US1453980A - Attenuation equalizer - Google Patents

Attenuation equalizer Download PDF

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Publication number
US1453980A
US1453980A US242567A US24256718A US1453980A US 1453980 A US1453980 A US 1453980A US 242567 A US242567 A US 242567A US 24256718 A US24256718 A US 24256718A US 1453980 A US1453980 A US 1453980A
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United States
Prior art keywords
attenuation
equalizer
line
frequencies
transmission
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US242567A
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English (en)
Inventor
Ray S Hoyt
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
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American Telephone and Telegraph Co Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by American Telephone and Telegraph Co Inc filed Critical American Telephone and Telegraph Co Inc
Priority to US242567A priority Critical patent/US1453980A/en
Priority to NL12194A priority patent/NL7010C/xx
Priority to FR515611A priority patent/FR515611A/fr
Priority to GB19251/19A priority patent/GB151140A/en
Priority to GB15857/20A priority patent/GB164239A/en
Priority to FR23266A priority patent/FR23266E/fr
Application granted granted Critical
Publication of US1453980A publication Critical patent/US1453980A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/04—Control of transmission; Equalising
    • H04B3/14—Control of transmission; Equalising characterised by the equalising network used
    • H04B3/143—Control of transmission; Equalising characterised by the equalising network used using amplitude-frequency equalisers
    • H04B3/144—Control of transmission; Equalising characterised by the equalising network used using amplitude-frequency equalisers fixed equalizers

Definitions

  • 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,
  • 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
  • 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;
  • Fig. 12 is a diagram showing attenuation curves for the system of Fig. 11.
  • 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:
  • 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.
  • 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-
  • 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 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:
  • 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.
  • 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.
  • 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:
  • 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,
  • the terminal impedances U and U are pure resistances and henceconstants whose values are independent of frequency.
  • 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.
  • 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,.
  • R, L, C are determined impedance, and therefore a, is. zero if Since this is to be zero at frequency f we have:
  • 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..'...'. . alone#19B.&S.gauge.
  • 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
  • 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.
  • 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.
  • mittance of the equalizer at zero frequency being simply l/R.
  • 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,
  • 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.
  • each section 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,
  • the characteristic impedance of a wave filter when terminated at mid-series is Fw/ l d 'Y /Q and when terminated at mid-shunt (that is, mid-section) K /Z Z 1 /4)
  • 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.
  • 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 line attenuation A for the 500 miles In any case it is a datum of the problem.
  • 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.
  • 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.
  • 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.
  • 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.
  • a transmission line 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.
  • 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.
  • Attenuation equalizer comprising resistance and casired range will be transmitted over the system with substantially equalattenuation.
  • 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.
  • a transmission line the attenuation of which varies with frequency in accordance with a known law
  • 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.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
  • Networks Using Active Elements (AREA)
  • Filters And Equalizers (AREA)
US242567A 1918-06-29 1918-06-29 Attenuation equalizer Expired - Lifetime US1453980A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
US242567A US1453980A (en) 1918-06-29 1918-06-29 Attenuation equalizer
NL12194A NL7010C (fr) 1918-06-29 1919-06-12
FR515611A FR515611A (fr) 1918-06-29 1919-07-23 Perfectionnements dans les systèmes de transmission pour signaux téléphoniques ou autres
GB19251/19A GB151140A (en) 1918-06-29 1919-08-05 Improvements in telephonic transmission systems
GB15857/20A GB164239A (en) 1918-06-29 1920-06-11 Telephone systems
FR23266A FR23266E (fr) 1918-06-29 1920-07-17 Perfectionnements dans les systèmes de transmission pour signaux téléphoniques ou autres

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US242567A US1453980A (en) 1918-06-29 1918-06-29 Attenuation equalizer
NL12194A NL7010C (fr) 1918-06-29 1919-06-12
FR515611T 1919-07-23
GB19251/19A GB151140A (en) 1918-06-29 1919-08-05 Improvements in telephonic transmission systems
GB15857/20A GB164239A (en) 1918-06-29 1920-06-11 Telephone systems

Publications (1)

Publication Number Publication Date
US1453980A true US1453980A (en) 1923-05-01

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Application Number Title Priority Date Filing Date
US242567A Expired - Lifetime US1453980A (en) 1918-06-29 1918-06-29 Attenuation equalizer

Country Status (4)

Country Link
US (1) US1453980A (fr)
FR (2) FR515611A (fr)
GB (2) GB151140A (fr)
NL (1) NL7010C (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2768351A (en) * 1951-03-13 1956-10-23 Hartford Nat Bank & Trust Co Multipole network

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2768351A (en) * 1951-03-13 1956-10-23 Hartford Nat Bank & Trust Co Multipole network

Also Published As

Publication number Publication date
GB164239A (en) 1921-06-09
NL7010C (fr) 1922-05-15
FR23266E (fr) 1921-11-02
FR515611A (fr) 1921-04-05
GB151140A (en) 1920-09-23

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