 3). This construction ensures that the

transformers

22 and 24 operate substantially independent of one another in that each of the transformers encompasses a separate volume of the ferrite core material so that the fiux produced by one of the transformers will not materially interfere with the flux produced by the other of the transformers, even though wound on the same core. The respective windings of the

transformers

22 and 24 are interconnected to form an impedance transformation circuit for effecting a 4:1 change between the respective impedances presented to the input and

output terminals

20a and 20b (FIGURES 2, 5 and 7).

As best seen in the schematic representation of FIG- URE 7, the winding 22a of the transformer 22 is connected between one of the terminal prongs 14 and one of the conductors of the coaxial cable 16, such as the metallic braid B, and the winding 24a of the transformer 24 is connected between the other of the prongs 14 and the inner conductor I of the coaxial cable 16. The other, or secondary, windings of the transformers, 22b and 24b, are interconnected by a blocking capacitor 28 at one end while the other ends are cross-connected between the coaxial cable conductors. That is, the winding 22b is connected to the inner conductor I of the cable 16 and the winding 24b is connected to the metallic braid B.

With the connections as thus described, the

transformers

22 and 24 form an effective and efficient impedance transformation circuit with a characteristic of offering relatively little impedance to balanced currents therethrough but a high impedance to any unbalanced currents. Assuming a characteristic impedance Z for the

transformers

22 and 24, the impedance between the terminals 20b connected to the prongs 14 will be seen to be twice that, or 2Z, while the impedance between the terminals 20a connected to the coaxial cable 16 will be one-half that, or Z/2. Hence a 4:1 impedance transformation ratio. The

transformers

22 and 24 are wound on the core 26 from ohm small-size twin-lead conductors so that the terminals 20b substantially match the 300 ohm impedance as presented by the input of a television receiver or the supply terminals of a television antenna and the terminals 20a substantially match the 7275 ohm characteristic impedance of the coaxial cable 16. The winding detail of the

transformers

22 and 24 are seen more clearly in FIGURE 3. In the preferred form, the respective windings are wound clockwise, viewing FIGURE 3, around the core 26 approximately one and one-half turns. The

windings

22a and 24a are shown in white and the windings 22b and 24b are shown in black.

Relatively little loss is exhibited by the impedance transformation circuit 20 in the transfer of signals between terminals 20a and 2012. This is primarily due to the fact that, while relatively intense high frequency fields are involved, the fields are essentially confined to the ferrite core 26. Further, with the relatively close impedance match effected between the various circuit impedances presented at terminals 20a and 2017, a low VSWR is obtained across a sufiiciently wide range of frequencies to encompass both the VHF-UHF television channels (50 to 1000 megacycles).

The coax connector unit 10 may be included as an integral and non-detachable part of the coaxial cable 16, as shown in FIGURE 5, or as a separate and detachable unit, as shown in FIGURES 1 and 2. For those applications where the unit 10 is to be placed outdoors and exposed to the weather, such as at the television antenna, it is preferred that it be an integral part of the coaxial cable without any disconnect feature. The detachable unit, however, is preferred for the cable end which is to be connected to the terminals of the television receiver. Where the receiver is to be moved, serviced, or the like, it is more convenient to simply separate the cable from the connector unit 10 and leave the latter attached to the television receiver input terminals.

As shown in FIGURES l and 4, the detachable coax connector unit 10 incorporates a coaxial fitting 30. The fitting 30 includes a male plug 31 connected to and made an integral part of the connector unit 10 and a female receptacle 32 connected to and made an integral part of the coaxial cable 16. The receptacle 32 has a cylindrical sleeve portion 34a with slots cut longitudinally therein so as to form a plurality of expandable, resilient-like fingers. An annular groove or ring 34d is cut in the underside or the interior surface of the sleeve portion 34a as shown in FIGURE 4. An opening 36 is included in the base 34b through which an end portion of the dielectric D of the cable 16 may extend a predetermined distance within the interior of the receptacle 32. A portion of the dielectric D is removed from the end of the cable 16 so that the inner conductor I is exposed and extends a short distance beyond the edge of the receptacle 32. A sleeve or flange 34c extending from the rear of the base 34b is dimensioned to slide underneath the metallic braid B before a ring or clamp 38 is crimped or otherwise secured around the outside of the cable 16.

The male plug 31 includes a sleeve portion 33w dimensioned for insertion within the female receptacle 32. The sleeve portion 33:: is tapered to one end and terminates in a beveled ring 35 to make sliding contact with the inner surface of the receptacle 32 and mate with the annular groove 34d to provide a locked connection between plug 31 and receptacle 32. When the receptacle 32 and the plug 31 are thus interfitted, the end portion of the inner conductor I inserts Within the hollow base of the solder pin 37 which is insulatingly supported in the base 33b of the plug 31 by the insulator 39, as shown. As best seen in FIGURE 2, the lead wires of the

windings

22a and 24a forming one of the terminal set 20a are connected to the pin 37 and the lead wires of the windings 22b and 24b forming the other of the terminal set 200 are connected to the base 33b of the plug 31.

As seen in FIGURE 6, the connecting prongs 14 are constructed with a ripple or U-shaped convolution 14a at the rear of the prong-that is, the end portion adjacent the transformer and which is to be embedded with the pod 12. The lead wires from the

windings

22a and 24b of the balun 21 are wound serpentine fashion several turns around the convolutions 14a of the prongs in the manner shown before being soldered thereto. In this manner, the prongs 14 are thus made relatively immune from slippage within the pod 12 and effectively operates to prevent strain from being exerted on the lead wires of the windings of

transformers

22 and 24. For the embodiment as shown in FIGURE 1a, however, a somewhat different mode of securing the prongs 14' within the pod 12 is required since the prongs 14' are constructed from a malleable material (such as tin-plated copper). Slippage of the prongs 14' is effectively prevented by soldering an eyelet 15 to the base of each of the prongs 14' which firmly anchors the same when embedded in the pod 12.

As shown in FIGURES 1 and 2, the prongs 14 include complementary S-shaped arcuate convolutions 14b at their forward ends which terminate in the flared-out portions 140. This configuration is effective to provide a camming guide action to facilitate connecting the coax connector unit to the screw terminals forming the input to a television receiver. As will be observed, there are two ways of effecting such connection. As shown in FIGURE 10, a squeezing pressure, as indicated by the arrows F,

may be exerted on the prongs 14 to pinch them inwardly toward one another. The dotted lines in FIGURE 10 represent the normal, unbiased position of the prongs 14. The prongs 14 may be placed in a position between the screw terminals, identified at T, and released whereby the prongs 14 spring outwardly toward their unbiased position. The flared-out portion to front and the rearward portion of the convolution 14b provides an effective guide action to correctly position the prongs 14 around the respective screw terminals. The other method of connection is effected by placing the flared-out portions 14c of the prongs 14 against the terminals as shown in FIGURE 10a and exerting a force forward, as represented by the arrow F. As the unit 10 is pushed forward, the flared-out portions 140 force the prongs 14 outwardly in the direction of the arrows 0 so as to provide a camming action with the forward portion of the convolutions 14b operating to correctly position the prongs around the respective screw terminals T.

As mentioned previously, the various component parts of the connector 10 in the assembled unit are encapsulated in a protective coding or pod 12. In the past, difficulty has been frequently encountered in positioning and maintaining the component parts internally of the pod 12 in the desired spaced relation to the mold sides. When any of the connector unit component parts are positioned too close to one or more of the sides of the molded pod, a rupture is likely to occur through fiexure of the unit 10 during usage. This seriously affects the service life of the unit and is an undesirable deficiency.

Such a deficiency, however, is overcome in the present invention as a result of the encapsulation process employed in fabricating the connector unit 10. In fabrication, the various component parts of the connector unit 10 are first electrically interconnected and assembled as a sub-unit and then attached to the male coax fitting 31 as shown in FIGURE 2, or alternatively, directly to the section of the coaxial transmission line cable 16, as shown in FIGURE 5. The sub-assembled connector unit is placed in a two-piece mold 50 consisting of complementary halfsections 50a and 50b. The formed cavity in the interior of the mold is shown in dotted line at 50c. Cylindrical slots or channels 51 are provided in the front face of the mold 50 and dimensioned to receive the terminal prongs 14. Similarly, a channel 52 is provided in the rear face of the mold 50' and dimensioned to receive the male fitting 31 of the embodiment of FIGURE 2, or the section of coaxial cable 16 of the embodiment of FIG- URE 5, as the case may be.

Entry ports

54a and 54b are provided in the face of one of the sides of the mold 50 as shown in FIGURES 8 and 9 through which the encapsulating material may be introduced within the interior cavity 500. As seen more clearly in FIGURE 9, the

entry ports

54a and 54b are slanted or inclined at an angle above and below a horizontal plane passing through the center of the mold apparatus 50. Preferably, the

ports

54a and 54b are inclined at approximately a 45 degree angle. The port 54a slants upwardly through the mold section 50a and the port 54b slants downwardly through the mold section 50b, viewing FIGURE 9. It is to be understood, however, that the precise angle of inclination is in no way critical and may be varied if so desired. Entry of the material through the port 54a and the path within the cavity 500 is represented by the arrows indicated at X and the material through the port 54b and within the cavity 50c is represented by the arrows indicated at Y.

When positioned within the cavity 500, the balun transformer 21 is suspended from the respective lead wires connected to

terminals

20a and 20b (FIGURES 2 and 5) and is thus free to move within certain prescribed limits in both the up-down and side-to-s'ide directions as viewed in FIGURE 9. As the encapsulating material is introduced into the cavity 50c, the material then flows in the direction indicated by the arrows X and Y between the respective sides or interfaces of the mold 50 and the balun transformer 21. It will be seen, therefore, that the encapsulating material fills the cavity 500 from the outside or interior faces thereof toward the center. The material is introduced into the cavity 500 under sufiicient pressure so as to move the balun transformer 21 to a position representing the equilibrium point between opposing flows of material. If substantially the same pressure is maintained for the material flowing through each of the

ports

54a and 54b, the equilibrium point will approximately coincide with the center of the cavity. It has been found that satisfactory results are obtained if the pressure of the encapsulating material is maintained at approximately 250 pounds per square inch. This value is not critical and may vary without departing from the scope of the present invention.

While only certain specific embodiments of the invention are shown and described herein, it will, of course, be understood that many variations and modifications may be effected without departing from the true spirit and scope of the invention. The appended claims are intended to cover all such modifications and alternative constructions that fall within their true scope and spirit.

What is claimed is:

1. A coax connector unit for connecting an unbalanced t transmission line to a pair of balanced terminals of an electrical device having a given input impedance, comprising in combination:

a length of coaxial transmission line cable having a center conductor an an outer conducting sheath and defining a longitudinal axis;

an impedance matching and balun transformer having a closed ferrite core upon which four separate windings are wound, said windings being interconnected to form pairs of primary and secondary terminals,

said primary terminals accommodating the unbalanced transmission line and said secondary terminals accommodating the balanced terminals of the electrical device;

means connecting the primary terminals of the transformer to the inner conductor and the outer conducting sheath of said cable, respectively, at one end thereof, said transformer being located on an extension of said longitudinal axis beyond said one end;

a pair of conductors each of which is connected to one of the secondary terminals of the balun transformer and in a generally parallel relation to an extension of the axis of the coaxial cable and away from said one end; and

a body of low-loss, plastic mold material embedding the end of the coaxial cable, the balun transformer, and a portion of said pair of conductors defining an integral unit with a portion of each of said pair of conductors extending beyond said molded body and defining means for connection to the terminals of the electrical device.

2. A coax connector unit in accordance with claim 1 wherein the length of the coaxial cable has a nominal characteristic impedance of 72 ohms unbalanced-toground and the associated windings of the impedance matching and balun transformer are interconnected to provide substantially a four-to-one impedance transformation ratio between the primary terminals connected to the coaxial cable and the secondary terminals for connection to balanced 300 ohms terminals of the electrical device, with one of said windings being connected between one of said primary terminals and one of said secondary terminals, another of said windings being connected between the other of said primary terminals and the other of said secondary terminals, and the remaining two windings being coupled together at one end thereof and cross connected to a respective primary terminal at their other end.

3. A coax connector unit in accordance with claim 1 wherein the body of low-loss, plastic material in which the end of the cable, the balancing transformer, and the portion of the pair of conductors are embedded is composed of a soft to medium-soft, pliable rubber material.

4. A coax connector unit for direct connection to a pair of balanced terminals of an electrical device having a given input impedance, comprising in combination:

a length of coaxial transmission line cable having a center conductor and an outer conducting sheath and defining a longitudinal axis;

an impedance matching and balancing transformer device having a closed ferrite core and associated windings defining pairs of primary and secondary terminals;

a pair of conductors each of which is connected to one of the secondary terminals of the balancing trans former and in a generally parallel relation to an extension of the axis of the coaxial cable and away from said one end; and

a body of low-loss, plastic mold material embedding the end of the coaxial cable, the balancing transformer, and a portion of said pair of conductors defining an integral unit with a portion of each of said pair of conductors extending beyond said molded material and defining means for connection to the terminals of the electrical device,

said pair of conductors being constructed from relatively stiff, non-deformable wire stock with complementary arcuate convolutions formed in the outboard ends extending beyond said molded body and which terminate in diverging flared-out portions, said arcuate convolutions being adapted to fit the supply terminals of the electrical device and the flared-out portions of the conductors providing a camming guide action for the conductors in connecting the same to said supply terminals.

References Cited UNITED STATES PATENTS The Radio Amateurs Handbook (42nd Edition) American Radio Relay League, Newington, Conn. 1965, TK6550 R162 page 505 relied upon.

HERMAN K. SAALBACH, Primary Examiner M. NUSSBAUM, Assistant Examiner U.S. Cl. X.R. 33 3-3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No: 3,488,759 Dated: February 9, 1970 John R. Winegard It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE SPECIFICATION:

Column 3, line 39: "8-8" should read "9-9"; Column 3, line 68: "2 and 7" should read "2, 3, and 7" Column 6, line 69: "21" should read "21 (Figure 3)";

IN THE DRAWINGS:

In sheet I, Fig. 2, the reference numeral 2l should be added and placed close to and above numeral 24a, with a connecting line from numeral 21 ending with an arrowhead in the area defined between winding 24a and the dotted line defining pod 12;

In sheet 1, Fig. 3, add reference numeral 21 close to and below numeral 20a, with a connecting line ending with an arrowhead pointing to the whole combination of Fig. 3;

In sheet 1, Fig. 4, add numeral 34a and place between numerals S and 30, with a connecting line extending vertically and touching the cylindrical wall delinenated as the cross-hatched portion of receptacle 32;

In sheet 2, Fig. 7, add numeral 12 close to and below numeral 20a, with a connecting line extending and touching the dotted line segment situated between numerals 20a and I;

In sheet 2, Fig. 7 add numeral 21 and place between

numerals

26 and 20a, with a connecting line extending and ending with an arrowhead in the area defined by winding 20a and the dotted line defining pod l2.

Signed and sealed this 25th day of August 1970 m "2 x AM