US2561494A

US2561494A - Switchless multiband radio apparatus

Info

Publication number: US2561494A
Application number: US763625A
Authority: US
Inventors: Wendell L Carlson
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1947-07-25
Filing date: 1947-07-25
Publication date: 1951-07-24
Anticipated expiration: 1968-07-24

Description

*' July 24,` A1951 w. L. CARLSON 2,561,494

SWITCHLESS MULTIBAND RADIO APPARATUS Filed July 25, 1947` v 3 sheets-sheet 1 :inventor Gttomeg July 24, 1951 w. l.. CARLSON SWITCHLESS MULTIBAND RADIO APPARATUS 5 Sheets-Sheet 2 Filed July 25, 1947 R o @o 0 o 0 o C 8000008000 'im IIIIIII A m Ilm U CM 0 O O O O 080 QOGGHII W QN Q N 1 m OO o o O 0 o O QOOOQQOOOO ,litigi y 00 0 O 0 o O 0000.0 00008 Ww S@ n Y #1% 0 o o o o o o 000000 ooooo m o o o o o 0 0 a oooooooooooo, l i

July 24, 1951 w. L. CARLSON swITcHLEss MULTIBAND RADIO APPARATUS 3 Sheets-Sheet 3' Filed July 25, 1947 A vv\ NE. Km

M/vofu Z.. Claw/v Cttorneg Patented .u'ly 24, S

PATENT `OFFICE 2,561,494 -s-WfTcHLEjssgMULTIBAND 'RADIO APPARATUS Wendell Carmona-Princeton, N. 'J., "assignr 'to `Radio Corporation of America, la corporation of Delaware Appxication-culyzs, 1947,-seriu1No. 763,625

rfolaims. (Umso-'20) tions from one set of coils used for one band to Vanother set of co'ils used for another band. `Aside "from the question of their cost, such Iswitches have Vbeen a source yof trouble because "their Contact resistance increases with age and V'so uincreasingly;` adversely affectsuthe perform- `ance; moreoverI the inductance of these switches andt'h'e variations of their inductance is a furlther source f difficulty in the-manufacture vand opea'tionofinulti-band receivers one or more of Whose "bands are 'in the ultra -high portion of the frequency spectrum. y y

lIn faccordance with "the present invention, lthe use f band-change 'switches is Y'dispensed with andfthefehangeover yfrornone frequency band to anotheriseffeeted without use of switches, plug 4"cont`act's' or other similar switching expedients: the coil or coils not to be used for a selected band "lern'ainn circuit/but are 'eectvly y`dsl)1'(-d by insertion therein of high-loss `magnetic core t'l'fl'trevfhleh Id'les the QAfth'e/Unusd Yccv'l or coils to very low magnitude.

lMore "particularly, and in preferred'forms of `the invention, -asa low-loss core'is Abeing moved 'inranyo'ne ofthe coils of a'eircuitfor tuning it "within :a selected band'offreq'ueneiesga highf'l'o'ss fcore, `mechanically connected to the low-loss "the "circuit 'to 'maintain the `Q 'thereof atinsignicantly low value "'Flirtli'er in accordance with the invention, the capacitance "inshuritto'the coil of a lower-fre- `tance"in"shunt to the coil of ra'higher'frequency `ban"d"to decouplethe two circuits.

Theinvention further resides inthernetho'ds ofandfin thefeatres of combination, vconstrucftionfand arrangement hereinafter described-and claimed.

For more detailed understanding of the invention," reference is made to the accompanying drawings inwhich: n

Figure l is a schematic diagram of a lportion of a radio receiver; v l

:Figures 2, 2A andl`2B are explanatory figures "referred to'in'discus'sion of the tuningof circuits shown' in Figure l;

2 Figures '3 vand 4 are explanatory figures re- V"ferred to in discussion of the'materials used in the cores of -Figure l;

4Figures v"5 and 6 are explanatory "'g'ures Yre- Figures #7 and A8 f'disclose Imulti-'band circuits using modifications f the invention;

fFig're-gillustrates a 'diilerer'it mechanical ar- Mrangernent"of the cores for `multib`a`nd 'operavl() tion; and

4.lig'ure 'l'illus'trates an oscillator circuit using the fcore arangement of (Figure 9. Y A'As typical of 'radio apparatus employing fthe invention, reference is niadeto Figure l which .15 Adiscloses the "front end or 'high-frequency'fpo'rtion of 'a 'multi-band v'superl'ieterodyne receiver tunable 'through Yt'vvo bands substantially 'separated "in "the frequency spectrum and in which thec'hangeover 'from `rece1'ntion'in one 'band to 5,20 "reception in v-another band is "effected Ywithout r'ecourse'toanycoilswitching. 'For purpose of "explanationandvvithout limitation 'of the in- `venti'on "thereto, lit is assumed "the receiver is tunable orreception'of 'signals in a 1o'w'band 5 `df'froln"0",54`to l'megacycles (the present AM broadcastband) and in arhi'gh band of from `88 to 108inega'cycles (theprese'nt'FMbroadcast band).

TIn "the input 'circuit of 'tube 10,W`hi'ch serves 4so as'theradiofrequency'amplifier tube,"are perma- 'nently eonnecte'd'in series the coil 13A 'tunable 'for reception in the high band and con 14A tiinable for reception inthe 1ow'band. Simi- "larl'y," in thein'put circuit f the mixer tube "I`I s "areprln'anently connected in series'the coil [3B "tfuna'bl'e for"reception in the"l`1i'gli bandand coil 'A'IB tunable for Jreception in the "low band, YThe"local"criseillat'or l2, Whose output isinjected :iiit'othe inixer ttube Il kyfor conversion of the y received "signals 'tothe' intermediate frequency at ers 'moving in the remaining coil o'r'coilsfof` `which further"`an1p1ication is effected 'by an lii'iterinedi'ate-fiequencyamplifier generically represented bythe block "il, e'omprises Vin circuit withthetube 'I2 a 'coil I'SCtunahle'through the Ll l proper range of frequenciesfor the"high'band quen'cy -hand vis usually greater than the capaci- "and "the "coil 111C tunable through Ythe proper "frange "of frequencies for the low band: these coils are al'so permanently connected inv series.

In the particular 'arrangement shown in ""thiogh the 'range of frequencies corresponding "withthefh'ighm bandloy thelo'wloss cores l SA, 'IBB and I`8'C Yrespectively,Sand the coils MA, I 4B adMC aretunablethrough the flow bandby eo .,pwdeifed iron: in either case, -themovement of 3 the core within the corresponding coil substantially changes the inductance of the coil but has slight effect upon its effective alternating current resistance so that the Q of the coil remains high.

With the low-loss core structures in the positions shown in Figure 1, theirI movement is effec'- tive to tune the coils I3A, ISB and I3C for reception of signals in the high band. It should be noted that the coils I4A, I4B and I4() are also in circuit but they are ineifective for the reason that there is disposed within them the high-loss cores 20A, 20B and 23C respectively, whose construction and characteristics are later more specifically discussed.

To adapt the receiver for reception of signals in the low band, all of the core structures are moved upwardly from the position shown in Figure 1 so that the low-loss cores IBA, IBB and IBC are replaced in the coils I3A, I3B and I3C by the high-loss cores 20A, 20B and 20C which effectively disable the coils and without recourse to any switching. This same movement of the core structures is effective to position the low-loss cores IBA, ISB and IBC within the low band coils I4A, I4B and I4C, so that further adjustment of the cores effects tuning of the coils I4A, I4B and I4C for reception of signals in the low band. This tuning of the high band and low band circuits and the band changeover or selection may be more fully understood by reference to Figure 2 which shows four significant positions of cores IB, I9 and 20 with respect to coils I3 and- I4. It shall be understood that the coils and cores of Figure 2 correspond with those of any one of the circuits or stages of Figure 1 or other figures later discussed, and that the insertion and withdrawal of the cores may be effected by movement of the coils, or the cores, or both.

With the cores I8, I9 and 20 in the #l position of Figure 2, which corresponds with the positions of the cores disclosed in Figure l, and assuming the low-loss core I8 is of magnetic material, the inductance of coil I3, because of maximum insertion of core I8, is at its maximum and the associated circuit is therefore tuned to the low frequency limit of the high band, Figure 2A. For the #l position of the cores, the high-loss" magnetic core 20 is to substantial extent disposed within the coil I4 and the Q of this coil is consequently so low that although it is in circuit with coil I3, it has inappreciable resonant effect and in any event prevents response of the receiver"''5 to signals in the low band. For the #l position of the cores, the low-loss core I9 is far removed from the coils I3 and I4 and has no appreciable effect upon them.

I8 is of non-magnetic material, such as copper or brass, the #l position of core 4IB affords the minimum inductance of coil I3 and the highest frequency of the high band; whereas, the #2 position of core I8 will afford the maximum inductance of coil I3 and the minimum frequency of the high" band.

As the core structures are moved from the #2 position to the #3 position, Figure 2, the highloss or damping core 20 is removed from the low band coil I4 and inserted in the high band coil I3 thus to reduce the Q of coil I3 to such low value that there is negligible response to signals inthe high band. For this position of the core structures, the tuning core I8 of coil I3 is substantially removed therefrom and has inappreciable effect upon it. However, for the #3 position of the `core structures, the low-loss core I9 is about to enter the low band coil I4. Assuming the tuning core I9 is of magnetic material. the inductance of coil I4 is at a minimum, and the circuit is resonant at the high-frequency end of the low band, Figure 2B. As at this time, the high-loss core 20 is well removed from the coil I4 whose Q is therefore of high value and the circuit is consequently sensitive to signals at or immediately adjacent the high-frequency end of the low band.

For continued movement of the core structures from the #3 position towards the #4 position, the iow-loss core I9 is to greater and greater extent inserted in the coil I4 progressively raising its inductance and so tuning the circuit to lower and lower frequencies of the low band until finally for 100% insertion of the core, the circuit is resonant at the low frequency end of the "low band, Figure 2B. Throughout this range of movement of the core structures,` the high-loss core 2l) remains within the high band coil I3 and so effectively damps its response to any signals in the high band. Assuming the core I9 is of non-magnetic material, such as copper or brass, the relation between the frequency response and core position, Figure 2B, is, of course, reversed.

From this discussion of Figure 2, it should now be clear that adjustment of the core structures Figure 1, which are preferably all mechanically interconnected for movement in unison, is effective to tune the several circuits of either the high band or the low band and without any switching in or out of coils in the changeover from one band to the other. The cables, rods or the like for mechanically coupling the cores are generically represented by members 9. Furthermore, in the superheterodyne circuit shown, the reception of signals in the undesired band is eectively prevented because the insertion of the As the core structures are moved from the #lago position towards the #2 position, Figure 2, the per-cent insertion of low-loss core I8 in coil I3 becomes less and less; and again assuming this core is of low-loss magnetic material, the inwith consequent increase in the frequency to which it is tuned, Figure 2A. Throughout this same range of movement, the high-loss magnetic core 20 remains to substantial extent Within the coil I4 and effectively damps the response of the" low frequency circuit. In brief rsum, as the cores are moved from the #l position toward the #2 position, the circuit comprising coils I3 and I4 is tuned through the high band, Figure 2A. It shall, of course, be understood that if the core ductance of the coil I3 progressively decreases"6`5 high-loss core 20 in the unused coil of the oscillator is effective to prevent generation of oscillations within the frequency range of that coil, and consequently even though some signals from the undesired band reach the mixer tube II, there are no locally produced oscillations which can `beat therewith to produce intermediate frequency signals which can be passed by the I. F. amplifier ln the specific oscillator circuit shown in Figure 1, one terminaloi the high band coil I3C connected through condenser 22 to the control grid 2i of tube I2, and one terminal of the low" band coil MC is connected to the anode 23 of tube I2. The other terminals of the coils are connected together, so that they are effectively in series, so far as radio frequencies are concerned, between the grid and anode of thetube l2. A positive terminal of suitable source of anode supply voltage is connected, as shown, to an intermediate tap 24 of low bandcoil I4C. Accordingly, when the high-loss core C is inserted in the low band coil 14C., the oscillator circuit is of the Colpitts type, the coil ISC serving as the signicant inductance of theY oscillating circuit and the low band coil I4C` serving as a choke coil in the plate-voltage supply lead. When the high-loss core 20C is inserted in the high" band coil 13C, the oscillator circuit is of the Hartley type, the coil 14C serving as the significant inductance of the oscillator circuit and the damped high band coil I3Cfrnay serve as a choke for parasitics.

In the system shown in Figure l, the coil I3'A serves as the secondary of a transformentheterminals of whose primary winding 2'4 are connected by transmission line to a dipole antenna 26. At its electrical mid point, the primary winding 24 of the high band transformer 24|3A is connected to a coil 26A which serves as a primary winding for the low band transformer, whose secondary winding is the coil MA. By this arrangement, use of band-changeover switches in the antenna circuit is also avoided. The purpose of the coupling condensers 21, 28 and grid resistors 29, and all other circuit components not specifically discussed are well understood by those skilled in the art.

By way of example, each of the low band coils |4A and MB for the specific receiver discussed may be one-quarter inch in diameter, one inch long and comprise 220 turns of No. 37 wire. The shunt condensers 29A and 29B for the low band coils I4A, [4B may be 100 micro-microfarad capacitors. When a high-loss core 20 (Fig. 2) is of cold rolled steel and has a diameter of 0.246 inch and a length of one inch, the Q of the associated low band coil drops from about 60 to less than 5, as indicated by the solid line curve 30 of Figure 3. Moreover, and as appears from curve 30, the Q of the coil remains high until-the end of the core closely approaches the adjacent open end of the coil, the zero insertion point of Figure 3, and reaches a very low value when the core is inserted to only a slight extent. Furthermore, the Q of the coil remains low and substantially constant as the kcore is to greater and greater extent inserted. When the high-loss core 20 is of sintered powdered iron, prepared as disclosed and claimed in copending application, Serial No. 770,729, iiled August 26, 1947, by Robert L. Harvey, the change in Q of the coil, as shown by curve 3l of Fig. 3, is somewhat more rapid as the core approaches the open end of the coil, the zero insertion point, and the Q of the coil when the core is inserted therein is somewhat lower than for the cold rolled steel core. However, so far as the coils used for the standard broadcast frequencies and lower frequencies areconcerned, the high-loss cores 20 may be ofV cold rolled steel.

At very much higher frequencies, for example, those of the order of 100 megacycles, the Q of the high band coils is reduced to a much` lower value when the high-loss cores are -of sintered powdered iron instead of drill rod, cold rolled steel or the like. As shown by curve 32 of Fig. 4, the Q of the high band coil is reduced from more than 160 to about 5 when the high-loss core is of-sintered powdered iron, whereas when the high-loss core is of cold rolled steel, the minimum Q is materiallyhigher, as shown by curve ..33 of Fig. 4. The high band coil I4 upon' which Fig.' 4

is based is a quarter inch in diameter and one inch long and consists of five turns of #18 wire: the effective shunt capacity 34, Fig. 1, inherent in the high band coil was 13 micro-microfarads.

For all bands, the high-loss core should be of magnetic material to concentrate the ow of the field flux through the core and for the very high frequency bands, sintered powdered magnetic material or its equivalent is preferred in order to. attain deep penetration of the core by thev iiux.

In general, as the losses in the core are due to eddy currents, the resistance of the core should notbe too low, for in such case the flux is repelled to such extent that the effective losses are low. On the other hand, if the resistance of the core is too high, the eddy currents are small and again the effective core losses are low. There is however abroad optimum range of resistance varying as a function of frequency, for which the core losses are high enough to afford the desired damping. The magnetic permeability of the core should be high to force the flux to penetrate deeply into the .core despite the repelling effect of the eddy current field.

For purposes of this invention, a coil may be considered to be high Q when the Q is in excess of 20 although in most cases the Q is 50 or even much higher. Whatever may be the Q of the band-coils, the unused coils may be retained in circuit if the Q is reduced by a factor of about 10 upon insertion of the high-loss coil.

When, as in the circuit of Fig. l, the same highloss core is used at different times to damp both a low band coil used in the standard broadcast range and a high band coil used at frequencies of the order of megacycles, it is desirable that the high-loss core be of sintered powdered iron. When in band changing, a high-loss core is selectively inserted in band coils used at frequencies of the order of standard broadcast frequencies or lower, it may be of cold rolled steel or similar magnetic material. If as in Fig. 8, different highloss cores 20 and 20D are used for insertion in different coils, those which are inserted in coils functioning at frequencies much lower than 100 megacycles, may be of cold rolled steel, drill rod or the like.

The curves 35 and 3S of Fig. 5 indicate the effect upon the Q of the high band circuit of Fig. l with different values of shunt capacitance across the low band coil. More specifically, curve 35 shows the relation between the shunt capacity of the low band coil and the Q of the high band coil with the high-loss core removed from the low band core: the curve 36 shows the relation between the capacity across the low band coil and the Q of the high band coil with the highloss core inserted in the low band coil. As apparent vfrom these curves, the capacity across the low band coil should be at least about three times the effective capacity 34 from the high potential side of the high band coil to ground to avoid undesired damping of or coupling of the damped coil of the high band circuit. With the cores'in position for reception in the high band, the large condenser across each of the low band 'coils effectively by-passes it so that although it isin lseries within the tuned loop comprising a high band coil and a condenser 34, its resistance effect does not damp the high band circuit. Thecurves 31 'and-38 of Fig. 6 are of the Q of the low band coil with the high-loss core respectively outlandin the high band lcoil vand with various capacitors shunting the low band coil. From these curves, it appears the use of substantial capacity across the low band coil to preserve the high Q of the high band coil for reception in the high band does not adversely affect the Q of the low band coil as used for reception in the low band.

It shall be understood that the invention is not limited to use with multi-band receivers suited only to receive .sound programs in the standard broadcast band and one or more ultra high-frequency broadcast bands: one or all of the bands may be for televised programs; furthermore, one or more of the bands may be for reception of amplitude-modulated signals whereas one or more of the otherI bands may be for frequency-modulated signals, and in such cases, if necessary, the appropriate intermediate frequency-amplifier and second detector are included in circuit beyond the converter tube concurrently with the bandchangeover of the preceding portion of the receiver. The band shifting of the intermediate frequency-amplifier may be effected by use of high-loss cores, as above described, or the changeover may be effected by switching as in my Patent #2,167,605.

It shall also be understood that the tuning of the coils of the several bands need not be effected by low-loss cores mechanically coupled to the high-loss cores used for band-shifting; for example, as shown in Fig. 7, the tuning of the band coils I3 and I4 may be effected by condensers 45 and 4B respectively which may, if desired, be mechanically coupled for actuation by a common dial having suitable scales for the different bands'. The band-shifting is effected by insertion of the high-loss core 28 into that coil whose Q is to be so greatly reduced as to preclude reception, for example of signals in the corresponding band. Though only a single circuit is shown, in Fig. '7, it shall be understood that the same arrangement may be used in the other circuit or circuits of the associated receiver, transmitter or other multiband radio equipment.

In the arrangement shown in Fig. 8, representative of a single-stage of any multi-band radio apparatus, the same low-loss core I8 is selectively insertable in either the high band. coil I3 or the low band coil I4, and is adjustable therein for tuning. Concurrently with insertion of core I8 in the high band coil I3, the high-loss core 20 is inserted in the low band coil I4 to minimize its Q for band shifting generally as above described. When the range of frequencies covered by the low band coil I4 is suitably low, the high-loss core may be of cold rolled steel, drill rod, or the like. When the low-loss core I8 is withdrawn from coil. I3 and inserted into the coil I4 for tuning in the low band, a second high-loss core 20D is concurrently inserted in the high band coil I3 to reduce its Q to negligible value. When the range of frequencies covered by the high band coil I3 is in the ultra high-frequency portion of the spectrum, the high-loss core 20D should be of sintered powdered iron.

It shall, of course, be understood the invention is not limited to use with radio gear suited to cover only two bands but may be extended to as great a number of bands as desired by use of a suitable number of high-loss cores and lowloss cores mechanically inter-coupled and with their spacing properly selected in accordance with the spacings between the coils to effect the desired changeover, which, as apparent from the foregoing, is accomplished by insertion or highloss cores in all of the coils except the one corresponding with the band in which operation is desired.

For a large number of bands, the physical overall length of the core-and-coil system may become quite great and require long leads to associated tube or tubes. In such cases it may be desirable to employ a band-shifting turret arrangement such as schematically shown in Fig. 9. As apparent from the drawings, the band coils I3A, I4A, I5A and IGA for one stage of the apparatus are permanently electrically connected in series and are symmetrically arranged about the axis 39 of a turret head 40 which supports a low-loss core I8 and a plurality of high-loss cores 2U, corresponding in number with one less than the total number of band coils. To select a particular band, the turret head 40 is withdrawn to the position shown in Fig. 9 and rotated to bring the low-loss core IB into alignment with that one of the coils corresponding to the band to be selected. The turret is then moved towards the coils to effect insertion of the low-loss core I8 in the selected band coil and concurrently to move the high-loss cores 20 into each of the remaining coils. If the equipment is for spot-frequency operation, nothing further is required, but if the selected band is to be tunable, the tuning may be effected either by adjustment of a variable condenser across the selected coil, or, as shown in Fig. 9, the low-loss core I8 may be moved axially of the selected coil in any suitable manner, as by adjustment of the knob 41 on the threaded shaft 4I of the low-loss core I8. This arrangement is suited, for example, for band shifting of the amplifier or converter stage of a multi-band superheterodyne receiver.

The arrangement shown in Fig. 9 may also be used for swtchless band shifting of an oscillator stage, such as shown in Fig. 10 in which the tube 42 is used as a cathode follower and the tube 43 is used as a grounded grid amplifier. The impedance 44 is common to the cathode return circuits of the tubes 42-43 and serves to couple the output circuit of tube 42 to the input or grid circuit of tube 43. The condenser 48 between the grid of tube 42 and the anode of tube 43 serves as a feed-back condenser for supplying to the grid of the tube 42 excitation of the proper phase and magnitude to insure continued generation of oscillations at the frequency determined by that one of the coils I3C, I4C and I5C in which is inserted the low-loss core I8. The high-loss cores 20 in the other coils so effectively dampen them that they are ineffective in production of oscillations.

From the foregoing, it will be apparent to those skilled in the art the invention is not limited to the particular arrangements disclosed, and that changes and modifications may be made within the scope of the appended claims.

What is claimed is:

l. A multi-band circuit selectably tunable to and throughout different frequency bands without switching comprising independent frequencyselective circuit means including separate tuning coils respectively corresponding with the different bands and electrically connected in series, low-loss core structure mechanically connected for insertion in a selectable coil for tuning thereof, high-loss core structure, and means mechanically interconnecting said core structures for movement in unison concurrently to move the low-loss core structure into a selectable coil for tuning to the corresponding band and to move the high-loss core structure into the remainder of said coils to minimize their Q and render them relatively non-selective.

2. A multi-band circuit selectably tunable without switching comprising independent frequency-selective circuit means including separate tuning coils respectively corresponding with the different bands, electrically connected in series, and mechanically aligned, high-loss magnetic core structure and low-loss magnetic core structure movable through said coils, and means mechanically interconnecting said core structures for movement in unison concurrently to move the low-loss core structure into a selectable coil for tuning to the corresponding' band and to move the high-loss core structure into the remainder of said coils to minimize their Q and render them relatively non-selective.

3. A multi-band circuit tunable over spaced bands of signal frequencies, said circuit comprising a pair of conductors providing a signal transfer path, a high band coil and an independent low band coil electrically connected in series across said path, a xed capacitor across the low band coil, a capacity connected between said pair of conductors, the capacitance across said low band coil being at least three times as great as the capacitance between said conductors, lowloss core structure movable into a selectable coil to tune said selectable coil throughout the corresponding band, and high-loss core structure interconnected for movement in unison with said low-loss core structure into the other of said coils to minimize its Q and render it relatively non-selective.

4. A multi-band superheterodyne receiver tunable without switching to different signal frequency bands comprising a heterodyne section and a local oscillator section, each of said sections comprising independent frequency selective circuit means including separate tuning coils electrically connected in series and respectively corresponding with the different bands, low-loss cores inserted in a selectable set of corresponding coils of the different sections for operation of the receiver in the corresponding band, and highloss core structure concurrently inserted in the remainder of the coils to minimize their Q and render them relatively non-selective.

5. A multiband tuning stage selectively tunable to one of a plurality of substantially dierent frequency ranges without switching contacts comprising in combination, a plurality of tuning circuits each circuit having an associated inductive winding, said inductive windings being electrical- 1y connected in series and having substantially different inductance values for effective tuning response in each of said frequency ranges, frequency range selection means comprising a plurality of separate interspersed relatively high and low loss core sections mechanically intercoupled along a common axis for unitary movement with respect to said inductive windings, and means moving said range selection means thereby selectively moving a high loss core section in inductive coupling relation to a rst of said inductive windings and simultaneously selectively moving a low loss core section in inductive coupling relation to another inductive winding to prevent resonance and effective response of said last named winding and associated tuning circuit to signals within the adjusted frequency range of the first inductive winding and associated tuning circuit, and said low loss core section including properties for causing response of the associated 10 circuits to signals within a different frequency range associated with said further inductive winding. I

6. A multi-band oscillator including circuits selectively operative as a Hartley oscillator in a low lfrequency band and as a Colpitts oscillator in a high frequency band, comprising an electronic amplier device having at least an anode, a control electrode and a cathode, two tuning coils of substantially different inductance having one end of each connected together, the coil of the higher inductance having a high potential end terminal connected to the anode and an intermediate terminal connected to the cathode of the ampliiier, a rst capacitor connected between said control electrode and the free end terminal of the coil of lower inductance, a second capacitor shunting the coil of higher inductance, and high-loss magnetic core structure selectively variably insertable in one or the other of said coils thereby to damp the oscillator circuits connected therewith for changing the oscillator from one mode of operation to the other.

7. A multi-band oscillator having a tuned circuit and a feedback lead for supplying excitation to continue oscillations at a frequency determined by said tuned circuit, said oscillator being selectively operative without switching in two bands as a Hartley oscillator and a Colpitts oscillator respectively, said oscillator tuned circuit comprising a pair of oscillator tuned circuit leads,

a rst capacitor, two inductive windings, a circ-uit serially connecting said windings and said rst capacitor between said leads, an intermediate connection on a rst of said windings, a second capacitor shunting said rst winding, a circuit connecting said feed-back lead to said intermediate connection, a damping structure comprising a high-loss core for reducing the Q of one of said windings upon movement into proximity therewith thereby effectively rendering the Winding inoperative, a low loss tuning core structure, and means mechanically interconnecting said core structures for movement in unison concurrently to move the low-lost core structure into proximity with one of said windings for tuning the corresponding oscillator circuit and to move the damping structure into proximity with the other of said windings, whereby a Colpitts oscillator circuit is eiectively provided when the damping structure is in proximity with said iirst winding and a Hartley oscillator circuit is effectively provided When the damping structure is in proximity with the other winding.

WENDELL L. CARLSON.

BEFEREN CES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,167,605 Carlson July 25, 1939 2,189,688 Thomas Feb. 6, 1940 2,295,383 Carlson Sept. 8, 1942 2,370,714 Carlson Mar. 6, 1945 2,402,260 Sands June 18, 1945 2,417,182 Sands Mar. 11, 1947 2,424,506 Sands July 22, 1947 2,433,805 Wolff Dec. 30, 1947 2,448,501 Tyzzer Aug. 31, 1948 2,461,306 Antalek Feb. 8, 1949 2,525,053 Vilkomerson Oct. 10, 1950