US1453980A - Attenuation equalizer - Google Patents

Description

May], 1923. 1,453,980

.' R. s. HOYT ATTENUATiON EQUALIZER Filed June 29 1918 3 Sheets-Sheet 1 E} I I 1E 1 E v 2 Fzyfl 7 I 1V Equalzzer TV I 'g i is J 4 v 2 4 P 3 f I 4 2 Equalizer Line [/2 .INVENTOR. H. SHoyz BY z. m

A TTORNEY 1,453,980 R. s. HOYT ATTENUATION EQUALIZER FiledJune 29 1918 3 Sheets-Sheet 5 4 3 4 Laaded Lilw with Mid-110ml Irminatia 4. 9 494 4 $4 2 sobmzesmadedmm T I W W 0 c c c 'c i' INVENTOR.

ATTOI iNEY A Improvements in Attenuation Patented May 1, 1923.

RAY S. HOYT, OF

BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

ATTENUATION EQUALTZER.

Application filed. June 29,

To all whom it may concern:

Be it known that 'I, .RAY S. HoY'r, residing at Brooklyn, in the county of Kings and State of New York, have invented certain.

Equalizers,of which the following is a specification.

This invention relates to transmission systems and more particularly to system for the telephonic transmission of speech. Its object is to provide means whereby the distortion of the received signals,

. ly 200 cycles per second, to 2,500 cycles per particular,

respect to second. It is evident that for clear articu- 'lation of the received speech it is desirable that the relative amplitudes of theseconiponents or harmonics shall be the same in the received wave as in the: transmitted wave. When such a. condition obtains, the transmitting system is called distortionless. In actual transmission systems, however, it is well known that-the distortion with respect to frequency 'is considerable, and, in when the transmission system includes long lines, the distortionmay be very large. The usual character of tion is a diminution of the amplitudes of the high frequency component currents with the low frequency currents, whereby the character of the received speech may be so modified as to seriously obscure the articulationand clearness of speech.

From the foregoing it will. be clear that ordinarily the required function of the at-- tenuation equalizer of this invention, is to discriminate against the low frequency com ponent currents to the end that the disthis distortype of equalizer;

1918. Serial No. 242,567.

crimination of the actual system against the high frequency component currents shall be substantially neutralized. It will be understood, however, that this invention is not limitedto such'a function since it may be used also to equalize transmission -over a system which discriminates against its low frequency components. I

Moreover, it will be understood that this invention is not limited to, the function of attaining exact equalization, but the equalizer may be soconstructed as to produce for the resultant system a desired variation of amplitude with respect'to frequency, which departs by'a predetermined amount fromv the exact equalization heretofore discussed. 5

This maybe accomplished by merely designing the equalizer with respect to an assumed variation in the transmission system proper, which differs from the actual variation bythe desired amoun The invention may now be more fully derstood by reference to scription when read in connection with the accompanying drawings. In the drawings, Flgure '1 1s a schematic diagram of a transmission system comprising two sections, said diagram being provided in order to assist in understanding the development of certain general formulae pertaining to transmission;

the following de-;

Fig. 2 is aschematic diagram of the system of Fig. 1 inserted;

Fig. 3 is a schematic with an attenuation equalizer diagram of "a line circuit with terminating impedances and having an attenuation equalizer inserted therein; Fig, 4 is a diagram of a series impedance Fig. 5 is a diagram of Fig. 4 applied'to a loadedline with midsection termination, that is, toa loaded line whichbeginswith a- I half loading-section, a loading-section being line section equalt'o a showing the equalizer i the portion-of line existing betweenany'two I succeeding loading coils,

Fig. 6 is a diagram showing a series of v I curves illustrating the attenuation ofthe va-' rious parts of the system of Fig.- 5;

Fig. 7 is a diagram of a shunt impedance 2 type of equalizer;

Fig. 8 is a diagram showing the equalizer of Fig. 7 applied to a loaded line with midload termination, that is, to a loaded line which begins with a half load coil, a. half load coil being one whose impedance is half the impedance of a normal or whole'coil;

Figs. 9 and 10 illustrate two types of pew riodic structures which may be used as attenuation equalizers;

Fig. 11 is a diagram showing the attenua tion equalizer of Fig. 10 applied to a loaded line with mid-load termination; and

Fig. 12 is a diagram showing attenuation curves for the system of Fig. 11.

The general theory underlying the attenuation equalizer of this invention will now be developed, after which the specific types will be disclosed and the appropriate design formulae will be derived.

Referring to Fig. 1, a transmission system is schematically represented, which is shown as consisting of two parts I and H connected together at terminals 3, 3. An E. M. F. E is illustrated as impressed be-- tween terminals 1, 1 and for generality an E. M. F. E between terminals 2, 2. If the current entering terminals 1 is designated by I, and the current in terminals 2 by 1,, then I, and I, are related to the impressed E. M. F.s. by equations of the form:

1 TIIEI TIZEZ 1 2 zi i zz z (1) In the above expressions T T T and T are the coefficlents of admittance of the system. T is equal to the current flowing into terminal 1 of the system when unit E. M. F. is app-lied between terminals 1, 1 and terminals 2, 2 are short circuited. Similarly T is equal to the current flowing through terminals 2, 2 under the same conditions.

T is equal to the current flowingv through terminals 2, 2 when a unit E. M. F. is applied to terminals 2, 2 and terminals 1, 1 are short oirc-uited.

When we are considering transmission from 1 to 2, E is set equal to zero, whence:

' The coefiicient T is the transfer admittance of the system, that is the ratio of the current received at terminals 2 to the E. M. F. im-

pressed at terminals 1. This coeflicient may be theoretically determined when the system is specified or it may be experimentally measured. In general, it will be found that v T is a function of the frequency of the impressed E. M. F.; it is the variation of T with respect to frequency which causes the distortion, which it is the object of this in? vention to eliminate.

Fig. 2 is a diagram of the system of F ig. l with an equalizer, schematically represented, inserted at terminals 3, 3. If we designate by V and V the voltages between terminals 3, 3 and 4. 4 respectively (the arrows associated with the voltages indicating the directions from lower to higher potentials), by A A A A the admittances of part Lby B 13 13 15 the admittanvcs of part II, and by C C C the admittances of the equalizer, the equations of the system are:

Confining our attention to transmission from 1 to 2- and consequently setting E equal to zero, the solution of equations (3) gives:

The significance of the admittance is easily seen. Thus, referring to Fig. 2, C is equal to the current flowing into terminal 3 of the equalizer when a unit E. M. F. is applied between terminals 3, 3 and terminals 4, 4 are sho-rt-circnitcd. Similarly C is equal to the currentflowing thru terminals 4, 4 under the same conditions. is equal to the current flowing thru terminals 4, 4 when a unit l); M. F. isapplied across terminals 4, 4, and terminals 3, 3 are short-circuited. From these definitions the meaning of the other admittancesis self evident.

If the equalizer is removed in Fig. 2 the equations of the system for transmission from 1 to 2 are:

Solving the above equations we obtain the following as the transfer admittance of Fig.

aeaeso Now in the actual system the transfer admittance T varies with the frequency in the equalized system the requirement is that T as given by shall be substantially constant over the frequency range required for the telephonic transmission of speech. This result is attained when equalizer, characterized by the parameters C C C C is so proportioned that the absolute value of T as given by (5) is substantially independent of the frequency.

If the equalizer consists merely of an impedance Z (which may be a single element or maybe a combination of elements) in series with the line the equations for transmission from 1 to 2 in Fig. 2 are as follows:

Solving these equations and notingthat C :C :C C :1/Z we obtain as the transfer admittance from 1 to 2 the following: I

i which can also be obtained from (5) by substituting c zc b c zl/z therein. If on the other hand the equalizer consists of an admittance Y in shunt across the line the equations of the systems fortransmission from 1 to 2 are:

i From these equations we may obtain the I If the system which is equalized consists of a transmission line of characteristic impedance K and propagation constant I i imitclosed by'the inipedances U and U and if the equalizer be inserted between the line and the impedance U as shown in Fig. 3, then where H, V V are the reciprocals of K,

U U respectively, and are therefore admittances.

Equations (12) in so far as these relate to the transmission line constant-s, follow.

from well known formulae, on the assumption that the line is so long that the sendingend current is independent of the receiving wirinanrfii z If, on the other hand, the equalizer con-.

sists of an admittance in shunt across the line, then by (11) and (12) If further this equalizer is inserted between a resistance. U and a long line (K, I), (see Fig; 3) whose A and B admittances are given by (12), then by reference to (5), (l2), and (15) it will be seen that the transfer admittance of this system is Neglecting the term which contains the factor 6 which is commonly ,small, (16) reduces to arm- 5 Series impedance type 0 f equalizer.

Equation (13) may be written eKU, J4KU K U a/eUjU K+ U K+U K+U -+Z It is now convenient to introduce a set of parameters defined by the following equa- In the above equations the two elements of each of the expressionson the left hand side of the equality sign are respectively the real and imaginary components of the cora id log urn,

whence, by equations (20),

. In the practically important case considered below, the terminal impedances U and U are pure resistances and henceconstants whose values are independent of frequency.

For such case it follows from (22) that distortion with respect to frequency will be The specific type of the attenuation equalizer now to be considered is shown in Fig. 4,

- and consists-of a resistance R in parallel.-

with the serial combination of an induce responding expressions on the right hand side, which latter expressions are in general complex functions. Thus, for any transmission system, the attenuation coefficient A is the real part of the pro agation coefiicient P of the system, while 2' is the imaginary component, of which A is areal expression and 2' denotes the operator 1.

From (19) it follows that wherein a pair of vertical lines enclosing an expression indicates that the absolute value of such expression is meant.

From equation (18) it follows that the absolute value of the transfer admittance of the system may be expressed as 445K U K+U K 31: HM (21) ,tance L and a capacity C. If p "denotes 27cf when f is the frequency, and i denotes the imaginary operator /1, the expression for the impedance Z is The general design procedure for this t pe of equalizer will now be laid down. ferring to'formula (22) it is evident that the resultant efi'ective attenuation of the system' is A+b+c+a, and that the equalizer afiects only one eoeficient, namely a. Thecoeflicients A, b, and c are given by formulae (20) and the line constants, whence the sum A-i-b-l-c may be taken as the data of the problem.

highest frequency f, of the range over which equalization is desired, it is evident that the resultant attenuation of the system will have a uniform constant value equal to forallfrequencies less than f and further that no attenuation will be introduced by Further, if -A +b +0 is the value of A+b+c at the quencies.

mental data by aid of formulae (.20), the

first step toward the design is to compute by (24) the values of the attenuation a which the ideal equalizer should furnish over the frequency-range contemplated. Since the equalizer here considered (Fig. 4) is char-- acterized by three independent constants (R, L, 0,) these constants can be so-evaluated that the equalizer attenuation will wherein R is known from (26). L is then have its ideal values at three different fre- One of these frequencies, namely ff has already been assigned; forthe other quency f,, the equalizer impedance should I equalizer elements as follows: By formula (23) the equalizer two it is convenient to choose the frequency 0, and a selected intermediate frequency f,. The ideal values of a for the three frequencies O, 7",, f, will be denoted by a 11 ,01 .Since, by (24), the attenuation a furnished by the equalizer should be zero at the' frebe zero at that same frequency. If the equalizer were to be proportioned in accord-' ance with these values, the equalization would be exact at frequencies 0, f and f However, the frequency zero is unimportant, and exact equalization at the-frequency f is also of minor practical importance. It has been found, therefore, that more satisfactory equalization may be secured by choosing a value of a slightly different from that for exact equalization at frequency O, and also making the impedance of the equalizer zero' at a frequency 7, which is nearly but not exactly equal to f Having therefore decided on appropriate values of a a, I

R, L, C, are determined impedance, and therefore a, is. zero if Since this is to be zero at frequency f we have:

Led amp 25 1 At zero frequency the impedancev of the' equalizer is simply It; therefore, by (20) R 1 TI'G QO when K+U, is the value'of- K+U, at-

and i the values of the' Byformulae 23 and" 25 the impedance 2 Z of the equalizer at frequency f zp /2'n 1s Z R1 (fl/far] 1 QT SVHRO Hence, by formulae (20),

' f1/fa) P1l( 1)1i 1 1 where (K+U,) is the value of (K -FL 1) at frequency f,. Solving this equation for C, in the practically important case for which (K+U,) .is pure resistance, we have determined from (25), which gives L:1/C(2 1rf (28) 'Desz'gn of series impedance type of equalizer for a specific ease.

The equalizer of Fig. 4.- will now be designed in accordance with the foregoing formula to equalize transmission over the system shown in Fig. 5, the system consisting of periodically loaded transmission line with terminal impedances U and U which are pure resistances of 1540 ohms each. The line is terminated at mid shunt (that is, mid-section) position and has the following specifications: Wire..'...'. .......#19B.&S.gauge.

Cap. per mile .064 10- iarads.

Resistance per mile. 86 ohms.

Leakage permile Proportional to freguency and equal to 0.896X10- at requencyBOO.

Load coil inductance .175 hepry.

Length of line. load ng sections, 69.6 miles.

Length of loading section... 1.16m11es.

so i

There uired ran e of fre uencies is from zero to about 2400' cycles per second. We have then Inductance per section, L .175. Capacity per section, C .0742 X 10-;

Further, L /C 1540.

Since the line is terminated at mid-section, I v

the characteristic impedance is given by:

The results of .a computation of the attenuation of 60 sections of the line by means of the known, formulae for v periodically loaded lines is illustrated in curve 1 of Fig. (6).

( 2) on a larger scale.

Curve (2) of Fig. (6) is a plot. of the required valve of a as given by equa-- 'tion (24:) While curve (3) is a plot of curve a .lse :2650

We have therefore 1- (192072650 21 1920 3250 .0092 X 10 farads.

and finally by formula 28) L= 10/.0092(21r2650) .391 henry.

Curve (4) of Fig. (6) shows the computed attenuation actually furnished by the equalizer having theabove given values While curve (5) is a plot of the resultant attenuation of the system. Itwill be seen that the attenuation is substantially constant over the required range of frequencies.

In the above specific case the object was to equalize the transmission; that is, to make the resultant attenuation conform to a preassigned horizontal straight line graph, curve 2 representing the attenuation which the equalizer must 'furnish to accomplish this object. If, instead, the object were to make the resultant attenuation conform to a T -r fz 1 defined by the followingv equation of the characterand These follow from (31) and (33), the ad- The design of-the equalizer of Fig. 7 will H+V H being the characteristic admittance of f we have esaeeo Hence by formula (26) I R:'(2.054=4t1) (3080):3250 ohms o By formula (27) I preassigned curved graph (instead of to a preassigned horizontal straight line graph) the design procedure would be exactly the same as above if curve 2 is drawn to repre- I sent the attenuation, which the equalizer must furnish to make the resultant attenuation conform to the preassigned curved graph. Similar remarks apply, of course, to the other types of equalizers described below.

Shunt admittance type of equalizer.

If theequalizer consists of an admittance Y, bridged across the line between the sending end admittance V and the line (K, I) closed through an admittance. V at the receiving end, the transferadmittance is given by (14), which may be written as the expression for the absolute value of i the transfer admittance.

Now let the bridged equalizer be as shown" in Fig. 7 and consist of a resistance element R in series with the parallel combination of .an inductance L and a capacity C. The adv mittance Y of this combination is 1 a. mama The design procedure is now similar. to that for the series type equalizer. Havin selected appropriate values of 0 f a an and, for the practicalliyl important case in which the admittances and V, are real,

whence, v

mittance of the equalizer at zero frequency being simply l/R.

now be worked out for the system shown in Figl} 8. This system is identical with that of ig. 5 except that the loaded line is terminated at mid-load instead of mid-section position. The formula for the characteristic impedance K is then 1/ o/ o1 (f/fy J 07 8 (see equation (4) of Patent No. 1,167,693). Hence the characteristic admittance H is 1 I 1540 /1-U 2s00 If we select the same values of the parameters as before, namely (t .720 I f,: 1920 a,: .484 f '=2650 I then, by substitution of these values in for 'riodic structure or wave mulae (35)(37) We have: I

Owing to the exact mathematical relation obtaining between the equalizers of Figs. (4) and (7), curves 4 and 5 of Fig. (5) are also valid for the particular design given above;

Wave-filter type of equalizer.

A third type of attenuation equalizer may be obtained by a special design of the pefilter which is disclosed in patent to Campbell No. 1,227 ,113 of May 22, 1917 .[The distinguishing prop erty of the structure, as fully set forth in the above mentioned specification, is that of transmitting freely or without attenuation all currents whose frequencies-lie within a preassigned range or ranges of frequency,

while attenuating currents of 'all' frequencies lying outside said rangeor ranges. In

the present invention the use made of this" characteristic property is quite distinct from that set forth in the above mentioned specificatiom'in that in the .,present invention, the wave filter is so proportioned that the attenuation introduced by said filter within the range of telephonic frequencies is complementary to the attenuation introduced by the transmission system' with which it is cooperatively combined to the end that the resultant attenuation shall be substantially constant over the desired range of frequencies.

, In other words use is made of the fact vthat in a periodic structure of the ty e disclosed in the above patent the attenuation does not.-

increase sharply at the cut ofl fre uencyof the band of frequencies transm tte ,but 1ntively, then, (39) and (40),

creases gradually to a large value, the structure this tioned, to render loaded linesystems substantially distortionless. r 1

The propagation. constant of the wave filter, or periodic structure, is determined by equation(2) of Patent No. 1,227 ,113

l (38) 2 In this equation ances in serieswith and in shunt across the line, respectively; and :Z /Z Furthermore the limiting frequencies of free transmission, here designated by f,- and f as stated in the above mentioned patent are determined by:

Letting 0:21: when f is any frequency and referring to the type of wave filter in which each section ;,consists of an inductance inseries'with the lines, 'and an inductance and Z and Z are the imped- "illustrated in Figs; '(9)-and (10) are par- 7 ticularly. adapted, when properly propore capacity in parallel in shunt across the line as shown in Fig. 9,

Z =tpL 2 1 p L C L 'Y 17; (1,IP?LZCZ) If p and 1),, denote 21d, and 21vf 1 1 3 2 I P2=P11/1 +4IL2/L1, I I II If 1/ denotes the ratio f /f zp/p then by substituting the value given by the first equation of (41) in the th rd equation of a (40) ,we find that eg -a 2 f equation of (41) gives res so- [12a If 1' denotes the ratio f /f ;p /p the last The corresponding equations for the type of filter shown in-Fig. 10 are:

(4 and (46) being identical with (43);

It may be shown that the characteristic impedance of a wave filter when terminated at mid-series (that is, mid-load) is Fw/ l d 'Y /Q and when terminated at mid-shunt (that is, mid-section) K /Z Z 1 /4) (48) Formula '(47) for K can be derived in a simple manner by considering in an infi- -nitely long Wave'filter, terminating at midseries, the first periodic interval extending from mid-series to mid-series position. If the impedance of this filter is denoted by K 5 the impedance of the remaining portion (which is also infinitely long) is equal to and thus the distant end of the first. periodic interval is closed through an impgdance equal-to K Now the impedance of the system consisting of one periodic interval (Z /2, Z Z /2) having its distant end closed (through an impedance K is clearly some function of this closing impedance K and of the preceding elements Z and Z In fact, as is now evident,

solution is the value, given by (47). F or- -mula (48) for K can be established in an analogous manner. u

If the values derived above for Z .Z and m parameters defined by Introducing a set of the equations c to loge z a I,

7 aresnbstituted in (47) and (48.) the midseries and mid-shunt characteristlc lmped- F ances of the filter'of F ig. 9 are respectively: 50

LI Elen om/i-w T -l K c; 1 1? e 'w Similarly for the type of Fig. 10,

K a w 7 1 I I I it 1:573 51 K b Von/W r w If the propagation ,constant 1" of the periodic structure is denoted by PzB-l-iB when B and B arev both real, it may be shown, from equations (38) and (43); or and (46), that v Cosh P But A cosh 1" =cosh (B+iB) =cosh B cos-B+'i sinh B sin B Now, if we consider frequencies below the range of 'free transmission (that is, f f so that w 1) the expression (1-|-r 2w (r -1) in the first equation for coshd" isreal; and consequently, in the second equation for cosh I", the term i sinh lB sin Bf must vanish whence H sinh B sin'Bz0 SinceB is finite sin 13' muste u al zero and cos B therefore equals unity. I onsequently 1-+r 2"u; @0811 B" 7 1 a y (52 05 h Vl-w? 2 r 1 where B is the attenuation per section. I If now the filter is to be applied, as in Fig. 3,'to the case of a transmission line (K, I) with terminal impedances U and U the appropriate formula is (17 which, for the present purpose, may conveniently be written in the form 1105 i fi i (53 K+K K+ U whence; a 1 15 KMU ea K'+K b 5 innv 1U,+K' Sec me n and remembering that lzA-l-iA' and T'zB-l-iB' so that we see, from equation (53), that T, (A+nB+a+bi-c) a" amt! Th application of these formulae indesigning the equalizer will be illustrated in connection with the specific case worked out below.

For the practically important case in which U and U are pure and constant resistances it follows that the problem involved in the design of the filter type equal:

izer is to make the sum A-l-nB-l-a-l-b-I-e' substantially constant over a specified range of frequencies, since then by equation (57) the transfer admittance of the equalized system is constant. The line attenuation A and the line impedance K are data of the problem. The choice of the type of filter, its termination (mid-series or midshunt, ordinarily), the number of sections n and the parameters 1),, 1' and v i/ z are at our disposal; 'as are also, inmamy cases, the absolute values of the terminal impedances U and U since their absolute values can be varied by the choice of sultable transformers, to connect them to the line and filter respectively. The choiceof these parameters is a matterof englneerlng study and trial and error by aid of the formulae already developed.

'- The design of the type of filter shown in Fig. 10 to equalize transmission over the system shown in Fig. 11 will now be worked out. It is required to equalize transmission between the limiting frequencies 200 and 2,000 cycles per second, for a system consisting of 500 iniles of 0 en wire No. 8 B. W. Gr. loaded line. The 'ine has a critical or cut-off frequency f, of 2350 cycles per second, and the value of w m r the line is 1900. The line is terminated at midload position whencev v ]i =1900 /1'- f 2350 (See equation (4) of PatentNo. 1,167,693.)

is shown by curve (1) of Fig. 1-2. This at tenuation curve may be theoretically calculated when the line constants are specified or may be experimentally determined.

The line attenuation A for the 500 miles In any case it is a datum of the problem.

After considering several tentative values, the following values of the deslgn parameters were adopted:

/L,/O =135 It was also decided to terminate the filter at mid-shunt position.

By reference to formulae previously do-- rived we have then K= steamy cosh B ,Solving these last equations the constants is thus computed for various frequencies.

by 51) I i l Its graph as a function of the frequency is shown in curve (2) of Fig. 12. It will be observed that its value is substantially-constant over the preassigned range from 200 to 2,000 cycles per second, and therefore the 4 required equalization of transmission is accomplished. The

absolute value of the resultant attenuation is considerably increased but the loss which is thus introduced by the equalizer may be compensated for by em-- ploying a repeater.

It will be seen that by means of this invention, the distortion due to the increase in at- 'lLC D tenuation with increase in frequency in a given transmission system, may be substantially eliminated by inserting in the system an impedance arrangement or network so designed as to increase the attenuation for the lower frequencies to such extent that the resultant attenuation of the system will be sub-. stantially constant over the range of frequencies equalized. While this necessarily involves an increase in the total transmission loss, the loss may be made up by repeaters.

It will also be obvious that the general principles herein disclosed may be embodied in many other organizations widely differing from those illustrated without depart-.

ing from the spirit of the invention as defined in the following claims.

What is claimed is: q

1. The combination with a transmission line in which the attenuation varies for different frequencies, of an auxiliary localized network associated with said transmission line at a point along its length and so constructed and proportioned that the attenuation therein varies with the frcquency 1n such a manner that the resultant attenuation .of the combined system will be substantially equal over a desired range of frequencies.

2. The combination with a, transmission line in which the attenuation varies for different frequencies, of an auxiliary localized network associated with said transmission line at a point along its length and so constructed and proportioned as to increase the attenuation of the less attenuated frequencies to such an extent that all frequencies over a desired range will be transmitted over the combined system with substantially the same attenuation.

3. The combination with a transmission line in which higher frequencies are attenuated more than lower frequencies, of an auxiliary localized network associated with said transmission line at a point along its length and so constructed and proportioned that lower frequencies are attenuated more than higher frequencies to such extent thatthe resultant attenuationof the combined system is substantially equal .over a desired range of frequencies.

4. The combination of a transmission line over which different frequencies are trans mitted with different atten'uations, and an attenuation equalizer for the line comprising a localized network associated with said transmission line at a point along its'length and whose elements are so related -to each other and to the line, and so proportioned,

that all frequencies within a desired range are transmitted over the line and attenua tion equalizer with substantially equal attenuation.

5. The combination of a transmission line over which higher frequencies are transmitted with greater attenuation than lower frequencies, and an attenuation equalizer for the line comprising a localized network associated with said transmission line ata are so related to each other and to the line,

and so proportioned, that lower frequencies are attenuated more than high frequencies to such extent that the resultant attenuation of the system is substantially equal'over a desired range of frequencies.

6. In a transmissionsystem, a transmission line over which different frequencies are transmitted with different attenuations, and an attenuation equalizer, said attenuation equalizer comprising a localized network associated with said transmission line at a point along its length and consisting of a plurality of elements, so proportioned and so related to each other and to the line, that all frequencies within a desired range will be transmitted over the system with substantially equal attenuation.

7. In a transmission system,-a transmission line over which higher frequencies are transmitted with greater attenuation than lower frequencies and a localized attenuation equalizer associated With the line at a point along its length, said attenuation equalizer being so constructed and. proportioned with reference to the line as to increase the attenuation of lower frequencies 1 point along its length and whose elements to such extent that all frequencies within a desired range will be transmitted over the system with substantially equal attenuation.

8. In a transmission system, a transmission line over which different frequencies are transmitted with different attenuation, and

an attenuation equalizer serially connected with the line, said attenuation equalizer comquencies to such extent that all frequen-- cies within a desired range will be transmitted over the system with substantially equal attenuation.

10. In a transmission system, a transmission line; and an attenuation equalizer, said attenuation equalizer comprising a localized network associated with said transmission line at a point along its length and whose elements are soproportioned and related to each other and the line that all frequencies within a' desired range will be transmitted over the system with substantially equal. attenuation.

11. In a transmission system, a transmission line, and an attenuation equalizer serially connected with said line said attenuation equalizer comprising resistance and inductance elements so proportioned and related to each other and the line that all frequencies within a desired range will be. transmitted over. the system with substantially equal attenuation.

12. In a transmission system, a transmission line, and an attenuation equalizer serially connected with said line said attenuation equalizer comprising resistance and casired range will be transmitted over the system with substantially equalattenuation.

14. In a transmission system, a transmission line the attenuation of which varies 'with frequency in accordance with a .known law, and a localized networkassociated with said line at a point along its length, said network being so connected and proportioned with respect to said line as to cause the attenuation'of the system comprising the line and network to vary with frequency in a different predetermined manner.

15. In a transmission system, a transmission line the attenuation of which varies with frequency in accordance with a known law, and an auxiliarynetwork the attenuation of which is predeterminable at different frequencies, said auxiliary network being localized with respect to the line and so designed and so associated with the transmission line at a point along the length thereof that the resultant attenuation varies with the frequency in accordance with a predetermined law.

In testimony whereof, I have signed my name to this specification this Q5th day of June 1918.

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