US 2047152 A
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Patented July .7, 1936 AUTOMOBILE RADIO CABLE Donald H.T Mitchell, chicago, nl., assignor to' Galvin Manufacturing Corporation, Chicago,
Ill., a corporation of Illinois Application October 22, 1932, Serial No. 639,082
My invention relates in general to automobile radios and more in particular to an improved type of cable adapted for connecting various portions of the apparatus employed in an automobile radio.
One of the greatest difficulties in installing an automobile radio satisfactorily is the elimination of interference due to motor pickup and the like.
This interference is found to affect the various cablesl connecting the various portions of the apparatus as, for example, the cables connecting the remote control, power cables, antenna cables, and the like.
The principal object of my present invention is the provision of improved cable adapted for use in an automobile radio.
` Another object is the provision of improved means of eliminating interference in such a radio. Another object is the provision of improved shielding means for such a cable.
Another object is the provision of such a cable adapted for carrying a single lead or va plurality of leads, as may be necessary by the requirements in a particular installation.
In accordance with the general features of the invention, I provide a relatively high inductance, preferably by inductively winding the lead wire about an insulating core. and
provide a suitably insulated shield around the inductance, thus providing a balancing capacity effect. I have found, by the'use of the inductance and capacity distributed substantially over the length of the cable and properly designed to suit particular conditions, the 'current which is normal to the lead wire will not be appreciably aifected but ally stray current such as those produced by the motor ignition will be effectively prevented from entering the radio set. The shielding preferably consists of a flexible braided metallic sheath. In one method of applying this sheath, I employ a double layer of shielding material separated throughout the length of the cable by insulating material, but electrically and magnetically connected at o ne end thereof.
`Other objects and features of the invention will be apparent from a consideration of the fol'- lcwing detailed description taken with the accompanying drawing, wherein Fig. 1 is an elevational view of one form of ca- Fig. 3 is a sectional view taken of Fig. 2;
on the line 3-3 Figs. 4 -and 5 are views similar to Figs. 2 and 3, but showing a modification employing double shielding;
Fig. 6 is an elevational view partly broken away to conserve space showing stlll another form 5 which the cable may take;
Fig- 7 is an enlarged fragmentary view with the different layers broken away to show their relationship; and
Fig. 8 is a sectional view taken on the line 8 8 l0 cally insulated from the other throughout its 15 length, and electrically connecting the metallic shields together at each of the opposite ends, a very low resistance shieldingloop is provided for the central conductor. Therefore with a eld set up around this shield by motor ignition or other 20 stray high frequency currents, in attempting to pass through the central conductor they set up a flow in the shielding loop itself where it is dissipated Without effectively entering or passing through the'inner conductor. I have found that 25 such double shielding is much more effective than a single metallic shield. Such double shield is then preferably connected to ground at one end lrather than to grounding the shielding at both ends. Now, considering first Figs. l, 2 and 3, I employ in one form which the invention may take a center core II formed of insulating material about which I coil a single covered lead wire I2. This coil construction runs the entire length of the cable, causing a relatively high inductance distributed the entire length of the cable. l About the lead wire I2 I provide a sheath I3 of insulating material. 'Ihis sheath I3 is preferably a relatively heavy braided tube formed directly on the cable. 40 On the outside of the insulating sheath I3 I provide a single metallic shield I4. This shield is formed of braided wire and also runs substantially the entire length of the cable; terminating a suflicient distance short of the ends thereof to affordample material in the lead for making the4 necessary connections and the like. The ends I4a of the shield are braided together to form a relatively small cros's section tubular extension by means of which the shield may be grounded at one or both ends as appears to be required by the conditions under which it is used.
v The cable shown in Figs. 1 to 3 has been used with very remarkablel success as the A supply in the radio receiver described in my copending appllcation, Serial-No. 639,081 filed October 22, 1932. I find that substantially every trace of motor noise was eliminated, whereas without the construction employed in this cable but when using conventional shielding it was impossible to eliminate all stray pickup. The form shown in Figs. 4 and 5 is the same as that `shown and described in connec- 'tion'with Figs. 1 to 3, with the exception that I employ an additional shield I6, with an insulating layer I1 between the two shields. The various portions of Figs. 4 and 5 corresponding to Figs. 1 to 3 are marked with the same reference characters and'need not be referred to again in detail. The two shields preferably are connected at one end, employing for example the construction shown in the following figures.
Figs. 6 to 8, inclusive, show some of the features of my invention applied to a two-conductor cable. In this form, I employ the two conductors I8 and I9 provided with a braided insulated covering 2| and 22, respectively. A metal shield 20 is provided about the insulator over conductor I9 and the two conductors preferably are twisted about each other in a conventional manner and a. single metal shield 23 is provided directly over both of them with successive layers of insulating material 24 and an outside metal shield 2B. The metal shields 20, 23 and 26 are in the preferred form made of braided wire, but, of course, other constructions producing equivalent results may be used.
'I'he shielding terminates short of the ends of the conductor to allow the necessary space for making contact. Suitable terminals 21 and 28 are provided at the ends of the conductors, and the conductors carry their braided insulation as they extend from the shield. At one end the shields are extended to partly cover the extending conductors, the inner shield being extended at 23a to cover one of the conductors and the outer shield being connected at 26a to cover the remaining conductor. The shields are in electrical and magnetic contact with each other where they are spliced to extend down to the portions 23a and 26a. The shields are also extended at 23h and 25h to form relatively small cross section tubular extensions adapted to be connected to a suitable ground.
At the opposite end the cables are unconnected, nor do they extend over the projecting portions of the conductors. They are, however, provided with extensions as shown. In employing thev cable, both of the extending ends 23o and 26e may also be grounded. Ina preferred form of the invention, the insulating sheath 24 is enlarged as at 24a topermit the insertion of a tubular extension from a metal containerl 21, in which radio apparatus is housed. This has the effect of placing the extension 23o inside of the metal container. grounding one of the shields to the inside of the container and the other to the outside of the container, very satisfactory shielding effects are ob- By then inductively disposed conductor, a metal shield extending around said conductor, and insulating material disposed around said metal shield, a second metal shield disposed around said insulating material, said shields being electrically connected 5 together at their opposite ends, and means for grounding both of said shields.
2. A cable adapted to be employed in an auto mobile radio installation, said cable comprising an inductively disposed conductor, a metal shield extending around said conductor, and insulating material disposed around said metal shield, a second metal shield disposed around said insulating material, means for grounding both of said shields at one end, and means for electrically connecting said shields together at the end of the cable opposite the grounded end.-
3. A cable for connecting the battery of an automobile ignition system with aradio installation, said cable comprising an insulating core, a 20 conductor helically wound on said core to provide a relatively large amount of distributed inductance running substantially the length of the cable, a metal shield disposed around said conductor, and means for grounding said shield, a second shield insulated from said first mentioned shield, and means for connecting said shields together at both ends of the cable.
4. A cable adapted to be employed in an automobile radio installation, said cable comprising 30 an insulated conductor, a shield disposed around said conductor, a layer of insulating material disposed around said shield. a second shield disposed around said insulating material, means for connecting said shieldstogether at one end of 35 the cable, and means for grounding said shields at the opposite end of the cable.
5. A cable adapted to be employed in an automobile radio installation, said cable comprising a pair of insulated conductors, a metal shield dis- 40 posed around said conductors, a sheath of insulating material disposed\` around said shield, a second metal shield disposed around said sheath of insulating material, said conductors projecting at the ends of the cable, one of said shields having 45 an extension at one end extending around one of the conductors, the second shield having an extension at the same end `extending around the second conductor, and said shields being in contact with each other at the end of the cable where they extend to the individual conductors.
6. Acable as defined in claim 5 wherein said sheath is slightly enlarged at the opposite end of the cable to extend over a tubular extension from a metal container, and whereby one of such 55 shields may be grounded to the inside of the container and the other ofthe shields grounded to the outside of the container.
7. A cable employed with a radio set installed adjacent an internal combustion engine, said cable including a central conductor, and means for minimizing interference effects including a metallic shield disposed around said conductor, I a layer of insulating material disposed around said shield, a second metallic shield disposed around said layer of insulating material, and means for electrically connecting said metallic shields together in simple conductive relationship at their opposite ends to form a closed conductive loop of low resistance.
DONALD- H. MITCHELL.