US1937564A - Radio receiving apparatus - Google Patents

Description

Dec. 5, 1933. A. H. GREBE RADIO RECEIVING APPARATUS Filed June 3, 1931 Patented Dec. 5, 1933 UNITED RADIO' RECEIvING'APP'ARATIjs i e r emmsnm Applicfiiqn 1 3 Serial 541,929

7 Claims. 01.178 41) and by a definite amount, at the wish of the) r v I coils L1 and L2 are ordinarily fixed in'theamount" operator.

Several. circuit arrangements suitable 'for' 10 carrying my invention into effect, are illustrated in the accompanying drawings, but Iido not wish to be understood asintending tolimit myself to the exact details shown,'as various changes'may be made therein within the meaning of the j'present invention, asset forth in the appended claims.

In .the drawing, Figure .1. shows the normal assembly of a superheterodyne receiver; Figure 2 shows a circuit. detail of one stage of the intermediate frequency amplifier, Figure 3 shows.

a circuit detail-of part of the intermediate frequency amplifier equipped with my resonance changing arrangement. Figure 4 shows the difference selectivity characteristics of the circuit,

3; Figure 6 shows a further modificationof my tuning" arrangement.

Referringjto Figure 1, A-is the tuned input cir'cuitof the superheterodyne receiver and B isthe local oscillator. 'The combined action of the local oscillator B and the tuned receivingcircuit A is to produce a signal modulatedwave having a frequency much lower than that of the v incoming signal. "This lowered frequency (calledthe intermediate frequency) is supplied to the intermediate frequency amplifier C, (hereafter From the amplifier, the signal ordinarily is supplied to an audio fre-" 40. quency amplifier D and thence vto the loud abbreviated I F A).

speaker E.

Myinvention has to do specifically with an it will be understood that my invention does" not [require any specific type of tube as it func- V tions equally well whatever type of amplifying tube'may be used. 7 A

as obtainable with my invention. Figure 5 shows. a-possible modification of the scheme of Figurethe"selectivity'curves ofthe IF A stage signal to g'et thespecified'output. r

Theinput circuitof tu'be T1 and the input'cir-' cuit 'of tube T: are both normally of 'thetuned type and theyare so shown in'Fig. 2. The values of L1C1",' and LzC2 are chosento giveresonance at that'fre'q'uency chosen for the intermediate frequency; I'have'supposed it to be 175 -kilo-- cycles, a valueordinarily used today'.; The twoof their inductance, and -in -'the degreefiof their I magnetic coupling and 'I have so shown them in' ggq Fig. 2. The condenser Ci and C are ordinarily of the adjustable type so that when the set is; assembled in the factory the two circuits' ;L1"--C1 and -L2-C2 can be properly tuned. These two;

circuits are generally adjustedonceio'r all fat o."

the factory, when the set is built. 7 y In- Fig.3 I haveshown a circuit detail of the I F A; (the amount shown inside the dotted rectangle of Fig. -"2) with my 'fimproved circuit arrangement attached? In serieswit'h" each of 75 the'two circuit's Li -Grand Lz -Cz I have added:

a condenser';"Ca and; 015 respectively.' These addedcondenser's are suitably of a-capa'citj much greater than-tlie capacity of condenser 01 and:-

C2. These twocondensers {Cg and 'Cb have-their 0 terminals brought to the connections of "atwo way switch S so arranged that when; thrown into one direction-C s i's-shortcircuitedand when' thrown in the other directi'on'condenser Cb' is" short circuited; f 5 5 "The i change in "circuit selectivity" for the ewe positions of the switch, when the circuit hasbeen adjusted for- '-proper "performance; is shoWn by the response curves" of Fig.4, -I-Iere areshow i 3, for the two positionsof switch-S. i 5

As will be explained later one positionj'of the switch S result's'in the two circuits being tuned" to each other; for this'position' the response 5; F curveof the I FAstage'isl shown'by' the solid95 .line'curve A, of Fig. 4. "Itis supposed that the frequency for'which'the I FA hase been built is kilocycles '(175 kc), and curveA shows that this frequencyirequires-the minimumimpressed Thus it may beseen that'it requires -l00 micro-voltsinput'togive the specified output at either 170 kc or kc, but it requires onlyabout 2 micro -volts at'1'7 -5'-kc.' At 'either "l60"-kc or 190 kc, the required input voltage isiaboutsbojo micro s V4 v ow. such aselectivitycurve'tends greatly to eliminate interference" between" two stations-1 transmitting on nearly the samefrequericy andit-- v is because of tlie'use of tund intermediate rig- 116" to bringthis about; curve B shows substantially frequency of,17 5 kc per second.

quency amplifiers of this kind that the superheterodyne receiver has become known as a high- 1y selective receiver.

Such high selectivity is however not always desirable, because of the circuits discrimination against the higher frequency audio tones carried by the modulated high frequency wave. It is many times desirable to diminish the sharpness of the resonance curve provided that gain in fidelity of reproduction of the audiofrequency signal can be obtained. Many makeshift schemes have been advocated to carry out this task but they have involved great loss in sensitivity of the receiver or difficulty in manufactur ment of the set. I I have found it possible to changethe formof the selectivity curve from that of curve A of Fig. 4 to that of curve B of the same figure.

Furthermore, I have found it'possible to bring about the change in form of the selectivity curve e anda justr without appreciably sacrificing the sensitivity of 6000 cycles'ofthe carrier frequency. It can be seen from curve B of Fig. 4 that I have been able the. same amplificationfor all frequencies between-1'10 kc andl kc per second. As stated before, the I F A has been designed for a resonant Referring again to Fig. 3, I will explain condensers C1 andpa in series. This means, of

course, that the capacity of C2 is adjusted to a value-:slightly les's than thatof 01 The exact difference between the capacity of C1 and C de" pends upon the ratio of the capacity .of'cona For thepurpose'of my invention, C1 may have a capacity 7 denser Ca to that ofthecondenserCn about 6% that of C2. I do not limitmyself to such-a proportion however because it may be ad-. visable to use-a larger or smaller proportion than 1 this under special conditions. I 7

The coupling between coils L1 and L2 must be suitably chosen if a selectivity curve such as that of curve A, Fig. 4, is tobe obtained. I am assum ing that such a value of coupling hasbeen chosen.

Thecapacity of Chis about the same as the capacity of Ca,.when C1 and C2 are of approximatelythe' same capacity. In case C1 andC2 are not approximately the same, then the capacity of Cb will not be the same asthat of. Ca; It will'be understood, of cours,e,.that when C1 is not equal to C2, the values of inductances, L2and L1 will correspondingly differ.

;I- Iay-ing now adjusted theset, with switch S in contact, as abovedescribed, the selectivitycurve will beabout as, shown by curve A of Fig. 4.

Bynow shifting theswitch S to position 2, the

selectivity curve changes inform to that of curve B- 1of"Fig., 4. This change in formof curve is broug t about by e de-tu i s o th rcuit paratus.

how thedesired result is obtained. In tuning'up, or -adjusting the I F A in the factory, the switch Sis thrown to position 11'. This short circuits 40.-condenser Ca-The two condensers C1 and C2, which are of the adjusta-bletypegare now regu latedfor capacity to bring about tuning of thetwo circuits. Ifthe two coils L1 and L2 have the Y same inductance, this tuningoperation involves the equilization of the capacityof C to that of in fidelity is accomplished with practically no loss in sensitivity.

Whereas I have shown the switch S'as' short circuiting a condenser, in one circuit or the other, it is quite possible to short circuit a small inductance instead. This possibility is indicated in the arrangement of Fig. 5, in which the two positions of switch 3 short circuit either coil La or coil Lb. These coils-would normally have an inductance about 6% that of L1 or L2 its exact value, however, may depart appreciably from this value. i "i In Fig. 6, I have showna scheme in whichfthe" switch S in the closed position shortcircuits condenser Cb in one circuit and inductance. Lain theother circuit and inthefopen? position removes the short circuit fromIboth pieces of ;ap.-*

The two circuits are tuned, with the. switch in either position, and the resultant se'-' lectivity is thatgof curve A,.Fig'. .4; Thenwhen the switch is thrown into its otherposition, the natural-frequency of one circuit is raisedand that of the other is lowered. This condition; results-in the selectivity curve shown at B of Fig. 4. Y

Having thus described my-invention, what I1 claim is:

1". In combination witha pair of loosely coupled tuned circuits, means including? auxiliary .reactances for increasing the'natural frequency of one s circuit by a small :amount and decreasingv :the natural frequency of thelother, circuit by approX-' I imately the same amount.

2. In a superheterodyne receiver having .an in'-' termediatefrequency amplifier using two coupled,-

tuned circuits between successive vacuum tubes, i:

means for changing the shapeof'the, selectivity: curve, the said-means includingauxiliaryreacev tances for detuning the two tunedcircuits by increasingthe natural frequency of one of the circuits by a small amount and decreasing thena *turalfrequency Ofthe other.circuit; ,by approxi imately the same amount as the first one lias been increased, V 3. In a superheterodyne receiver having; an intermediate frequency amplifier using .two coupled tuned circuits between successive vacuum tubes, means for successively increasing the natural fre-,: quency of one of the circuits by a small-amount andthen decreasing the natural frequencyof the other circuit by the same amount; 1

4. In the intermediate frequency amplifier of".

a. superheterodyne receiver, utilizing coupled tuned circuits for interstag'e coupling, a switch ing arrangement for successively increasing the capacitive reactance of one of the tuned circuits by a small amount and thendecreasing the ca pacitive reactance of theoth er tuned circuitby';

approximately the same amount.

5. In a superheterody ne receiver having a tuned intermediate frequency amplifier, said amplifier'utilizing magnetically :coupled, tuned circuits between successive amplifying tubes, said tuned circuits each havinga coil and two 0on densers connectedin series-switching, means for:

successively removing a short circuit fromla conintermediate frequency amplifier, said amplifier, 1

switch for increasing the natural frequency of one of the circuits by a given amount, and de creasing the natural frequency of the other circuit by approximately the same amount.

'7. In a superheterodyne receiver having a tuned using coupled tunable circuits, a single control switching arrangement which serves practically to instantaneously change the electrical characteristics of they two circuits so that the tuned frequency of one circuitis increased by a given amount and the tuned frequency of the other circuit is lowered by approximately the same amount. v

. ALFRED H. GREBE.

DISCLAIMER 1,937,564.Alfred H. G'rebe, Hollis, N. Y. RADIO RECEIVING APPARATUS. Patent dated December 5, 1983. Disclaimer filed April 14, 1936, by the assignee, Radio Corporation of America. Hereby enters disclaimer to claims 1, 6, and 7 of said Letters Patent.

[Ofiicial Gazette May 12, 1936.]

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