US1615911A - Apparatus and method for regulating attenuation and phase on transmission lines - Google Patents

Description

H. NY'QUisT l. v

Feb, 1, 1927. N 1,615,911

- -APPARATUS AND METHOD FOR REGULATING ATTENUATION AND PHASE ON TRANSMISSION LINES` l/ff 1 j@ f INVENTOR A TTORNE 1/ 1,615,911 Feb. 1, 1927. H NYQUIST l APPARATUS AND METHOD FOR REGULATING ATTENUATION AND PHASE ON TRANSMISSION LINES v Filed Feb. 29, 1924 v 4 Sheets-Sheet 2 [N VEN TOR I By www ATTORNEY Feb. 1, 1927. 1,6159

' H. NYQUIST APPARATUS vANDl METHOD FOR REGULATING ATTENUATION AND PHASE ON TRANSMISSION LINES Filed Feb. 29, 1924 '4 Sheets-Sheet 3 0 500 m00 4500 v w00 A TTORNE Y Feb. 1 1927-.

A-PPARATUS AND METHOD FOR REGULATING ATTENUATION -AND PHASE 1,615,91l H. NYQUIST ON TRANSMISSION LINES Filed Feb. 29, 1924 4 sheets-sheet 4 E 7 {M/0m Frei/Jamey y 200 000 000` '800 /000 1200 .i400

A N VEN TOR m5/WM TTORNE Y Pawnee Feb. 1, 1927.

vUNrrED STATES PATENT'OFFICE.

HARRY N'YQUIs'nor JACKSON HEIGHTS, NEW Yomr, AssIGNon 'ro AMERICAN TELE- rnoNE AND TELEeEArH COMPANY, A coRroEATIoN or NEW Yonx.

A PiPARATUS .ND METHOD FOR REGULATING ATTENUATION AND PHASE O N TRANS- MISSION LINES.

Application led February 29, 1924. Serial No. 696,049.

. It is an object of my? invention to provide a new and im'rove transmission `system adapted to maintain the current intensityv and the phase relations substantially constant at the receivingstation over a considerable frequency range. .Another object of my invention is to provide for keeping' constant phase relations at the receiving station in a transmission system notwithstanding varia- -tions of resistance due to temperature changes or other causes onthe line. These and various Aother `objects of my invention will'become apparent on consideration of a limited number of examples of the invention which I have chosen for illustration and which I now proceed to disclose in the fol# lowing specification taken with the accompanyng drawings. It willbeI understood that the following disclosure relates to these examples of the invention and that the scope, of the invention will be defined in the api pended claims.

Referrlng to the drawings, Figure 1 is a diagram of a loaded line to which ref erence will he made in discussing the principles involved in my invention; Fig. 2 is a diagram of a'transmission system emh'odying my invention; Fig. 3 is a diagram of a potentiometer employed in vthe system of Fig. 2; Figs. 4 and 5 are diagrams of-imned-- 4ance combinations that may be .considered for the steps of potentiometer; Flg. 6 shows impedance asa" function of frequency for the combinations of Figs. 4 and 5; Fig. 7 isV Ianother impedance combination alterna-tive to Figs. 4 and 5: Fig. 8 shows impedanceas a function of frequency for the main part of the potentiometer and Figs. 9, 10 and 11 show special* alternative. designs -fr this -main part. p On an alternatmg current transmission l line, as the resistance changes due to change of temperature, it is Well known that the attenuation also changes, and moreover, 1f

there are 'various frequency components in the current, their phase relation at the re. ceiving end will be different for different resistances. It lis an object of my invention to providev means for adjustment, so that whatever the changes in resistance on the linewithin normal limits, the received currents will. always come in with a certain intensity and with unchanging phaserelations among their components. It is important to maintain local sources of current at `the receiving end that shall be accurately in step with the respect-ive components of the received carrier current, and to this end it is important that those components shall'not vary in relative phase with changes in resistance on the line. r

Fig. 2 shows a transmission system with a plurality of repeaters at a station. A 22- ty'pe repeater is shownwith the balancing networks N. In all of these repeaters the amplifying elements are designated A. The pair of conductors 11 is one pair of a fourwire line on which the transmission is from west to east, and the corresponding pair for transmission from eastto west is designated 12. On each Vof these pairs there may be a plurality of carrier currents of respective diii'erent frequencies and on each of these frequencies there may be several message channels. with phase discrimination and magnitude discrimination.

The foregoing example indicates the importance of transmitt-ing'with constancy of current intensity and constancy in the phase 'relations at all frequencies at the receiving suitable distance each way, as at 15 and 16,

the conductors 13 are interrupted and their ends joined together so as to forma complete circuit on the battery 14 through the winding 17 offa Vrelay at theA same `station with the battery 14 as shown in the drawing.

The points 15 and 16 may be at any suitable distance, which may be several times the interval between two consecutive repeater stations on the line.

Whatever the' change in the resistance of the conductors 11 and 12, there will be a corresponding change in the resistance ofthe conductors 13, in the same cable with 11 and 12. The change of resistance in the conductors 13 will produce a change of the current in the circuit of the battery 14.' By means-of thebiasing winding 18, anormal neutral position will be established for the relay armature 19. 4

On the input side of each repeater amplilier at the station is a potentiometer 20, and the movable contacts vof all the potentiometers 20 are mechanically connected to be adjusted by displacement of the crosshead 21. The Wheel 22 is rotated continuously by the motor 23 and is adapted to be displaced by the armature of the relay 19, so that .one Way it engages to move the crosshead 21 one Way, and for displacement of the armature 19 the other Way, the wheel 2 2 engages to move the crosshead 21 the other way. Thus it will be seenthat any changes in the resistance of the pilot condnctorsl, such. as due to temperature changes, lead to a' change in the current iowing through the relay having the Winding 17, and this relay adjusts the potentiometers so as to bring the current back to the normal value in the conductors 13, and at the same time the relay adjusts all the input potentiometers 20 for the 'repeater amplifiers atthe station.

These potentiometers 20- varedesigned in such a Way that at all adjustments they keep the attenuation constant over the length of line from 1'5 to 16, and they keep the phase displacements constant for all essential frequencies in the transmission between the points 15 and 16.

C, theinductance perloadingf section is L and the resistance per loading section is a. Assume that in one of the loading sections .1 small additional resistance Ar is inserted and let us investigate the ellect on the received current. Assume that the impedance looking one Way is KE and lookingr the other Way is KW.` The total impedance before inserting the resistance r is KTH-KW and the total impedance after inserting the resist-` ance is KE-l-KW-l-Ar.

Hence the resultant eiect on the .received current will be given by the complex ratio R, lWhere KJFSL (1) KE-i-KW-i-Ar '1 0 a close approximation, since Ar is relatively small, it follows that Thevalve of KE+KW varies along the load-' ing section, being a minimum at the loading coil and a maxlmum at the midpoint of the section. Assume that the increment A1',

instead of being lumped as in Fig. 1, is distributed uniformly ovei the loading section; then instead of equation (l2), We shall have A y dr 10g Rr o am; 3)

Ar in each oi. n loading sections, the corresponding equation 1s Awhereinl Am is the total increment of vresistance in all the sections. AThe real part ot equation (5) gives the total attenuation in napiers and the imaginary part gives the total phase change in radians. Y

To le'et a practical idea of the actual changes involved in such a case as that under consideration, consider a medium heavy loaded 19-gauge sidecircnit with 1,000 loading sections and assume that the resistance increment is 1 ohm per loadingl section, that is, assume that A1121. Reasonable values under the/foregoing assumptions Will be that L/Czl5402: I11:100 (approximately); and L:0.1T5. Substituting these values, equation. (5) becomes 1000 10g R: I 10o for the respective phase shitt 1O 39, 0o 51,

and 0o 34:. 1

From these valuesit is apparent that in the case of medium heavy loaded circuits the phase displacement is probably small enough practicable.

so -that it can be taken care of by manual But for an extra. light loaded adjustments.

19-gauge side circuit the .case is different; liereL/Cz7802, rzlOO, and L:0.045. Proceeding inthe same way as for the case of the medium heavy loaded 19-'gauge cuit,

are considerably greater than those obtained for medium heavy loading, and so great as to make manual adpistments quite im Referring to the potentiometers 20 of Fig. 2, it will be seen that these face amplifiers are of the audion type, and have very high input impedances; hence the current drawn from a potentiometer to its amplifier is negligible and the voltage, impressed on Ythe amplifier is proportional to the impedance of the part'of the potentiometer'within the amplifier input terminals. Let this impedance at any adjustment be denoted by Z. The effect on the input voltage of the amplifier due to` a change AZ may be given by the complex ratio` f Z-l-AZ and since'AZ is small compared to Z, it is approximately true that side cirwe find that for frequencies of 500,

'- 1 00() and 1,500,the phase shifts are, respectively, 10o 3, 6 2', and 4 11. These values l A11 increment of resistance Am` on the'line would decrease the receivedcurrent in a certain rato R as expressed in equation (5)'. It is desired to increase the amplifier input voltage in the reciprocal ratio sos to conipensate andlzcep the `current constant. The condition foi` this is that Rzl/R oi' log RI-log R and accordingly from equations` (5) and (8) it follows that Z L' r Mehta@ Fui-ther, to facilitate design and within the freedom of choice aorded by the foregoing difference equation, we impose the condition that the top ste-ps of the potentiometer 20 shall approach pure resistances,in other words, that the last few increments AZ shall approach a real value. This gives for the 'value of the impedance of the potentiometer at its top tap where M is an arbitrary real constant. Putting equation (9) in the form of a di'erential equation and solving, and making use ofthe boundary condition afforded by equation (10), the result is obtained that The assumption was Amade that the top few steps of the potentiometer are real. But having passed to a differential equation, these become infinitesimal, and the top finite step in Fig., 3 is seen to be other than a pure resistance, though its reactancecompo'nent is small as will appear presently.

` If Z is chosen according to equation (11) for all the steps.l the regulating network will peratui'e and at the temperature under consideration. By putting p equal to a large, value in `equation it will lbe apparent that the expression l will equal the whole difference in attenuation for a high frequency; accordingly, this expression will be denoied by the svmbol aA Also, for conve1ic1ico,tlie expresSionYr/L will be denoted by the symbol Z). Equation (5) then takes the form 7While 7) may no determined from the measurements of 1' and L by taking their ratio-.- it may be preferable to determine b other;4k wise as oiitli'ned below and thereby' compensate for approximations involyed in deriving equation (12). To do this,-nieasure the at-L tenuation and phasechange for two temperatures and for a 4number of frequencies, including some rather high values of fre.-

fluency, where I1 is small in comparison with p. From theseiiieasurements compute the values for the complex ratio R. The value ot' the logarithm of R is obviously equal to -a for large values of p. Substituting the values for R and a in equation (12) and solving for b, the result is obtained.

If these values for 7i are computed and plotted as a function of' p, they will give a substantially horizontal line.

Owing to the manner in which I) enters equation (12), it will be apparent that an ei'ror inthe choice of b has the san-ie effect This gives the' total impedance forV the potentiometer on any tap. At the top tap a should be zero. Assuming that the potentiometer steps ai'e to be in so-called standard miles this-impedance correctly to three terms are two, and each of them consists of one condenser and two resistances. The first ot these is made up of a resistance A in series with a parallel combination' comprising another resistfance Band a capacity C', as shown in Fig. 4. The other net work will consist of a resistance E and capacity F in series` this combination being connected in parallel with another resistance "D, as

shown in Fig. o. The impedance expressions for these net works can each he written out ill) in a power series corresponding ro that of ,equation (16), and the first three terms ot' each series caiithen be respectively equated to the corresponding,terms in equation (16) the resulting equations may be solved tov obtain the values for A, B and C or D, E and l", as -the case may he. Carrying this work through, the following results are obtained:

The simplest networks that will reproducev at high frequencies, and that we are dealing j withv the extra light loaded 19-gauge side circuit heretofore specified, a should have the value 0.109 at the second tap, 0.218 at the third tap, 0.327 at the fourth tap, etc.

An obvious i'ocedui'e to compute the individual inipeeance steps would be to compute .the values of' Z from equation (14) for any twovadjacent vsteps and take the difference of pthe two results; It 4will make the computation simpler and lead to substantiallyfthe saine result to obtain the first derivative of equationi(14) with respect to a at the midpoint of the step, and multiply that derivative by the increment of a, which is 0.109. This gives for the increment corresponding to any one step AZ 0.109M

= Vaca/ima (15) llore a is to be given the values 0.100 x 0.5,v

given in equation (15), and the result is obtained as a'power series in i (a-wFe-m) (15) Substituting the values for a and the value for in these expressions, it becomes possible to compute the corresponding network elements as they are designated -in Figs. 4 and 5. 10 get an idea as to how closely theoresulting networks obtained from equations (17) to (22) would simulate the Videal networks specified by equation (16), computations have been carried out Jfor two values of a, namely 0.8 and 1.6, using the value 52100/0045, which is approximately' correct for extra light loaded 19-gauge side circuits. The results are shown in Fig. 6. The curves marked Y v required by equation (1(5). marked Y, are obtained by using the three element networks of Fig. l or Fig. 5 as defined by equations (17) to (22 The curves marked Y2 are obtained by making use of a two element network as shown in Fig. 7, whose elements are determined by equations (17) and (10). lt will be apparent 'from Fig. 6 that for the important part ot' the frequency range,'the three element network of Fig. 21 or Fig. 5 gives very close approximation to the ideal of equation (16) The curves are the ideal curves with results as follows:

A. B. C'. SteP- ohms. ohms. M. F.

2130 78.8 7.75 1010 220 2.08 1710 342 1. 93 1540 Y 44s 1.54 1300 53s 1. 33 1240 017 1.22 1110 085 1.15 094 745 1.11 890 707v 1.00 700 S42' 1. 09 710 884 1.10 042 922 1.12 570 958 1.15 517 995 1.18 403 1030 1.23 415 1070 1.28 372 1110 1.34 v334 1170 1.41 300 1230 1.40` 209 1310 1.58

From the expression 3 0, which occurs in'some of the equations (17) `to (22), it will lbe seen that these equations break down `Where' a='3 and beyond this point, for the reason that the expressions will then call f for negative values for either the resistance *or the capacity. However, this is not a serious ob]ection because the value (1:3 cori Then the expression for the impedance of the circuit of Fig. 10 is expanded., giving thev i' following:

" Zno alfa/iii the first four coefficients of d ip ' vEquating VVequationsv (24) and (25), and solving, the

followin values are obtained for the elements o the network of Fig. 10.

c :0.00221 ld :0.000236'; Y e'=0.3651.

y These numerical vvalues were next substi- Athe curves are in tuted in the expression for the impedance lof-thenetwork of Fig. 10 and the resulting-j alu'es of impedance were plotted on Fig.

TheA value for the arbitrary constant M whchfhas been vused above is 20640. The -fo re mg lvalues of a,d and e are multiplieiby 20640,'and the value of c is divided number of steps beyond this main 'part is 20.

Ve turn to equation (14) and substitute .for (L the value10.109 X20,jor 2.18. VEquation (14) then` becomes A Z2O Y 1,l 1(2.-2V.isv(1-Lbf1p)1`/7 The same valu-e of b heretofore mentioned, namely .100/0.045 has been used to evaluate equation (23) and the result is plotted in full lines in Fig. 8. From these full line curves it is inferred. that networks of the type shown in one of Figs. 9, and 11 could vbe made to simulate this impedance closely; 'lhey have all been investigated carefully and Fig. 10 has been adoptedas mostsatisfactory. The procedure for Fig. 10 will be given and may be taken as an example for all three Figs. 9, 10 and 11. A

To obtain the numerical values for the elements of the network of Fig. V10,requation (2 3) is first utilized to. express N? as a power series in with the following result:

if 1.2 .13 4113+339@+110,000(,p) 222-10 (ip) (24)l by '20640, and thus are obtained the followlng values for the elements as indicated on Fig. 3,

' (#112330 ohms. @l 40.107 mf. (Z1 :4.87 h. 1:7540 ohms.

` I claim:

1. A conductor system for transmitting currents of various frequencies, said system beingsubject to changes of condition 'tending to change the phase relations among the various frequencies, a pilot circuit comprised in saidsystem, and automatically adj ustablc compensating means `controlled thereby to .keep the -said phase relations constant.

2. A conductor system for transmitting currents of various frequencies, said systemy being' subject 'to changes of condition tending to change the phase relations among the various frequencies, apilot circuit comprised 'in said system, and compensating means` controlled thereby to keep the said phase relations constant.

3. A conductor system for transmitting an altegnating current, said system being` subject to changes of condition tending to change the attenuation 'and tending to produce a different phase displacement atgthe receiving end at diercnt times, means responsive to such changes, and compensating means controlled thereby to keep the attenuation substantially constant and to keep the phase displacement substantially constant.

4. Al conductor system Jfor transmitting an alternating current offseveral components, .said system being -subject to changes of vcondition tending to change the phase relations of said components at the receiving end, a pilot circuit comprised in said system, and compensating means controlled thereby to keep the said phase relations con- Lli) CII

stant.

In a multiplex carrier current 'system subject to changes of condition tending to change the phase relations among the ele- Lineiitary currents of the system, a pilot cir- 7. A cable comprising a plurality (if conf ductor pairs, potentiometers interposed in these pairs respectively, one of thesaid conductor pairsbeing appropriated 4to a pilot circuit, and means responsive to a variation of current in ,the pilot circuit to adjust. the said potpntiometers, the steps of these.A

potentiometers being formed to keep the phase displacement constant in the circuits.

comprising the said pairs of conductois.

A8. A circuit comprising a potentiometer consisting of impedance steps,each step comprising' a resistance element and a reactance element .so proportioned that at all adjustments the phase relations amongfcurreiit components ot diierent frequency in the output of the'circuit are kept substantially'.` constant fora constant'relation among these components 'in the input of the circuit. a s

E). A potentiometer consistingof iinpedance steps, each step comprising a resistance to changes of condition tending to Ichange the current through said circuit, Aand the steps of said potentiometer being constructed so that its adjustment .will compensate for phase displacements producedby such change of condition.

l0. In combination, a transmission line subject to a change of resistance due Ito temperature changes along its length, a pilot line'exposed like the transmission line to the same temperature influences, a potentiometer in the transmission line having steps adapted to change the 'phase relations of currents ot different frequency in that line, and means controlled by current in the said pilot circuit to adjust'said potentiometer to compensatet'or phase displacements occasione by the tempei'atiire changes. f

.11. llllie inethod,ot` maintaining the phase relations among a plurality of alternating currents subject to varying conditions at a certain part of their circuit er circuits, which consists in passing those currents through a potentiometer adapted to 'give Various phase displacements at various adjustments and automatically adjusting said potentiometer in accordance with the change of the conditions referred to.

12. In combination, a transmission line subject to attenuation changes and phase displacement changes from time to timefa potentiometer comprising resistance ele-4 ments' and reactance elements in its steps and adapted at its Various adjustments to compensate for such changes, and an associated pilot circuit cont-rolling said potentiometer.

13. rIhe method of maintaining denite phase relations at the receiving end in a multiplex carrier current system, which con-` sists in testing temperature conditions at points along the transmission line and adjusting for amplitude and phase relations as determined by these conditions in order to keep the amplitude and phase relations substantially unchanged at the receiving end.

14.1,'I`he method of maintaining'definite phase relationsfat the receiving end in a multiplex carrier current system, which consists in testing temperature conditions at `points iii a pilot circuit along the transmis- February 1924.

HARRY' NYQUIST.

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