US2248343A - Carrier wave system - Google Patents

Description

July 8, 1941- H. F. ELLIOT-r 2,248,343

CARRIER WAVE SYSTEM Filed Aug. -25. 1934 s sheetssheet 1 Ffegweraay @suon/99g INVENTOR ATTORNEY July 8 l941- H. F. ELLIOTT 2,248,343

CARRIER wAvE SYSTEM y Filed Aug. 25. 1954 s sheets-sheet 2 INVENTOR BYP TTORNEY July 8, 1941- H. F. ELLlo-r'r 2,248,343

' CARRIER wAvE SYSTEM Filed. Aug. 23, 1934 3 Sheets-Sheet 3 INVENTOR L4 BY K iiers and selectors. in order that the knob controlling these functions may be operated to obtain the sensitivity, selectivity and quality desired Without upsetting other relations in the receiver it is important that effective and automatic means be provided for holding constant the level of the signals applied to the detector or demodulater, so that the level of the signals delivered to the loudspeaker or succeediirT apparatus will be maintained constant and not disturbed the other adjustments. The provision of such means and its coordination with the sensitivity, selectivity and quality control is an important feature of my invention. For controlling volume or output suitable manual means preceding or succeeding the detector or demodulator may be used. A compensator for raising the relative level of the low frequencies may be interlinked With the volume control if desired. A suitable control knob for tuning the variable capacitors or other earlier selector means will of course be used and switches may be provided for selecting various Wave bands if desirer.. `deans for suppressing carrier noise While tunirnr may, of course, be provided when desired.

Figure 2 shows one form of circuit control which may be utilized for carrying out the sensitivity, selectivity and quality control features of my invention. Tube l represents a carrier frequency amplifier preceded by a tuned selector circuit 2 and succeeded by another such circuit 3, the ci cuits eing tuned by variable capacitors 4 and 5 which have a common tuning control 6. In the arrangement illustrated, the inductors 'l' and 8, have taps and switches 9 and le with a common control il, whereby the inductance of circuit may be increased While at the same time the indu-stance of circuit 3 is decreased. Two sets oi variable resistors l2 and i3 are provided and so arranged that the resistance of circuit is increased as its inductance is increased, While the resistance of circuit 3 is increased as its inductance is decreased. Il the circuits are designed so that each is eX- actly resonant to a given carrier frequency when the switches S and lil are in the positions shown in full lines, the ampliiier stage comprising tube l and circuits 2 and 3 will tien have a comparatively sharp resonant curve as illustrated by E .in Fig. to the able values are chosen for the added and subtracted inductances and the added resistances, a responsive curve shaped like that shown at H in Fig. 4 may be obtained. Similarly, intermediate curves as shown at F and G may be obtained by suitable choice or inductances and resistances. hus the amplifier stage may be made highly senr .Je and highly selective when operating on curve E, and progressively less sensitive and less s"lectivo when operating upon curves ill, G .d Carrier frequency ampliiiers may thus be proportioned so that relatively narrow bands are passed in the selective position While bands sui able for high quality reproduction of speech, music or other intelligence are passed in the less selective positions. The couplings ctv/een the primarie. lil and l5 and their respective secondary coils i and 8 may be d adjusted in xed or may be made variable an coordination with the motion of sivitc es 9 and li] as indicated by the arrows and dotted lines when necessary to obtain the desired electrical relations and response characteristics. If capacitive coupling is used, either in conjunction with inductive coupling or separately, this may also be varied if necessary.

An ampliiier stage of the type just described is suitable for carrier frequency amplification in transmission systems, receivers or transmitters of a variety of forms. It is Well suited, for example, for the radio frequency stage, or stages, of either tuned radio frequency or superheterodyne types of radio receivers. It may be used also for the intermediate frequency stages of superheterodyne receivers.

Another circuit arrangement suitable for a variety of services and especially well adapted for intermediate frequency stages in superheterodyne receivers is shown in connection With tubes l5 and I7 in Fig. 2. These tubes are shown as interconnected by a fully tuned carrier frequency transformer, such as is Widely used in broadcast receivers for the intermediate irequency stages. The primary and secondary I8 and I9 have tuning capacitors 2U and 2l, which, may be of any of the usual types. Supplementary adjustment for controlling the band Width and tuning characteristics of the stage may be incorporated directly in the main tuning elements, coils I3 and i9, capacitors 29 and 2l, and coupling 2S, or alternatively, supplementary elements such as variable capacitors 22 and 23 and variable resistors '24 and 25 may be employed, with suitable common control 21. A great variety of arrangement may be employed to give the desired result, which is a family of characteristic curves of the type shown in Fig. 4. Thus, a curve of the type given at E may be obtained by employing low loss capacitors and inductors at Eil-2l and iti- 19, relatively loose coupling at 2G and very high resistances, or none at all, at 24 and Z. he tuning characteristic may then be broadened by increasing the coupling at 28 and suitably lowering resistors 24 and/or 25, giving progressively curves as shown at F, G and H. If required, capacitors 22 and 23 may be used for supplementary adjustment the one being increased while the other is decreased. The resistors 24 and 25 may be replaced by suitable series resistors if desired.

For the control of the low frequency response characteristics oi the receiver, any suitable form of band filter, tone control or the like may be employed, using either continuous varia-tion or stepwise control with switches. By Way of eX- ample, tube 28 in 2 may be an audio frequency amplifier in a broadcast receiver in which tube l serves as a radio frequency ampliiier and tubes i6 and il operate at intermediate frequencies. Tube 28 may have suitable filters in ei her its input or output circuits, or both. In Fig. 2, an output tone control lter is shown, comprising inductor 2Q, capacitor 30, potentiometer 3! and transformer 32. The control 33 of these elements be interlinked with the controls Il and 2T of the preceding stages that the band Width, selectivity, sensitivity tone quality are all varied simultaneously in suitable relation. Ii it is desired, the sensitivity varia-tion arising from the change of resistances associated with the selector circuits of the carrier frequency stages may be supplemented with variation of the amplification of the tubes employed by changing the potentials on the elements of the tubos as by control 34 operating potentiometers 35 and e5. For eX- ample, if pentcde type multi-mu tubes are employed for the carrier stages, the amplification and sensitivity may be controlled by adjusting the potentials on any or all of the grids. Potentiometer 35 may be employed to adjust the relative levels of the control grids and cathodes and 36 may be used on either the suppressor grids or screen grids. Alternatively a third potentiorneter may be utilized and all three grids varied. The anode-cathode potential may also be used for control purposes ii desired. Added controls of one or more of these types may be used Where necessary to keep the level of signals at the demodulator Within the desired limits, the rate of variation of the potentiometer or resistor being proportioned so that this objective is attained.

Figure 3 shows the circuits of a radio broadcast receiver of the superheterodyne type embodying my invention. Tube 51 is a radio frequency ampliiier, tube a frequency converter or first detector, tube 39 an oscillator, tube Il@ an intermediate frequency amplifier, tubes il and fait are governor or automatic gain control tubos, tube 43 is an automatic gain compensator operating at intermediate carrier frequency, tube is a deniodulator, tube fili is an audio ampliiier, tube it is the usual rectil. er for energizing the anode and grid circuits and Vi is a tuning indicator. The functions performed by the foregoing tubes are similar to those of standard superheterodyne receivers except the governor and compensator tubes which, with the associated circuits, operate to give signals of very constant level at the dernodulator rEhe manner in which this is complished is described in detail in my copending application, Serial Number 703,054 filed Dec. i9, 1933, and therefore need not be gone into here beyond stating that the governor tubes il and i2 receive carrier wave signals from the intermediate frequency ampliiier amplify and rectify these signals and supply potentials to the gain control circuits of tubes 33 and 455i. This much of the system constitutes a carrier Wave amplifier with automatic gain control delivering signals at the output of tube it Whose level rises slowly as the strength of the signals applied at the input of tube 3l increases. Compensator tube i3 which is interlinked with governor tubes il and Il?, receives the slowly changing carrier Wave signals delivered hy tube d@ and automatically compensates for the variations, delivering carrier Wave signals substantially free from distortion or change in level to the deniodulator Referring now to the elements associated with the coordinated sensitivity, selectivity and quality control shown in Fig. 3, the radio frequency amplifier 3l has a tuned input it and feeds into a tuned output circuit Il@ through the medium ci coupling means which may be of any forni suitable to the frequency and operating conditions. When the sensitivity, selectivity, quality control 5@ is adjusted for maximum sensitivity and selectivity, circuits and itil are both tuned closely to the incoming carrier frequency and have minimum damping. AS the control is shifted to decrease sensitivity selectivity and to increase the width of the admitted band of irequencies. the resonant period oi one of the circuits is increased While the other is decreased and the damping of both is increased, that is, their losses are increased. rlhis action is similar to that descriced for tube i in Fig. 2, but the case shown in 3, continuously variable means instead of switches are provided for changing the inductances and resistances of the circuits. There are a wide variety of Ways ci accomplishing this; the inductors may be inade Wholly or partially in the form of variometers, one of which is increased as the other is decreased; the inductors may be constructed with short circuited discs or rings which advance into or recede from the coils to decrease or increase their eTective inductance; alternatively the capacitances of the circuits may be increased and decreased by manipulating the main tuning .capacitors or by operating upon capacitors in shunt or series relation thereto. The damping of the circuits may be varied simuleously with the change in resonant period by either shunt or series resistors of suitable values and suitable resistance variation characteristics.

Wo very simple and eiective methods of accomplishing the desired continuous variation in the resonant periodic and dampings of the circuits are shown in .Figures 5 and 6. Referring first to numeral lil indicates a coil form and 52 is coil ofv suitable inductance wound thereon. A laminated iron core s3 is provided and so arranged that it be drawn into the magnetic field of the coil or withdrawn therefrom by means of a small rod 5ft or other suitable mechanisin. When core 53 is outside the field of the coil 52, it of course no influence thereon, but when it is drawn into the `held as shown in dotted lines at 3', it will have an influence upon the effective inductance and resistance of the coil the nature of this influence will depend upon the size and shape of the larninations, their thickness, their material, and the frequency of the current in the coil. If the laniinations are of very thin iron, or if a core of very nely divided iron or other magnetic material is used, the inductof the coil will be materially increased and the resistance will be only nominally increased as the core is drawn into the coil. If thicker laminations are used, the increase in inductance will less and the increase in resistance will be greater. If a solid core is used, the inductance may even be reduced While the resistance is increased, both due to the ei'lect of eddy currents in the core. By a suitable choice of material, size thickness of lamination, it is therefore possible to increase the inductance and the resistance each in suitable proportion to obtain the desired tuning characteristics.

if circuit du has its inductance and resistance increased by operation in a given direction of control then circuit i9 will require a decrease of inductance and an increase of resistance. Fig. t5 shows one simple and effective Way of accomplishing this. Numerals 55 and 5t indicate a coil forni and a coil respectively. A disc, or short-circuited ring, or a Winding of suitable resistance material is shown at 5i with operating rod 58. This has no effect on the coil When out of the field thereof, but when drawn into the eld as shown in dotted lines at it decreases the effective inductance and increases the eifective resistance of the coil. L? the material is of lour electrical resistance. a considerable decrease in inductance may be obtained with very little increase in effective resistance, but if higher resistance material is used the change in inductance will be less marked and the ease in resistance greater. By suitable choices of materials, sise, and motions for core 53 and ring 5l', coils 52 and 5t may have their inductances increased and decreased and their resistances increased so that a family of tui ng curves like those shown at E, F, G and H Fig. 4 may be obtained.

The motion of the cores discs may be worked out in a great variety of ways, by levers, earns or other linkages. One simple system which permits the coils and their cores, shields and other parts to be located in any desired arrangement upon an amplifier base or chassis is to use flexible wire controls as indicated in outline at 59 and 59 in Figures 5 and 6, together with suitable cams and followers as shown in outline in Fig. 8. Numeral 60 represents a shaft carrying cams, shown at 6l and 6l', with followers 62 and 02 which in turn manipulate flexible wires or other linkages 63 and 63', leading to the elements to be operated. Such a system may, of course be designed to give almost any desired law of motion. Shaft B may also operate one or more reactors, resiste-rs, potentiometers or other elements indicated in outline at 64. If desired, any or all of these motions may be interlinked with other motions in the apparatus to obtain desired mutual relations. For example, shaft 65, controlling one or more reactors, resistors, potentiometers or other elements within the set, indicated in outline at 66, may be connected with a cam 51, follower 68, link 69 and auxiliary cam 'l0 in follower 62, so arranged that the motion of 63 depends upon the motion of both shafts 60 and G5. An example of the utility of such an arrangement is the case wherein shaft 55 operates capacitors used to tune radio frequency amplifier circuits 48 and 49, Fig. 3, while cam follower 62 and control 63, control core 53 and ring 5l, Figures 5 and 6 which regulate. the width of the band passed by the amplifier. By a suitably shaped auxiliary cam at 10, the motion of 63 may be made such that bands of substantially the same numerical width are passed by the amplifier over its whole tuning range even though the circuits have quite different constants at different points in the range. Another application of such an arrangement would'be the interlinkage of a volume control and a band width control. Usually, however, such elaborate mechanisms are unnecessary, and simple shafts, cams or levers may be used to operate core 53, ring 51 and other elements which are to be controlled simultaneously with them. The options which are available in the sizes, shapes and materials of the moving elements, such as 53 and 5l'usually make it possible to obtain the desired operating relations without resorting to elaborate motion mechanisms.

Depending upon tube characteristics and circuit requirements, any suitable form of coupling may beL used between coils 52 and 5E and the associated tubes and input and output circuits.

If variable inductive coupling is indicated this i may be operated in conjunction with controls '59 and 59', or separate controls cooperating with the control mechanism 5S may be used. If variable capacitive coupling. is employed any suitable form may be used and interlinked with control 50 directly or through cams.

Fig. 7 shows in outline a form of tuned transformer which may frequently be found very effective for amplifier stages such as those shown at il, l2 and 13 in Fig. 3. One coil 14, usually the primary, may be mounted upon a suitable fixed support as shown in Fig. 7. The other coil 'l5 may be made movable and connected through a suitable operating linkage as 59", to the central control 50. When sharp tuning is desired to give high sensitivity and selectivity, coil 75 may be in the position shown in full lines, with a resultant tuning curve of the type shown at E or F in Fig. 4. When less sensitivity and selectivity and. a broader band of passed frequencies are desired, the coil 15 may be moved toward the position shown in dotted lines at 15'. This brings its eld into close relation with 15 which may be an open or partially open circuit tertiary winding of resistance material or a split ring of iron or other suitable material. Often a simple split iron washer will be found satisfactory. It may be located between coils 'I4 and l5 in such a position that it only nominally effects the coupling and losses when the coils are separated as shown in full lines, but so that material losses are introduced into the system when tighter coupling is employed. The double humps which would accompany the closer coupling are then smoothed out and tuning characteristics of the type shown at G and H in Fig. 4 are obtained.

For tuning the coils 14 and 'l5 any suitable form of capacitors may be used as for example the variable air and mica dielectric capacitors frequently employed in superheterodyne indicated in outline at 1l and 'Il' in Fig. '7. A base for the capacitors is outlined at 11 and a support for the coil and ring is indicated at 18. Obviously an almost endless variety of arrangements may be employed for the details of mechanisms such as are outlined in Figures 5, 6 and 7. No attempt is made to go into such details here since their inclusion is not necessary to an understanding of the principles involved and would only add confusion to the drawings.

In the circuit diagram, Fig. 3, the tuned transformers 1l, l2 and 'I3 are shown as comprising two coils with adjustable tuning capacitors, variable coupling and variable resistance. The combination shown in Figure 7 gives results equivalent to such a circuit arrangement. Obviously, if desired, two simple variably coupled coils may be employed and variable resistors either in series or shunt relation to either or both circuits may be used to adjust the losses and smooth the tuning-humps in place of the ring or winding 16, Alternatively, coils, cores and rings of the type shown in Figures 5 and 6 may be utilized, or tapped coils and switches as shown at 9 and I'D in Fig. l may be used. The objective is that each circuit employed in the amplifiers and selectors operating at carrier frequencies shall be coordinated with each other circuit in the provisions for adjusting the width of the admitted side bands and that lters or tone controls used in the audio frequency amplifiers shall be coordinated and controlled with the carrier frequency band varying mechanism.

In a carrier wave device employing several frequencies such as the superheterodyne receiver shown in Fig. 3, the numerical width of the band passed should preferably be approximately the same for each unit. For example when the radio frequency amplifier 31 and associated circuits 48 and 49 are adjusted to pass side bands 8,000 cycles Wide, the intermediate frequency amplifier 40, compensator 43 and associated transformers 1l, 'l2 and 13 should also be adjusted to pass side bands of approximately 8,000 cycles. Likewise the audio frequency filters or tone control circuits associated with the demodulator 44, and audio amplifier 45 or subsequent audio frequency apparatus should be adjusted to pass approximately 8,000 cycles. When, as in the superheterodyne, more than one carrier frequency is employed, it will be evident that the band passed expressed in percentage relative to the associated carrier frequency becomes larger as the carrier frequency becomes lower and is in fact inversely proportional to the carrier frequencies. For examplaa side band of 8,000 cyclesmaybe 0.8% of' a carrier frequency of 1,000,000 cycles in the radiofrequency-amplifier 31, and 5% of acarrier frequency of 160,000 cycles in theY intermediate frequency amplifierd. It is not essentialthat absolutely mathematical precision be attained in coordinating the relations betweeny the widths' of thebands` passed and the cut' off frequencies* ofv the variousv sectionsandstagesV of the selectorsvand amplifiers. The coordinationV should besuch, however, that each section performs-itsA own-functions properly in each position and condition of adjustment. For example, if thecoordinating controll isy set so that side bands ofv 8,000-cycles are admitted, it may be desirabletohave the audio frequency filter cut off quite; sharplyabovefthis frequency so as to suppress 10,000Y cycles carrier whistles and other beats or overlapping fringes between side bandsv of adjoining carriers. At the same time, the intermediatefrequency section may be' adjusted so as-to attenuate adjoining carriers 10,000 cycles from the admitted carrier and to suppress alsoy thesidebands associated withthe lower frequency modulations of the adjoining carriers. The radio frequency amplifier section may be required to aid in these selections or its main function may bethat ofy suppressing the image frequencies whichv arel a problem in superheterodyne vtypey receivers.

InA a radio receiver or other apparatus of. the type described, i-t is important to have mea-nsof gain controlwhich` automatically hold the output of the system substantially constant over. Wide variations of-input and also over wide variations of sensitivity asldeterrni-nedby the controls. Also it is important to have suitable meansl for indicating the optimum setting of the tuning. control. The method of automatic gainv control and the tuning indicator shownY inr Fig. 3l are especially well suited toI accomplishthese objectives. The method of automatic gain control, which is described in detailin my copending application S. N. 703,054 filed Dec. 19, 1933.to which reference has previously been made, holds they input to theY demodulator, and. therefore the output, very constantover a. wide range of input potentials. It also serves to; hold thelevel at the demodulator very constant over a wide range of adjustment of. the sensitivity-selectivity-quality f control. As described further hereinafter, suitable supplementary adjustments coordinated with this control may be provided to maintain proper balance in the gain of the various amplifier, governor, and'. compensator tubes ifnecessary. However, the automatic gain control system can usually be porportionedr to maintain the conditions at the `demodulator sufliciently constant without supplementary controls. In connection with the tuning indicator, the resonant circuits which interlink the governor amplifier 4|, and the governor rectier 42, may be made highly selective and the coupling between them set so that a single sharply defined peak resonant at the carrier frequency is obtained. By having these circuits sharply tuned to the carrier at all times, a tuning indicator, as 41, associated with any portion of the circuits having currents or potentials responsive to the output of the governor will indicate when the receiver is tuned to a carrier regardless of the adjustment of the sensitivity-selectivity-quality control. The circuits in the amplifiers, such as' 48, 49, 1|, 'l2 and 13 may be broadened to pass bands on either side of the carrier but with the circuits. associ'ated with the governor sharply tuned to the carrier at all times, the tuning indicator` will show when the tuning control is centered-on the carrier. Obviously many forms ofv tuning indicator, either instruments or tubesi may be used. The example shown in outline at 41fis a gaseous glow indicator tube with supplementary electrodes suitable for suppressing carrier-noises when tuning. Other indicators or otherfforms of noiseA supprcssionfmay ofcourse be employed, as desired;

In connection with the audioY frequency apparatus, a great variety of lters and tonek control circuits areavafilab-leandy the choice will depend upon ther operating conditions and permissible expenditure. Often a simpletone control or a single section filter of onefof the well known types will suffice. In other casesfa'more elaborate filter with several sections having eithertapped or Variable inductors, capacitors and resistors maybe used. In Figure 3, a filter IS of two sectionsemploying variable reactors and a variable terminaly load resistor is shown. Ordinarily only a portion ofthe elements would be madevariable, the choice depending upon the characteristicsto be obtained and the iactorsof cost and convenience. The filter may be located at any convenient poi-nt in the audio system, its characteristics being proportioned to match the terminalconditions. l v f In coordinating the control of sensitivity,-'selectivity and quality of reproduction, it may be desirable to interlink with the centralcontrol 50, one or more of the elements which determine the gain and operating characteristics of some of the amplifier, converter, governor or compensator tubes; Examples of suchinterlinkage are shown in rheostat 80 which may be used to control the gain of tubes '5l and 40, potentiometer 8l controlling the governing action on tubes 37, 38 and 40, potentiometer 82 and resistor 83 associated with compensator tube 43?, and Apotentiometers il@ and 85 controlling grid and screen potentials in any or all ofA the tubes. Ordinarily these added controlsI will not be required sincethe losses introduced in the various selector circuits in increasing the passed' band widths automatically reduce the sensitivity as the selectivity is reduced. However, directly controlled or cam operated variable resistors and potentiometers may be employed when the need for refinement in operating conditions indicates their necessity. I-n some cases, a suitably proportioned potentiometer or resistor at 32 and/or 83 may bel desirable for controlling the output of compensator l3- when control E0 is operated.

t will be obvious that an almost endlessvariety of modifications may be employed in carrying out details connected with various applications of the invention. For example, in some instances it may be desirable to use switches and tappedfor lumped elements of reactance and resistance throughout. In some cases, it will be desirable to use only continuously variable means while in still other cases a combination of switching means and continuously variable elements may be found best. In some instances it may be de'- sirable touse switches with contacts having varying or overlapping arcs of rotation in combination with continuously variable apparatus` at other points. When movable cores or rings or coils are used, these may often be mounted directly on a coordinating control shaft which also operates variable resistors, potentiometers, reactors or switches for changing other elements.

Again a single shaft carrying suitable cams may be used to control the motions of cores, rings and coils in the carrier frequency sections in unison with resistors, reactors and potentiometers of suitable proportions in the audio frequency section. In some cases it may be found convenient to vary couplings or introduce losses by variations in capacitance or through suitable dielectric variations. Often circuits such as are shown in connection with intermediate frequency amplifiers hereinbefore will be found useful for radio frequency stages and vice versa. The examples of applications of the invention have all been given in connection with radio receivers, but its methods and means are not limited to this use but may be applied to repeaters, filters, transmitters and transmission systems of all sorts.

It may be well to point out that the arrangements of tubes shown in the various figures are subject to wide variations. For example, in many instances, several functions may be combined in a single tube where two or more tubes, each with its own function, have been shown in the diagrams for the sake of clarity. By way of examples, the frequency converter tube 38 and the oscillator 39 may be combined in any of the several ways now in common use; the amplifier and rectifier functions of tubes 4l and 42 may be combined by utilizing combination tubes now available; also tubes 43 and 44 may sometimes be combined. Rectiers of the copper oxide or other types may be substituted for tubes 42 and 44 if desired. The volume control for the audio amplier 45 may have either electrically or mechanically operated means for compensating tone quality as volume if varied. My invention is not limited to the particular methods and systems disclosed but covers broadly the contributions to the art defined in the appended claims.

Having thus described my invention, I claim:

l. A radio wave system comprising means for amplification and selection in successive stages operating at a plurality of frequencies, variably coupled and variably damped selectors for varying and coordinating the passed band widths in at least two of said stages and at least two of said frequencies separately, variable cut-off audio frequency tone control means, and single control means for operating the selectors simultaneously and in unison with said tone control means.

2. In combination in a carrier wave system, means for selecting waves at at least one carrier frequency, variably coupled and variably damped means for varying the widths of the bands passed at said frequency, separate tone control means for varying the cut-off at audio frequency, and single control means for controlling and coordinating said varying means and said tone control means.

3. In a superheterodyne radio receiver having separate means for selection and amplification at radio frequency, intermediate frequency and audio frequency, variably coupled and variably damped means for varying the band widths passed at at least one frequency, tone control means for varying the cut-off at audio frequency, and single control means for operating said varying means in coordination and in unison with said tone control means.

4. In a radio receiver having variably coupled and variably damped carrier frequency selecting means, demodulating means and separate variable audio frequency selecting means, single control means varying the width of the band 75 passed by the carrier frequency selecting means in unison and in coordination with tone control means varying the audio frequency cut-off.

5. In combination in a radio receiver, variable cut-off audio frequency tone control means, variably coupled and variably damped carrier frequency selective means, and single control means for operating the tone control means and adjusting the width of the band passed by the carrier frequency selective means by varying both the coupling and the damping in proportion to the cut-off period of the tone control means.

6. In a superheterodyne radio receiver having a radio frequency amplifier with tuned input and output circuits, an intermediate frequency amplifier with variably coupled and variably damped tuned coupling transformers and an audio frequency amplifier with filter circuits for varying the frequency response characteristic thereof, single control means varying both the coupling and the damping for varying the selective characteristics of the radio frequency amplifier circuits and the intermediate frequency coupling transformers in unison and coordination with the audio frequency filter circuit variations.

7 A carrier frequency receiver having variably coupled and variably damped carrier frequency selectors whose passed band width is variable, audio frequency filters whose passed frequency characteristic is variable and single control means for adjusting the passed band width by varying both the coupling and the damping and adjusting the passed frequency characteristic simultaneously and in predetermined proportion to one another.

8. A carrier frequency amplifier having tuned coupling circuits with variable means for increasing the coupling and increasing the damping simultaneously wherein the variable means comprises means for varying the relative coupling between two coils and also between at least one coil and means for producing electrical energy loss.

9. In a radio receiver, a plurality of coupled tuned circuits, means for varying the coupling between any two of said tuned circuits, means for varying the damping of at least one tuned circuit, variable audio tone control means and common means for effecting variation of all aforesaid means.

l0. A carrier frequency amplifier having a tuned input circuit and a tuned output circuit with continuously variable means for simultaneously increasing the periodicity of one circuit, decreasing the periodicity of the other circuit and increasing the damping of both, said means for increasing the periodicity and damping of one circuit comprising a movable ring of resistive material and the means for decreasing the periodicity and increasing the damping of -the other circuit comprising a core of resistive magnetic material.

11. A carrier frequency amplifier having tuned coupling circuits with continuously variable means comprising a mass of resistive material and a coil and a second coil movable relative to the first said coil and mass of resistive material for increasing the coupling and increasing the damping of the circuits simultaneously and automatic means for holding the power output substantially constant.

l2. A carrier frequency amplifier having tuned coupling circuits with continuously variable means for increasing the coupling and increasing the damping simultaneously wherein the continuously variable means comprises means for varying the relative spacings betweenftwo coils and also between at least one coil and a ring of resistive material.

13. A radio receiver comprising a tuned radio frequency amplifier with a movable ring of resistive material for simultaneously increasing the periodicity and increasing damping of one circuit and a movable core of resistive magnetic material for simultaneously decreasing the pcriodicity and increasing the damping of another circuit, an intermediate frequency amplifier with tuned coupling circuits having coils movable relative to one another and also relative to a ring of resistive material, an audio frequency amplifier having variable cut-off characteristics and single control means for operating the variable elements of the amplifiers in predetermined relationship with one another.

14. A radio receiver in accordance with claim 13 wherein the single control means comprises cams and linkages operated by a single knob for adjusting the rings, cores and coil spacings in unison.

i5. A radio receiver in accordance with claim i3 with the addition of auxiliary cam means interconnecting the single control means and means controlling other` response characteristics of the receiver.

16. A carrier wave system comprising successive amplier stages operating at a plurality of frequencies with separate selectors for varying the widths of bands passed at each frequency, variable cut-off audio frequency tone control means and single control means for operating said selectors and tone control means in unison and adjusting the width of the band passed at f each frequency in inverse proportion to the frequency.

17. A carrier frequency coupling transformer comprising a tuned input circuit, a tuned output circuit, damping means for introducing losses in at least one circuit by induction, and adjustable means for varying the eifective coupling between the two circuits and between at least one circuit and the damping means with the damping increasing as the coupling increases.

i8. The method of controlling the response characteristics of carrier wave apparatus which comprises adjusting the cut-off at audio frequency and varying the coupling and damping to vary the width of the band passed at at least one carrier frequency simultaneously and in predetermined relationship.

19. The method of controlling the response characteristics of carrier Wave apparatus having variable cut-olf audio frequency tone control means and variably coupled and variably damped carrier frequency selecting means which comprises simultaneously adjusting the tone control cut-oif and the effective coupling and the effective damping to vary the response in the same direction.

20. The method of controlling the response characteristics of carrier wave apparatus having variable cut-off audio frequency tone control means and variably coupled and variably damped carrier frequency selecting means which comprises providing simultaneous relatively low audio frequency cut-off loose coupling and light damping for weak signals, and providing simultaneous relatively high audio frequency cut-off close coupling and increased damping for strong signals and providing automatic control of ampliiication to maintain constant power output.

21. A radio wave system in accordance with claim l with the addition of automatic gain control.

22. A radio receiving system comprising, in combination, a source of signal-modulated high frequency incoming waves, a local source of high frequency waves for beating with the incoming signal waves, means for combining said waves t0 produce a signal-modulated beat frequency wave, means for converting said beat frequency wave into a signal wave of audio-frequency, an adjustable coupling system comprising variable coupling and variable damping means interposed etween said first mentioned means and said second mentioned means, said coupling system being designed to pass only a relatively narrow band of frequencies including the beat frequency but having means for rendering adjustable the width of the band passed, an audio-frequency low-pass lter having its input connected to said second mentioned means, said filter being provided with means for adjustably varying the point of cut-off thereof, and means common to said coupling system and said filter for effecting the aforementioned adjustments in unison.

23. A superheterodyne receiver including a frequency converter, an intermediate frequency amplifier, an intermediate frequency detector, and a low-pass filter connected to said detector, a plurality of coupling systems in cascade interposed between said frequency converter and said detector, each of said coupling systems being designed to pass a relatively narrow band of frequencies including the intermediate frequency and having variable coupling and variable damping means rendering adjustable the width of the effective frequency band passed thereby, said vfilter including means for adjusting its point of cut-off, and means common to said coupling systems and said filter for effecting the aforementioned adjustments in unison.

24.111 a superheterodyne receiver, a source of signal-modulated high frequency incoming waves, a local source of high frequency waves for beating with the incoming signal waves, a translator for combining said waves to produce a signal-modulated intermediate frequency wave, an intermediate frequency amplifier including, in combination, a plurality of transformer units, each having a stationary Winding, said transformer units having a movable winding inductively coupled thereto and means for varying the damping simultaneously with variations in the coupling, a coupling adjusting mechanisml common to said units and operable to effect movement of said movable windings in unison, a detector operable to convert the intermediate frequency wave into a signal wave of audible frequency, and tone control means operatively connected with the coupling adjusting mechanism.

25. In a superheterodyne receiver having a radio frequency amplifier with tuned input and output circuits, an intermediate frequency amplier with variably coupled and variably damped tuned coupling transformers and an audio frequency amplifier with filter circuits for varying the frequency response characteristic thereof, single control means for varying the coupling transformers in unison and coordination with the audio frequency filter circuit variations.

HAROLD F'. ELLIOTT.

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