US2517968A - Line balance converter - Google Patents

Description

Aug. 8, 1950 G. H. BROWN LINE BALANCE CONVERTER INVENTOR.

WMME

flTTflAAEY I E fi'mrgcllbmwn Filed Jan. 17, 1945 of Delaware alarm-e conanced circuits or"line's:"-'Ilie te arena-erli ii' including two are electrically symmetrical neutral or reuh'eipomt; The fer's' to Ea-"line of circuit "Af dipole rad ator; comp h jjtwo -elements ex- "tending in opposite directio'n's'froin a neutral point and fed at that point so that current is flowing intoone elementwhile an equal current "flows ,o'utbfthe other, i's' balan'ced. It is frequentlynecessary to couple'l an unbalanced line *orisol rCe to a balanced load, oryviceflvers'a, and line balance "'Icor'ivertors are used for this pur jpose. [Typical prior art" line balancefconv'ertors "are described on page 855 of aaqioann'gine rm ammer- F1 Terrnanrpublish y McGraw :Hillf'Bo'ok cdm a'nm e is,

Y'f' lt'is tje" rincipal :bject'of the pres'ntinvem jtion to provide improved line' balance fconvertor 5 systems capable f ,off'jeflicient power" transfer "throughout a" wide sa der; radio-hum us.

.Otherf obj ect. of the inventio is to provide ba n onve 't 'srs em wh h 'me'in "accurate balance, independently of frequency;

. vf h r o iectiq vthi in en tq' r v fli n "balancejjconvertors' which r ruc'turally 'i'sli l iii fl e' d nd, e r c mes-aw:-i rm roadiband "performance requirements.

, The invention will be described withreference t'otheaccompanying drawingk'ofwh Figures 1 and 2 are schematic diagra' s of 'typical prior art line balance conv"'efrtor's Figur'e 3 'i s-a schematic diagrarii of a li ne'halance converter embodying theip'resent invention, andlii w, l 11m r-"W Figure 4-is a modification of th' structure oi Referring' to- Figure 1,: one well-known type of line I balance converter" includes a-cylindrical 'conductive sleeve l surrounding a quarterswave- -leng'th sectionril at the end of a coaxial trans- 'syinmetrical or unbalanc'ed circuit orthefleon --vertor;.-:'.= The -'sleeve l: is Iconne'ct'ed 1 to (the-1 line :s'ectioni3 :byla: conductivedisc 1:1- A=pair,of .trans amissionz-lines A9: and A! I: 'areiconnected' tofthe inner 1r; mb;

Georgy Hr;Brown;)Princetohgz:Nr'Ji, ,assignor to l --Radio Corporation of America, a corporation gandziouter :conductors firespectively1v oriithe-iiline 56 Application January 17, 1945- Serial No. 573,217

. 5 Claims. (Girl-78AM section 3. The upper 'end of the sleeve "I is closed byadiscB. r The operation of the system. of Figure 1 is as follows: Assume that the line 5 is fed by a radio frequency source, E, and thatequalloads, Z and Z, are connected to the lines 9 and H. When current is flowing upward on the inner: conductor of the line 3, an equalicurrentimustifiowidownward on the inner surfacesof the outer conductor ofthe line':3;- Therefore, theflcurrent flows out on the inner conductor of 9. The return*cur- =rent,.on the inner surface of the outer conductor ofhline 9 flows across the disc-8 to the inner'surface of the outerconductor of line H, through the'load Z and back to the outer-conductor-of line -3. The current cannot fiowvinto'the high imp'edanceof the stub I, 3-and'must'gorback downthe inner surface of the outer conductor -oiline 3; Thus the same current flows through "bothloads Z and Z, but in opposite directions, i; e. toward ground in one load-while away iroin "ground in the other. The loads Zand'Z are effectively in series with each other across theinthis line across the line' I I is substantially infinite,

-'=and*doesnot affect the new of current to "the load Z At frequencies other than" resonance, the short-circuited quarter wave section presents a relatively low impedance across the 1mm but not'across the line 9. The greater the 'diii'erence between actual frequency and the resonant frequency, the greater will be'the difference between the currents flowing to the loads Z and Z. In accordance with prior art practice'; the effect of'the short-circuited line I :3 is balancdf' by means of a second short-circuited quarter 'wave line 'se'ction I, 3'; shunted-across the line t as illustrated in Figure2. In'the system of Figure 2, the lines 9 and H are shunted by substantially identical quarter wave stubs, and although the reactances of the stubs vary with frequency; the 's'ameamount of reactance is shunted-across each of'thej balanced lines at all frequencies; so that the balanced'line currents are equal, -independjently of frequency. However, if 'the "frquenc'y of; operation is varied widely from the resonant frequency, the reactances of the short' circuited stubs will vary accordingly; seriously afiecting the 'efliciency of the power transfer throughithe "convertor circuit. The band width' over which theyconverter-twill operate effi'cientlydependsyupon 5 Z, and Zc being related to the terminal impedance has a value within the range of 90 to 100 percent Z0 of the convertor as follows: of that of the quantity:

F WT? l+ 1+4( 5 1+ 1+4 Z0 0 2 2 Z5 0 5. The invention as set forth in claim 1 where- GEORGE H. BROWN. in saidlast-mentioned quarter wavelength line section-has a surge impedance Z5 equal to that 10 REFERENCES CITED between-the outer conductor of said first-men- I The following references are of record in th tion'ed quarter wavelength line section and said fil f this patent; conductive sleeve, and said half wavelength line section has a surge impedance Zc, the impedances UNITED STATES PATENTS zljand'zc being related to the terminal imped- 15 Number Name Date ance Zu of the converter so that the quantity 2,2 Lm nbl d July 22, 1941 Z 2,266,502 Lindenblad Dec. 16, 1941

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