US2159105A - Oscillator for multiple wave band receivers - Google Patents

Description

y 23,1939- J. D. REID 2,159,105

' OSCILLATOR FOR MULTIPLE WAVE BAND RECEIVERS Filed April 50, 1937 2 Sheets-Sheet 1 f 6/1 62 15 60 a W 4 I run/x5e 1w 40 75 rSM/YG TOMA/6 2-: xwo m/a/mme 66 2 4o v 6 7 f Ihwentor M J. M

. I B y l r0 salve,- SWITCH/0'6 attorney May 23, 1939. J. D. REID 2,159,105

OSCILLATOR FOR MULTIPLE WAVE BAND RECEIVERS Filed April 30, 1937 2 Sheets-Sheet 2 9/ L g pia 99. 11% waxzzzxa" 77 I d? g I 2 s L go/v4 I 4 v amrrA/wq 7v J 1%? 4 L k l b w W/ 59 w Zhwentof attorney Patented May 23, 1939 PATENT OFFICE OSCILBATOR FOR MUL'riPILE WAVE BAND RECEIVERS? John vn. Reid, Philadelphia, 1a., assignorto Radio Corporation of- America, a," corporation of Delaware ApplicationApr-il 30, 1937; 'seriaiivo. 139,846-

13 Claims'.

The present invention relates to oscillators for multiple wave band receivers, and mcr'e parti'cularl yto a multiple wave bandtunableoscillator of the Hartley ty'p'e fof "multiple"wajve, band 5 spread tuningsystems; wherein separate inductance coils ar'e used inea'ch of the tuningibands having grid,- an'ode, andi'ntermediate cathode circuit connections, and hasior its objectto provide a simplified switching-system f'or'the circuits and coils of 'anoscillator of that type.

It is also an object-of this invention to' pro' vide a simplified switching system for anoscillat'or Y of the above type whereby it maybe-utilized efiecti vely in-a bandspread" system for tuning-a multiple wave band-receiving system as shown,

described and" claimed -inmy copendin'g applicaticnSerial No. 1393847, filed April 30', 1937;: for

Multiple waVe bane? receivers; and assigned to the same assignee as this application. Such a s stem maybovef-al plurality ofnarr'ow tuning ranges or bands which may be" chosen as whereby improved band spread of the tuning indicti'oii-may be obtained, the 300 kc: tuning range in each of several bands being-less in kilocycle 5 Width than the standardbroad'cast band for the same tuning indicator'range In any system for" Wave band change, 'it is desirable to decrease the number of" circuit changes to a minimum, and" it is therefore an 49 object of the present invention toprevid'e an' oscillator for'multiplewave band reeeiverswl'ieie' in the multiple wave band-switching ofthe oscillator is not" only simplified; but-also the number of switching contacts tobe changed isreduced 1 45 to a; minimum.

It is also an object of the present invention to' provide an improvedcoil switching system for a multiple frequency band oscillator of the Hartley type, wherein a plurality of" oscillator 50 inductances are-provided for a pluralityof'fre quency' band's 1 and wherein switching of the oathode' and anode" connections may"be eliminated" orreduced to a 'Incarrying thisobject into effect, in: connection with a band spread 55 or-multi ple wave band tuning system, the switch-- ingope'rationfor thecathode and for the anode maybe eliminatedand t'he band changing may ber'educe'dto a single switching connection for the grid.

Otlier objectsand advantages of the inveri- 5 tioriwill" be seen from-the following description when' corisidered in connection with the accompany'ing' drawings, and itsscopewin'be pointed out in the appended claiins.

In the drawings, Figure I is a schematic cir- 1O cuitdiagram 'of a multiple fre'quency'oscillatoi" for a multiple Wave'handreceiver; showing-"one embodiment of: the i'nventiomand Figure 2 is-a similar schematic circuit diagram of a modification of the circuit of- Fig. 1, show 15 ing aiui'the'r'embodiment "of the invention.

Referring to'Fig. 1-, an oscillator tube 5* hav= ing a cathode 6', an anode I, a control grid 8, together with screen and suppressongrids 9-and Hirespectively,.is selectively connectable with'a 2O sei ies of-= tuning inductances H to IT inclusive; through: a control switch t8, preferably of'the rotary t p the contacts of which are shown in the drawingsas' projected in a plane, for a better'under'standin'g of its operation. In a mul-- tiple wave band receiver, the switch'is' one unit of agang wavebandchanging switch, as-indi cate'd A variable tuning capacitor i=9 isprovi'ded for tuning the various inductance's referred to, and this is also one unit-of a gang tuning 'capacitor in 'a multiplewaveband receiver, as indicated'.

The' switching-arrangement provided by the switch l8"issuch that, th'roughthe usual grid capacitor" 42 0"; the control grid 8 is selectively'com nectablewitli the high potential or grid ends of the t'uning 'in ductances It to' H; inclusive, in a succession of steps provided by contacts indicated at 21 Thi's connct'ion is providedin the switch by a movable conductor or contact element 22 engages a; fixed contact 23='for the grid connection and'is provided'vvith a contact 24- for engaging successively with the contaets'ilfor the various inductancest Tl'ie'inductances H to" I 1, inclusive; may be considered to'lae tunable to provide oscillations for mixing with incoming signalsineachband, to provide adesired intermediate frequency in the" receiver. The mixer connection is made from the cathode by a connection lead as indicated example, the section 26 may provide the usual variable tuning capacity range of substantially 480 In. in. f. and the section 21 provides a range of substantially 15 m. In. f. as the rotor 28 is moved through the same tuning range of movement.

The switch I8 provides additional contacts 30, 3| and 32 for changing connection with the tuning capacitor stators 26 and 21. Connections are shown whereby themain stator 26 provides tuning control through the A, B and 0 bands with the coils ll, l2 and I3, respectively, as the conductor 22 is moved progressively upward, as viewed in the drawings, in three successive steps by the operation of the switch. Manual control a of the switch is indicated by the control knob 33.

For the A band, a series tuning capacitor is provided at 34, for the B band at 35, and for the C band at 36, whereby the tuning capacitor I9 is caused to track with other tuning functions in the receiver through the desired frequency ranges. The capacitor 35 is connected through a lead 31 with a contact 38, and the capacitor 36 is connected with the contact 32.

It will be noted that the contacts 23 and 3| are arranged to remain connected together through the conductor 22 for the B and C bands, and that the additional stator 21 is in circuit. This permits the B band coil |2 to be connected with the contact 3| in common with the stator 21 through .a lead 39, so that an additional switching connection is eliminated.

All of the coils except the A band coil are connected to ground or chassis at the opposite terminal from the grid terminal, as indicated. For the A band, a separate grounded cathode coil 4|) is provided, having a cathode connection provided by leads 42 and 43 through the switch ill at contacts indicated at 44, 45 and 46. For the contacts 44 and 45 a conductor element 41 movable with the element 22 is provided, and the conductor has a contact 48 for engaging the contact 46 in the A band position as shown. The conductor 4'! is joined through an insulating means 50 with a conducting element 5|, which in turn is joined with the conductor 22 through a second insulating element 52, whereby the movable switch elements may be moved together to provide a predetermined contact relation in seven successive steps.

The cathode switching connections provided by the contacts 44, 45 and 46 permit the cathode to be connected with the cathode coil 43 for the A band, and then selectively with a trimmer capacitor 54, through a contact 55, for the B band connection. At the same time, the cathode connection is changed from the A band coil 40, through the conductor 5i and a contact 56, to provide the cathode tap connection 51 on the B band coil l2. This is maintained thereat for eachof the succeeding higher frequency bands, as the conductor 5| engages and connects the contacts 58, 44 and 45 together.

Feed-back from the anode and the screen grid, to ground and the grounded ends of the inductances for the various tuning bands, is provided through a ground connection indicated at 65, and a by-pass capacitor 5| from the screen grid and anode. Operating potential is provided for the screen grid and anode through a coupling resistor 62 from any suitable source (not shown).

The variable tuning capacitor section Ell is utilized in tuning the short wave or band spread bands, and in order to obtain stability of the oscillator with respect to small changes of capacity as caused by vibration and movement of leads in the operation of the oscillator, a padding capacitor 63 is arranged to be connected in shunt across the 49-meter band tuning circuit by a contact element 64 on the movable conductor 22, and is maintained in connection across the circuit by additional contacts 65, 56 and 61, also connected with the movable conductor 22 as shown.

To keep the tuning range substantially the same throughout in a relatively narrow kilocycle band of substantially 300 kc. for the other higher frequency bands, additional padding capacitors 63 and 69 are connected with switch contacts It and (I through the contacts 54, 55, 66 and 61, in the same manner as the contact 12 for the padding capacitor 63. By the switching means shown, the additional padding capacitors are shunted across the oscillator tuning circuit as the switch I8 is moved to adjust the tuning in the higher frequency ranges. In the present example, substantially m. m. f. is added by each of the capacitors 63, 68 and 69, making a total of 300 m. m. f. shunted across the oscillator circuit for the 25 and 19 meter bands.

The padding capacitors 63, 68 and 69 are of a design having a slightly negative coefficient with regard to capacity with increase in temperature to compensate for the normal increase in in.- ductance of the tuning coils with temperature, thus holding the frequency and dial calibration constant.

In a band spread tuning system for which the oscillator is particularly effective, a change of 10 kc. may result in a five degree movement on a dial scale having, for example, a scale covering substantially and because of excessive overlap at the ends of the bands this would reduce the effectiveness of the band spread.

By maintaining the cathode connection permanently at the cathode tap on a lower frequency band coil, such as the B band coil, which has a higher inductance than that of the other shorter wave coils, the latter may each be connected at the grid end, selectively in parallel with the coil having the fixed cathode tap connection. This selective connection is provided through the contact 3|, which is connected with both the short Wave tuning stator 21 and the grid end of the B band coil l2 through the lead 39. This connection is maintained by the movable switch conductor 22 engaging the contacts 23 and 3| continuously as it successively engages the contacts 2| for the short wave band coils.

By this arrangement, a compound Hartley circuit is provided for the short wave bands, with the cathode tapped near the center of the lowest frequency band spread oscillator coil, and the higher frequency oscillator coils are successively connected in shunt across this coil and with the oscillator grid circuit and tuning capacitor stator, without shifting the cathode tap and by merely making successive grid connections with the shorter wave band coils.

The switching connection thus effectively changes only the grid connection with the grid ends of the successive untapped coils, while all other connections in the oscillator circuit are maintained substantially fixed. The switching arrangement, therefore, for the band spread and short wave'ranges is reduced to a single switching operation for the oscillator circuit with the successive high potential ends of the tuning coils.

As previously pointed out, the band changing switch I8 is shown schematically on the diagram in a projected plane and, in order to permit. a better understandingof the operation, the contacts are shown displaced with respect to their normal positions on opposite sides of the moving elements. For example, the contacts 6lthrough to 32 would normally occupy certain of the dotted positions indicated at 15, the contact 32, for example, being the same as the contact 61, and for this reason the two contacts are shown .interconnected'by a lead 16.

The tuning inductances for the narrow band, short Wave tuning in the 49 to 19'meter bands are provided preferably with adjustable magnetic cores 11, whereby the initial tuning adjustment may bemade, and this type of tuning is also providedfor the Aband coil H, as indicatedat: 18. The A band coil is also provided with padding capacitors 19-19, and is connected with automatic frequency control leads indicated at 80,

' whereby suitable means may be provided for automatic frequency control on the A band if desired. The capacitor 8| is an additional trimmer capacitor providedin shunt with the main variable tuning capacitor for the A band only.

The oscillator is provided with a grid leak 82, and is adapted for automatic volume control from a circuit 83 connected to the grid through a-seriesresistor 84.

The operation of the oscillator is such that it is selectively tunable through frequency ranges corresponding to the main broadcast band and the series of narrow band short wave tuning ranges; as well as other ranges,such as the B and C bands, with proper intermediate frequency 'separation, utilizing the Hartley circuit and an effective variable tuning capacitor arrangement comprising two sections, one of which is for the standard broadcastband and the other of which is for the short wave bands. The latter may be the only variable tuning element in circuit in the receiver for the narrow band or band spreadranges in certain receiver designs.

In covering a large number of difi'ering frequency bands, it may be necessary and desirable toprovide an additional cathode tap on the coil having the highest inductance in a particular group of coils. For the lowest frequency range and highest inductance coil in a particular group.

of coils, such as the band spread coils for the 49, 31, 25 and 19 meter bands, the cathode tap is made upon the coil l4. 1 This connection may be provided in a casewhere the continuously tunable, medium and short wave bandsB and C are eliminated for the sake ofsimplifying the tuning; system to a greater degree.

Also, it may happen that either one sectionor the :other' of the coil. providing the cathode tap may resonate in one or more of the tuningranges of coils which are to be switched in shunt therewith, in which case a cathode tap may be made onan additional higher frequency coil providing the next largest inductance.

A switching arrangement for meeting a condition of operation where an additional tap ismade upon thehighest. inductance coil of a group inthe short wave band is shown in Fig. 2, wherein a similar system to that shown in Fig. 1 is provided, with like parts bearing the same reference numerals as in Fig. 1.

Referring to Fig.2, the oscillator tube 5 is ar-- ranged to be connected with the tuning. band coils. I.|:.to ll, inclusive,- and with the variable tuning. capacitor l9 through the switch Hi, to provideetuningin the various bands in conjunctionwith the tuningcapacitor stators 26am. 2'',

in the sameamanneras. described in conjunction with Fig. 1. The right hand contacts on the switch, however,-have been moved, together with the movable conductor element 22, into a slightly'differing relation to the left hand fixed contacts and the movable conductor elements 41 and 5|.

The connections'of the right hand fixed contacts have also'been slightly. altered for the purpose of permitting an additional cathode tap on the 49 meter band coil I4; as indicated at 90. As above mentioned, this has been found to be desirable-when either section of the tapped coil normally used, such as the tap l 2 for the B band, is found toresonate within the tuning band of certain of the higher frequency coils which are to be switched in parallel therewith. In the present example, if the B band coil'is found to resonate with its distributed capacity, within the C band or any of the other higher frequency bands, the additional tap is made upon the next lower inductance coil, which may be the 49 meter coil in the present example.

In doing this, the contact 55 of the switch is utilized to provide the tap connection through a lead ill with the tap 51 on the B band coil I2, and the contact 56, formerly utilized for the B band coil tap, is connected through a lead 92 with the tap 90 on the 49 meter band 'coil, so that the 49 meter band coil is connected into circuit and remains in circuit for the C band and the narrow band or band spread ranges for the 49 to 19 meter bands, as the cathode tapping coil.

With the contacts shifted as shown, whereby the-contact 66-is opposite the lowermost contact 2|, the 49 meter high frequency secondary terminal is connected through a lead 93 with the contact 23, which is opposite the contact 44. The-B band high frequency. terminal is connected through the B band series tuning capacitor 35 and a lead 94 with the contact 65, and the A band coil is connected through the series tuning capacitor 34 and a lead 95 with the contact 66. Otherwise the connections with the left hand contacts of the switch arethe same and for the same purpose as in the circuit shown in Fig. 1.

Since the contact 56 is utilized for connecting the tap 90 on the 49 meter band coil with the cathode lead 43 through the contacts 44 and 45 when the switch is moved to the C band posi tion, butnot for the B band position, the length of the movable conductor element 5| is such that it does not engage the contact 44 until the C band position of the switch is reached.

The grid of the oscillator is coupled directly to the tuning capacitor stator 21 and to the grid capacitor 20, and is also connected to the fixed switch contact 10' which is arranged to engage the movable conductor element 22. The stator element 26 is also connected to the movable conductor element 22 through the contact 64, in series with a fixed capacitor 36 which is effective forthe C band as well as the A and B bands.

In the A band position shown, it will be seen that the A band coil H is connected'through the contact 66 and the contact 24 of the movable conductor 22, to both sections of the capacitor l9 and to the grid of the oscillator. In the second position, the contact 65 for the B band is connected to the grid of the oscillator and to both sections of the capacitor l9. In the third position, the contact and the contact 2| for the C band are bridged and the oscillator gridand tuning capacitor-section 21 remainconnectedin- 75 tion of the stator, 21, is utilized for tuning in circuit as before. At the same time, the conductor 22 engages the contact 23 and places the 49 meter band coil M in parallel with the C band coil to provide the cathode tap for the C band tuning which is then completed through.

the movable conductor 51, then in engagement with the contacts 55 and 44.

The B band center tap is made in the second position of the switch when the contact 43 engages the contact 55. This connection is opened as the contact 48 moves beyond the contact 55, for the C' band position.

In the 49 meter band position, the contact 24 of the switch conductor 22 engages a contact 9'! which is connected with a trimmer capacitor 98 for the 49 meter band and, since the contact 64 is then out of circuit, only the smaller secthis band and the following band spread or narrow band tuning ranges. For each of the subsequent high frequency band positions, the coils l5, l6 and I1 are successively connected with the conductor 22 which then bridges the contacts 18, 23 and the contacts 3D, 3! and 32 in succession to increase the load across the oscillator circuits as hereinbefore described, and thereby to provide stability of operation, through the addition of the capacitors 63, 6B and 69.

In this arrangement, each of the coils l3, l5, l6 and I! are successively connected in parallel with the cathode tapped coil M by switching a single grid connection to the successive coils, thereby greatly simplifying the switching required. In addition, it will be seen that provision has been made for additionally tapping a second coil to eliminate distributed capacity resonance of one tapped coil from falling within the tuning range of the remaining coils of the sequence, in adjusting the wave band response toward the high frequency end of the tuning range of the oscillator.

In certain designs, depending upon the type of tube and the available voltages, it may become desirable to provide additional feed-back for the oscillator on the higher frequency range, in which case, as shown in the present example, the oscillator anode is coupled back to the highest frequency secondary coil through a coupling coil indicated at 99, and is then connected to ground along with the screen grid through the capacitor BI and the ground til, as shown. In this manner, the feed-back is also applied to the grounded portion of the cathode tapped coil to provide the oscillator feed-back in each band.

As in the preceding embodiment, the oscillator is adapted to operate in conjunction with a multiple wave band superheterodyne receiver, in which case the switch is provided as one section of a gang and the tuning capacitor is likewise connected to the tuning capacitors of the other tuned circuits of the receiver, as indicated.

In the present example, as in Fig. 1, the oscillator potential is delivered to the mixer or converter tube through the output lead 25 connected with the cathode lead 53, coupling in the present example being provided by a coupling capacitor Hi across a grid or output coupling resistor [01. This connection is made preferably to a suitable mixer grid in the converter tube (not shown).

In the present example also, the padding capacitors for the A band coil i are omitted for the reason that they may be placed in the automatic frequency control apparatus, connection with which is indicated by the leads 80.

Since the operation of this embodiment is the same as the preceding embodiment, except for the feed-back on the highest frequency band and the provision of additional tapping of a second wave band inductance for the cathode circuit. further description is believed to be unnecessary.

From the foregoing description, it will be seen that a stabilized Hartley oscillator circuit may be provided in accordance with the invention with a minimum number of switching connections to cover a relatively large number of wave bands, and that by means of separate coils for the short wave broadcast bands, full scale tuning may be obtained in each band, thereby providing band spread in the oscillator to at least as great an extent as in the domestic or standard broadcast band, and that, in addition, other tunable bands may be provided whereby the oscillator is made to cover a relatively wide frequency spectrum.

A preferred application of the invention to a radio receiving system of the superheterodyne type contemplates the omission of the coils for the B and C bands, and the use of only the broadcast and the 49, 31, 25 and 19 meter bands, whereby the switching may further be simplified by the omission of contactsv and connections necessary for these additional B and C bands. In this manner the oscillator may provide signals for mixing in the main broadcast bands for both foreign and domestic reception, with the wide range tuning of the short wave bands in widely spaced bands of relatively narrow kilocycle width, while the same tuning control may be used for all bands with the same scale width of'tuning indication.

The use of two differing tuning capacitor sections, with a common rotor and selective switching means for the sections, permits the oscillator to be tuned more effectively and to provide a higher and more uniform voltage output through the use of proper design of and higher inductance in the tuning coils.

It will also be seen that by providing separate tuning bands for the short wave broadcast frequency ranges, a coil design may be utilized such that a differing intermediate frequency may be produced for the short wave bands than for the broadcast band in any or all of the short wave tuning ranges.

By providing an oscillator having a plurality of tunable frequency ranges, one of which may cover a frequency range corresponding to the standard broadcast band of substantially 1,000 kilocycle width, and a plurality of relatively narrow band tuning ranges of substantially lesser kiiocycle width, the band spread on the tuning dial of the receiver may, in the short wave bands, be made equal to or greater than that for the first named frequency band, and the oscillator may be utilized as the tuning means for the receiving system in the short Wave bands.

I claim as my invention:

1. A multiple frequency range oscillator for multiple wave band signal receiving systems and the like, comprising in combination, an oscillator tube having control grid, cathode and anode electrodes, tuning means for the oscillator including a variable tuning capacitor and a plurality of tuning inductances adapted to be tuned thereby through a plurality of differing frequency ranges, each of said tuning inductances being connected at one end to the anode electrode, means for connecting said tuning capacitor and the oscillator grid jointly with the oppo- 7 site end of each of said inductances; selectively,

means providing connections for maintaining one of said inductances :in; circuit withv said tuning capacitorand grid for a'plurality of said selective connections, and means providing a fixed cathode tap connection on .saidlast named inductance only.

2. A multiple frequency range oscillator for multiple wave band signal receiving systems and the like, comprising in combination, an oscillator tube having control grid, cathode and anode electrodes, tuning means for the oscillator including a variable tuning capacitor and a plurality of tuning inductances adaptedto be'tuned thereby through a plurality of diifering'frequency ranges of substantially equal kilocycle width, each of said tuning inductances being connected at' one end to the anode'electrode, means for connecting said tuning capacitor and the oscillator grid-jointly with-the opposite end of each of said inductances selectively, means providing connections for maintaining one of said inductances in circuit with said tuning capacitor and grid for a plurality of said selective connections, means providing a fixed cathode tap connection on said last named inductance only, and selective switching means forv controlling said grid and cathode connections jointly in predetermined relation to each other.

3. A.mu1tiple frequency "range oscillator for multiple wave band receiving systems and the like, asdefined by claim 1,-f-urther characterized I by the fact that 'meansare provided for tuning said oscillator through a frequency range having a kilocycle width greater than said-first named frequencyranges and that said first named frequency ranges are of substantially equal kilocycle width.

4. In a tunable oscillator, the combination of an oscillator'tube having an anode, a cathode and an input grid circuit, a variable tuning capacitor, means providing a plurality of wave band tuning inductances each having a feedback connection with the anode, one of said inductances having a higher inductance value with respect to others of said inductances for tuning in a lower frequency band, means for connecting said grid circuit and said variable tuning capacitor jointly in parallel with each of said inductances selectively, means for, maintaining said parallel connection for said one inductance throughout a series of said selective connections for certainof said inductances, and means providing a connection for saidcathode withsaid one inductance intermediate its terminal ends.

5. A multiple frequency range oscillator for multiple wave band signal receiving systems and the like, comprising in combination, an oscillator tube having a control grid, a cathode and an anode electrode, meansproviding an alternating current path .to ground for said anode electrode, tuning means for. said oscillator including a variable tuning capacitor, and a plurality of tuning inductances adapted to bev tuned thereby through a plurality of differing frequency ranges, each of said tuning inductances being connected to ground at one end, selective switching means for connectingsaidotuning capacitor and the oscillator grid jointly with each of said inductances at the ungrounded end thereof, additional means independent of said last named means for maintaining the lowest frequency inductance in circuit connection with said tuning capacitor and grid, and means providing a fixed cathode tap series while said first named connection for said tube on .saidlast named in- :ductance only.

6. In a multiple frequency range oscillator, the combination with an electric discharge device,'of multiple frequency tuningv means therefor coil :for the lowermost frequency tuning range .of a series of higher frequency tuning ranges,

means providing a substantially fixed cathode circuit tapconnection for said tube with said one coil, means'for connecting a portion of the tuning capacitor selectively with each of said icoils;and means providing selective grid circuit connections forsaid tube with each of a plurality of the remaining higher frequency coils in said grid and cathode circuit connections are fixed.

'7. In a multiple frequency range oscillator, the combination with an electric discharge device having a cathode, a control grid, and an anode electrode, of multiple frequency tuning means .therefor comprising a variable tuning capacitor and a plurality of inductance coils adaptedto be tuned thereby through a plurality of differing frequency ranges, each of said inductances hav ing a grid terminal and. an anode terminal, means providing a fixed alternating current path between the anode electrode and said anode'terminals jointly, means providing a circuit connection between the grid terminal of a low frequency band inductance coil and the grid, means for maintaining said connection and selectively connecting said grid with each of the grid terminals of the remaining inductances successively, and means providing a fixed connection between an intermediate terminal on the firstnamed inductance and the cathode, whereby a Hartley connection is provided in each of said tuning ranges successively by shifting the grid connection with the several inductance coils.

8. In a multiple frequency range oscillator, comprising an electric discharge oscillator tube having an anode circuit, a cathode circuit and a control grid circuit, the combination of tuning means therefor, including a plurality of tuning inductances at least one of which is tunable through a predetermined lower frequency range, and a plurality of which are tunable through spaced higher frequency ranges of lesser kilocycle width than the first named range, a variable tuning capacitor having a first section for tuning said first named inductance and a second section for tuning said plurality of inductances through said higher frequency ranges, means providing a common fixed anode circuit connection for said tube with one end of each of said inductances, means for connecting said grid circuit with the opposite end of one of said higher frequency inductances, means for maintaining said connection and selectively connecting grid electrodes, of a tuning inductance having its terminals connected with the anode and control grid electrodes of said oscillator tube and having a cathode connection with said tube intermediate said terminals, a variable tuning capacitor connected substantially in parallel with said inductance providing therewith a predetermined oscillator frequency tuning range, a separate tuning inductance for each of a plurality of higher frequency bands tunable through each of said higher frequency bands by said variable tuning capacitor in band widths of substantially equal kilocycle width, and a selector switch unit for connecting said last named inductances selectively in parallel with said first named inductance and tuning capacitor.

10. In a multiple frequency range oscillator,

the combination with an electric discharge oscillator tube having anode, cathode and control grid electrodes, of a tuning inductance having its terminals connected with the anode and control grid electrodes of said oscillator tube and having a cathode connection with said tube intermediate said terminals, a variable tuning capacitor connected substantially in parallel with said inductance providing therewith a predetermined oscillator frequency tuning range, a separate tuning inductance for each of a plurality of higher frequency bands tunable through each of said higher frequency bands by said variable tuning capacitor in band widths of substantially equal kilocycle width, and a selector switch unit for connecting said last named inductances selectively in parallel with said first named inductance and tuning capacitor, said selector switch unit including separate movable conductor elements for controlling the cathode and the grid circuit connections and additional contacts for the grid circuit connecting element, and a plurality of padding capacitors connected with said last named contacts for stabilizing said oscillator in the higher frequency tuning ranges, said capacitors having a negative co-efiicient of capacity change with increase in temperature.

11. In a multiple frequency range oscillator, the combination with an electric discharge oscillator tube having anode, cathode and control grid electrodes, of a tuning inductance having its terminals connected with the anode and control grid electrodes of said oscillator tube and having a cathode connection with said tube intermediate said terminals, a variable tuning capacitor connected substantially in parallel with said inductance providing therewith a predetermined oscillator frequency tuning range, a separate tuning inductance for each of a plurality of higher frequency bands tunable through each of said higher frequency bands by said variable tuning capacitor in band widths of substantially equal kilocycle width, and a selector switch unit for connecting said last named inductances selectively in parallel with said first named inductance and tuning capacitor, said tuning capacitor having two variable capacity elements, and said selector switch unit having contacts for selectively connecting said variable tuning capacitor elements with certain of said tuning inductance windings.

12. In a multiple frequency range oscillator,

the combination with an electric discharge oscillator device having an anode, a cathode and a control grid, of tuning means therefor including a tuning inductance having its terminals connected with the anode and control grid electrodes of said oscillator device and having a cathode connection with said device intermediate said terminals, a variable capacitor connected substantially in parallel with said inductance providing therewith a predetermined oscillator frequency tuning range, means for shifting the tuning of said oscillator through a plurality of differing spaced narrow band higher frequency bands comprising a separate tuning inductance for each of said bands having a common connection at one end of each inductance with the anode connection of said first named inductance and being tunable through each of said higher frequency bands by said variable tuning capacitor in band widths of substantially equal kilocycle width, and a selector switch unit for connecting the grid end of the first named inductance selectively with each of said additional tuning inductances at a terminal end thereof opposite from the anode circuit connection therewith, and means for stabilizing the operation of said oscillator in each of said higher frequency tuning ranges comprising a plurality of padding capacitors selectively connectable in shunt with said tuning inductances through said switch means, said padding capacitors having a negative temperature coefficient of capacity with increase in temperature thereby to compensate for the normal increase in inductance of the tuning inductances.

13. A multiple frequency range oscillator for multiple wave band signal receiving systems and the like, comprising in combination, an oscillator tube having a grid'circuit, an output anode circuit and a cathode circuit, means for tuning said oscillator through a plurality of frequency bands, differing by a predetermined intermediate frequency from corresponding signal receiving bands, comprising a plurality of tuning inductance windings, one for each of said bands, each having a connection at one end with said anode circuit, and one of said inductance windings hav-' ing a tap connection intermediate its terminal ends with the cathode circuit, a variable tuning capacitor for said inductance windings having a rotor connected with said anode circuit and inductance windings and having two stator sections of differing variable capacity range common to said rotor, and switch means having a series of contacts connected with said tuning capacitor stators, said grid circuits and each of said tuning inductance windings at a terminal spaced from the anode circuit connection, movable conductor elements in said switch means providing a fixed grid circuit and tuning capacitor connection with said terminal of the inductance winding having said cathode tap connection, and selective grid circuit connections for said terminal with the terminals of each of a plurality of higher frequency band inductance windings, whereby each of said windings is successively placed in shunt with said one winding.

JOHN D. REID.

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