US2325279A - Signal collecting system - Google Patents

Description

July 27, 1943- w. A. SCHAPER SIGNAL COLLECTING SYSTEM Filed March 8, 1941 INVENTOR. lV/LL/HM/Z SCHflPE/Q.

Patented July 2751943 tion of Illinois This invention. relates to signal collecting sys terns for radio receivers and particularly to signal collecting systems :of the type that employ an "exposed, inductive element commonly called aloop.. .1

Aloopconsists generally of a number of turns of (wire mounted upon a framework of insulating material and-its two-ends' are usually connected with a'condenseij-to-form a resonant circuitwhich is commonly-called the loop circuit. :11? aloop circuit is tuned to resonance with a desiredsignal f the; intercepted voltage ismaterially increased. Loop circuitsthereioreinclude usually a variable condenser or avariable inductance in orderthat they maybe tuned over a desired range-otfrequenciest 1 I ."--The present invention relates to inductively William A. Schaper, Cicero, Ill., assignorto l'loh son Laboratories, Inc., Chicago, Ill.',a corplo'r Application-March 8, 194 1,Serial l lo.-

; I 1:? ioiaims. (cipzso g mj Therefore, to prevent the loop from reducing the tuning range f obtained 'bel'ow an essential minimum 'it is' necessaryjtd, restrict itsiinductance, that is, to keep the number of its turnsk'at a minimum and-etc m'ake it small in size. Howeven' -the signal eiiergyrintercepted by 'a loop is directly proportionalto the number and size of its turns.:i Additionally; ,itxj inherently decreases with'iidecreasi'ng 'l frequency; therefore the loop must be of adequate size and have an adequate numberef turns- 1r. -satisiai'ztoryi reception and satisfactory performance Qfs'the' receiver .is

had over the total'tuningirange.: i a

- It is' 'an olojectof the present invention provide a'movabler-coreetuned signal collecting systemof theztype employing anexposed inductive tuned loop antenna systemsemploying variable inductors of the movable core type.

- Tuning by the relative movement of a co'l and a magnetic core, is now generally known. Over other tuning devices the movable .core inductor offers the advantage of compactness and durability and it allows theper formance ofthe circuit which it tunes to be predetermined within wide limits Therange-of-inductahce variation 0btcinable with a movable core inductor is deter- {ni'ned by the efiectiv epermeability ofjit's core. The permeability of cores-intended for highfrequency operation, however, is limited by the iact that the magnetic material from which they are rnade must be finely subdividedand, the resultelement, and whichcovers an adequate range of frequencies; a; 1;

: Additionally it isran object of. the present invention to provide a',=movable-core-tuned signal 7 collecting xsystem'remploying a loop and combinant {particles carefully insulated to impede the formation of eddy currents in the core and this severely reduces the permeability initially possessed by the magnetic materials fromwhich the 7 cores are-made. The; effective permeabilities which the art has been able torealize in high frequencycores without excessive eddy current losses are of the order offlO to 15; they are more than adequateto tune high frequency circuits over wide ranges of frequencies such as the broadcastrange. 1

However, when a loop circuitis tuned by a ,-movable,core variometer. the 1oop,.which forms part of the totallinductancewoi the system but which is removed irom the effect of the tuning core materially reduces the range of inductance :variationobtainable withinthe' circuit; and-the larger the loop and thegreater the number of -lecting .system--for-. radio receivers and thelike .and of the type employingan; exposed inductive its turns the more pronounced will be this range reducing effect until the'permeabilities now: avail- -able are no 3 longer adequate to" tune the loop ,systemover asufiiciently wide range of frequencies, such as for instance the broadcast-band.

ing adequatetuning. range with adequate signal interception over theuwhole of. saidyrange. 1 :It isxanot-her objectof the present invention to provide a loop-systemoflthetype tunedby movable core inductors and covering a widerange of frequencies while maintaining the signal voltage supplied";tolthexgrid of the first tube-independent of frequency. I

,.-=Additionally ;it is anxobject-of the present invention :tO'npIQVidega/ loop system of the type tunedaby movable core inductors which, while providing, for adequate signal interception, is oapable-rofgbeing tuned overa wide'range'of frequencies with thessignalyoltage supplied to the grid of l the: first-- tube being independent of frequency: q

' The presentinvention furnishes a signal 001- element, which includes an unexposed inductive element/comprising a-winding nd a core structure, said core-nstructure having. a conductive vention said 'core portions may be given such proportion as the signal energyf'ihtercepteg'fby.

made o'fcornniinutedmagn'eticmaterial: sucni as vary the inductance of said winding to change 5 the resonant frequency of the system they simultaneously vary the resistance of said winding in such aminner thatt-he ratio R of the system varies substantially inversely as the frequency In this manner mT-gaim Ofth'ej" "*range of inductance variation than can be realsignal collecting circuit increases in the same the exposed inductive element'dec'reas'esiwith'the" result that the voltage supplied to the grid of the first tube remains indepentliiii of 'frequencyi over the total frequency range covered and is. proportional only to the strength of the signal'receivedr 1 5 In"- the accompanying draw lngtr preferred em-r bodmient of the I presentinvention i is explaincd by wayl'oi -examples 5: i Fig". 1* shows the wiringi; diagram of-qa signal collecting system:embodyingeflteipresentiinvention; and 7 Y 1;; Fig. 2- sh'o ws an enlarged I sectional-L viewrofi the movable core inductor-'- employedi in ther system 831. j .i The' 'signal collecting-system ofl xFig. l zcomprises aio'op' I ,a movabie core inductor tandcmd'enser 5 connected to form ae seriesresonantcircuit, "one endot saidloop and-'jon'e-zelectrode; or saidt-co'ndenser bein'g' cQn-necteditogmundp Movable core iiiducstor 2conststs' oi'a rwindingijanti a core stricture 4; movable relatively to said winding to vary its inductance and to thus time theccir can" over: an range crfrequenciessjj 'r-n incomsigh'alis interceptewbyt loop" I; is: amplified ifi sries resonant circult l'gslmndaS; and therr'ese ona'nt potential developed across condansen 5 ;is applied to grid 0 or vacumn tube l; the:..junction between inductor 2 and ccndenser 5 being connectd directlyto"slld gridl' e witl'i 'refreiice to"- Fig; zdnmicto 8 "Winding 3 wound Moon 0011 fdmn 8101* insulating materialand having a length several times" its diameter. Within coil form ltlie're 'i's movably rdu'ghlyto the lengthof winding'm "An opera't iiig handle 9 *oi non magnetic-material isprtivided a't one endoftli'e core structure: iPoi'tionwwis iron or ironalloytlie individual partlcles otswhich have been insulated from one another and have 'tieen compounded undr prom'eintoaoore body of predetermined 'sha'pe' and permeability; cores of this ftv'p'e' are -wei1 -known -in the art and are, for instance, disclosed in='Uriited States Patent 6 li fifi twpfjlydbl'bfl'l "Cdl pdifibfl lb-is made 01 a conductive material such: as copperaluminum or brass 1 and nas -prerrably' the shape of pressinguninsulatedmet-a1 owdere mto a body 6 stanoe-bytliemctai tube-'or coreportlonwli being 7 trated in: the -drawing; that is;'.whentits conduc- 'tive portion-lbzisicompletely within windingvl the inductance of inductor 2 is at its minimum 7 5 :mum inductance.

iaedbv the use of a magnetic core portion alone. 5For-ins tance; if the effective permeability of the magnetic-core portion relative to the particular winding shown isll, and if theconductive core portion" isbonstrubted to reduce the inductance of w-inding 3 to one third of its value in air, the 0 inductance of the device changes from L/3 to 11L"; 'thatis, the'devic'e provides an inductance change of a ratio'of 33. I l v Reverting now to Fig. 1 the inducta'nceofldop l-restrictsthe inductance variation produced by 5 movable core inductor 2 in circuit l, '2 a'nd 5 ini'the same manner as an'yj-Iotherseries conn cted-coil'of fixed inductance value: Thus, if variable inductor 2 were 0f the ordinary 'type providing an inductance variation of say"11, and 0 if the signal 'collecting'sy'stm were expected to operate over arange or "frequencies "such as the broadcast range, which requires atotal induct ance change or approximately 9, T it would only be possible to cover-this range if the loop induct 5 ance were not" larger" than approximately one fifth of the total inductance of the circuit 'atthe high frequency end of the tuning range. A loop of such a low inductance; however, would notprovide a'n adequate-"amount of'signal interception to secure satisfactory performance of thereceiver over thetotal tuningrange. 'Therefore in the construction of movable core tuned'.loopcircuits art was faced'with'the alternativeto either 5'0 intercept an, adequate amount of signal "energy even" at the low frequency end of the range, and yetreta'in,coverage'of a'wvi'de "range of frequencies suchasthe broadcasflrange." Bearing in mind the inductance value that "loop'l is to have 5 for adequate interception, Iso' proportion'core portions 4 and w {relative to one another and -relativato winding"?- that movement of core structure 4 withTespect to winding 3 will produce such an inductance change as will varythe 0 total inductance'of circuit'l 2 and 5 to therequired degree, in'spite' of the range re'ducing ef- 'fect" of the loop inductance. Forinstance, by constructing my variable inductor 2"to'provide a ratio-of inductance variationof, say, 33 my 5 1oop"n 1a yhave3 times-as much inductance'as my variable inductorjf'atithe high end of the ifrequency range; thusprovidin'gior an adequate amountoi signal voltage to be intercepted,' and yetthe systemm y readily be tuned over a range ohas wideasjthe broadcastrange.

tion I ma'y so construct my antennasystem'lth'at whatever signal voltage Iain able to supply'to ;th e;gr-id of the first tubeat theghighjrequenc 5 end-may be maintainedsubstantiallyindependrifice; range coverage in order to secure greatent of frequency over the total range of opera tion, in spite ofthe inherent characteristic; of

loops to receive signals of a lower'frequen'cy with lesser power than signals of a higher frequency.

In order to compensate for this inherent nonuniformity of loops'Ico'nstruct variable inductor 2 in such a manner that the gain of my signal'collecting system will vary inversely'as the frequency. In signal collecting systems, the

gain is a function of the Q or of the circuit, and by proper choice of the permeability of core portion 4a "and of its loss characteristics, and by proper choice of thewall thickness of tube 4b and the dimensions of both core portions relative to one another and relative to winding 3 and the frequency range 'to be covered, I may construct these core portions to produce such a change of the 'circuitresistance relative to the change in circuit inductance I and circuitfrequency that the expression varies inversely as the frequency; For this purpose I may construct the-conductive core portion from a blend of metallic powders of. different conductivity and I may. vary the character. of the'blend lengthwise in the core so as to give Also I may employ a blend of magnetic and non-magnetic metal powders for parts of my.,

core structure.

In a practical embodiment of the present-in vention constructed in accordance'with Fig. 1 the signal collecting system was tunable over a range of frequencies from 1560 to540 kc. Loop l'had 13 turns of wire No. 20/44 S. S. E. 7 inches high and 7 /2-incheswide, the length :of the Winding space being 2 -inches. The calculated inductance. of this loop was 65 H.

Winding 3 was of the typeknown as progressive universal winding and was wound with wire No. 7/44 S. S. E. over a length of l%-inches on a coil form having an outer diameter of -.221- inch. Its inductance in air was 52.3 [LI-I.

it predeterminedly'varying loss characteristics.

Portion 4a of core structure-4 was L e-inches long and had an outer diameter ,of 2-inch. It

was made of a finely divided tin-iron alloy coninch. Its length was 1%inches.- Whencom pletely within winding-3 it'decreased the induct-. ance of said winding from 52.3 H to 20 H.

Condenser!) had a capacitance of 123 ,UJLF which tuned circuit l 2 and 5 to a frequency of 1560 kc. with copper tube 4b 'completely'within winding 3. The total resistance of the circuit at this frequency was 23.8 ohms. Hence the Q or of the circuit was 35 at the upper end of the frequency range. 'With the core moved so that core portion 4a was completely within'winding 3, the inductance of inductor Zhad r-isen' to'640 of the circuit was 26.4 ohms andthe effective Q of theztotal circuit therefore was 91.2 at the low end of. the ifrequency'range. Thus, as the circuit was tunedfrom 1560 kc.to 540 kc.'its Q value had increased from 35 to 91.2. Therefore while.

the energy intercepted-by the loop had dropped to h of its original value the gain of .the circuitfhad increased byfa factor cit- 2.61. with the result that the voltage applied =to1'the grid of the first" tube had emainedsubstantially constant.

A The following practical; data (were obtained from the embodiment of the invention described above.

Grid gain Frequency ratio cast range;

By-grid. gain ratio-I" means the ratio'of the output voltage of the system measured in microvolts to the field strength measured-in micro-volts. per meter that existed at the pointof interception and which had been adjusted to a substantially constant value throughout thezrangex.

The above data show that the voltagesup plied to the gridof the-first tube .had remained substantially constant .over the frequency range covered inspite of the "inherentcharacteristic of the 'loop. to receive signals of a lower fre-i quency with =lesser1pow'er than signals of a higher frequency; i Still greater frequency independence of .the voltagesupplied by the loop circuit to the grid of the first' tube may be 'obtained, forv instance;

by core portion 41)- being constructedas of var-i9 Q able wallf thickness or of variable shape. Also core p or'tion 4a may be constructed to havevari able loss-characteristics withrthe end entering the windingli first being preferably constructed to have relatively higherllosses per unit volume than other parts thereof (measured at the same frequency); Likewise core member 4b may be constructed from a number of'metals of diiferent electrical conductivity; -Moreover the two core members maybe constructed to. partly overlap one another at their junction in 'a manner similar to'that indicatedin Fig. 2. I While I have-"explained' my invention with the aidbf a particular embodiment thereof, it will be understood thatI do not limit myself thereto. Thus, the present invention may be used in signal co11ecting'syster'ns other than the one specifically illustrated and ov er ranges other than the broad- Having thus described my invention WhatI claimis z' r a c 1.'An improved resonant circuit and tuning means "of the class, including anunexposed'in ductive'winding'," a fixed tuning capacitor, and a core structure movabl e relatively to said unexposed'induetive' element to change'the inductance of'the resonanti circuit .to tune it throughout ia band of frequencies, said core structure including ,uH; The circuit then resonated at a'frequency of 540 kc. .At this frequency the total resistance:

two; portions in endito end relationship; a first oi'i'saidacore portions being-'magnetic andrvarying the inductanceaof saidiunexposed inductive windsv ingifrom substantially the amount due to-unity permeability or an airmagnetic path toa substantially larger and maximum inductance value due,

posed inductive winding; said improvedltuning means including atwo part corejconstruction of the class above describedin which the'magnetic core part comprises comm'inuted ferromagnetic particles closely associated in solid form and havinga; high effective permeability when fully inserted into said unexposed inductive winding e and capable unaided of tuning said resonant circui't over at leasttwo-thirds of said frequencyband from the low frequency end thereof, and

' the non-magnetic and electrically conductive core pa'r't comprises a tube of metal'of good electrical conductivity and having a thin wall limiting. the maximuminductance-reducing eifect thereof in such manner that said'non' magnetic core part will unaidedtunesaid resonantcircuit over not morethan one third of'said frequency'band from theihigh frequency endthereof.

V2:-An"improved resonant circuit andtuning means of thezclass' including 'anunexposed inductive windingafixed tuning capacitor, and a core structure movable relatively to' said unexposed inductive element to change the inductance of the resonant circuit to tune it'throughout a bandof frequencies, said core'structure including two:portions inend to end relationship, a-first of said core portionsbeing magnetic and varying the inductance of said unexposed inductive winding'i'rom substantially the amount due to unity permeability of anrair magnetic path to a -substantially larger and maximum inductance value duelto the greateriefiective permeability of said magneticportion, and :the other of said coreportions being non-magnetic andof electrically conductive material acting .to' reduce the inductance ofisaid unexposed inductive winding below its inductance resulting from unitipermeabilityof its magnetiopath depending upon theposition oi. said: other core portion relatively to saidunexposed inductive winding, which improved resonant' circuit includesin serieswith said unexposed inductive..- winding, an exposed inductive element having an airpathinductance at least as great as the air path inductance otthelfliexposed inductive winding, said improved tuning means including a two'part core-construction of the class above described in which the magnetic' core part comprises comminuted ferromagnetic particles closely associated in solid form and hav-, ing a'higheffective permeability when fully insorted, :into: said unexposed; inductivewinding and 'capable unaidedcf; tuningsaid resonant circuit .over at least two-thirds of said frequency band jromrthe'low frequency end thereof, and -the:non'-magnetic and electrically conductive core partucomprises a tubeof; metal "of good electrical conductivity and having a thin wall limiting the.

maximum;inductance-reducing effect thereof in such manner-that said 'non-magnetic-core part will unaided tune. said resonant circuit overnot more than one thirdof said frequency band from the high frequency-endthereofgsaid core con-' struction having such dimensions andsuch dis-, tribution, of eifective permeability and effective resistance relatively to the-form,,size and inductance of said unexposed inductive winding as to vary the ratio coL MY 7, of the resonant circuit substantially inversely as the tuned frequency throughout the tuning band.

3. An improved resonant circuit and tuning means of the class including an unexposed inductive winding, a fixed tuning capacitonand a core structure movable relatively to said unexposed inductiveelement to change the inductance of the resonant circuit totune-itthroughout a band of frequencies, said core structure including two portions in end to end relationship, a first of said core portions being magnetic and varying the inductance of said unexposed inductive winding from substantially the'amount due to unitypermeability of an air magnetic path to a substantially larger and maximum inductance value due to the greater effective permeability of said magnetic portion; and-the other of said core portions being non-magnetic and ofelectrically conductive material acting to'reduce the inductance of said unexposed inductive winding below its inductance resulting from unit permeabilityofits magnetic path depending. upon the position of said other core portion. relatively-to said unexposed inductive winding; which improved resonanti circuit includes in 'series with said unexposed inductive winding an exposed inductive element having anair pathinductanceat least as greatas the air'path. inductance of the unexposed inductive winding, said'improved tuning means including a two part core construction of the class above describedin which'the magnetic core part comprises comminuted ferromagnetic particles closely associated in solidform and having a high effective permeability, when fully inserted into said unexposed inductivewinding and capable unaidedof tuning said resonant circuit over at least two-thirds of said frequency band from the low frequency end thereof, and the nonmag'netic'and electrically conductive core part comprises a tube of metal of good electrical conductivity and having athinrwall limiting the maximum-inductance-reducing efiect thereof in such manner that said non-magnetic core-part will unaided tune said resonant circuit overnot more than one. third of :said frequency band from the high frequency end thereof, the effective permeability of said magnetic, core part, when fully inserted in said unexposed element being at least of the order of ten, and the thickness of wall of said non-magnetic core part being of the order of one'sixty-fourth of an inch? 4. An improved resonant collector circuitand tuning means of the classincluding a permeability tuning coil,.a fixed tuning capacitorconnected with said coil, and a core structure movable into and from said coil to tune said resonant circuit throughout a band of frequencies, said corestructure including a magnetic portion and a non-magnetic and electrically conductive por tion connected in end to end relation, which improved resonant collector circuit, includes the combination of a loop collector, a permeability tuning coil connected in series with said. loop collector, said coil having an axial length'at least three times its internal diameter and said loop collector having an air path inductance at least as great as the air path inductance of said coil, a fixed capacitor having its terminals connected around the series related loop collector and coil, and a tuning means comprising a cylindrical core portion-of powdered ferromagnetic material in solid form and a non-magnetic and electrically conductive tubular core portion axially aligned with and connected end to end with said cylindrical core portion, the external diameter of said tubular core portion being substantially the same as the diameter of said cylindrical core portion, said cylindrical core portion having a high effective permeability when fully inserted in said coil by which said cylindrical core portion unaided will tune said resonant circuit throughout at least two-thirds of said frequency band from the low frequency end thereof, said tubular core portion having a thin wall effecting the tuning of said resonant circuit throughout not more than one-third of said frequency band from the high frequency end thereof, said two core portions being each substantially'as long as the length of combination of a loop collector, a permeability tuning coil connected'in series with said loop collector, said coil having an axial length at least three times its internal diameter and said loop collector having an air path inductance at least as great as the air path inductance of said coil,

a fixed capacitor having its terminals connected around the series related loop collector and coil, and a tuning means comprising a cylindrical core portion of powdered ferromagnetic material in solid form and a non-magnetic and electrically conductive tubular core portion axially aligned with and connected end to end with said cylindrical core portion, the external diameter of said I tubular core portion being substantially the same as the diameter of said cylindrical core portion, said cylindrical core portionhaving a high effective permeability when fully inserted in said coil by which said cylindrical core portion unaided will tune said resonant circuit throughoutat least two-thirds of said frequency band from the low frequency end thereof, said tubular core portion having a thin wall effecting the tuning of said resonant circuit throughout not more than onethird of said frequency band from the high frequency end thereof, said two core portions being each substantially as long as the length of said coil, said cylindrical core portion havingfan effective permeability when fully inserted into said coil of at least the order of ten and said tubular core portion having a wall thickness of the order of one sixty-fourth of an inch.

i 6. An improved resonant collector c-lrcuit'and tuning means of the class including a permeability tuning coil, a fixedtuning capacitor connected withsaid coil,"'and a core structure movable into and from said coil to tune said resonant circuit throughout a band of frequencies, said core structure including a magnetic portion and a non-magnetic and electrically conductive portion connected in end to end relation, which improved resonant collector circuit includes the combination of a loop. collector, a permeability tuning coil connected in serieswith said loop collector, said coilhaving an axiallength at least three times its internal diameter and said loop collector having an air path inductance atleast as-great-as the air path inductance of "saidcoil, a

. fixed capacitor having its terminals connected around the series relatedloop collector and coil, and a tuning means comprising a cylindrical core portion of powdered ferromagnetic material in solid form and a non-magnetic and electrically conductive tubular core portion axially aligned I with and connected end to endwith said cylin-' drical core portion, the external diameter of said tubular core portion being substantially the same as the diameter of said cylindrical core portion, said cylindrical core portion having a high effective permeability when fully inserted in said coil by which said cylindrical core portion unaided will tune said resonant circuit throughout at least two-thirds of said frequency band from the low frequency end thereof,-said tubular core portion having a-thin wall effecting the tuning of said resonant circuit throughout not more than one-third of said frequency. band from the high frequency end thereof, said two core portions being each substantiallyaslong as thelength of saidcoil, said core portions having such dimen-' sions, proportions andcompositions relatively to the form, size and inductance of said coil as to vary the ratio of the resonant circuit substantially inversely as i the tuned frequency throughout the tuning band.

7. A signal collecting system for radio receivers and the like including an' exposed inductive element, an unexposed inductive element, and a capacitance connectedto form a resonant circuit,,said unexposed inductive element comprising a winding and a core structure having first and second portions arrangeden'd to end for successive movement into and from said winding,

' said first core portion comprising a ferromagnetic body of comminuted magnetic material in cylindrical-form and said-second core portion comprising a thin walled'non-magnetic tube of 'good electrical conductivity, the materials of said core portions and their proportions relatively to each other and to the inductance of said winding being such as to vary the ratio WILLIAM A; SCI-IAPER.

Images