US2137266A - Multiband receiver - Google Patents

Description

Nov. 22, 1938. 'K N. P.cAsE y' 2,137,266

y MULTIBANDl RECEIVER f original Filed Mai; 25, 1955 4 sheets-sheet 1 AUORNEY.

Nov; 22, 1938.1.

N. P. CASE MULTIBAND RECEIVER original Filed May 25; 1935 4'. Sheets-Sheet 2 INVENTOR. Naso/'v 455 ATTORNEY.

Nov. 22, 1938. N. P. cAsE MULTIBAND RECEIVER 4 Sheets-Sheet original Filed MayV 25,' 1935 INVENTOR,

o o @gri c im /VEL sow' R 5E ATTORNEY.

Y N. P, AsE

Nvfzz, 193s.'

MULTIBAND RECEIVER originai Filed May 25,. 1935 INVENTOR.

' Naso/v f? C455 ATTORNEY.

Patented Nov. 22, 1938 PATENT OFFICE 2,137,266 *n MUL'rmAND' RECEIVER Nelson P. Case, Bayside, N. Y., assignor to Hazeltine Corporation,l a corporation of Delaware Application May 25, 1935, Serial No. 23,376 Renewed October 2.7, 1936 11 Claims.

This invention relates to multi-band radio re ceivers, and particularly to multi-band tuning systems for radio receivers and to methods of operating the same.

Popular interest in radio reception now includes not only those programs transmitted in the general broadcast bands, but those programs, transmitted in the various high-frequency bands. ,In response to this interest, radio receivers, tunable over wide frequency ranges, have been placed on the market. These receivers, commonly termed all-wave receivers, are generally difficult vto tune to any particular channel in the highfrequency bands due to the fact that small displacements of the tuningA element tune over a large number of channels. Slow motion equipment of some character is, therefore, customarily provided between the operating control and the tuning element or elements actuated thereby. Such slow motion equipment, however,` add's considerably to the expense of the receiver, especially l when made so that there is no backlash therein.

In addition, such slow motion equipment impedes rapid shifts between widely separated frequencies and is generally unnecessary and objectionable when tuning in the general broadcast band.

It is an object of this invention to provide a method of tuning a receiver by which tuning to individual channels in the high-frequency portions of the radio spectrum is as easy as tuning to individual channels in the low-frequency portions.

It is a yfurther object of this invention to provide'a radio receiver which is easy to tune in e'aoh of two or more frequency bands widely separated in the frequency spectrum, either by other bands of the receiver or by bands over which the receiver is notV tunable, which has a high gain per stage in each .frequency band, and which is simple in construction and relatively inexpensive to build. f

Other objects of this invention will become apparent from the specification taken in conjunction with the accompanying drawings and the subjoined claims. s

The invention contemplates either a radio receiver which is tunable both over the generalv broadcast band and over one or morerelatively narrow bands in the high-frequency portion of the radio spectrum, or is tunable over` two or more relatively narrow high-frequency bands, at least some of which are widely spaced from each other along the frequency spectrum. The general broadcast band, in the United States, is a band of about' 1000 kilocycles (1.0 megacycle) frequency coverage extending from around 550 kilocycles to around 1550 kilocycles (0.55-1.55 megacycles). The relatively narrow high-frequency bands are preferably so located and of such frequency coverage as to include only the high-frequency broadcasting channels, domestic and foreign, inasmuch as the'overwhelming majority of the general public is interested only in the reception of lprograms from broadcast stations. In receivers forsuch broadcast reception, the tunable ranges of the receiver, in the highfrequency bands, are preferably bands of 500 kilocycles (0.5 megacycle) frequency coverage. Although 'the invention is not limited to a receiver tunable over bands of equal frequency coverage in any two bands, the preferred tunable ranges of an all-broadcast receiver, in accordance with this invention, are the following:

0.55-- 1.55 megacycles 5.8 6.3 megacycles 9.5 10.0 megacycles 11.6 12.1 megacycles 15.0 -15.5 megacycles 17.5 18.0 megacycles The invention further contemplates, in the incorporation of the above features in a receiver tunable over two or more such broadcast and high-frequency bands by the operation of the same tuning member,proportioning the reactive elements utilized for tuning each of the two or more such bands so that operation of the tuning member between its limiting positions tunes the receiver, for each of such bands, substantially exactly between the limits of the selected bands. This provision of the inventionl results in great ease of tuning in all bands as all the channels within the limits of each of the selected bands are, in each band, spread over the complete operating range of the tuning member. Further, the channelsin each band are-spread over the full range of the indicating dial, and the individual channels within the respective bands are separated on the dial by spacings having magnitudes in a ratio, from band to band in the order of decreasing frequency, which is substantially greater than the inverse ratio of the mean frequencies of the bands, it being understood that adjacent signal channels in each of the bands are generally separated-by a constant frequency difference, such as 10 kilocycles. Thus, when the fre` quency coverage vof the several bands is the same, as is the case for the high-frequency bands of the lexample given above, the individual channels within the respective bands are separated on the dial by spacings of the same order of magnitude for all of the bands and tuning of the receiver is thus as easy in any one band as in another, even though widely separated `therefrom in the frequency spectrum and in any event tun- `ing over the high-frequency bands is greatly facilitated over that with arrangements of the prior art. Furthermore, the dial of the receiver may be permanently calibrated for each band so as to enable quick tuning of the receiver to individual channels ln the respective bands.

In accordance with the invention, a high gain is procured by maintaining a high L/C ratio for each tuned circuit, not only in the general broadcast band'but also in each high-frequency broadcast band.

Further, in accordance with the invention, the same variable tuning element may be utilized for tuning a receiver over both the general broadcast band and one ormore high-frequency bands, or, alternatively, `a tuning element having a. smaller value and/or a smaller range of values may be provided for the high-frequency bands. In the latter case, the two tuning elements preferably are controlled by the same tuning member and have their displacement indicated on the same scale member, although, less desirably, the two tuning elements may be controlled by i'ndividual tuning members.

In accordance with another provision of the invention, certain of the tunable systems of the receiver may, for reception in certain bands, be simplified in certain cases, particularly in the case of a superheterodyne receiver, by utilizing, in one or more of the signal-selecting circuits, fixed tuned circuits resonant substantially to the mid-frequency of the band selected for refception.

En the drawings, Fig. 1 is a chart of the radiofrequency spectrum to aidl in explaining the invention; Fig. 2 is a circuit diagram, partly schematic, illustrating one embodiment of the invention as incorporated in a multi-band superheterodyne receiver; Fig. 3 is a similar circuit diagram illustrating another embodiment of the invention; Fig. 4 is a circuit diagram of a multihand receiver similar to, but somewhat less complex that illustrated in Fig. 3; Fig. 5 is a circuit diagram of a portion of the receiver of 8 illustrating another modification thereof; Fig. is circait diagram of a portion of the receiver of ating still another modification th" 'I is a circuit die 'fram of a portion. or c cy ver of Fig. 3 illustrating aneth t of the invention.

Ref l, the radio-frequency spectrum is tted in megacycles. The crosshatched portion designated c represents the general broadcast The other cross-hatched portions, designated b, c, d, e and f, are nonccntigucus hands ci 0.5 magacycle frequency coverage in the high-frequency portion of the radio-frequency spectrum, positioned therein so as to include all, or substantially all, of the highfrequency broadcast channels of the world. in this connection, the term high-frequency portionof the spectrum is herein defined as including all radio frequencies above 5.0 magacycles and as excluding all frequencies lovv 5.0 megacycles, and the term high frequency is herein dened es any radio frequency above 5.0 megacycles. The preferred limits of bands a, b, c, d, c and are, respectively, those set forth in the previous tabulation of preferred tunable ranges. As may be seen from Fig. l, these bands are bands of the same order of frequency coverage. However, in terms of relative values, in which the relative width of a band ls defined by the ratio ofthe frequency coverage of the band to the minimum frequency of the band, band a is quite a wide band (the ratio being 1.82), while bands b, c, d, e and f are relatively narrow bands (the ratios ranging from 0.086 to 0.029). As herein employed, the term relative band width refers to the relative measure of the band width as dened above, and the term frequency coverage is herein employed to indicate the absolute range of frequencies included within a band, independently of its position in the radio-frequency spectrum. A relatively narrow band is herein defined as a band in which the ratio of the frequency coverage of the band to the minimum frequency of the band is a minor fraction (i. e.,

less than 0.5). In accordance with this invention, and as will be seen from Fig. 1, the relative widths of the several high-frequency bands are less than that of the general broadcast band, so that the frequency coverages or tuning ranges of the several bands are substantially less than directly proportional to the mean frequencies of the bands, and the magnitudes of the displacements of the tuning means required to effect separation of adjacent signal channels within the respective bands are in a ratio, from band to band in the order of decreasing band frequency, which is substantially greater than the inverse ratio of the mean frequencies of the corresponding bands. Such an arrangement is to be contrasted with the `conventional arrangements of the prior art in which the relative Widths of all the bands are approximately equal, the frequency coverages are directly proportional to the mean frequencies of the bands, andthe magnitudes of the displacements of the tuning means required to effect separation of adjacent signal channels within the respective bands are in a ratio, from band to band in the order of decreasing frequency, which is inversely proportional to the mean frequencies of the corresponding bands. Although not limited thereto, it is desirablethat the several high-frequency bands be relatively narrow bands having a frequency coverage oi the same order as, preferably between one-half and twice, that ci the general broadcast band. and leaving hand Widths equal to a .minor fraction, preferably not greater than two-tenths. While eac of the receivers herein described is tunable rfi the rela ely road, general broadcast y narrow high-frequency hands the limits of which substantially corre- .f respectively to above-described limits of hands o, c, d, e and having equal frequency coverages, it will ice understood that the invention is equally applicable te any receivers deed to tune over any :temeer or high frequency f either equal or unequal frequency cove having relative band widths substantially narrower than those the arrangements of the prior art. in case the bands are ci unequal frequency coverage, the displacements of the tuning elemernJ of the receiver required to effect separation ci adjacent signal chananels Within the several rgir-frequency bands may be less than for the lower frequency band but still they will be substantially greater than inversely proportional to' the mean frequencies of the bands, as in the conventional arrangements of the prior art. With of such limits and location as are given in the example specifically mentioned above, .ita is to be observed that the separation between at least some of the high-frequency bands and `others thereof is large compared to the frequency coverage of such bands, being of the order of at physical arrangements of these inductances preferably being that indicated, in whichpri` mary lnductance II1 is coupled principally to' secondary inductancesl4a and I4b, in which primary inductance Ilz is coupled principally to secondary inductances I4c and I4d, and in which primary inductance IIa is coupled principally to secondary inductances I4e and I4f. Adjustably fixed'condensers I8a, 2lb, 2Ic, 2Id, 2Ie and 2li are connected across secondary inductances I 4a, I4b, I4c, I4d, I4e and .I4f, respectively, to form tuned radio-frequency wselective circuits. The

high potential terminals of these tuned circuits are'selectively connected through contacts I5 of a switch I5 to the control grid of a vacuum tube I1,

illustrated as of the pentode type and `connected to operate as a radio-frequency amplifier. The other terminals :of these circuits are connected to ground I3 through condenser I2.. A variable condenser is connected across secondary inductance I4a, between ground I3 and the terminal of inductance I4a that is connected to switch contact I5a."

The anode of vacuum tube I1 is connected through coupling condenser 23 to the control grid of the signal-translating portion of the vacuum ytube 24, illustrated as a heptode utilized as an oscillator-modulator. Arranged tol be selectively connected in the signal input circuit of vacuum tube 24, as by the switch 25 having cong tacts 21, are a plurality of tuned radio-frequency circuits comprising inductances 26, individually designated 26a, 2Gb, 26e, 26d, 26e and 215i-, and adjustably fixed condensers 29a, 3Ib, 3Ic, 3Id, 3Ie and 3| f, respectively. Oneterrninal of each of the inductances 26a-26j, inclusive, is connected to ground through a fixed condenser 28. A

' variable condenser v30 is connected across inductance 26a. The anode of the oscillator portion of the oscillator-modulator tube 24 is connected to ground through serially connected blocking condenser 32, a plurality of primary inductances 33, individually designated 333, 332 and 331, and an adjustably fixed\condenser -34. Primary inductances 33 are inductively coupled to a plurality of secondary inductances 35, individually designated 35a@ 35h, 35e, 35d, 35e and 35j, the physical arrangement of these inductances preferably being that indicated, in which primary inductance 831is coupledV principally to secondary inductances 35a and 35h, in which primary inductance 332 iscoupled principally to secondary inductances 35e and 35d, -and in which primary inductance 333 is coupled principally to secondary inductances 35e and 35i.

The high potential terminals of the secondary inductances 35m-35j, inclusive, are connected to ground through adjustably fixed condensers 43a and' 44h-44j, respectively, while the low potential terminals of these inductances are connected to ground through the adjustably xed condensers 34 and 45b45f, respectively, to form a plurality of oscillation circuits for the several selected bands. These oscillation circuits are selectively connected to the control grid of the oscillator portion of the tube 24 through a coupling condenser 38 and the contacts 36 of a switch 31. A tuning condenser 42 is selectively connected in parallel with the condenser 43a between the high potential terminal of the secondary inductance 35a and ground, and in parallel with condensers 45h-45j, inclusive, between the low potential terminals of the secondary inductances 35h-35j, inclusive, through the contacts 40 of a switch 4I.

The output of oscillator-modulator tube 24 is coupled, by means of a transformer 41, 5I, tuned yby the adjustablyrf'lxedcondensers 4 6 and 52 to the intermediate frequency, to the input of the intermediate-frequency amplifier- 53. The output of amplifier 53 is connected to a detector and source of automatic volume control bias voltage 54. 1The output of detector 54 laconnected to an audio-frequency amplifier 55, which in turn feeds into a suitable sound reproducer 56.

Preferably, variable tuning condensers 2i), 3l)- and 42 are ganged for uni-control, as indicated by the dotted line 60, Also, switches I6, 25, 31

`and 4I are preferably ganged for uni-control, a i

indicated by the dotted line 6I. It is vnot believed necessary to describe the conventional connections by which the various operating voltages are applied to the elements of the vacuum tubes, or by which the AVC bias voltage is applied to the control grid of vacuum tube -I1 and to the control grid of the modulator portion of the tube 24. All these connections, unimportant to this invention, are clearly indicated in the diagram. It is believed sufficient to note that the cathode of vacuum tube I1 is connected to ground through a biasing circuit 52, that the cathode of vacuum tube 24 is connected to ground through a biasing vcircuit 63, and that the element 64 in the direct-current feed to the anode of vacuum tube I1 is a radio-frequency choke coil. In considering the operation of the above-described system, it is assumed that the switches I6, 2'5, 31 and 4I are initially in the positions in which they are illustrated in Fig. 2. Under these conditions, inductance I4a is connected in circuit in the input section ofthe tube I1, in-

ductance 26a is connected in circuit between the output section of the tube I1 and the modulator section of the tube 24, and inductance 35a. is

, connected` in circuit in the oscillator portion of the tube 24. With these connections, variable tuning condenser 20 tunes the circuit 20, I2,

I4a; variable tuning condenser 30 tunes the circuit 30, 28, 25a; and variable tuning condenser 42 tunes the circuit 42, 35a,- 34. Condensersv I2 and 34 serve as capacitive coupling devices to complement the electromagnetic couplings in their respective circuits, in a manner well understood in the art. Condenser 28, and also -condenser 34,V serve as series padding condensers and may be adjustably fixed condensers. Adjustably fixed condensers Iila, 29a and 43a serve as parallel padding condensers.` The padding condensers, once adjusted by the manufacturer, are not ordinarily altered.

The values of inductance I4a, variable tuning I condenser 20, xed condenser I2 and adjustably fixed condenser I8a. in the rst radio-frequency selecting circuit, the values of inductance 26a, variable tuning condenser 3.0, fixed condenser 28 and adjustably fixed condenser 29a in the second Iradio-frequency selecting circuit, and the values I of inductance 35a, variable tuning condenser 42- and adjustably xed condensers 34 and 43a in the tuned oscillator circuit, are so chosen as to obtain satisfactory operation .of the superhetero- 5 dyne' receiver in the general broadcast band fa, (Fig. 1), utilizing all, or substantially al1, of the full range of variation of variable condensers 20, 30 and 42. During such operation in the general broadcast band, the radio-frequency selecting circuits are tuned to resonance with the signal frequency by variable condensers 20 and 30. The incoming signal frequency is thus selectively amplied and applied to the control grid of the modulator portion of vacuum tube 24. The signal frequency is therein modulated by the frequency produced in the oscillator portion of vacuum tube 24, the frequency of the oscillations being controlled by the tuning of the oscillation circuitby variable condenser 42. As is well understood in the art, such modulation of a` signal frequency produces a constant intermediate or beat frequency, which frequency is amplified in the intermediate-frequency amplifier 53 land is detected or rectified in the detector 54 to produce audio frequencies of modulation of the incoming signal wave. 'I'hese audio frequencies are ampliiied in the audio-frequency amplifier 55 and are then translated into sound by reproducer 56. Automatic control of the amplification of the receivedA signals is effected by the action of automatic volume control bias potentials produced in the detector and automatic volume control unit 54, and applied to the control grids of vacuum tubes i1 and 24 and of the vacuum tubes in the intermediate-frequency amplifier 53.

When switches it, 25, il`` and @i are actuated s'o that the Varms of these switches are in engage'- ment with contacts i512, 27h, 3th and fliib, respectively, inductance iib is connected in circuit in m the input section of the tube l1, inductance 25h is connected in circuit between the output section of tube I and the modulator section of the tube 223, and inductance 35h is connected in circuit in the oscillator portion of the tube 2&3.' Inductance Mb, together with adjustably iixed condenser 2ib, functions as a xed tuned circuit. Similarly, inductance b and adjustably iixed condenser Sib `Eunction as a fixed tuned circuit. inductance is element in the circuit iifib, N d'2 with the adjustably i j the inductance The values ci inductance fixed condenser ib in trie selective circuit, e and adjustabiy radio-frequency sc e cir and/cr adjusted as te obtain i stages a xed tuned circuit tin to the mid-frequency of high-freeman (Fig. l). The values of inductance Sii i @5 ably nxed condenser 'lyizand fixed condense* in the oscillatcr stage are so chosen and f^r ad justecl, having consideration for the and minimum values er variahie tin denser t2, that the frequency of the oscii l generated in the oscillator portion of the tane 2d varies between such limits as tc produce tiieprede= termined intermediate frequency for received sig nals falling between the limits ci high-:frequency band b, as variable tuning condenser i2 is varied between its maximum and minimum vaines. In

accomplishing this, condensers 44h and 45h reduce the maximum 'effective capacitance of the oscillation circuit and also the effectiveness of variable tuning condenser 42. As herein employed, the term effectiveness of a tuning ele- '5 ment is used to denote the ratio of the maximum eifective value of circuit reactance of the same type as that of the tuning element to the minimum eiective value of such circuit reactance, as the tuning-element is varied between its maxi- 1o mum and minimum values. l

Thus, as a result of the action of condensers 44h and 45h in reducing the maximum eifective value of the capacitance of the oscillation circuit and in reducing the eiectiveness of variable tun- 15 ing condenser 42, the maximum effective capacitance in the oscillation circuit is considerably smaller than the maximum capacitance of vari,- able condenser 42 and the net eiective capacitance variation in the oscillation circuit incident 20 to variation of condenser 42 between its maximum and minimum values is considerably 4less than the diiference between the maximum and minimum capacitances of tuning condenser 42.

In a similar mannenwhen switches $635.3? and 25 4I are actuated so that the arms of these switches are in engagement with other contacts, the inductances connected to such other contacts are connected in the circuits with which the respective switches are associated. Thus, only those in- 30 dividual inductances of inductances i4, 26 and 35, having the same lettered suiiix, are connected in circuit at any one time. Furthermore, each individual inductance connected in the first and second radio-frequency selective circuits, except ina5 ductances Ilia and ita, is shunted by a separate adjustably fixed tuning condenser (2l for the rst radio-frequency selective circuit and 3| for the second radio-frequency selective circuit) to form a lxed tuned circuit tuned substantially to 40 the mid-frequency of the band of corresponding letter (Fig. l). Also, each individual inductance connected in the oscillator circuit (except inductance 35a) is provided with a separate, adjustably fixed condenser filiv in series with, and a separate 45 iixed condenser` in parallel with, the tuning condenser @2, prc'perly to fix the tuning limits of the corresponding oscillation circuit by appropriately reducing the en'ectiveness of the variabie en between the limits of the c pending ie .-.lues ccen'se, Subject to tfailatien ever-a ce tively wide range de..endii en design, ie tion and ef'tiie bancs, .n i other so tai* oi" denite lues for the varlcns elements wili Yee of but little t:J

ance. Certain practical ccnsiderations :n.ff 'ce mentioned, however, and the relative order ci magnitudes of certain elements indicated.

'For satisfactory Vcperation cf a superheterodyne "c receiver over the general broadcast band d, eacfc of the variable tuning condensers 26, 3@ and ft2 may have a maximum value of the order ci 45C inicro-micrcfarads and a minimum value of the order of 15 micro-microfarads. Adjustabiy :fixed 'gg "condensers Isa, 29a and 43a generally are small single-leaf padding condensers having a' range from 2.5 to micro-microiarads.- Fixed condensers I2V and 28 generally are of the order of 2000 micro-microfarads. Adjustably xed condenser 34 generally is a multiple-leaf padding condenser having a range from 200 to 500 micromicrofarads and set to a value around 450 microl microfarads.

The satisfactory operation of the superheterodyne receiver of Fig. 2 in high-frequency bands b, c, d, e and f generally requires thatin each radio-frequency selective circuit and in the oscillator circuit of the receiver the inductances having correspondingly lettered-suffixes decrease in value progressively in the band order mentioned. Adjustably xed condensers 2lb-2li, inclusive, SIb-3U, inclusive, and 44b-44f, inclusive. are preferably small, single-leaf condensers having a range from 2.5 to 30 micro-microfarads. Fixed condensers 45h-451', inclusive, increase in value progressively in the order mentioned and generally are at least several times greater than the value to which the corresponding series condenser 44 is set. Illustrative of one set of values of fixed condensers 45 which has been used satisfactorily, when the intermediate-frequency was approximately 460 .kilocycles, are the following:

Micro-microfarads 5b -L 100 5c 150 45d A 175 45e .200 Ef 210 In summary, tuning of the superheterodyne receiver of Fig. 2 iseiected by first actuating the control member 6| for the ganged switches i6, 25, '31 and 4| to the position corresponding to the band desired and then actuating the control member 60 for the ganged tuning condensers 20, 30 and 42 to tune the receiver to individual channels in the selected band. It is to be observed' displacements of the tuning member which are of the same order of magnitude forall of the bands. thus equally facilitating timing 0I the receiver in all of its tunable ranges. This feature has been obtained in the receiver of Fig. 2 without increasing `the number of variable condensers over that customarily provided lin a receiver tunable only over the general broadcast band.

Furthermore, the superheterodyne receiver of Fig. 2 has a high over-al1 gain-in 8,11 bands. This is'liecause of the fact that, in the first and second radio-frequency selective circuits,Y the values of thefinductance and capacitance for each fixedA tuned circuit therein are so chosen for the several bandsas to provide high LIC ratlos. High L/C ratios of the same order of magnitude for all bands are also obtained in their circuits, notwithstanding the use, in the high-frequency bands, of the same relatively large variable tunf ing condenser that isused fortlming-the oscil- Alatorcircuitintliegeneralband. Y highL/C ratiosintbecircuitare obtained by the use of different inductances 35 for the dinerent bands and by utilizing across the respective inductances for the high-frequency bands the relatively large variable` tuning condenser 42 in series with a small adjustably fixed 5 condenser 44 and in shunt with successive ones of the fixed condensers 45b-45f, inclusive, of greater value progressively in the order named.

It is to be observed that in the superheterodyne receiver of Fig. 2, not .,only may the frame and 10 rotor of variable condenser 42 be maintained at ground potential, but also one terminal of each adjustably fixed condenser 44b-44f, inclusive, may be maintained at ground potential. Adjustment of condensers `44h-M, inclusive, 15

may thus be made without the introduction of error dueto the body capacity -of the person making such adjustments. circuits by which this is accomplished results in no substantial sacrifice of the available volt- 20 ages across the secondary inductances, for most of the voltage across the secondary inductance of the oscillation circuit for each high-frequency band is impressed upon the control grid of the oscillator portion of tube 24. This desirable re- '25 suit occurs notwithstanding th'e subtractive eifect of variable condenser 42 and xed condenser 45 in the inductive leg of theoscillation circuit, since in the high-frequency bands the reactances of these condensers are small relative to those of 30 the condensers 44,

It is to be observed further that, in the superheterodyne receiver of Fig. 2, the selection of individual channels in the general broadcast band a is effected by the tuning action of the ganged 35 variable tuning condensers 20, 30 and 42, while the selection of individual channels inthe highfrequency bands b, 0,412, e and Vf is effected by the tuning actionv of variable tuning condenser 42 alone. The physical actuation of variable tuning condensers 20 and 30 simultaneously with the actuation of variable tuning condenser 42 has l no eiectV when tuning in the high-frequency bands` as, at such times, the former are disconthe radio-frequency' selective circuits of the receiver. 'I'he use of such fixed tuned circuits, tuned substantially to the mid-frequencies of the respective high-frequency bands, contributes materially tothe simplicity of the receiver of Fig. 2 and isnot an objectionable expedient for use in low price receivers inasmuch as the frequency coverage of the respective high-frequency'bands is relatively small, so that the attenuation of signal frequencies at the upper andlower limits 55 of such bands fis not excessive.

In receivers of better quality, it is preferred to vary the tuning of thel radio-frequency selective circuits in each high-frequencyv band as well as in the general broadcast band. Fig. 3 60 illustrates a superheterodyne receiver in' which lthis is accomplished. Elements in Fig. 3 corresponding to similar elements in Fig. 2 are similarly designated. v

The principal difference' between 3, relative to the radio-frequency selective cir- Y cuits, is that in Fig. 3 the secondary inductances 'I4 and 26 are variably tuned within each highfrequencyband, as in the case of the secondary The arrangement of the Figs. 2 and 65 nected and iixed tuned circuits are employed in 45 inductances 35 of the oscillation circuit of Fig. 2. 70

A further difference between Figs. 2 and 3 is thatv in Fig.- 3 the condensers for eachhigh-frequency band of vboth the radio-frequency selective circuits and of the oscillator stage are connected totheir respective inductances only when the tuned circuitsformed thereby are connected in circuit in the several stages. This provision insures that the response of the receiver is not iniiuenced by absorption dips which might otherwise be present due to the action of unused, spuriously energized, tuned circuits.

Referring more particularly to the irst radiofrequency selective circuit, adjustably fixed condensers 18h-13j for "-inductances I4b--I4f,4 respectively, in the ilrst radio-frequency selective circuit of Fig. 3, correspond to adjustably xed condensers 44h-44j for inductances 35b-35f, respectively, in the oscillator circuit of Fig. 2 and serve selectively to limit the maximum capacitances in the several tuned circuits of the iirst radio-frequency selective circuit to values considerably smaller than the maximum capacitance of tuning condenser 2li and to reduce the eectiveness of this condenser. The condensers 18 are selectively connected, through the contacts 1I, 12 of a switch 18, between the high potential terminals of the inductances I4 and ground, the arm of switch 1I! being connected to the control grid of vacuum tube I1.

Fixed condensers 11b-11j in the iirst radiofrequency selective circuit of Fig. 3 also serve selectively to reduce, in the high-frequency bands, the effectiveness of variable tuning condenser 20,

and correspond to xed condensers 45h-45j, for variable tuning` condenser 42 in the oscillatorl circuit of Fig. 2. 'I'he condensers 11 are selectively connected, through the contacts 15, 16 of a switch 14, between the low potential terminals of the inductances I4 and ground and eil'ectively in parallel with the tuning condenser 28. It is -to be noted that no condensers 13 or 11 are provided for the secondary inductance I4a corresponding to the general broadcast band.

Referring now `to the second radio-frequency selective circuit, it will be seen that it dliers further from the corresponding selective circuit of Fig-2 in that inductances 28 are inductively energized by primary inductances 181, 182 and 18a.' In this selective circuit, adjustably iixed condensers 8321-831, selectively connected in circuit with inductances 28h-2U, respectively, in the high-frequency bands by means of a switch 88 having sets of contactsBI and 82, correspond to adjustably ilxed condensers 13b- Hf for inductances I4b-I4f, respectively, in the rst radio-frequency selective circuit, and serveselectively to limit the maximum capacitance in the several tuned circuits of the second radio-frequency selective circuit to values considerably smaller than the maximum capacitanceof tuning condenser 38 and to reduce the effectiveness of this condenser. Fixed condensers 81b-81f, selectively connected in circuit with inductances 28h- 28j by means of aswitch 84 having sets of contacts 88 and 88, also serve vselectively to reduce, in the high-frequency bands, the effectiveness of variable tuning condenser 88, and correspond to ilxed condensers 11b- 11j for variable condenser 28 in the iirst radio-frequency selective circuit. Further description of the second radio-frequency selective circuit is believed unnecessary since it is fundamentally similar to the rst radio-frequency selective circuit.

Referring now to the oscillator circuit, the condensers 44 and 48 are selectively connected in circuit with their respective inductances 38 by means of the switches 88 and 84, having sets of contacts 8|, 82 and 88, 88, respectively. and connected similarly to the selector switches 10 and 14 or 88 and 84 of the radio-frequency selective circuits. Further discussion of the oscillator circuit of Fig. 3 is believed unnecessary. 'I'he remainder of-the circuit illustrated in Fig. 3 is similar to, and functions similarly to, that of similar designation illustrated in Fig. 2, so no further description thereof is given.

It may be noted that two automatic volume control connections are provided for the first radio-frequency sele'ctive circuit; one, including high resistance I8a; is connected to the low potential end of'inductance I4a and is effective when the receiver is operating in the general broadcast band a; the other, including high resistance |92, is connected to the ungrounded terminal of variable tuning condenser 20 and is eiective when the receiver is operating in any of the high-frequency bands b, c, d. e or f. Resistance lila may be of the order of 0.2 megohm. Resistance |92 is preferably of the order of 2.0 megohms in order vto minimize the loading eiect on the tuned circuit when operating in band a. The second radio-frequency selective circuit is provided with two automatic volume lcontrol connections, similar to those associated with the rst radio-frequency selective circuit, the first connection including resistance 38a and the second connection including resistance 88a.

In general, the operation of the superheterodyne receiver of Fig. 3 is the same as that previously described for the receiver of Fig. 2; that is, the switches (10, 14, 80, 84, and 84 in this instance, and preferably ganged for unicontrol, as indicated by the d otted line 81) are set to the position corresponding to the band desired, and then ganged tuning condensers 20, 80 and 42 are actuated to tune the receiver to the individual channels in the selected-band. Further, the receiver of Fig. 3 has the feature of the receiver of Fig. 2 by which the individual channels in the various bands are, in general, separated by displacements of the tuning control member 68, and of the scale co-operating therewith, having magnitudes in a ratio. from band to band in the order of decreasing frequency, which is substantially greater than the inverse ratio of the mean frequencies of the bands. The Fig. 3 arrangement is similarly specific to the feature of proportioning the auxiliary reactance elements oi.' the radio-frequency selector system, so that the individual signal channels in the several bands are separated by displacements of the tuning condenserthat are oi' the same order of magnitude for all of the bands. 'I'he principal additional feature of the receiver of Fig. 3 is that the radio-frequency selective circuits are variably tuned in each high-frequency band by receiver is adjusted for reception in general broadcast band a, a11 the individual channels within such band are covered by substantially the entire motion of these variable condensers between their minimum and maximum values. Further, the values oi theinductances I4b-I4f, adjustably fixed condensers 13b-18! and xed condensers 11b-11j associated with the-tuning condenser 28, and the values of the inductances 2Gb-2812 adjustably flxed condensers IIb-83! and fixed condensers 8112-81! associated with the tuning condenser 30. are such that all the indiividual channels within each of the high-fre- 1 quency bands are also covered by substantially 1I 2,137,2166 the entire motion of the variable tuning condensers between their minimum and maximum' values.

A compromise between the simplicity of the receiver of Fig. 2 and the advantages of the circuit are variably tuned in each high-frequency band as well as in the general broadcast band, and this by the'same variable tuning condenser in each circuit that is utilized to tune the corresponding circuit in the general broadcast band. Further, in the receiver of Fig. 4 the condensers for each high-frequency band are connected to their respective inductances only when the tuned circuits formed thereby are connected in the related circuits of the receiver. However, in this case only one inductance is used in each circuit for all high-frequency bands. This, of course, somewhat reduces the gain obtained in certain bands (particularly in bands b and c) dueto the lower L/C ratio, but the resulting receiver still possess a moderately high over-all gain, as well as possessing great ease in tuning to the individual channels in all bands.

The principal diiierence between Figs. 3 and 4 is that the separate secondary inductances I4, 26

and 35, each with lettered suflixes b to f, inclusive, are replaced by three secondary inductances |42, 262 and 35e, in the rst and second radio-frequency selective circuits and the oscillator circuit, respectively. Incident to this diierence is the further difference that primary inductances Ilz, H3, 182, 18a, 332 and333 are dispensed with. To improve the operation l,of the receiver in the higher frequency bands, an open-ended primary winding 98 for secondary inductance 26a is preferably provided. I-

All of the elements in Fig. 4, corresponding to similar elements in Fig. 3, are similarly designated. It is believed that a detailed description of Fig. 4 and its operation is unnecessary.

- high potential terminals of the windings I4 and` 4When the variable tuning condenser employed in tuning in the general broadcast band is also.v

employed in tuning in the high-frequency bands, the arrangements heretofore described have been such as to connect the variable condenser in the inductive leg of the tuned circuit when operating in the high-frequency bands. As explained .in connection with the variable tuning condenser 42 ofthe receiver of Fig. 2, no substantial sacriiice of the available voltage across the tuned inductance results'from such arrangements. it is desired,-ho,wever, to utilize in any circuit all the available voltageacross each tuned inductance, the circuit arrangement for such circuit or circuits may be as illustrated in Fig. 5,

which is a modification of the iirst radio-irequency selective circuit of Fig.,3.

All the elements in Fig. 5 corresponding to similar elements of Fig. 3 are similarly designated. The basic change in Fig. 5 over Fig. 3 is that for the high-frequency bands, adjustablyl xed condensers .13 and their respective fixed condensers 11 are connected in series between the ground, while the variable tuning condenser 20 is connected in parallel with the iixed condensers 11 through the contacts 16 of switch 14. By this expedient, the second arm of switch 14, and con- .tacts `15 engaged thereby, are dispensed with,

the low potential terminals vof secondary inductances I4b--I4f, inclusive, 'being connected through condenser I2 to ground. l

' of the tube I1, the subtractive effect of condenser I2 being entirely negligible due to its extremely small capacitive -reactance at the high frequencies.

The circuit diagram of Fig. 6 illustrates, for the firstqradio-frequency selective circuit of the receiver of Fig. 3, an embodiment of the invention utilizing a relatively large variabletuning cony denser4 20 for tuning the receiver over the general broadcast. band and utilizing a very smallvariable tuning condenser |01 for tuning the receiver over each of the high-'frequency bands.

, All the elements of Fig. 6 corresponding to similar elements of Fig. 3 are similarly designated.

The principal difference between the iirst radio-frequency selective circuit of Fig'. 6 and the vcorresponding circuit of Fig. 3 is the'substitution of the small variable condenser |01 for the combination, in the several high-frequency bands, of variable tuning condenser 20 and the condensers 13 and11. As a result, condensers 13b-13j and 11b-11j, and also switch 14, are dispensed with. Further differences are: the addition of adjustably fixed condensers |08b|08f, connected similarly to condensers 13b-'Hf in Fig. 3, to pro- Videpredetermined iixed capacitance selectively in parallel with the small Variable tuning condenser |01 selectively to reduce the effectivenessy of the small variable condenser |01 for the respective` high-frequency bands; the connection of the low potential terminals of secondary inductances I4b-|4f, inclusive, to ground through fixed condenser I2; and a rearrangement of the connection for variable tuning condenser 20 so with the arrangement of Fig. 5, 1t is to be obthat it is connected in circuit only when switch 10 isp-in the position corresponding 'to general broadcast band a. `If desired, adjustable condenser Illa, used as a parallel padding condenser condenser 20, in which case condenser v|01 is conveniently constructed by insulating an end stator plate of condenser 20 from the other stator plates of the condenser, and utilizing such separately insulated end stator plate and the adjacent end -rotor plate as variable condenser |01. As a result, actuation of variable tuning condenser |01 is effected (as illustrated) by operation of the same tuning control member 60 that serves to control the vtuning of the receiver to the individual channels in the general broadcast band.

-An electrostatic shield is preferably interposed between the separately insulatedend stator plate and the other stator plates in order to minimize undesirable couplings between such stators when operating in the high-frequency band. Alternatively, but less desirably, variabletuning condenser I 01 may be a structurally separate condenser the control of which is effected by a con.- ,75

` trol member individual thereto, with provision that the displacements thereof are indicated on the same scale as the displacements of tuning control member 60. Still less desirably, the control of a structurally separate variable tuning con denser |01 may be eiected by a control member individual thereto having its own indicating scale. It' is essential, however, in each case that variable tuning condenser 20 be excluded from the tuned circuit for each high-frequency band and that the entire tuning in each such band be obtained exclusively by denser |01.

The minimum and maximum values of tuning condenser |01, together with the values of the inductances Ilb-llf -and adjustably fixed condensers |08b-|08f, are so chosen that the individual channels in each high-frequency band are separated by displacements of tuning control member 60, and of the scale operated therewith, having magnitudes in a ratio to the magnitude of the displacement of the variable'tuning condenser 20 required to effect separation of the individual channels in the general broadcast band which is greater than the ratio of the mean frequency of the broadcast band to the mean frequencies of the respective high-frequency bands.

Preferably, the values of the elements enumerated are such that all the individual channels within each band are, for each band, spread over the complete operating 'rangeof tuning control member 00. In effecting this relationship, adjustably xed condensers |00b|08f are set so that they progressively reduce the effectiveness lof variable tuning'. condenser |01 as the band 4within which the receiver is arranged to tune is higher in the frequency spectrum.

The principles of the modication illustrated in Fig. 6 may beutilized in any one or more of the tuned circuits of the receivers heretofore described.

The diagram of Fig. '7 illustrates, for the rst radio-frequency selective circuit of a (receiver, a modification of the circuit diagram of Fig. 6. All the elements of Fig. 7,l corresponding to similar elements of Fig. 6, are similarly designated. There are two principal differences between Fig. 6 and Fig. 1. The rst of these diiferences is the elimination of the small variable tuning condenser |01 for tuning within each of the high-frequency bands, and the assumption of the functions of condenser |01 by the relatively large variable tuning condenser 20. This is effected by inserting a small iixed condenser |09 in series with variable tuning condenser 20 when switch 10 is in the position corresponding to any high-frequency band, together with an arrangement such that switch 10 short-circuits small fixed condenser |09 when it is in a position corresponding to the general broadcast band a. 'I'his first diierence may be incorporated directly in the diagram of Fig. 6 by dispensing with variable condenser |01 and' connecting small xed condenser- |09 between the control grid of -tube I1 and the un- The second principal difference between li'ig.` 6

and Fig. 7 is the permanent connection of the ungrounded terminals of adjustable condensers. |8a and |08b|00f, inclusive, to their respective variable tuning con.

secondary inductances Il, and the permanent connection of contact 1|a of switch 10 with the ungrounded side of variable tuning condenser 20,

thereby eliminating the necessity of contacts 12 of switch 10. To insure that the response of the receiver is not influenced by absorption dips which might otherwise be present, due to the action of any unused, spuriously energized, circuits, switch ||0 having contacts is provided. In practice, switch I |0 may be on the same switch deck with switch 10. In'such case. switch ||0 and its contacts correspond structurally to the portion of switch-10 in Fig. 6 having contacts 12. To avoid confusion, however, switch ||0 is illustrated and designated in Fig. 7 as a separate switch. Switch ||0 is arranged to short-circuit the secondary inductance I4 for the high-frequency band next below the high-frequency band to which the receiver is tuned, as a result of the position of switch 10.l The1short-circuiting of only the secondary inductance corresponding to the adjacent lower high-frequency band is `sufficient' for many commercial purposes, since it is found that such objectionable absorption dips as 'band a.

When switches 10 and ||0 are inthe position corresponding to any'hlgh-frequeney band, the

tuning of the illustrated selective-circuit of the receiver over such highffrequency band is effected by variable tuning condenser 20 having fixed condenser |09 in series therewith, the operation in other respects being 'similar to the operation of Fig. 6 except that in high-frequency bands c, d, e and f the secondary inductances Hb, Mc, Md and He, respectively, are snorted.

If it is desired to short-circuit the secondary inductances for all high-frequency. bands below that in whichthe receiver is tunable, this may readily be effected in a conventional manner by means of an arcuate follower at the outer end of the arm of switch |I0 arranged to maintain circuit between such arm and the contacts for bands below that for which switch ||0 is positioned, or in any other conventional manner.

It is to be observed that in the diagram of Fig. 7, secondary inductance lla, together with coupling condenser l2, is always connected across variable tuning condenser 20, irrespective of the band to which the receiver is tuned.' N o substantial difllculty results from such an arrangement, however, due to the fact that when the receiver is operating in any high-frequency b d the reactance of secondary inductance Ila s relatively so high in comparison to that of variabletuning condenser 20 that its effect on the circuit is negligible.

The circuit elements illustrated in Fig. 7 are so proportioned, as in Fig. 6, to obtain the previously described desirable operating characteristics in the several bands.

A The radio-frequency selective circuit of Fig. '1.

lends itself to a simple, compact and inexpensive construction for secondary coils I4 and adjustable condensers |8 and |00. Furthermore, such an ar 75 cuit of Fig. 7 is considerably higher, particularlyA rangement utilizes only one switch bank, only one fixed condenser and no tuning condenser otherv than the tuning condenser necessary to tune the receiver in the general broadcast band. In addition, the gain obtained with the selective cirin the higher frequency bands, than that customarily obtained in multi-band receivers, and fairly uniform for the several bands.v

If it is desired to obtain gains -for the highfrequency bands greater than those obtained with the 'selective circuit of Fig. 7, and to have.. such gains still more uniform for the several bands, the selective circuit of Fig. 7 may be .modified by employing a separate condenser |09, preferably of the adjustably fixed variety, for each of the high-frequency bands, and selectively conhecting such condensers |09 in series with varilable tuning condenser 20, preferably atl the low potential terminals of such condensers |09, by a suitable switch ganged with switch 10. In the resulting circuit, condensers '|09 serveselectively to reduce the maximum eectiv'e capacitance in the tuned circuits for the several bands to values considerably less than the maximum capacitance condensers 44 for the variable-tuning condenser 42 of Fig. 2), while condensers |08, assisted by condensers |09, serve selectively to reduce the effectiveness of the variable tuning condenser 20 l similarly, respectively, as do condensers 45 and 44 for the variable `tuning condenser 42 of Fig. 2. In Fig. 2, however, the condensers 45 are in parallel with the variable condenser 42 alone, while in Fig. '7 (both as illustrated and as modified as outlinedabove) the corresponding condensers I|08 are in parallel with the combination of the variable tuning condenser and the small series condenser. In the latter cases, therefore, the relatively large and somewhat expensive fixed condensers 45 are not required.

Although the invention has been described in connection with the tunable systems of superheterodyne receivers, the invention is applicable to the tunable system of any type of receiver.

'Furthen although the invention has been described in connection with certain preferred bands of frequencies, the invention is applicable where other bands of frequencies are involved. Thus, the location and/or frequency coverage `oi? such other bands of frequencies may differ from those herein described, but so long as the receiveris to tune to the general broadcast band and to at least onehigh-frequency band, or is to tune to at least two high-frequencybands widely spaced in the frequency spectrum either by other Ibands of the receiver or by frequency ranges over which the receiveris not tunable, this invention provides that in such-cases the receiver will be tunable with ease, and with substantialdial spacings, to individual channels in all such bands.

Inasmuch as many changes could be made in the 'above constructions and many apparently,

widely different embodiments of this invention could be made without departing from the scope Y thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of operating a multi-band radio receiver having band-selecting'means and tuning means adjustable between minimum and maxi-,f

mum settings, which comprises `adjusting `the reactive constants of the receiver selectively to tune it to any one of a plurality of bands while maintaining L/C ratios for the several bands that are v of the same order of magnitude, and varying the effectiveness of said tuning means in accordance with the bandselected to effect separation of adjacent signal channels of the same frequency separation within the respective bands by displacements of said tuning means that are of the same order of magnitude for all of said bands.

2. In a multi-band radio receiver, a tunable system 7comprising reactance means ofA a given type, variable tuning reactance means of the opposite type connected in circuit with at least a portion of said first-named reactance means to form a` circuit tunable overa given frequency band, auxiliaryreactance means of said opposite type, and switching means for including said.

auxiliary reactance means in circuit with said tuning reactance means and at least a portion of opposite type connected in circuit with at least a portion of said first-named reactance means to form a circuit tunable over a given frequency band, auxiliary reactance means of said opposite type, and switching means for including said auxiliary reactance means in circuit with said tuning reactance means and at least a portion of said first two reactance means to form a circuit tunable Vover a second frequency band and to modify the effectiveness of said tuning means in tuningthe circuit, said auxiliary reactance means being lso proportioned, relative to the first two reactance means and their circuit relation, that the L/C ratios of the circuits for the respective .bands are of the same order of magnitude and adjacent signal channels of the same frequency separation within the respective bands are separated by displacements of said tuning means of the same order of magnitude.

4. In a multi-band radio receiver, a tunable system comprising*V a plurality of reactance means of a given type, variable tuning reactance means of, the opposite type, a plurality of auxiliary Vreactance means of `said opposite type, and switching means for connecting, in one position thereof, a selected one of said first reactance means in circuit with said tuning means to form a circuit tunable over a given frequency band and for connecting, in the several other positions thereof, selected ones of said first reactance means in circuit with said tuning means and selected on'es of saidauxiliary reactance means to form circuits severally tunable over 4different high-frequency bandseach' .widely spaced upwardly in the radio-frequency spectrum from said given band, each of saidauxiliary reactance means being so'proportioned relative to said other reactance means and so connected in circuit `therewith by said switching means that the L/C order of magnitude.

5. In a multi-band radio receiver, a tunable system comprising; a plurality of inductance elements of different values; two variable condensers of substantially different maximum values; a plurality of auxiliary condensers, one for each of said inductance elements; and means for connecting said auxiliary condensers effectively in shunt with their corresponding inductance elements and for selectively connecting the larger variable condenser effectively in shunt with the largest inductance element to form a circuit tunable over a relatively wide low-frequency band, or the smaller variable condenser effectively in shunt with the other inductance elements individually to form circuits severally tunable exclusively by the smaller variable condenser over different and relatively narrow high-frequency bands, said inductance elements and condensers being relatively so proportioned that adjacent signal channels of the same frequency separation within the several bands are separated by displacements of the variable condensers tuning the respective bands having magnitudes in a ratio, from band to band inthe order of decreasing frequency, which is substantially greater than necting said auxiliary condensers, effectively inshunt with their corresponding inductance elements and for selectively connecting the larger' variable condenser effectively in shunt with the largest inductance element to form a circuit tunable over a given wide low-frequency band, or the smaller variable condenser effectively in shunt with the several other inductance elements individually to form circuits severally tunable exclusively by the smaller variable condenser over different high-frequency bands each widely spaced upwardly in the radio-frequency spectrum from said given band, said inductance elements and condensers being relatively so proportioned that the displacements of the larger variable condenser in tuning between adjacent signal channels within the given band are of the same order of magnitude as are the displacements of the smaller variable condenser in tuning between adjacent signal channels of the same frequency separation in the several high-frequency bands.

'7. In a multi-band radio receiver, a tunable system comprising; two inductance elements of substantially different inductance; a variable condenser; two auxiliary condensers; `and means for connecting said variable condenser effectively in shunt with the larger inductance element to form a circuit tunable over a given wide lowfrequency band and for selectively connecting one of said auxiliary condensers in series with said'variable condenser and said series-connected condensers and said second auxiliary condenser effectively in shunt with the smaller inductance element to form a circuit tunable over a highfrequency band widely spaced upwardly in the radio-frequency spectrum from said given band, said inductance elements and condensers being relatively so proportioned that adjacent signal channels. of the same frequency separation within 'the high-frequency respective band are separated by a displacement of said variable condenser having `a magnitude in a ratio to the magnitude of the displacement of said variable condenser required to'produce separation of adjacent signal channels of the same frequency separation within said given frequency band, which is substantially greater than the ratio of the mean frequency of the given frequency band to the mean frequency of the high-frequency band.

8. In a multi-band radio receiver, a tunable system comprising; two inductance elements of substantially different inductance; a variable condenser having a relatively large ratio of maximum to minimum capacitance; two auxiliary condensers each having a capacitance substantially smaller than the maximum capacitance of said variable condenser; and means for connecting said variable condenser effectively in shunt with the larger inductance element to form a circuit tunable over a relatively wide low-frequency band and for selectively connecting one of said auxiliary condensers in series with said variable condenser and said series-connected condensers and said second auxiliary condenser eiectively in shunt with the smaller inductance element to form a circuit tunable over a high-frequency band widely spaced upwardly in the frequency spectrum from said low-frequency band, said inductance elements and condensers being relatively so proportioned that adjacent signal channels of .the same frequency separation within the high-frequency band areseparated by a displacement of said variable condenser having a magnitude in a ratio to the magnitude of the displacement of said variable condenser required to produce separation of adjacent signal channels of the same frequency separation within said lowfrequency band which is substantially greater than-the ratio of the mean frequency of the lowfrequency-band to the mean frequency of the` high-frequency band.

-9. In a multi-band radio receiver having a' vacuum-tube input circuit oneside of which is .ing oneterminal thereof effectively grounded;

two auxiliary condensers; and means for connecting said variable condenser eectively in shunt with the larger inductance element with the ungrounded terminal of said variable condenser connected to the ungrounded side of said vacuum tube input circuit to form a circuit tunable over a relatively wide low-frequency band, and for selectively connecting one of said auxiliary condensers in series with said variable condenser at the high potential side thereof and said series-connected .condensers and said second auxiliary condenser effectively in shunt with the smaller inductance element with the high potential terminals of both said auxiliary condensers i connected to the ungrounded side of said input circuit to form a ,circuit tunable over a highfrequency band widely spaced upwardly in the frequency spectrum from said low-frequency band, said inductance elements and condensers being relatively so proportioned that adjacent signal channels of the same frequency separation within the high-frequency band are separated by a displacement oi.' said variable condenser having a magnitude in a ratio to the magnitude ofthe displacement of said variable condenser required to produce separation of adjacent signal channels'of the same frequency separation within said low-frequency band which is substantially greater than the ratio of the mean frequency of the low-frequency band to the mean frequency of the high-frequency band.

10. The method of operating a multi-band radio receiver having band-selecting means and a-tuning element variable between minimum and maximum values, which reactive constants of the receiver selectively to tune it to any one of a maintaining L/C ratios for the several bands that are of the same order of magnitude, and varying the effectiveness of said tuning element in accordance withy the band selected to efiect separation of adjacent signal channels of the substantially greater typev same frequency separation within the respective v bands by displacements of said tuning element having magnitudes in a ratio, from band to band in the order 'of decreasing frequency, which -is than the inverse ratio of the mean frequencies of the said bands.

11. In a multi-band radio receiver, a tunable system comprising reactance means of a given variable tuning reactance `means of thev opposite type connected iny circuit with comprises adjusting the pluralityof bands while at least l a portion of said rst-named reactance means to form a circuit tunable over a given frequency band, auxiliary reactance means of said opposite type and switching means for including `said auxiliary reactance means in circuit with said tuning reactance means and at least a portion of said rst-named reactance means to form a circuit tunable over a second frequency band and to modify the effectiveness of' said tuning means in tuning the circuit, said auxiliary reactance means being so proportioned, relative to the rst two reactance means and their circuit relation, that the L/C ratios for the respective bands are of the sameorder of magnitude and adjacent signal channels of vthe same frequency channel Within the respective bands are separated by dis- Yplacements of said tuning means having magnitudes in a ratio from one of the bands to the other in the order of decreasing band frequency, which is substantially greater than the inverse ratio of the mean Trequencies of the corresponding bands.

NELSON P. CASE.

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