US2474978A - Circuit arrangement for use with widely separated frequency bands - Google Patents

Description

y 5, 1949. J. D. HOLLAND 2,474,978

CIRCUIT ARRANGEMENT FOR USE WITH WIDELY-SEPARATED FREQUENCY BANDS Filed Aug. 18, 1945 3 Sheets-Sheet l Inventor Town bcuolms HaLLfi D Filed Aug. 18, 1945 i I I I July 5, 1949. J. D. HOLLAND 2,474,978

CIRCUIT ARRANGEMENT FOR USE WITH I WIDELY-SEPARATED FREQUENCY BANDS 3 Sheets-Sheet 2 I nventor \Temn Dauemecu-n9 1 July 5, 1949. J. D. HOLLAND 2,474,978

CIRCUIT ARRANGEMENT FOR USE WITH WIDELY-SEPARATED FREQUENCY BANDS Filed Aug. 18, 1945 3 Sheets-Sheet 3 Inventor Inm mOuGLfiS New;

I Attorne Patented July 5, 1949 CIRCUIT ARRANGEMENTS FOR USE WITH WIDELY SEPARATED FREQUENCY BANDS John Douglas' l lolland, London, England; assignor, byniesne assigiiments, to International StandayardElectric' Corporation, New York, N. Y., a

corporation xofDelaWar-e A ses es Au ust 18, 1945, Serial'No. 611,378

"" In' Great Britain September 1, 1944 The present invention relates to thermionic valve circuits and particularly to circuits for translating or generating signals occupying two difi'erentbands of frequencies. Y

"=Itis of-course well-to amplify all the channels of a multiechannel system simultaneously' in the-same amplifiers and toseparate the channels afterwards Joy-means of filters. In such a case Waves of-al'l f-requencies are-simultaneously applied to the inputelectrodes-of any valve in the amplifier, and the-amplifiedwaves areall' simultaneously derived from't'he output electrodes thereof -I '1 I ln -thecase of the present-invention; the amplifier or other translating device is provided with a multi-electrode'valve haying-at least three grid electrodes between the" cathode and 1 the anode which is treated as 'two -tr'iodes having a common cathode-and sharing the-same electron stream; One ofthese-component triodes is used to translate. or generate waves "occupying one band of frequencies; andthe other to translate or generate those occupying another band.

In this way=the two channelsare kept-separate, though they are dealt: with by thesame-valve.

It is also well-known to employ a- -pentagrid= valve. as ra -frequency changer =for a single band of. frequencies"'byvusingnthecathode and the first two grids as a triode oscillator andthe-third' grid and: anodewitmthe cathodesas a modulator. Thus Whereas; in: thiszarrangement the valve is employed only "tov "dear with oneband. of signal frequencies; according to the'rpresent invention the'two parts-oflthe valve are each employed for separate-bands-offrequencies. w The several :features-.- ofathe: invention are set out asuclaimsl-,.2rand 3.respective1y, of the statem nt ofclaim.;-':r1121, a: 'Ihea'invention will be described with reference to the-accompanying drawings: in which FigS.lIfTa1Ild1i2 show simplified schematic circuit diagrams of arrangementsaccording. to. the

invention; m Y w Fig. 3 shows aschematici-circnit diagram of atWc-path radio receiver according to the invention. "Fig. 4 shows amodification: of; partofFig. 3..

, .Fig. 5 shows a radio receiver according to the invention providing twosepara-te signal channels;and'-" w Fig. 6 shows a. double-oscillator according to the invention.

The type of, multii-gridvvalve shownvin the above circuits for the purpose of illustrating the inventionviscne sometimesicalledta ipentagrid,

having five grids. interposed between the cathode and the anode. The third and fifth grids are. connected together to form a single screen electrode for th-eiourth grid. For thepurposeof the present invention the.-.screen. electrode.is not, essential. andv can be omitted, the minimum re.- quirement being that there. should be at least three grids between. the cathode and the anode. There may, of course-,bany number of grids in: excess of three the extra. grids-being suitably polarized.v

Fig. 1 shows diagrammatically. an arrange:- ment according to the invention. A pentagrid valve l= comprises: ascathode :2, three grids 4 and 5,.a screen grid electrode ,6 and an anodel. The electrodesl, a and i /constitute one triode; portion, of whichelectrodex i serves as the anode, and electrodes 2,15 andl: constitute another trigode portion. The-cathode 2 is connected to the grounded negative terminal .8 of the high tension supply, the positiveterminal 9 of which is con-- nected: directly to the screen grid B and to elQQ- trodes 4- and'lathrough impedance elements Hiand ill-respectively. The control grids ,3 and :5 are connected to inputterminals Hand 13 re:- spectively,.and the anodes 4- and Tare connectedto output terminals l4: and: 15 through blocking, condensers l6 and ,lil', respectively. A suitable bias network ,zpflqm-ayrbeainserted in series with the cathodeas shown. A condenser 2 I serves. as a lay-pass condenser shunting .the high tension source;..-.. H

The impedance .elements 18 and I}! represent input circuits reach carrying a separate channel ofi-signals. I Thesignalinput voltages are represented bythe symbolsei and as in series with the elements -I8'and.l;9. .The amplified or otherwise translated signals are obtained at the output terminals M andzla5 thecorresponding output voltages bein-glEi and E2. as indicated.

Let f1 and f2 be=the signal frequencies corresponding tolthe .inputpvoltages e1 and 62, and suppose that the valve 1 i is employed'as an amplifier. .Then when both. setsof signals are applied to the respective input grids,..the electron stream proceeding from thecathode will contain variations at both frequencies, so that. amplified. signals at bothfrequencies will. appear at bothfof the anodes 4. and .L. The impedance elements Hil and II accordingly represent any suitable tuned icirc-uitszor filters, or. the like, adapted. to suppress one of -theirequencies andto allow the other to pass. In order that this. may be achieved without undulyzcomplicating the impedance, elementa -the;-ztwov frequencies f1. and f2 should preferably be widely separated; for example, one should be not less than about double the other, and preferably also one frequency should not be a harmonic of the other. Where the signals comprise two bands of frequencies, then the lowest frequency of the upper band should preferably be at least double the highest frequency of the lower band.

Furthermore, the two triode portions of the valve I will usually have different mutual conductances (the upper portion having generally th higher value) and in order to minimise interference the associated circuits should preferably be arranged so that the gains of the two amplifiers do not differ by more than about 10 decibels. As the output circuit which operates at the lower frequency will usually have a higher dynamic impedance than that operating at the lower frequency, it is desirable to operate the triode portion 2, 3, 3, at the lower frequency so that by associating with it the high impedance output circuit the gains of the two amplifiers will tend to be equalized.

If the two triode portions of the valve 1 are not operated simultaneously, then it is not important that the two frequencies f1 and f2 should be very widely separated, or that they should be harmonically unrelated, and a larger difference of gain for the two amplifiers can be allowed, since interference does not arise. In any case however, it is desirable that the valve should be so biassed that neither of the amplifiers are overloaded.

It will be evident that the signals applied at terminals l2 and I3 are independently amplified and are kept to separate circuits throughout. The two corresponding channels may be used simultaneously or separately. The arrangement is equivalent to two separate amplifiers each with its own valve, but the two valves are part of the same pentagrid valve. The valve I may also be used as a double frequency changer. In this case the strap between the terminals 22 and 23 shown in the grid connection is removed and these terminals are connected to a suitable local carrier frequency oscillator (not shown). The bias circuit 20 is chosen so that both sections of the valve I operate as modulators. Then if f is the local carrier frequency, side bands fo+f1 can be obtained from the anode 4 and sidebands fo-l-fz from the anode I. The circuit elements It! and H could then comprise band filters each of which is adapted to select a corresponding side band and to supply it to terminal I 4 or [5. So long as the frequencies f1 and f2 are well separated, the band filters represented by the elements I {I and H need not be very selective.

The two channels may be provided with different local carrier frequencies by means of a simple switching arrangement, such as that shown in Fig. 2, in which the elements which are similar to corresponding elements of Fig. 1 are designated by the same numerals.

In Fig. 2, 24 and 25 represent the sources of the voltages er and 62 at frequencies f1 and f2. A switch 26 connects the source 24 to the input terminal l2 in the position shown, and in the other positions it disconnects the source 24 and instead connects the source 25 to the input terminal 13. A carrier frequency source 2! of voltage es and frequency is is connected by the switch 28 when in the position shown to the terminals 22 and 23 in series with the cathode 2. This will produce a side band f3+f1 at terminal 14 of voltage E3. When the switch 28 is operated to the other position, it substitutes for the source 21 a source 29 of voltage at at frequency ii. If the two switches 26 and 28 are mechanically connected so as to be operated together, then a. side band f4+f2 at voltage E4 will be obtained at terminal I5. Thus by means of the two switches 26 and 28 it is possible to select either one of the sources 24 and 25 and to provide at the same time a corresponding carrier frequency. Moreover, the corresponding side bands are obtained in separate channels.

It will be evident that the arrangement of Fig. 2 can be either a modulator or a demodulator for either channel; and it could be a modulator for one channel and a demodulator for the other. In the remaining figures of the accompanying drawings three different types of circuit according to the invention are given as illustrations of the general principles described with reference to Figs. 1 and 2. These types are as follows:

(1) A circuit in which the two channels which pass through the multi-grid valve or valves are not intended for use simultaneously, but one channel is used for signals covering one part of a frequency band and the other for those covering another part of the band.

(2) A circuit in which the two channels are completely independent throughout and may be used simultaneously or separately.

(3) A circuit in which the two triode portions of a multi-grid valve are used as oscillators for generating two different frequencies.

Fig. 3 shows a circuit according to the invention suitable for a radio receiver adapted to cover a very wide range of frequencies, for example 15 to 26,000 kilocycles per second (kc. s.). Such a large range cannot be satisfactorily covered by the use of a single intermediate frequency for reasons of selectivity, image suppression, and gain. It is desirable therefore to divide the range into two parts, for example 15 to 500 kc. s. using an intermediate frequency of 40 kc. s. and 500 to 26,000 kc. s. with an intermediate frequency of 560 kc. s. According to the present invention two channels are provided in the receiver, in which intermediate frequencies of 40 and 560 kc. s. are respectively derived and amplified in the two corresponding portions of the valves.

In the radio receiver shown in Fig. 3 the waves are received on an antenna 30 and are passed to the high frequency amplifiers and selective circuits 3| which may be arranged in any convenient way. A switch 32 enables the output of 3| to be applied to the upper or lower input grid of a pentagrid valve 33 arranged similarly to the valve I of Fig. 2. A carrier frequency oscillator 34 of adjustable frequency corresponds to the oscillator 21 of Fig. 1 and is connected to the cathode circuit of the valve 33 through a transformer 35. The usual bias network for this cathode is shown at 36.

Two tuned output transformers 3'! and 38 couple the two triode portions of the valve 33 to the corresponding triode portions of an amplifying pentagrid valve 39. This amplifying valve has the usual cathode bias network 40, and also a coil 4| connected in series with the cathode; the purpose of this coil will be described later. A pair of tuned output transformers 42 and 43 similar to 31 cults (which will be described in detail later), are

to. liottiriue icy-ampli ing alto b ejt p cr gich m r-t c-e el m... a peutcd orch nta rid or smira tc. Z ihe am f -ost mmthctermin l ti-and 2 nggcted t q the anode circuit of the valve by a transformer 48. .Itrill, be ee that.

meted-t b fi ntio ly .imthe s meway as the 1-:

valve "I of Fig. 1, the tuned transformers 42 and oo xc tzo dieg. r nectivelyt i hei.e ements, wa U cf this. figur tuned tra s q mexsfl and 42 operate as h n pa -filte s a d-.shomd' o'dec i n tenets. a cinte m dia e' freq ency-toas I .Tb t sdtronsfqrmet and #3 s oul m s e Joe. dcs igned to pass an intermediate frea, H,: u l "1. 4. A m 1 two anodes of the valve 39. are, each con: nected through the primary winding. of. the. cor:

iesm tl ng tuned-t a sform r to. the positive tor:-

nit al f the .high,.tenion supply,- Athc. neaa tive mma 511 c;which,is, connected.to ground)...,

and the screen grid is connected directlythereto'. v ;mates nding conne tions to. the valve-.33 are similar, except that. .two. normally closed a di hWc ecn-intermsed as shown. for. .Rutpo e .toh explained, later inconnection w thanother.embodim nt.otthcinvcntioncT ey ar not needed for theiemb diment now being deg1, n u d e m t edv, .p lous t flemtioned dete t r. c rcu t com ris s. do lo cr si ton 53 nds-5 shun ed by condensers 55 and ,56,-each .connectedhetween oir mndmgtm t ombo e-n (II-7.4.3, an r? Lil. T eii p o -terxn i i ach.secon an! W nd ng is conn c t -rou dt r g --tho orr ondi R ie he. ouble stida44.-,,- .Tha 1 o tese ob a n a m s eioaflco t- P 191: staple th ou h-t ancc 1 or as. i ad ust npo ono meter 59 or to the on rol an orth va ves ai fa ta sr t a or. he am li y n Valve-3 s Thisiv lta c. isa

l qq t u tqr 62. owb hsthe. i ut eras oft v ml .th tor t cq ss Q i,,. as .1 1 atr n to me silaan 3 T-l nd ans c 1 ha... .APP .Priat .smq hm Show may peincludedin theconductors .61;

68 according to" the usual ra t ce; qr vp (res is any amgcont th .inco ng slgnal H mm eame m ned lim ttov be empl X -.edv i. na out..-

1. r the secondary Wind g'p fir? a d 6,4 orr s ond-Q .i nc tw -d ea; n mitt? i1 int, e, tthandihalf. aof rtheidoubl' diod 44 The aectifiedz'signalstare-then applied-through' thiresistancet 5.1-zandvpotentiometem5 9:. to= theflow fre- Auencyt, mplifier valved!) andrthencexto-the out-- put; ten. .mals :96 and-J41; .aThe motentiometer 59 may he :adi ustedctoagive tan iappropriate i output level. At the same time the double diode 6| protillficsca suitable gain control voltage whicheis -ap- 'fi'ntbfl-sltlwcnrinputg grid ofrtheiamplifying 39 through the resistances 69 and conductor galve the;hrgher'rangezareibeing res theSW-tflh-fiizis set in'the upper position; an heiteqllcnqyrfiiztheroscillator ist set in order to btain; thehigher;z.intermediate frequency (560 's isno generated inthe upper-portion F I guenoy; changing :valvest 3:;and' amplified he mper portiom oh the amplifying valve39,

a is rectified in the right hand half of the doumed at on :.Ifhermectified -signal's are applied through resistance;58 rand adjustable potentiom etgn ti fl to-the l wirequen'cyvalvedi The gain 7 U H orcthe nppertporticn of the ham 1 {wine hex dc fluis:generatedcby the double:

nductor 521 vf-"i aizia'um': in Will hhllSfibfi SEBHrthBJtthGFtWO channels pros V $51.- byct elvalvesfiitand 39tare never.-employed d ode fi l .and applied through resistance 10 and lmu lfilte l sly. flForcthissneason ibis-immaterialthat the upper intermediate ferquency happens to t e the l th-harmonic ofgthe ;-lower intermediate firequ mv" .TIhe adyantagaof the arrangementsirdihfi? 1- SWEWGhiIlg in\zthesintermediate. ire. 17w detectingricimuits- .is :avoided; the and 1 .2 notnloeingpused in: .this r emsalready explained, and being pref- Tim: -1 2: i -W imshown connected inrseries withtthe:

e valve;39 .-may be: USEdrtOfiHtIOdll'Ct-E- toasts negativetteedpaok for; stabilizingthezoperation: of

or triode portion vof the valve withoutafiecting 1 wer ;t1;iode.\;t-lihe,,rwindih AI shoulm oficou-rse -i be; o poledz at theenergy isfedback in negative 9. 1% qzlzprden to obtain". the desired stabiliza-i smaybe omitted and replaced by onnection wp (5.1%"

di W loyanmother suitablerectifying devices Q H ts.such-astd ztc e ti x Qbcteddcd- 33, each such stage congpri m electrode e-errata e .similanyacmhervaive-39.

J smecessary. to 1 provide-lion stand-by: reqeptl ll- Q1 high, equate-y;amplifiers-rand:- selective circuitsadagtedior the range 2 tionc glearly the ropil;;A-L-.could.- alternatively be"- t thcatltainstormer 43 int-iwhichtcase the" A edloack will .be applied/to. the upper flofilfi ns ead? ,Q vliomthe zlowerntriode. :1 int-case it:- is not desired to use any negative feedback at l betievident tthatzei ther or bothoi the dipdes; may; be replaced by. two separate y umben of ampliftyingstages. tnot shown): ither ,tbeforec or after the :valver 25,000 kc. s. for ex- :1 iafigmhrisfisiiselective.andaamplify t rec fled ing circuits for the stand-by range 488 to 515 kc. s.

The carrier frequency oscillator 34 is as before, and is adapted for the range covered by the amplifier 3i. A switch 15 allows the antenna 30 to be connected to either of the elements 31 or 14, and another switch 76, which may be coupled to 15 is provided for disconnecting the oscillator 34 when the antenna 30 is connected to the element 14.

Referring now to Fig. 3, the valve 33 should be biassed in such a manner that the lower triode portion operates as a simple amplifier for the stand-by range 488 to 515 kc. s., while the upper triode acts as a modulator for the high frequency range as before, and the oscillator 34 is set to produce a suitable intermediate frequency such as 1,000 kc. s., to which the transformers 38 and 43 will be tuned. The transformers 31 and 42 will of course be tuned for the stand-by range. Selection by the double diode 44 for both ranges takes place as before.

The advantage of this arrangement is that the operator may set his apparatus to receive on some frequency in the high frequency range, and by simply operating the two switches 75 and 16 (Fig. 4) he may listen in at any time on the stand-by range without upsetting the normal adjustments of the apparatus for the high frequency range. It is to be noted that the switch 16 disconnects the oscillator 34 when the valve 33 is acting as an amplifier for the stand-by range.

It will be seen that the stand-by range is demodulated directly without the introduction of an intermediate frequency, and the two portions of the valve 33 perform different functions.

There are, of course, other ways in which the switching may be carried out. Another method utilizes the switches and 52 included in Fig. 3. In Fig. 4 the switch 15 may be omitted and the antenna 39 may be permanently connected to both of the devices 3| and 14. Then when it is desired to receive on the high frequency range, the switch 5| (Fig. 3) is opened, thus disabling the lower triode portion of the valve 33, and the switch 16 (Fig. 4) is left in the position shown. In order to listen in the stand-by range, the switches 52 and 16 are opened, and switch 5| is closed. The upper portion of the valve 33 is now disabled and the oscillator 34 is disconnected. The three switches 5|, 52 and 16 may clearly be mechanically connected so that all the necessary switching is performed simultaneously for each range.

Fig. 5 shows an example of a pentagrid valve arranged according to the invention to produce amplification in each of two entirely separate signal channels which may be used separately or simultaneously. The valve 39 with its tuned transformers 37, 38, 42 and 43 is arranged practically in the same way as in Fig. 3 except that the feedback coil 4i and the automatic gain control arrangements are omitted.

The first channel comprises an antenna 11 connected to receiving circuits represented by the block i8 and including ferquency changing means supplying a first intermediate frequency to the tuned transformer 31. This channel also comprises a detecting circuit 19 connected to the tuned transformer 42 and supplying the detected signals to the receiver 80. The second channel comprises the antenna 8|, receiving and frequency changing circuits 82 supplying a second intermediate frequency to the tuned transformer 38, and a detecting circuit 83 connected to the tuned transformer 43 and supplying the detected signals to the receiver 84. The two intermediate frequencies (which should preferably be well separated, as already explained) are amplified, by the respective portions of the pentagrid 39 as previously described, and are separately detected and supplied to corresponding receivers. The two signal channels so obtained are thus quite independent of one another.

Additional stages of amplification (not shown) may be provided by other valves arranged in the same way as the valve 39.

The circuits represented by the blocks I8, 19, 82 and 83 are not shown in detail, and they may be provided in any well known way.

In Figs. 3 and 5, the tuned transformers 31, 38, 42 and 43 represent only one possible form of selective circuits which may be used for keeping the two channels separate. Various other types of tuned circuits could be used, or wave filters of various configurations. What is required is that the selective circuits used in one channel shall transmit the waves corresponding to that channel and shall exclude those corresponding to the other channel.

Referring again to the valve 39 shown in Fig. 5,

' which is arranged as a simple amplifier in both channels if the output sides of the tuned transformers 42 and 43 were connected back to the respective input grids of the valve 39 in place of the transformers 37 and 38, instead of being connected to the circuits '8 and 79, as shown, then a double oscillator would result giving two different frequencies respectively determined by the tuning of the transformers 42 and 43.

A similar result would be obtained whatever type of selective circuit were employed, provided, of course, that the poling of the connections is such as to produce positive feedback, and that the gain of each of the triode portions is sufficient.

Fig. 6 shows an example of a double oscillator designed according to this principle. The valve 85 is a pentagrid as before. is closed, the anode of the lower triode portion is coupled back to the control grid by means of the inductively coupled coils 81 and 88 which are tuned by the condenser 89, the circuit being completed by the relatively large blocking condenser 99 and by-pass condenser 9|. In a similar way when the switch 92 is closed, the anode of the upper triode portion of the valve is coupled back to the control grid by means of the inductively coupled coils 93 and 94 which are tuned by the condenser 95, the circuit being completed by the blocking condenser 96. The upper and lower control grids are connected to the cathode by the high resistances 9! and 98. The high tension supply is intended to be connected to the terminals 99 and l 99 as indicated and the negative terminal I99 may be connected to ground.

Thus so long as the windings 81 and 88 and the windings 93 and 94, respectively, are poled so that positive feedback is obtained in both cases, then oscillations at one frequency determined by the tuning of the circuit 81, 88, 89 will occur when the switch 86 is closed, and may be obtained from a coil I ill coupled to the coils 81 and 88. Like wise if the switch 92 is closed oscillations at another frequency determined by the tuning of the circuit 93, 94, 95 will occur and may be obtained from a coil I02 coupled to the coils 93 and 94.

The oscillator of Fig. 6 may be conveniently employed in combination with Fig. 3 for the reception of continuous wave telegraphy. The output coils HM and H12 may be respectively connected to corresponding additional windings (not shown) When the switch 86 on the transformers 42 and 43 of Fig. 3. Assuming that the intermediate frequencies corresponding to the two continuous wave channels are 40 k. c. s. and 560 k. c. s. as before, then the lower and upper triodes in Fig. 6 may be tuned to oscillate at H and 561 k c. s. for example, giving a beat note of 1000 cycles with the above mentioned intermediate frequencies.

Then the switches 86 and 92 may be mechanically coupled with the switch 3| so that when receiving n the lower channel of Fig. 3 the switch 86 is closed, and when receiving on the other channel the switch 92 is closed. Another switch (not shown) associated with the oscillator 34 may if desired be also mechanically coupled to the switch 3| so that the proper local carrier oscillator frequency is obtained automatically in each case.

It will be evident, of course, that the oscillator of Fig. 6 may be designed to produce any desired pair of frequencies.

What is claimed is:

1. An electric wave translating arrangement for a wide band of frequencies comprising a thermionic valve having a cathode, an anode, and at least three grid electrodes mounted in order therebetween, a source of signals of a wide band of frequencies, a switch connected to said source and having two contacts connected respectively to the first and third of said grid electrodes counting from said cathode, and two selective filter circuits connected respectively to the second of said grid electrodes and to said anode, the filter circuit connected to said second grid electrode being designed to pass the lower frequencies of said band of frequencies and to exclude the higher band, the filter circuit connected to said anode being designed to pass the higher frequencies of said band of frequencies and to exclude the 1ower band, whereby said switch is positioned to make contact with said first grid contact for said lower frequencies and with said third grid contact for said higher frequencies, said arrangement passing said broad band of frequencies.

2. A translating arrangement according to claim 1, wherein each of said filter circuits comprises a band filter composed of a transformer having tuned primary and secondary windings, each of said filter circuits being designed to exclude frequencies passed by the other of said filters.

3. A translating device according to claim 1, wherein said signal source and said switch are connected in series between said cathode and the one of said grids to which said switch is connected and which further comprises a source of a constant frequency connected in series with said cathode and said signal source for beating said constant frequency with said signals.

4. A translating device according to claim 1, which further comprises a source of operating potential for said tube connected in series with said cathode and both said filter circuits, whereby said tube amplifies said signals.

JOHN DOUGLAS HOLLAND.

REFERENCES CITED The following referenlces are of record in the

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