US1576459A - Electric retardation line - Google Patents

Description

G. W. PIERCE ELECTRIC RETARDATION LINE "March 9, 1926. I 1,576,459

Filed Dec. 24, 1921 l ments,sa1d mutual Patented Mar. 9, 1926.

UNITED STATES 1,576,459- PATENT OFFICE.

GEORGE W. PIERCE, OF CAMBRIDGE, MASSACHUSETTS,'ASSIGNOR TO SUBMARINE SIG- NAL COMPANY, OF PORTLAND, MAINE, A CORPORATION OF MAINE.

ELECTRIC RETARDATION LINE.

Application filed December 24, 1921. Serial No. 524,807.

To all whom it may concern:

Be it known that I, GEORGE W. PIERCE,

a citizen of the United States, residing at Cambridge, Middlesex County, Massaclur,

setts, have invented a new and useful Im provement in Electric Retardation Lines, of which the following is a full, clear, and exact description. I I

The present invention relates to electric retardation lines, and more particularly to a retardation linefor introducing definite time retardation of electric currents in a manner such that currents of a complex character will be retarded in a rational and predeterminable way, without essential distortion, over a significantrange of frequencies. tion results in a considerable extension over previous retardation lines the range of frequencies for which the -1 etardation "time is independent of frequency. I

The present invention is an improvement over the artificial retardation line disclosed in my pending application, Serial No. 306,- 689 filed June 25, 1919, for electric compensators. The present invention, however, is not limited to the application of the retardation line herein disclosed, to an electric compensator, as the present invention is capable of wider application and may be employed wherever an artificial line isdesired which will retard electric currents without essential distortion over a considerable range of frequencies.

In my application for electric compensators I showed an artificial line' consisting of inductance elements .in" series and capacity elements in shunt for introducing predetermined elements of time retardation into electric currents transmitted through the artificial line. v

The present invention relates particularly to the introduction into such a line of mu-' tual induction-between the inductance eleinductancebeing properly roportioned to the self-inductance of t e elements. I have discovered that the mutual inductance between inductive elements, or coils, of such a line, if given a certain unique relation to the self-induc- The present invendispersionless herein as descriptive of a line or system through which a complicated wave form may pass and be essentially preserved in its wave form in that the different significant frequency components of the wave form pass with essentially equal time retardations. The significant frequency components are those which are necessary or desirable in the electric current for the purposes employed. For example, in electric current of audible frequency used in connection with auditory translalting devices, such as telephone receivers, the signiti cant frequency components of the wave form are the audible or principal audible frequency components.

In the drawings, Figure 1 is a diagram showing an artificial line illustrating the present invention; and Figure 2 is a detail view in section indicating diagrammatically a mounting of the inductance coils.

Referring to the diagrammatic illustration of the invention, an artificial line is illustion of the line which contains the retarda- Theretardation line is made tion sections. up of a plurality of recurrent sections each comprising an inductance 3 in series with the line and a capacity 4 shunted across the line. In the diagrammatic illustration five sections are illustrated, it being understood, however, this is merely for the purpose of illustration and that in practice the number of sections will generally considerably exceed this, depending of course upon the purposes for which ihe line is used and the amount of time retardation desired. I When the retard-.tion line is to be used in an electriccompensator as shown, for example, in my electric compensator application Serial No. 306,689 referred to -above, the line will vbe provided with the necessary taps and contacts whereby the number of effective sections may be varied at will. The inductance coils 3 are preferably placed end to end, and may be wound on a common core, as indicated schematically in Figure 2. The showing in Figure 2 isintended merely as a general diagrammatic illustration and it will be understood that in winding and mounting the coils, the diameter of the coils, the size of Wire, the spacing of the coils apart, etc., will be calculated in accordance with the formulae hereinafter referred to. The windings of adjacent coils are so spaced from one another that the mutual inductance between adjacent coils 3 is approximately one-tenth of the self-inductance of each coil. The-computation of this 1 to 10 relation is based on the following considerations.

Let L be the self-inductance of each of the inductance coils. M be the mutual inductance between adjacent coils, and, as notation, let

where wzthe angular'velocity of asinusoidal electromotive force. impressed at the input end of the line, and, as furthernotation, let

Logw

then, we have In equations (4:) and (5) a is the attenuation constant and w the retardation angle introduced by the line into the current per section of the line. The same sign must be employed before the inner radical in the two equations, and that sign must be selected to If now we temporarily let take the sine of both sides of (5), square both make a and 5 both real quantities; The sides, and expand the result in series for equations (4) and (5) are exact. values of A greater 1 we obtain Let us now expand Q, as defined by equation (3), in the form and write (7 in the form where F LC w and G M02602- (1 1) Now substituting (10) into (9), and keepmg only significant terms, we obtain make the retardation angle (p proportional to a); and since F is proportional to m equa-;

tion (12) suggests the advisability of makmg It is seen that (14) leads to a these conditions (16) gives, in view of (11) M:L/12, approximately. If now we replace L by its value from (1), we obtain M:L,/10, approximately. (17) Therefore, if we make the line to have between neighboring coils a mutual inductance, as given by (17),approximately equal to one-tenth of the self-inductance of each coil, we shall have the effect that the range of frequencies over which the time retardation per section is essentially independent of the frequency is much greater than the .range with M equal to zero as in the practice heretofore. In fact the specific value of M given by equation (17) is uniquely the best value to give to M to make the line one of low dispersion.

Equation (17 is stated only approximately, in that this value may be shifted slightly one way or the other tomake slight adjustments-for some of the small neglected terms- Also in practice, it may be desirable for structural reasons to depart somewhat from (17).

To obtain the time retardation T per section of the line, it is only necessary to divide the retardation angle (p by the angular velocity to. By (13) and (11) this operation gives forv a significant range of frequencies T: L, +2lVl)O J w/5; provided M 1/ The principles of the above mathematical discussion are to be found in my book entitled Electric Oscillations and Electric Waves published by McGraw-Hill Book Co. Inc. New York, 1920, and particularly in Chaper XVI and specifically on page 316 and following. On page 316 of this book,

sion, the words and if there is no magnetic leakage should be stricken out, as I have found that the results are general. Reference may be made to this book for details of the principles above treated.

Itwill be noted that the present invention constitutes a transmission line of low dispersion, and in addition to this important feature it has the advantage of being easier and cheaper to construct than a line without the novel feature of properly propor-' tioned mutual inductance, in that the coils maybe wound in solenoidal form and may be compactly arranged which obviates the expense of toroidal windings or of wide spacing as must be employed in artificial lines not having my novel features.

It willbe seen by computation or experiment that a slight departure, for exam-' ple 10 percent, from the relation M=L,/l0 may be made with only slight departure from the low dispersive effect of the line.

For general computations as to attenuation, retardation, and surge impedance of the lineand apparatus of the present invention use may be made of sections 283, 28 1 and 285 of my book abovereferred to, which sections are contained on pages 316 and following. In using these sections for calculation of apparatus of the present invention, the value M L /lO, or in case of a small departure from this relation the value of M specifying the departure, should be employed and substituted into the formulas of the book.

By having the induction coils with the mutual inductance relation as specified in this application, the range of frequencies for which the dispersion is low and practically insignificant may be from three to ten times as great as the range for lines without the mutual inductance. As' above pointed out the present invention, however, is not limited to the use of a, retardation line in an electric compensator. shown in my electric compensator application, but the apparatus and method of the present invention is one of general application. It is to be understood that the present inven ion is not so limited but relates to a retardation line, or artificial electric line, and its method of use broadly as set forth in the following claims:

I claim:

1. An electric retardation line having capacities in shunt and inductance elements in series and having the mutual inductance between adjacent inductance elements approximately equal to one-tenth of the self-inductance of the elements, substantially as described.

2. An electric retardation line having 'capacities in shunt and inductance elements in series, having the self-inductance between neighboring points of attachment of the ca.-

pacities approximately ten times the mutual inductance between the inductance elements, substantially as described.

3. An electric retardation line having low distortion and comprising capacities in shunt and inductance coils in series having their self and mutual inductances so proportioned that the line is substantially dispel sionless as well as of low distortion over a considerable range of significant frequencies, substantially as described.

4. An electric retardation line comprising a series of recurrent sections each comprising a capacity shunted across the line and an inductance coil in series with the line and so located with relation to adjacent sections as to have mutual inductance therewith in the neighborhood ofone-tenth of its self-inductance, substantially as described.

5. An electric retardation line comprising a series of recurrent sections, each having a capacity shunted across the line and an' inductance in series with the line permitting the substantially free passage of alternating located with respect to each other as to l have such mutual inductance as to minimize dispersion of the significant frequency components of the current waves, substantially as described.

6. An electric retardation line having capacities in shunt and inductance coils in series, the inductance coils each having substantially the same self-inductance and each pair of adjacent coils having substantially the same mutual inductance, the self and mutualinductance being so proportioned that the line is substantially dispersionless over a considerable range of frequencies, substantially as described.

7. An electric retardation line comprising a series of recurrent sections, each comprising a capacity shunted across the line and an inductance in series with the line so located as to have mutual inductance with the inductance coils of adjacent sections in substantial accordance with equation est-pea. aigret. t -(1...)!

so that the retardation angle is approximately proportional to the angular velocity over the significant range of frequencies, substantially as described.

8. An electric retardation line comprising a series of recurrent sections, each including a capacity shunted across the line and an inductance in series with the line and whose retardation angle per section is an antisine function of the frequency of the impressed clectrolnotive force, the inductances of adjacent sections being so located with respect to each other as to reduce said retardation angle to substantial proportionality to said frequency, substantially as described.

In testimony whereof I have hereunto set my hand.

GEORGE W. PIERCE.

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