US 1904199 A
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A ril 18, 1933. F. T. BREWER 1,904,199
INDUCTANCE Original Filed June 27, 1931 1x gwvewtw EEK/523m 1157.5
a5? v 'hmclm'maq l mmnu trical qualities inmost Patented Apr. 18, 1933 ASIGNOR TO GENERAL 'MOTORS RADIO COR- OHIO, A CORPORATION OF OHIO mnucranon Application filed June 27, .1931, Serial No. 547,213. Renewed August22, 1932.
This invention relates to a radio frequency coil and the shield therefor.
In a radiofrequency coil having an air core, or a 11on-magnetic core made from insulating material, such as wood, bakelite, or other similar materials, it is desirable that the ratio of inductanceto effective resistance should be high. Effective resistance as here used is the resistance as measured when currents higher than audio frequency currents are passed through the coil. Hereafter all currents having a frequency higher than audio frequency currents will be designated radio frequency or high frequency currents. Three types of coils are usually used, that is, a single layer helical coil, a flat spiral or pancake coil, anda multiple layer coil. The multiple layer coil is advantageous for the reason that it is very compact but its eleccases are not as good qualities of the single layer coil, or the spiral coil. If a multiple layer coil is used within a shield, the losses as are the electrical due to eddy currents are usually very great so that it is necessary to use a very'large shield in order to keep the ratio of the in ductance to the resistance sufliciently high. This being the case the single layer coil has gained favor in the design of radio receivers in that these are more easily shielded. These shields, however, have to be fairly large in order to prevent the losses from becoming excessive. The ideal condition would be to'have a multiple layer coil which is easily produced compact and which occupies a very small space mounted within a shield that is just a little larger than the coil so as to use the minimum amount of material and space for mounting. .Heretofore this has been thought impossible for the reason that the losses due to the .shield are entirely too great and the ratio of the inductance to the resistance too low.
An object of this invention isto use a multiple layer coil mounted within a small shield without decreasing the efficiency of the coil. This has been accomplished by passing a conducting member grounded to the shield through the core of the coil. This structure has been found to decrease the overall dimensions of the shield to only a small fraction of the dimensions of the shields used priorto my invention Without sacrificing performance.
It may be that the desired results are obtained by a redistribution of the flux linking the coil, this redistribution probably being due to the eddy currents generated in the metallic conducting member passing through the core of the coil, or it may be due to a redistribution of the electrostatic forces acting on the coil. Whether the above is the right explanation is not to be construed as a limitation in the claims; Whatever the reason may be, it has been found that the ratio of the inductance to the resistance of a multiple layer coil that is provided with a conductor passing through its core made from a non-magnetic material has on the average a value throughout the broadcast range comparable to that of the coils formerly used, and mounted within large shields.
Another object of this invention is to improve upon the mounting of this shield and the coil located therein. This has been accomplished by mounting the coil on an insulating support held in position by a-brass screw or fastening member passing through the support and clamping the support to the shield. The shield and the coil mounted therein may also be attached to the frame 11 the radio receiver by the same screw or fastening member.
Further objects and advantages of the pres ent invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred embodiment of one form of the present invention is clearly shown.
In the drawing:
1 discloses the sectional side elevation of the coil, its support and its shield.
Fig. 2 discloses a view taken substantially in the direction of thearrow ofFig. 1,
Fig. 3 is a modification similar to the modification disclosed in Fig. 1.
In the drawing the reference character 10 indicates the frame of a radio receiver having mounted thereon a cup-shaped support 12 held in position by tongues 14, extending 7 40 through which passes a i i A shield 32 is mounted over so as to electromagnetically and electrostatitached to the support 12 by solder 30. It
seems that the brass bolt 24 either redistriba utes the flux linking the coil 20 or it redistributes the electrostatic forces acting on the coil 20 or both to increase the efiiciency of the coil. In certain cases it may le to be desirab use other material than brass for the bolt24.
cal-1y shield the coil 20 from all external electromagnetic and electrostatic forces as well redistributing the flux of thecoil.
In the modification disclosed in Fig. 8, like reference numerals represent like parts. The
frame 10 has been provided with an aperture brass bolt 44 that functions electrically the same as the brass bolt 24 in the modification of Figs. 1 and 2. A tubular spacing member 46 has been placed intermediate the cup-shaped member 12 and the frame 10. The nut 50 cooperates with the head 52 to hold the supports18 and 12 and the frame 10 in a relatively fixed relation.
. The cup-shaped support 12 is prevented from rotating on the base 10 by suitable tongues or ears 54 extending into apertures provided therefor. 7
While the form of embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.
What is claimed is as follows: 1. Ahig'h frequency coil assembly comprising in combination, a multiple layer coil, said coil having a non-magnetic support core, a non-magnetic conductor extending into and through the entire support core of said coil whereby eddy currents are generated in said conductor, a shield for shielding said coil, said conductor and said shield cooperating to maintain a high ratio of inductance to resistance of the coil.
2. A high frequency coil assembly including a coil, an insulating support core for said coil, a metallic shield enclosing saidcoil, and a metallic non-magnetic conducting member passing through the core of said coil and having electrical communication with said shield, said coil mounted. in said shield and around said conducting member having a higher average ratio of'inductance to reslstance than without the use of said conducting member.
3. A high ,the'ratio of the inductance the assembly a frequency coil assembly including a coil having its windings arranged in superimposed layers, a meta lic cylindrical shield enclosing said coil, said cylindrical shield being mounted coaxially with respect to said coil, the diameter of said shield being less than twice the maximum diameter of said coil and the length of said shield'being less than half of the diameter of said shield, and; a conducting member electrically con; nected to said shield, said conducting mem-' ber extending into the core of said coil, so that to the resistance of the coil is higher than without said conducting member. r
4. A high frequency coil assembly including a coil having a'diameter of unit magnitude, a metallic shield enclosing said coil, the diameter of said shield being greater by substantially one-fourth of said unit magnitude,
an insulating support for supporting sai shield and said coil on substantially concentric axes, and a non-magnetic conducting member grounded to said shield, said conducting member extending into thecore of the coil whereby the ratio of the inductance to the resistance has a higher average throughout the broadcast range than without said conducting member. a
5. A high frequency coil assembly including, a shielding base, an insulator, multiple layer coil carried by the insulator, a shield can closely disposed about the coil and engaging the shielding base, and a metallicconductor disposed at the axis of said coil'and securing the same to its base, said conductor being grounded to the shield of the coil and forming a shunt for redistribution of the flux in the coil coupling.
6. In combination with a high frequency coil, a support therefor, said coil being pro vided with a non-magnetic core, a conductive shield surrounding the coil, said shield being a little larger than the coil to use the minimum amount of material and space for mounting, and a non-magnetic conductor disposed within said core, said conductor being electrically connected to the shield.
7 In combination with a high frequency coil, a support therefor, said coil being provided with a non-magnetic core, a conductive shieldsurrounding the coil, said shieldbeing a little larger than the coil to jusethe minimum amount of material and space for mounting, and a non-magnetic conductor disposed within said core, said conductor being electrically connected to the shield and means for rigidly securing said conductor to said support.
8., In combination, for, the coil having a core, a metallic shield surrounding the coil, and'a metallic bolt in the field of said coil securing the coil to the support, the bolt being in electrical connection with theshield. v I
9. combination with the" frame of a radio receiver, a metallic shielding can mounted on the frame, a false metallic bottom provided Within the can, a non-conductive coil support being disposed on said bottom, said support being of a size sufficient to occupy a major portion of the space between the said bottom and the top of the can, a coil provided on the said support, and a conductive bolt disposed Within the support, the bolt being in electrical contact with said bottom. 10. In combination with the frame of a radio receiver, a metallic shielding can mounted on the frame, a false metallic bottom provided Within the can, a non-conductive coil support being disposed on said bottom, said support being of a size sufficient to occupy a major portion of the space between the said bottom and the top of the can, a coil provided on the said support, and a con- 2 ductive bolt disposed Within the support, the
bolt being in electrical contact with said bottom and means for securing one end of the bolt to said frame.
11. In combination with the frame of a 2 radio receiver, a metallic shielding can mounted on the frame, a metallic bottom provided for the can, a non-conductive coil support being disposed on said bottom, a coil provided on the said support, and a conductive pin disposed Within the support, said pin being coaxially arranged With respect to said coil and can, the pin being in electrical contact With said bottom.
In testimony whereof I hereto aflix my signature.
FRANCIS T. BREWER.