US1988498A - Radioreceiver - Google Patents

Description

Jan. 22, 1935. l.. L. JoNEs RADIORECEIVER Filed Nov. 26, 1929- INVENTQR Leser L.. Jones BY Z AT1-OR y ground circuits? Patented 12.11.22.19.15

- RADIORECEWER y Lester `L.-'J0nes, OradelL' N.- J. `Apyglication November ze,1929, seria1-No.4o9,see v zclaims. (o1. 25o-27) This invention relates to radio receivers, and more particularly to a method and `means for `the eliminationof 'humsrandlinterference in power line' operated radio'ireceivers.

'The primary objectof the present invention is to improve the qualityoflthe reproduction ob' tained from powerline. operatedv radio receivers. It is found thatinspitefof extreme.preeaution in the matter of 'circuit design Vand shielding the quality of the reception may be vspoiled bydisturbances,v the source of whichis exceedingly puzzling and*'little'understood""Ihe problem is further complicated by the fact that thesame or similar receiversi'seem fto behave differently in this respect whenV located in' different places or when connectedP'to'different antenna and :Ih'ave found Kthat these disturbances are of two 'general L kinds which, for convenience o f 'referencel shall refer to as modulation lhumgand undesired interference. 'Modulation hum arises-only infreceiver's operated from alternating currenttpowerllines, and

' may occurat'tlie frequency ofthepower supply or at doubleth`is frequency; It'ordinarily is masked'by the `signal-When ay signalr is being re,- ceived, but becomes audible .when the received 'carrier isnot modulated. I have found that this Aform of disturbancalk inthe caseg of 'a well designed and constructed receiver,` although not present when the receiveris connected to a good ground, frequentltT *arises 'when the-l receiver is connected to a medium-or poori ground. I have further found thatthe-probable reason for this modulation humresidesinthe'fact'that a circuit for radio frequency energy'.` may 'be traced from thev receiver through theepower unit vthereof to the power line, so' that-this circuit includes vwant of ya better V'name-may in series therewith the power supplyrectifle'r. of q the receiver. The power linefacts as a `counterpoise or ground, and therectier in series with this ground connection variesrwidely in impedf' ance at the power supply frequencygland consequently modulatesy the received carrier energy in the antenna circuit.

One object of the prese t invention is to obviate this modulation hum, and thismay be done by either bypassing thepower supply rectifier of the receiver circuit including thek power" supply rectifier against the flow vof'radio frequency energy, or both. Y j f The'other kinds of disturbance, which, for be called undesired interference, may occur in alternating or direct simultaneous elimination,

withirespectf to radio frequency energy, or choking "the radio frequency lseries H trating one form of my invention;

current operated receivers, andappearsin many forms. Y It mayevidence. itself by a reductionin the selectivity ofthe receiver, or, 1in the case of loop sets, by a broadeningof the directivityof the loop. The interference, instead of being in- 5 terfering signals, may occur in `theform of static or strays, or. noises originating.. from4 snap switches, sparking commutators," or. other electrical machinery. i y

" Another object of the present invention is-;tol0

overc'omeor minimize such Vundesired interference` as Well as"` to eliminate modulation hum.

I havefound that these variousdisturbances maybe picked up and transmitted intolthe' rev ceiver bythe powerline; I have further found l5 that even though the set has been 'carefully designed and shielded against audio frequency disturbances they 'may ap'pearinxthe setbecause of the fact that radio frequency energypicked up onfthe power line becomes modulatedby these 20 disturbances.' andl the receivent while shielded against audiov frequency disturbances, vis not shielded againsty radio` frequency disturbances reaching it by way of the'power line.`r Tofovercome this difficulty it Vis merely necessary to 25 choke the power line with respect to radio yfreque-Ilcy energy atV a .point near .the receiver. Shunt `condensersimay beradditionally provided,

in which case the radio frequency Venergy 'on the .power line is actually filtered from the power 30 line, preferablygat a point adjacent the receiver in order to prevent further energy pickup on the line between the'fllter andthe receiveni Furtherobjects offmyinventionare tozprovide suitableV means for the elimination of .modula- 3 5 f tion hum, to .provide suitable VmeansL-fory the elimination of undesired interference, to devise f Y my yinvention consists -in Athe method andthe` l'circuit elements andftheir relationv one ','to the otheras hereinafter 'are more particularly Vde- ,50 scribed lin the specicat'on and sought tobe' dened in the claims. The specificationis vaccompanied by drawing inwhich: y f y Fig. 1 is a fragmentary wiring; diagram illusselection and followed by an untuned or an. au tomatically tuned amplifier.` The receiver may` be assumed to be shielded, as by the shieldlS,

and the latter is ordinarily groundedan'dracts as the ground of the receiver.

For a proper understanding? of 7thislfinventionit is important to distinguish between this ground of the receiver and what I shall term' thereal ground.v fThe vrealI groundin the present case is indicated at 18, and is electrically equivalent .to one plate of. acondenser, indicated at.22, representing the capacitance of the antenna 24 with respect tok ground. The ground of thereceiver is' ordinarilyconsidered as having thesamepotential :asthe ;rea1 ground, .but this is true only.v in thespecialcase where the ground of the receiver is connected to the real. ground by an efcient low impedance path. The ground lconnection ordinarilymay be, to a radiator, as

is schematicallyindicated at 26, orto la gas pipe, and in such case it not infrequently happens that the ground connectionv 28hasconsiderable resistance, indicated at-,30, between the ground of the receiver andthe realground. `In dry country. whe'rethe uppersurfaceof `the ground isv lacking ininoisture'it .may be difficult to obtain'a Lgood ground even if thephysical connection between-the ground o'f :the receiver andthe .dry 'soil is'fmadeecientVand-in such case also the situation-may be represented by a high resistance connectedin series between the ground of the receiver and the4 real ground, thatis, the ground which iseffecti've withfrespect to the antenna. i y ,N The powerfsupplyunit 20v includes the usual 4power transformer32,.rectiiier 34, andf'ilter 36.

The transformer 32 comprises a primary v38, a

z high potential secondary 40 thev output of which :is 'rectified to obtain asteady anode potential for primary B8 and the secondary42.v

the receiver, andra'y low potential secondary 42, the-output-cf-whichv isused for heating the .cathodes ofthe various tubes iti-,the vreceiver. It

is customary .to windtheytransformerA with the secondary 40.adjacehtftheprimary 38, and with Ithe secondary 42'wound outside the secondary 40, presumably because Vthe secondary 42 con-L sists Vof afew turns of coarse'wire andtherefore may more advantageously be wound at a larger diametermthan the .secondary 40, consisting of a verylargenumber, of turns of relatively expensive fine wire. For fth'is kreason there is considerable capacitance between'the primary .38 and the secondary40, indicated bytliedotted condenser 44,-.which is notpre'sent between the The alter 36 consists of vseries chkes '46 and shunt vt'z'oiiden'sers '48, i'n the,conventional manner. This filter i'sdesigneditosmooth-outfripples having ythe relatively/'low power supply 'frequency or harmonics thereoffa'nd condensers 48 aretherefore o'f"relativelylarge magnitude, say

"two microfarads. f

It will be robsefrvec that .fa-radiofiecu'ency :matic diagram of Fig. 2.

path is readily traced from the receiver ground 16 through the Iilter condensers 48, the power supply transformer secondary 42, the rectifier 34, the transformer secondary 40, the capacitance 44, the transformer primary 38, and thence to the power line 50. The power line 50 possesses considerable distributed capacitance with respect to the real ground 18, indicated at 52, owing to its great length and distribution, and it thereforev may act as a ground for the receiver, ina mannersimilar to a counterpoise sometimes intentionally employed as a ground.

n YTheresulting situation may be more clearly understood by referring to the simplified sche- In this diagram the antenna 24 is grounded to the real ground 18 through any suitable form of coupling impedance 25 in the receiver, and a resistance 30 caused by the receiver4 ground 16 being connected to only a medium or poor ground. The receiver `ground 16 is also connected withV the real ground 18 by'another circuit in parallel with the resistance 30, this'circuit consisting ofa lowimpedance large. condenser 48, ,a low impedance small inductance 42,;a, rectifier 34, ka capacitance' 44 between the adjacentwindings of a trans- .former primary38 and secondary 40, and a power line 50 possessing considerable` distributed capacitance 52l with respect to the .real ground 18.

Only one side of the rectifier circuit and one conductor of the power line have been indicated because ordinarily the capacitance 44 is sovery much larger `between the adjacent lwindings of the primary and secondary of Lthe transformer,

and therefore between the terminals 4connected to this side kof these windings, than it is between the remote sides of the ,windingsv and the terminals connected thereto, that for all practical purposes the radio frequencyfseries circuit may be considered as passing through only one side of the full wave'rectiiier and power line, just as is indicated in Fig. 2.

The rectifier 34 varies V,very ,widely impedance in each cycle, ordinarilybetween infinity and say? only to 600 ohms.,v 4If the resistance 30 is extremely high the receiver `will ground .itself entirely, through the `power line, and it is obvious that this` ground has-in series therewith a variable impedance whichr will modulate` the carrierflowing therethrough. If theresistance 30 is only moderately high, asgif the receiver has a medium ground, a considerable portionof the received signal lwillllowjthrough the rectifier,

v*and the effective total impedance Vof'y the two parallel ground circuits vwill be sirni1arly'varied,.

althoughof course,vnot,to so greata magnitude as, when the ground isi very poor. n

With the foregoing analysis of. the difficulty in mind the remedies for modulation hum are rela- ,tively simple. The first is to provide agQOd ground. Y However, for the purpose of the presentdiscussionit is assumed that the ground is either medium or poor, and asapracticalmatter the manufacturer of radio receivers must anticipate this condition .becauseit very frequently arisesin practice. The next general solution is to bypass the rectier 34 with respect vto .radio frequencies. vA radio frequency bypass condenser may. be connected'rdirectly -'across the rectifier,

but this .has the disadvantage of necessitating that the condenser be capabler of withstanding extremely high potentials. I prefer to bypass the rectifier .34 with aradio frequency condenser '60' connected asis indicated in vFig2, that is,

.between theeround .of thereeirer. 1.6. @neil-.1.2mm

fil

the-j"-terminal of l 'the 1'transformer,Lv primaryf 38 nearest to the transformer-fsecondaryAO. 1

'-Anothergeneral solution'is to choke the radio frequency series circuit extending from-the radio receiver ground 16 to the`y powerfliney 50, -and including the rectifier 34,'A Vwith-respect to radio frequencies. vThis is indicated bytheJradiOfrequency choke 70 connected in series: with the power line V50. This solution `is applicablefto the lease where the yreceiverfhas av medium ground, but is not desirable when the rreceiver 'hasa fvery poor'ground because the introduction ofthe choke '70 will impede the naturallyadoptedground of the receiver. f It is clear-that when ythe receiver has a-medium-groundthe condenser -60 and the choke 70 may both be simultaneously employed, which is of valuel inthe event 'off the thel receiver ground 16 and-the terminal of the transformer primary 38 adjacent the transformer secondary 40. Also,` a radio'frequency choke 70=is lmost readily connected in series with the radio frequencyA circuit including thevre'ctifierby "beingconnected' to the` terminalf of the power `line at the receiver. Thecondenservo may `-be as" small as- 0.002' microfarads, and a magniture `of0.005lmicrcfa'radsis quite sufhcient. "Theca- -AVpacitance may Vbe increased largely aboveY these "'valuesfbut it isdesirable not tolfcarry'this in- "crease too far, in order to avoid placinga capacitive-loaden the 'power line with respeetto the have ian impedance ofthe orderiof 10,000 ohms in the Aradio frequency range -`for"i-"v'vl'iich the receiver visdesigne'd. y

If desired, a condenser 60' andV a choke 70' may be connected in circuit as shown, making the circuit symmetrical. This avoids the necessity for knowing the internal construction of the power supply transformer, and also prevents a double frequency hum such as might' occur due to passage of radio frequency currents through both rectiflers should appreciable capacitance exist between both ends of the primary and secondary of the transformer.

It may not be amiss to point outy that the method of my invention, which includes bypassing the rectifier with respect to radio frequency energy, may be fulfilled by constructing the power supply transformer in a special manner so that' the low potential secondary 42 thereof is wound adjacent the primary 38 and is therefore given considerable capacitance with respect to the primary, which capacitance will bypass the rectifier, and meanwhile will shield the secondary from the primary.

In addition to the fact that receivers may be connected' to different kinds of ground connections the receivers may be energized from different kinds of power lines. Undesired interference may be cause by transients along the power line originating with electrical machinery of Various kinds, and even from switches and the like. The power line may also pick up undesired signals and transfer these through the various distributed capacitances in the receiver. Such energy not being passed through the selector of the receiver tends to reduce the selectivity thereof. In the case of a loop receiver it reduces the directivity of the loop. 'I'he precautions inherentlyprovided in evenan alternating current receiveragainst` audio yfrequency disturbances are not eifectivebecause the present disturbances "are at radio frequency,- and`v even audio frequency-1 disturba'x'icesV are transmitted into the receiver ninltheform of a modulation superimposed' on some radio '-frequency carrier or signal'pickedzfup'by the power line. To prevent this undesiredinterference I ndy'it desirable-to -choke ytliepower line with respect to radio frequfencies 'at "apoint Vnear-thereceiver. .'This 4-functionmay be advantageously fullled'by'the chokes# 70 and A'70' already disclosed in Fig.- l. `.Alsoffthef radiorfrequency-"shunt condensers 60 and 60'v may aid'in thedesiredelimination or jfilteringl' ofy radio frequency? energy from the power 'Supply energy `entering `the receiver. This isan additionalwadvantagein usingl the sym'- 'metrical arrangement shown in Fig. 1, employing -more`condensers or/and chokes than' would ordinarily bef necessary merely *for` the elimination indicated in Fig.y 1 is shown, except that fthisjset rlisillustrated as-havingajgood ground connec- -tion,as;at80.` -A- radio vfrequency fllter82fm`ay bejco'nnectedinseries -With` the power line -150 ata point-iat or near but not linside the receiver It should be -near V-thereceiver `to prevent'energ'y pickup on the line between `the filter and the 1:

receiver. It should be outside vthe shielding of Vthe set in -order to prevent the 4radio frequency energy from gettinginside the set, for once inside there are numerous! obscure paths Vby `which Af"Radio'frequency choke`s84vand 84" alone-may be-used,-or1-radioffrequency shunt condensers H86 and *86e may-beused, orboth.y 'Ihe shunt ca- -pacitance`, l:ifused, is'preferably provideddn the form of two equal condensers grounded Hat their adjacent.A terminals for the sake of symmetry with respect to the power linev and ground. The

frequency energy may reach the deground connection 88 should preferably be an independent connection rto the real ground, as is indicated in the drawing, because if grounded to the set ground 16, first, the lradio frequency energy will reach ground through the shield and a portion of the antenna to ground circuit, second, it may also reach Vthe detector directly, and third, there is a tendency to bypass the chokes. In accordance with the present invention the filter 82 further includes radio frequency bypass condensers 90 and.90', which are grounded to the set ground 16, as shown, which incidentally prevents bypassing the chokes 84 and 84. The condensers 90 and 90 operate in a manner analogous to the condensers 60 and 60' in Fig. 1, so that should the receiver be connected to a medium instead of the indicated good ground, modulation hum will be prevented. f

It is believed that the method and circuit arrangements for the practice of my invention, and the advantages thereof, will for the most part be apparentfrom the foregoing description thereof. It will be appreciated that various combinations of conditions may arise, which may be counteracted in many ways. 'I'hey may be briefly enumerated as follows. With a good ground and a quiet power line no di'iculty arises. With a good ground and a noisy power line the power line should be choked or ltered with respect to radio frequency energy at a point adjacent the receiver. With a very poor ground and a quiet power line the power supply v*rectifier shouldn beshimted with .lispfxit to Vradio -frequency energy@ With v; a v-very @ground .andg a noisy power; 1ine -noth ing-, c an done -to o bviate both modulationhnm andgundesired interference; butI the f. rectifier1 may be .fhlinted in order to eliminate modulation;hump-@and meanwhile improvingi4 the ground-fanddtheref ore fthe; antenna pickup.- f ;With; y a .fgmedium yground-and a .quiet power-line .the reetier .may

10*ergst thereby elimnatinemodulation limproving lthe 'ground vof the receiverxfi,,WithA a medium' groundy rand. 12.- :noisy power "g linethe Y ypower 1in-ede preferablyfehoked; with respect to radio frequency .,lenerey, gtherlebreliminati-ng be shunted 1 with respect ,to radio ,-frequencyenhum-aud modulation h um and power line;-di stur loances v a1- thoughfvnot improving: the -reeeivergmund.J If

the receiver 'is designedi gtooper-,ate` from a loop withinv the set'it is preferableftu employ fseries eholeesf and, Y,of course, Je :ground ether 1. .there the power line -iffa er0und is. needed,- aS-:if Vthe@loop is to be made unidirectional. i Ihe \san i eg applies tennae withinthe 41 r e ce,i\ f er. c a1 oin e t It willbe apparent f that while I .ghave shown to receivers :using-a zpltieVA `antenna o r other 4anand e .described myfainventionf in `the ,preferred forme; many. Changesendfmodieatiensomey be y made in the methodlidxcircuits disclosed-without ,departingv from .thesnirtv `ofvfthe. invention, dened in.thetio11owing-claims 4 l r f I c1aim:-

1. The combina I radici-receiver energized from an alternating, ,current Hpower lline and responsive, y,to radio ,frequency'- .energy of a desired frequency collectedgon.;` a ,col1intional antenna, said receiver by the rece including they-usual i f grounded shie1ding,- antenna to ground :circuit power transformer, L,rectiijeig and filter; circuits, kor rrneans to preyent-tmodulationifhumcaused -of thereceiver. iver beingrgroundedfthrough hezpowy er line comprising a'radio frequency bypass"` con'- ydensen connected lay- 4 short; :direct leads ybetween the terminal vattheyside ofthe primary of the :power .transformer nearest the transformer sec- ,ondary;;andf the groundedshielding of the receiverincrder towform a lowA impedance path for the said1, desired radio` frequency fenergy, said `.condenserbeing devoid of any-.connection to an external ground except .insofar as it may be indirectlyi connected to said external ground through its1zdirect connection to the shielding of the .22 ,Thecombination withav radio Vreceiver energized yfrom an alternatingcurrent power line and responsive to 2 radio.;` frequency energy of a desired Yfrequency ,collectedifon 4a conventional `antenna includingthe usual:grounded shielding, 'antenna (to groundfcircuit, `powerl transformer, frectier,r and lterlcircuitsof meansto prevent i,mo/f lulationfhuinvcausedlloy the receiver being grounded through the power line comprising a radio f requencychoke for the said desired radio vfrequency fenergyconnected in Yseries with the terminal ofthe powerline which is connected to that side of thel primary of the; p ower `transformernearesttothe transformer secondary, so as to 4`prevent radio frquency energypnthe power line from reaching-v thev receiver.-; and a l radio Vfrel 'quencygbypass condenser Connected by short ydirectl leads, between the terminal atthe side of the primary of thei powertransformer nearest the transformer secondary and the grounded shielding of thereceiverin order toform a low impedance path fortheisaid ,desired energy, said condenserfbeing .devoidof anyuconnection to an external.- ground exeept; ins,ofar as` ity may be indirectly connected to2-v said external ground through its direct connection toV the shielding

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