US1896480A - Balanced inductance device - Google Patents

Description

Feb. 7, 1933. A. J. CHRISTOPHER BALANCED INDUCTANCE DEVICE Filed June 29, 1931 3 Sheets-Sheet l v /N VENTOR A .J. CHRISTOPHER A TTORNE' Y l933 A. J. CHRISTOPHER 1,896,480

BALANCED INDUCTANCE DEVICE Filed June 29, 1931 3 Sheets-Sheet 2 //v VENTOR A .J. CHRISTOPHER ATTORNEY Feb. 7, 1933. A. J. CHRISTOPHER BALANCED INDUCTANCE DEVICE 3 Sheet-Sheet 3 Filed June 29. 1931 FIG. 6

i fl IN VEN TOR AJCHRISTOPHER ATTORNEY Patented Feb. 7, 1933 UNITED STATES BALANCED IN DUCTANCE DEVICE Application filed June 29,

This invention relates to inductance devices and more particularly to those comprising a plurality of windings.

An object of theinvention is to provide an air core repeating coil or transformer which has a low transmission loss and a low reflection coeflicient at frequencies within the so called carrier frequency range.

Another object of the invention is to provide an air core repeating coil or transformer which has a high degree of coupling between the primary and secondary windings thereof, and at the same time an electrostatic shield between the windings to prevent the passage of noise or longitudinal currents from the primary to the secondary winding.

Another object of the invention is to provide an air core repeating coil in which are combined the properties of voltage transformation and of broad band frequency selectivity.

A feature of the invention is a winding arrangement for a repeating coil or transformer in which two primary and two secondary windings are applied partly as a quad and partly as individual twisted pairs.

Another feature comprises a winding arrangement in which the primary winding or windings are placed inside of a hollow or cylindrical conductor or conductors and the secondary; winding or windings are twisted with the hollow or cylindrical conductor or conductors.

Another feature of the invention is the proportioning of the number of turns of the primary and secondary windings which are twisted together, and the number of turns of the primary and secondary windings which are separately applied to secure the desired object.

The equivalent performance of a broad band pass filter can be obtained in accordance with the invention by designing the air core repeating coil so that it has windings with proper self-impedance values, proper coupling coefficient between the primary and secondary windings and, when required, adding shunt capacities across the primary and secondary windings. The theory of such an arrangement is the same as that given in.

1931. Serial No. 547,618.

United States Patent No. 1,714,149, dated May 21, 1929, granted to H. Whittle and me, jointly.

The following formulae, the development of which was explained in the United States Patent No. 1,714,149, referred to above can be applied to the design of repeating coils in accordance with this invention.

(1) Coefficient of coupling (5) Primary capacity W which is the minimum value of the image impedance W of the coupling circuit, is chosen as approximately equal to the terminating resistances R- which are equal in this case. C is the effective shunt capacity across the primary or secondary winding including the effective distributed capacity of these windings. f and f are respectively the lower and upper limiting frequencies. is is the coefiicient of coupling. 7, is the resonant frequency. L is the primary inductance. W. is the image impedance of the coupling circuit to which the primary winding of the receiving coil is connected and is equal to the secondary inductance. W, is the minimum value of From equation 1) it will be found that is approximately equal to .975 where f is to have a value of 35 kilocycles and f is value of 4 kilocycles. It is impossible to I00 rangement as obtain this value of k with the winding aremployed in the prior art on air core coils. However, by winding the repeating coil in accordance with one of the embodiments of the invention as described below, this value of 76 can be obtained. In winding'the repeating coil, the first part is applied as a quad (two primary and two secondary windings twisted together) which is applied with approximately equal turns in each section'of a two-section spool. The two primary windings and the two secondary windings each consisting of a twisted pair, are then separated, the two primary windings being applied over the quadded section-in one section of the spool,while the two secondary windings are applied over the quadded section in the other section of the spool. This results in an arrangement in which part of the primary winding is closely coupled with the secondary in the quadded section and loosely coupled in the outer section. By properly 'proportioning the number of turns in the quadded and outer sections of the windings, a wide variation in the leakage inductance or coupling factors can be obtained for a predetermined value of self-impedance of the individual windings to satisfy equation -(1) above. External condensers may be added when required across the primary and secondary windings so that their value plus the effective shunt capacity of the windings will satisfy equa tion (5) above- With winding arrangements such as described above, it is impossible to electrostatically shield the primary windings from the secondary windings by the usual methods employed in the prior art. However, in accordance with another embodiment of the invention it is possible to construct a repeating coil having a high coupling coefficient, and at the same time winding electrostatically shielded from the secondary winding. This is accomplished by employing a shielded conductor, or a twisted pair of wires enclosed in a shield, and twisting the shielded conductor or conductors with the conductor or conductors which form the secondary windings, before applying the windings to thespool." Preferably the shield is grounded at the midpoint of the windings. The longitudinal current flowing from the circuit to which the shieldedwinding is connected to ground will pass from the shielded winding to the shield and as the flux created by the current flowing in the shield will be opposite in the two halves of the shield, the resultant impedance to the flow of these currents through theshield can be'made very small. However, only .longi-I t'udinal' current will flowthrough the shield surrounding the conductors as the shield will assumepractically the same potential as the sentation .of the having its primary.

winding which a shields all along its length with respect to the transmitted voltage.

The invention will be better understood by reference to the following detailed description and accompanying drawings in which:

Fig. l is a conventional schematic representation of a coupling circuit in which the invention may be embodied;

Fig. 2 is a cross-sectional view of a repeating'coil showing the method of applying the windings over the core in accordance with one embodiment ofthe invention;

Fig. 3 is a'conventional schematic representation of therepeating coil shown in Fig. 2; p

r Fig. 4 is a cross-sectional view of a repeating coil showing the method of applying'the with windings over the core in accordance another embodiment of the invention;

Fig; 5 is'a conventionalschematic repre repeatlng coil shown in Fig.4;

Fig. 6 is a cross-sectional view of a repeating coil showing the methodof applying the winding over the core in accordance with still another embodiment of the invention; and

Fig. -7 is a conventional schematic representation of therepeating coil shown in Fig.6.

Referring to Fig. '1: the coupling circuit comprises an anti-resonant circuit 11 con-' nected through equal impedances 12 to a source of varlable voltage 13' and a second anti-resonant circuit 14 inductively coupled to circuitll and connected to an output impedance 15. Circuits 11 and 14 preferably comprise the primary and secondary windings respectively of an air core repeating coil as shown in Figs. 2 and 3 and are preferably proportioned to resonate at substantially the same resonant'frequency. The primary and secondary windings are'preferably elect-rostatically shielded from' each other by a grounded shield S to which shield one end of the secondary winding is preferably connected. NVhen the electrostatic shield S is not used the midpoint6, 1 of the primary winding is preferably grounded. The coeiiicicnts'of capacity elements in the anti-resonant circuits 11 and 14 are C and C respec tively, and the inductances are L and L respectively. C; and C are preferably made equal to-each other and preferably comprise the effective shunt capacity across the pri mary winding 5, 6, 1, 2 and secondary winding 7, 8, 3, 4 respectively, although individual capacities maybe added when required across the primary and secondary windings to obtain the proper value of capacity. The inductances L and L of the primary and sec onda'ry. windings are preferably made equal to each other and'the sum of the two impedances 12 is equal to impedance 15. g i-The air core repeating coil shown in Figs. Q'and 3 preferably comprises a spool 16 having a central partition 17 forming spool sections 18 and 19. A primary winding 5, 5A, 5B, 6, 1, 1-B, 1 A, 2 and a secondary winding 7, 7B, 7-A, 8, 3, 3-13, 3-A, 4 are applied over the spool. The primary winding is preferably made up of four sections 5, 5-A; 5B, 6; 1, 1B; and 1A, 2, with the terminals 5- connected to 5-B, 6 connected to 1 and 1B connected to 1-A so that the sections are connected in series aiding relation. The secondary winding is preferably made up of four sections 7, 7A; 7B, 8; 3, 3B; and 3-A, 4, with the terminals 7-A connected to 7B, 8 connected to 3 and 3B connected to 3A so that the sections are connected in a series aiding relation. The conductors forming the sections 5, 5A and 1A, 2 of the primary winding and those orming the sections 7, 7-13 and 3A, 4 of the secondary winding are preferably twisted One-half of the conductors in each spool together. The conductors forming the sections 5B, 6 and 1, l-B of the primary winding are preferably twisted together to form a pair and wound in section 18 over the quadded winding. The conductors forming the sections 7B, 8 and 3, 3-B of the secondary winding are preferably twisted together to form a pair and wound in the section 19 over the quadded winding.

The individual conductors forming the sections 5, 5-A and 1-A, 2 are preferably surrounded by individual electrostatic shields S concentric with the conductors, which shields ied before the conductors are formed The ends of the shields S are connected together adjacent the connections of the terminals of the concentric conductors therein as shown in Fig. 3. The sections 5B, 6 1, 1-B of the primary winding are preferably enclosed in an electrostatic shield 20, which shield 20 is connected to the electrostatic shields S as shown in Fig. 3.

If desired the conductors forming the seesection connected with the twisted pair.

hen it is unnecessary to have the primary and secondary windings electrostatically shielded from each other, concentric shields S and the shield 20 may be omitted.

In a specific embodiment of the invention constructed the conductors forming the winding sections 5, 5A; 1-A, 2; 7, 7B and 3-A, 4 were formed in a quad and 190 turns of the quadded conductors were applied in each spool section, the conductors forming the winding sections 5B, 6 and were formed in a pair and 60 turns of the paired winding were applied over the quadded winding in one spool section and the conductors forming the winding sections 7-A, 8 and 3, 3-B were formed in a pair and 60 turns of the paired winding were applied over the quadded winding in the other spool section. The individual sections of the primary winding and the individual sections of the secondary winding were connected together in a series aiding relation.

Each of the individual conductors comprised No. 24 double cotton covered copper wire. No individual electrostatic shields concentric with the conductors were employed in this particular embodiment. The spool was formed from wood, the core being circular and having a diameter of 2 inches. Each of the two spool sections was '7 inch wide and 1% inches deep. The central partition between the two spool sections was inch wide.

Tests made on this coil showed a transmission loss over a range of frequencies from 5KC to 30KC of less than one decibel and a variation in transmission loss of less than one-half decibel. The reflection coefiicient over the same frequency range was less than 20%.

In Fig. 3 the inherent capacities existing between the sections of the primary and secondary windings and between the shields S and 20 and the windings are shown. These capacities between the individual sections of the secondary respect to the center and ends of the winding; the capacities between the individual sections of the primary winding are symmetrical with respect to the center and ends of the winding; and the capacities between the shield sections S and 20 and the primary and secondar windings are symmetrical to the shield 20 at the ground connection thereto.

The longitudinal currents flowing from the source 13 through the two balanced impedances 12, to which the shielded primary winds ing 5, 6, 1, 2 is connected will flow from this winding to the shields S and 20 and to ground andv as the fluxes created by the currents flowing in the shields S will be substantially equal and opposite in the two sections 18 and 19 of the spool. 16, the resultant impedance through the shields S to this long current is very small. This substantially eliminates stray circulating currents in the secondary winding due to longitudinal current present in the primary side of the circuit. As the shield sections S will have the same potential as the concentric conductors of the primary winding therein, only longitudinal currents will flow the hollow conductor shields S.

The midpoint 6, 1 of the primary winding may be grounded when the primary winding of the repeating coil is connected to a balanced circuit by the connection 21.

winding are symmetrical with M through CID at the outer ends of the windings By varyin the number of turns in the sections 5, 5- ,and 1A, 2 of the primary winding the number of turns in the sections 7, 7 -B and 3A, l of the secondary winding, which sections are wound as a quad, with respect to the number of turns in the sections 5B, 6 and 1, 1B of the primary winding and the number of turns in the sections 7 13, 8 and 3, 3-B of the secondary winding, a large variation in the coupling coefficient may be obtained.

The repeating coil shown in Figs. 1 and 5 comprises a primary winding 55, 56, 51-, 52 and a secondary winding 57, 58, 53, 5 1 wound on a spool 16 having a central partition 17 to form spool sections 18' and 19. Each of the sections 55, 56 .and 51, '52 of the primary winding is preferably enclosed in an individual electrostatic shield S which is concentric with the conductor forming the individual section. The section of the secondarywinding 57, 58 and the section of the primary winding, 55, 56 with its concentric shield are preferably twisted together and wound in the spool section 18 and the section 51, 52 of, the primary winding with its concentric shield and the section 53, 54; of the secondary winding are preferably twisted together and wound in the spool section 19 in an opposite direction to that of the winding in the spool section 18. The outer terminals of the winding sections are connected toether as shown and the ends of the conceni ric shields S surrounding the primary windmg are connected together and to ground spool sections 18 and 19. i

This construction provides a high degree of coupling, especially in the case of an air core coil and also prevents noise or longitudinal currents from passing from the primary winding to the secondary winding.

The repeating coil shown in Figs. 6 and 7 comprises a spool 16 having a partition17 forming spool sections 18 and 19, a primary winding7 5, 76, 71, 72 and a secondary winding77, 77B, 77A. 78, 73, 73-B, 78--A., 7 4:. Each of the winding sections 5, 7 6 and 71, 7 2 of the primary winding is preferably enclosed in an individual electrostatic shield S which is concentric with the conductor forming the individual winding section. Seetions 71. 72 of the primary winding and 7 8, 73B of the secondary winding are preferably twisted together and wound in the spool section 19. Sections 75. 76 and 77A. 78 of the secondary winding are preferably twisted together and wound in the spool seetion18 in an opposite direction to that of the winding inspool section 19. The inner ter-,

minals 71 and 76 of the primary winding sections are connected together terminals 7 3 and 78 of the secondary winding sections are connected togetheras shown. The shield sections S are connected togetherin the two and the inner and to ground adjacent the terminals 76 and" 71. Each of the winding sections 73 A, 7 4L and 7 7 7 7B of the secondary winding comprises a relatively few turns which are the coupling coefficient to obtain uniform transmission over a range of frequencies and a low reflection coefficient. The winding section 72 -A, 74: ispreferably wound in spool section 18 over the twisted pairof windings and employed to adjust to the desired value the winding section 77, 77B is preferably wound in the spool section 19 over the twisted pair. These w nding sections 7 3A,7 a and t! r7-B are connected in a series aiding re-:

lation to the secondary winding sections 7 3, 78B and 7877-A as shown.

. When it is unnecessary to electrostatically invention have been shown and described in deta l it isto be understood that the invention is generic in ch araeter and is not to be limitedto the particular embodiments since numerous modifications thereof may be made by persons skilled in the art without departing from the sp rit of applicants invention, the scope of which is to be determined by the appended claims.

, What is claimed is:

1. An inductive device comprising a spool and two primary and two secondary windings thereon, said windings being applied to said spool partly as a quad comprising turns 7 of both primary and secondary windings and partlyas individual twisted pair primary turns and twisted pair secondary turns.

2. An inductance device comprising a plurality of conductors twisted together to form a-unitary cord, and means for reducing the direct electrostatic capacity between one of said conductors and at least one other of said conductors, said means comprising a hollow conductor concentric with and insulated from sail one conductor to electrostatically shield said one conductor from the other of said conductors. v

3. A repeating coil comprising a non-magnetic spool having two winding sections and two primary and two secondary windings thereon, said windings being applied partly as a quad with approximately an equal numberof turns in each winding section and partly as individual twisted pair primary and secondarywindin gs with the twisted p air primary winding portion wound in one of said winding sections over the quadded winding portion and the twisted pair secondary winding portion wound in the other of said ice winding port-ion.

4. A repeating coil comprising a spool and at least one primary and one secondary winding thereon, said primary and secondary windings being applied partially as a unitary cord formed of twisted conductors and partially with said primary and secondary windings as individual units separated from each other.

5. An inductance sections over said quadded winding device comprising primary and secondary windings, each of said windings comprising a plurality of sections, the conductor or conductors of at least one of said sections of said primary winding being twisted together with the conductor or conductors of at least one of said sections of said secondary winding, and means to electrostatically shield at least one of said twisted primary and secondary sections from each other, said means comprising an electrostatic shield coaxial to and surrounding one of said conductors.

6. A repeating coil comprising a spool and at least one primary and one secondary winding thereon, said primary and secondary windings being applied partially as a unitary cord formed of twisted conductors and partially with said primary and secondary windings separated from each other, and means to electrostatically shield at least a portion of the conductor forming one of said windings from a portion of the conductor forming the other of said windings, said means including a coaxial shield surrounding the portion of said one conductor which is applied as a unitary cord with said portion of said other conductor.

7. An inductance device having a band frequency characteristic comprising a spool and at least one primary and one secondary winding thereon, part of said primary and secondary windings being applied as a unitary cord in a manner such that a low leakage inductance between the windings is obtained and another part of said windings being applied as individual primary and secondary conductors so that a high leakage inductance between said windings is obtained.

In witness whereof, I hereunto subscribe my name this 26th day of June, 1931.

ARTHUR J. CHRISTOPHER.

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