US2270539A

US2270539A - Intertube intermediate-frequency coupling system

Info

Publication number: US2270539A
Application number: US330278A
Authority: US
Inventors: Leonard R Malling
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1940-04-18
Filing date: 1940-04-18
Publication date: 1942-01-20
Anticipated expiration: 1959-01-20

Description

Jan. 20, 1942.

L. R. MLLING l INTERTUBE INTERMEDIATE-FREQUENCY COUPLING SYSTEM Filed April 18, 1940 INVENTOR EONARD R. MALLING ATTORNEY ssuodsag ssuodssu Patented Jan. 20, 1942Y nv'rnn'runn murmura-FREQUENCY j.

coUruNG srs'rmu Leonard R.. Mailing, Dougiaston, N. Y., assignor to Hazeltlne Delaware Corporation, a corporation of LApplicmxnm April 18,1940, serial No. 330,278

(ci. usp-111) l Claims.

This invention relates generally to intertube intermediate-frequency coupling systems for modulated-carrier signal receivers and particularly to such coupling systems 4suitable for use in television signal receivers.

It is frequently desirable to provide an inter-v tube intermediate-frequency coupling system for a modulated-carrier receiver which includes a double-tuned selector circuit and means for modifying the response of the coupling system at a fixed frequency outside of, but adjacent to, the normal pass band of the selector. For instance, a trap circuit fixed-tuned to an undesired signal has been utilized in series with one of the windings of such a double-tuned selector to provide substantially infinite attenuation of such undesired signal. However, when a receiver including such a coupling system is to be constructed in accordance with the usual production methods, it is necessary to provide some way of adjusting the pass-band characterlstic of the other receivers which operate at a relatively high frequency to add any capacitance to the circuit. At the same time, it is desirable to provide a coupling system of the type under discussion, the band-pass characteristics of which can be adjusted without affecting undesirably the operation of a trap circuit associated with the selector.

It is well known, of course, that the band-pass characteristics of a double-tuned selector circuit, can `be adjusted by varying the mutual inductance between the windings of the selector circuit. However, in general, vthis has the effect of adjusting the band-pass characteristics of the selector symmetrically, -thus undesirably impairing the selectivity of the selector at the cutoi frequency other. than that being adjusted, and at the same time modifying the operation of a trap circuit associated with the band-pass selector. ForV this reason, this method of adjusting the band-pass characteristics of doubletuned selector circuits of the prior art to align th'e coupling system of such type with other selective circuits in a modulated-carrier signal receiver has not been satisfactory. I-t is, therefore, very desirable to provide a coupling system of the type under discussion in which these diiliculties are not present. Also, in television systems, intertube intermediste-frequency coupling systems have been utilized which comprise a double-tuned band-pass selector effective to translate the vision intermediate-frequency signals. However, in television systems the sound intermediate-frequency signals are conventionally transmitted on a carrier wave closely adjacent the frequency band within which the vision signals are transmitted. It is, therefore, frequently desirable to increase the response of an intertube intermediate-frequency coupling system, which includes a double-tuned band-pass selector for translating vision intermediate-frequency signals, at the frequencies occupied by the associated sound signals. If a tuned circuit is used for this purpose, it should be resonant at the intermediate-carrier frequency of the sound signals. However, the same diillculties mentioned above are present in an arrangement of this type; namely, it is diiilcult to adjust the band-pass characteristics of the double-tuned selector circuit provided for translating the vision signals so that the circuit is correctly aligned with other selective circuits of a television receiver without adding additional capacitance to the circuit. Also, if the mutual inductance of such a double-tuned band-pass selector isadjusted to procure alignment, the response of th'e tuned circuit provided to secure increased response to sound signals is changed, unless special precautions are taken which have :is nio; hitherto been known to those skilled in the y It is an object of the invention, therefore, to provide an intertube intermediate-frequency coupling system of the type under discussion in which the mutual inductance of a double-tuned selectorV circuit can be varied to align the circuit with other selective circuits of a receiver without substantially affecting the frequency of maximum response of a resonant circuit associated with' one of -the windings of the doubletuned selector circuit.

It is a further object of the invention to provide an intertube intermediate-frequency coupling `system including a double-tuned selector circuit having a trap circuit vconnected in series with one of its windings in which vthe response characteristic of the selector can be adjusted without varying substantially the effect of the trap circuit.

It is a further object of the invention to provide, in a superheterodyne receiver including an intertube intermediate-frequency channel adapted tc translate vision intermediate-frequency signals and associated sound intermediate-frequency signals, a double-tuned selector circuit effective to translate the vision intermediate-irequency signals and having in series with one of the windings thereof a parallel-resonant circuit eective to accentuate the response of the system to the sound intermediate-frequency signais, in which the mutual inductance between mediate-frequency signal, a substantial part of the capacitance being the inherent capacitance of the circuit and associated tubes. In a preferred embodiment of the invention, the capacitance isv wholly composed of the inherent capacitance of the tubes and circuits of the selector. A parallelresonant circuit is also coupled in series with one of the windings to modify the response of the coupling system primarily at afrequency outside of, but adjacent to, the desired pass band of the selector, the parallel-resonant circuit comprising capacitance of a value greater than ten times that of the above-mentioned capacitance. Means are further provided for adjusting the mutual inductance between the windings to adjust the coeilcient of coupling of the transformer within a range of i 10% thereby to adjust the band-pass characteristics of the selector without substantially altering the response of the coupling system due to the above-mentioned parallel-resonant circuit. 1

In a preferred embodimentof the invention, the parallel-resonant circuit is a trap circuit included in series with the primary winding of the transformer to provide high attenuation against undesired signals on an adjacent channel. Also, in accordance with a preferred embodiment of the invention, the receiver is a television receiver adapted to transmit vision intermediate-frequency signals and associated sound intermediatefrequency signals and the above-mentioned bandpass selector is adapted to translate the vision intermediate-frequency signals. In this embodiment of the invention, the parallel-resonant circuit may be coupled in series with the secondary winding of the coupling transformer and utilized to increase the response of the coupling system at the frequency of the sound intermediate-frequency signals, thus rendering at least a portion of the separate sound intermediate-frequency amplification usually provided unnecessary.

Also in accordance with a `feature of the invention, an intermediate-frequency signal-translating channel for a television receiver includes a plurality of intertube coupling systems coupled ,Y in cascade, each of which comprises, a transformer including closely-coupled primary and secondary windings individually adapted to .be tuned by capacitance to form a band-pass selector for passing vision signals of a wide frequency range, the capacitance being wholly composed of the inherent capacitance of the circuits and the tubes to which the windings are coupled, and means for aligning the coupling systems comprisingly solely means for adjustably fixing the mutual inductance between the transformer windings. By this arrangement the coupling systems can be aligned with each other and the overall-response of the intermediate-frequency coupling system can be adjusted to transmit with a uniform amplitude a desired wide band of picture signals.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a circuit diagram, partly schematic, of a complete television signal receiver system including an intermediate-frequency coupling system in accordance with the present invention, while Figs. 2 and 3 comprise graphs utilized to explain the operation of a portion of the circuit of Fig. 1.

Referring now more particularly to Fig. 1 of the drawing, the receiver there illustrated comprises a television receiver of the superheterodyne type including an antenna system III, II connected to a radio-frequency amplifier I2 to which are connected in cascade, in the order named, an oscillator-modulator I3, a vision-signal and sound-signal intermediate-frequency amplitler I4, a vision-signal and sound-signal intermediate-frequency amplifier I4', an intermediatefrequency amplifier and vision-signal and sound-k signal separator I5, a vision-signal detector and.

AVC supply I6, a video-frequency amplifier II, and an image-reproducing. device I8, forexample, a cathode-ray signal-reproducing tube. A linescanning generator I9 and a field-scanning generator 20 are also coupled to the output of detector I6 through a synchronizing-signal separator 2| and to the scanning elements of the imagereproducing device I8. In order to provide sound reproduction in the receiver shown, there is coupled to intermediate-frequency amplifier I5, a sound-signal intermediate-frequency amplifier 22, to which is coupled in cascade, in the order named, a sound-signal detector 23, an audio-frequency amplifier 24, and a sound-reproducing device 25. A bias is derived from unit I6 and applied over the conductor marked AVC to one or more of the tubes of stages I2-I5, inclusive, to control the amplification thereof inversely in accordance with the received signal strength. The stages or elements III-25, inclusive, excepting amplifiers I4 and I4 constituting the present invention and presently to be described, may all be of conventional well-known construction so that detailed illustrations and descriptions thereof are unnecessary herein. f

Referring briefly to the operation of the system just described, sound and vision modulatedcarrier signals intercepted by the antenna circuit I, II are selected and amplified in the radio-frequency amplifier I2 and supplied to the oscillator-modulator I3 wherein they are converted to intermediate-frequency signals which,`

in turn, are amplified in intermediate-frequency amplifiers I l and I4'. The signal output of amplifier I4 is further amplified in amplifier I 5, from which vision intermediate-frequency signals are delivered to detector I6. 'I'he modu-V lation components of this signal are derived in 2,270.51 j 3 In order to modify the response of the coupling the detector i3 and are supplied to the video= frequency ampliiier 1, wherein they are amsystem of the invention primarily at a iixed frepliiied and from which they are applied to a" brightness control elemento! image-reproducing quency outside of, but adjacent to, the normal pass band of the selector, and specifically in order device I3. Theintensity of the scanning beam -5 to provide a trap circuit effective to provide ahigh of device I3 is thus modulated or controlled in accordance with the video-frequency voltages impressed on its control electrode in "the usual manner. A control-bias voltage developed by the AVC supply Il and proportional to the averlo age vision-carrier amplitude and independent oi its modulation components'is supplied in the usual manner to the control grids of tubes in one or more of the stages |2- I5, inclusive, for

maintaining the signal input to detector I3 with- 15 in a relatively narrow range for a wide range of received signal intensities.

'I'he modulation signal output of detector I6 is also applied to synchronizing-signal separator 2| from which suitable synchronizing-signal go components of the signal are supplied tov linescanning generator I3 and field-scanning' generator to synchronize the operation of these circuits with corresponding apparatus at the transmitter. Saw-tooth current or voltage scanning waves are developed by generators |3 and 2li and these waves are applied to the scanning elements of device I3 to produce scanning fields, thereby to deiiect the scanning beam in two directions normal to each other so as to trace suc- 3 cessive series of parallel lines or fields on the target of the image-reproducing device' I3 toreconstruct the image. Sound intermediate-frequency signals derived from amplifier I3 'are further ampliiied in sound intermediate-freplanation of the operation of the portion of the quency amplifier 22and delivered to detector 23, wherein the audio-frequency components are derived. These components are, in turn, ampliiied by audio-frequency ampliiier 2l and deattenuation of undesired Signals on such nxed provide an increased response for the associated sound intermediate-frequency signals, there isv provided a parallel-resonant circuit 33, 43 connected in series withsecondary winding 34. Means indicated by an arrow are provided for adjustably fixing the mutual inductance between the windings 33, 3l. Trap circuitsl 4| and `l2 are Y included in the cathode circuits 'of tubes and 3|, respectively, to provide increased attenuation lof undesirable signals on adjacent channels.

"cn-cunts u anun as wen as circuits s1, :a and 33, 30 are preferably tuned by means of an adjustably-iixei magnetic core in'the inductance element of the circuit, the capacitance element in each case being xed. It will be understood that there may also be included in ampliiier I4 anintermediate-i'requency coupling system identical with that oi amplifler Il and that units Il and- II',- therefore, provide a plurality of similar intertube coupling systems coupled in cascade. Y

Reference is made to Figs. 2 and 3- forl an ex- -A the desired frequency-response characteristicof the band-pass selector, per se', of the interlivered to sound-reproducing device 25 for re- 4 mediatfrequency coupling System of the inproduction in a conventional manner. The AVC bias derived from AVC supply source I6 and apy plied to stages |2|5, inclusive, also serves tomantain the signal inputto detector 23 within vention. 'I'his response characteristic extends over a broad frequency range including a frequency range f1, fz over which it is desired to Y procure -a relatively high and uniform response relatively IlarlOW limits fOr 8 Wide range 0f lea by means ofthe double-tuned band-pass selector ceived signal intensities.

Referring now more particularly to the portion of the system of Fig. I embodying the present invention, there is provided an intertube intermediate-frequency coupling system for a modulated-carrier signal receiver for coupling the output circuit of a vacuum tube 30 of amplifier- I3' to the input circuit of a succeeding vacuum tube 3|. It will be understood that only the portions of the circuits of tubes 30 and 3| neces- 55 sary for an explanation of the present invention are shown in detail and that the other necessary portions of these two circuits may be in accordance with conventional design. The intermediate-frequency coupling system of the inven- 0 tion comprises a transformer including closelycoupled primary and secondary windings 33 and 3l individually adapted to be tuned by the inherent capacitance of the circuit and of the tubes to which they are coupled to form abandpass selector for passing vision intermediate-frequency signals. The tuning capacitances ofwindings 33 and 3l are indicated by the dotted-. line condensers 35, 36 for the reason that these capacitances may be comprisedin whole or in

circuit

33, 35 and 33, 36. The actual band-pass characteristic of the circuit before an aligning operation has been performed'thereon may be of the form illustrated by dashed-line curve B which comprises resonance peaks in the response characteristic which are widely separated in frequency. The band-pass characteristic of the circuit after the mutual inductance between

windings

33 and 34 has been adjusted to procure the desired response over the frequency range f1, l: is illustrated by the curve C, and is preferably such that the double peaks thereof are outside of the frequency range f1, fr. If -ampliiier llalso comprises an identical coupling system, its response characteristic may be aligned in a similar manner.

'I'he desired over-all response characteristic of the coupling system of the invention or of a vplurality of such coupling systems coupled in cascade is illustrated in Fig. 3. The curve of Fig. 3 comprises a portion of'increased response at a frequency f3 which is thecarrier frequency of the intermediate-frequency sound signals associated with the vdesired intermediate-frequency sound signals.- this increased response being due to the parallel-resonant circuit '33, Il which is resonant at the carrier frequency of the intermediate-frequency sound signals. The curve of Fig. 3 also has a high attenuation at'a frequency f4 which is due to

theV trap circuit

31, 33

trated in Fig. 1, it is usually found that, due to variations in the electrical constants of the elements which are assembled to produce the coupling system -and variationv of inherent wiring inductance and capacitance, the desired response characteristic illustrated by curve A of Fig. 2 is not obtained. Specifically, in the example chosen for illustration, the response characteristic of curve B may be obtained. Y'I'he procedurein procuring the desired over-all nesponse characteristic may be as follows: the desired maximum response in the over-all coupling characteristic illustrated in Fig. 3 at frequency f3 may be first procured Aby adjustably fixing the inductance of inductor 40 to tune the resonant circuit 33, 43 to the frequency fa and thereafter inductor 33 may be adjustably fixed to tune the resonant circuit 31, 38 to the frequency f4, thereby to procure maximum attenuation at frequency f4. If an attempt is then made to procure the desired over-all band-pass characteristic from the system by means of adjustment of trimmer condensers or other means used in prior art arrangements, it is found that the frequency of increased response f3 and the frequency of maximum attenuation ,f4 tend to vary with such adjustments.

Therefore, in accordance Vwith one feature of the present invention, the L/C or inductance-tocapacitance ratio of the parallel-

resonant circuits

31, 33 and 33, 40 is designed to benly a small fraction of that of the

resonant circuits

33, 35 and 34, 36 in series with which they are respectively connected. Under these conditions the mutual inductance between

windings

33 and 34 maybe adjusted over a range sufficient to adjust the coefficient of coupling over a range of i-10% to cause the band-pass characteristic of

selector

33, 35 and 34, 36, assumed to be represented by curve B to be broadened, as illustrated by curve C to include the range f1, fz within the portion over which it has a. maximum and substantially uniform response. This adjustment has substantially no effect upon the over-all response 'characteristic represented in Fig.' 3 at the fre-` quency of increased response f3 or at the frequency response of maximum attenuation f4. In other words, if the parallel-resonant circuits 31,' 33 and 33, 40 individually comprise capacitances of a value of the order of, or greater than, ten

times that of the capacitances 35 and-36, respectively,the circuit of the invention may be aligned with other selector` circuits of the receiver by adjustment of the

mutual inductance betweenwindings

33 and 34 without substantially altering the response of the coupling system due to the parallel-

resonant circuits

31, 33 and 39, 40. At the same time the over-all selectivity is not impaired at the cutoff frequencies due to the effect of tuned

circuits

31, 33 and 33.43.

It will be understood that, while

parallelresonant circuits

31, 33 and 39, 40 have been shown as being connected to the low signalpotential terminals of

windings

33 and 34, respectively, these parallel-resonant circuits may be connected to the high signal-potential windings of their respective circuits and that certain of the benefits of the invention still will be procured. However, if the parallel circuits are con- `coupling system similar to that of amplifier I 4 andhaving a band-pass selector response characteristic as illustrated by curve B of Fig...2, it can also be properly aligned by means comprising solely means for adjustably fixing the mutual inductance between the transformer windings in the manner just described.

. While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the artl that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true-spirit and scope of the invention.

What is claimed is: l l. An intertube intermediate-frequency coupling system for a modulated-carrier signal receiver comprising, a transformer including closely-coupled primary and secondary windings indivldually adapted to be tuned by capacitance to form a band-pass selector for passing a wide band intermediate-frequency signal, .a substantial part of said capacitance being the inherent capacitance ofthe circuits and the tubes to which the system is coupled, a parallel-resonant circuit effectively in series with one of said windings to modify the response of said coupling system primarily at a frequency outside of, but adjacent to, the desired pass band of said selector, said parallel-resonant circuit comprising capacitance of a value greater than ten times that of said firstmentioned capacitance, and means for adjusting the mutual inductance between said windings to adjust the coecient of coupling of said transformer within a range of i 10%thereby to adjust the band-pass characteristics of said selector without substantiallyv altering the response of said coupling system dueto said parallel-resonant circuit.

2. Anintertube intermediate-frequency coupling system for a modulated-carrier signal receiver comprising, a transformer including closely-coupled primary and secondary windings individually adapted to be tuned by capacitance to forma band-pass selector for Vpassing a wide band intermediate-frequency signal, said capacitance being composed wholly of the inherent capacitance of the circuits and the tubes to which the system is coupled, a parallel-resonantcircuit effectively in series with one of said windings to modify the response of said coupling system primarilyat a frequency outside of, but adjacent to, the desired pass band of said selector, said parallel-resonant circuit comprising capacitance of a value greater than ten times that of said firstmenticned capacitance, and means f'or adjusting the mutual inductance between said windings to adjust the coeiiicient of coupling of said transformer within a range of thereby to adjust the band-pass characteristics of said selector without substantially altering the response of said coupling system due to said parallel-resonant circuit.

3. An intertube intermediate-frequency coupling system for a television receiver adapted to translate -both sound and vision intermediatefrequency signals comprising, a transformer including closely-coupled primary and secondary windings individually adapted to be tuned by capacitance to form a band-pass selector for passing vision signals of a wide frequency band, said capacitance being wholly composed of the inherent capacitance of the circuits and the tubes to which the system is coupled, a parallel-resonant circuit effectively in series with said secondary windingto increase the response of said coupling system4 primarily at the carrier frequency of said sound intermediate-frequency signals, said parallel-resonant circuit comprising capaciresponse of said coupling system due to said parallel-resonant circuits.

6. an intertube intermediate-frequency coupling 'system for a modulated-carrier receiver comprising, a transformer including closely-coupled primary and secondary windings individualv ly adapted to be tuned by capacitance to' form a band-pass selector for passing a ,wide band intermediate-frequency signal, said capacitance being wholly composed of the inherent capacitance of the circuits and the tubes to .whichv the system is coupled, and a parallel-resonant circuit tance ofa value greater than ten times that of said mst-mentioned capacitance, and means for adjusting the mutual inductance between said windings to adjust the coefficient of coupling of saidtransformer within a range of `\i f10% thereby to adjust the band-pass characteristics of said selector without substantially altering the tenuate theresponse ofisaid coupling system primarily at a fixed frequency of .an undesired signal outside of, but adjacent to, the desired pass band of said selector, said parallel-resonant circuit. `comprising,capacitance of a value greater than ten times that of said rst-mentioned .capacitance, and means for adjusting the mutual inductance between said windings to adjust the coeicient of coupling of said transformer within a range of thereby to adjust the band-pass characteristics of said selector without substantially altering the response ofv said coupling system due to said parallel-resonant circuit.

5. An intertube intermediate-frequency coupling system for a modulated-carrier receiver adapted to translate associated vision and sound intermediate-frequency signals of a television signal comprising, a transformer including closely-coupled primary and secondary windings individually adapted to 'be tuned by capacitance to forma band-pass selector for passing a wide band intermediate-frequency vision signal, said capacitance being wholly composed of the inherent capacitance of the circuits and the tubes to which ghe system is coupled, a parallel-resonant circuit effectively in series with said primary winding to attenuate the responseof said cou'- pling system at a frequency corresponding to the sound intermediate-carrier frequency of an adjacent television signal, and a parallel-resonant circuit coupled in series with said secondary winding to increase the response of said coupling system primarily at the intermediatecarrier frequency of the associated sound signals, said parallel-resonant circuits eachoomprising capacitance of a value greater than ten times that of said mst-mentioned capacitance, and means for adjusting the mutual inductance between said windings to adjust the coeicient of coupling of said transformer within a range of il0% eilectively in series with the low-potential ter- .minal of one of said windings to modify the respouseof lsaid coupling system primarily at a frequency-outside of, but adjacent to, the desired pass band of said selector, said parallelresonant circuit comprising capacitance of a value greater than ten times that of said ilrstmentioned capacitance, and means for adjusting the mutual inductance between said windings to adjust the coefficient of coupling of said-transformer vwit-hin a range of :10% thereby to adjust the band-pass characteristics of said selector without substantially altering the response oi said coupling system due to said parallel-reso- 7. An intermediate-frequency signal-translating channel for a television receiver including a pluralityof intertube coupling systems coupled in cascade, each of which comprises, a transformer including closely-coupled primary and secondary windings individually adapted to be tuned by capacitance to form a band-pass selector for passing vision signals of a wide frequency range, said capacitance being wholly composed of the inherent capacitance of the circuits and the tubes towhich the system is coupled, a parallel-resonant circuit effectively in series with one of said windings to modify the response of said coupling system primarily at a frequency outside of, but adjacent to, the .desired pass band of said selector, said parallel-resonant circuitcomprising capacitance of a value greater than ten times that of said first-mentioned capacitance, and; means for adjustably fixing the mutual inductance between said windings to adjust the coeillcient of coupling of said transformer within a range of :10% thereby to adjust the band-pass characteristics of said selector without substantially altering the response of said coupling system due to said parallel-resonant circuit.

8. An intermediate-.frequency signal-translating channel for a television receiver including a thereby to adjust the band-pass characteristics plurality of intertube coupling systems coupled in cascade, each of which comprises, -a transformer including closely-coupled primary and secondary windings individually adapted to be tuned by capacitance to form a vband-pass selector for passing vision signals of a wide frequency range, said capacitance being wholly composed of the inherent capacitance of the circuits and the tubes to which said windings are cc upled, and means for 'aligning said coupling systems comprising solely means for adjustably xing the mutual inductance between said windings, whereby said coupling systems can be aligned with each other and the over-all response of said intermediate-frequency coupling system can be adjusted to transmit with a uniform amplitude a desired wide band of picture signals.

9. An intermediate-frequency coupling system for a television receiver including a plurality of intertube coupling systems coupled in cascade, each of which comprises, a transformer including primary and secondary windings having a coeiilcient of coupling therebetween of over 40% and individually adapted to be tuned by capacitance to form a band-pass selector for passing vision signals, said capacitance being wholly composed of the inherent capacitance of the' circuits and the tubes to which said windings are coupled, and means `for aligning said coupling systems comprising solely means for adjustably ilxing the mutual inductance between said windings to vary the coemcient of coupling between said windings over a range of :10%, whereby said. plurality of intertube coupling systems can be aligned to pass a predetermined desired band of frequencies with a substantially uniform response.

l0. An intermediate-frequency coupling sys-` tem for a television receiver including a plurality of intertube coupling systems coupled in cascade.

each of which comprises. a transformer including closely-coupled primary and secondary windings individually adapted to be tuned by said capacitanceto form a band-pass selector for passing vision signals of a wide frequency range. said band-pass selector having resonance peaks jin its response characteristic which are widely separated in frequency, and said capacitance being composed wholly of the inherent capacitance of the tube circuits in which said windings are coupled, and means for aligning said Icoupling systems comprising solely means for adjustably xing the mutual inductance between said windings to adjust said intertube coupling systems to pass a relatively wide band of frequencies between said resonance peaks with substantially uniform response.

- LEONARD R. MALLING.