US2246696A - Oscillator system - Google Patents

Description

June 24, 1941. REID 2,246,696

OSCILLATOR SYSTEM Original Filed Aug. 31, 1935 2 Sheets-Shet l ushiyh l 63% Home on. GUN 4 Sm w w mum HBM f w w hum 7 mum m l .EWQN 6 W M x A QQNN EN mum W4 93 u .W QHN m %Wv m an INVEN'I'OR John D. Reid Patented June 24, 1941 osomLA'ron SYSTEM John D. Reid, Philadelphia, Pa assignor to Radio Corporation of America, a corporation of Delaware,

Original application August 31, 1935, Serial No. 38,762,, now Patent No. 2,149,231, dated February 28, 1939. Divided and this application,

tion January 31, 1939, Serial No. 253,829

21 Claims. (01. 250-36) The present invention relates to an oscillator system and more particularly to a variably tuned oscillator for a superheterodyne radio receiver operating over several different frequency bands or ranges including an ultra high frequency range.

This application is a divisional of my application Serial No. 38,762, filed August 31, 1935, now Ratent No. 2,149,231, issued February 28, 1939, the invention being directed to the oscillator.

An object of the invention is to provide a stable oscillator tunable nverany of several frequency ranges, particularly an ultra high frequency range, and characterized by substantial uniformity or sufliciency ofsignal strength or gain throughout any of said ranges.

More particularly, it is an object of my invention to provide a highly stable oscillator, tunable throughout a -wide ultra high frequency range with uniform or adequate signal output throughout said range. y

In accordance with the invention, the principal object is attained by providing a variably is caused to be connected for differing modes of operation in a Hartley type of circuit generally and modifications thereof, depending upon the wave band or frequency range to be covered. Coupling with a mixer tube of improved electrode arrangement is provided between cathode and ground of the oscillator.

The invention will, however, be better understood irom the following description when taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims. j

In the drawings,

Fig. 1 is a schematic circuit diagram of a por-- tion of the signal input circuits of a superheterodyne receiver, including a frequency changer system embodying the invention, and- Figs. 2, 3 and 4 are simplified schematic. circuit diagrams of the oscillator portion of the circuit of Fig. 1, showing connections for three differing modes of operation as provided by the circuit of Fig. 1.

tuned oscillator with a plurality of feedback paths from different anodal electrodes, one of which is a screen grid or additional electrode, the feedback path from the anode feeding back principally the lower frequencies 01'. the tunable working range in complementary relation to the screen grid feedback path which is deficient in output signal strength at the lower end of the range, thereby reinforcing the lower end and giving adequate or substantially uniform gain throughout the range.

It is a further object of the present invention to provide an improved frequency band or tuning range changing systemfor an oscillator for a superheterodyne receiver and an improved coupling arrangement therefor whereby the frequency changer system in which it is included provides a signal output of substantially uniform amplitude. i

Stated more fully, it is an object of the invention to provide an improved, mu1ti-range, tunable, oscillator system embodying an electric discharge oscillator device and an improved frequency changer device in connection therewith so interconnected and jointly controlled in the Various wave bands that uniform amplitude of oscillation,

high stability and decreased reaction betweeen the elements of the frequency changer device may be obtained together with a uniform detector signal output at all frequency bands.

In accordance with the invention, the oscillator,

embodying an electric discharge oscillator device,

Referring to Fig. 1, a radio frequency amplifier including an electric discharge device 5, is coupled through an adjustable coil system, of which one coil or transformer l is shown, to a source of si nal energy such as an antenna 9. The amplifier 51s in turn coupled through a coil system represented by a transformer II, with a first detector, frequency changer or mixer tube l3, of the elec tric discharge type. An electric discharge oscillator device is indicated at iii and forms part of an oscillator system, hereinafter described, for supplying oscillations to the mixer tube i3. I latter is coupled to output leads i7. through ii intermediate frequency coupling transfer-n -i The coil system for-the highfrequency amplifier 5 and first detector 59 may be of any suitable type, controllable by suitable tap switches ii i, it, it and 21, connected for single control or gang operation by suitable means as indicated by the dotted connection 3! with a control knob 29. The switches 23 and 21 represent means for shifting the grid connections of the tubes 5 and it while the switches 2i and 25 represent similar means for shifting the antenna and the plate connec tions for tube 5 simultaneously with the switches 23 and 2.1, to'the differing sets of coils in circuit with the tubes 6 and i3, to provide a multirangr-ituning system for the radio frequency amplifier; and first detector. The system is, however, adapted to provide a wide frequency range of operation. In'the present example the switches are arranged to cover five differing wave bands which are arbitrarily designated as the X, A, B,

bands only being shown to illustrate the particular connections provided in the present preferred system. In the circuit diagram, the coils are shifted in conjunction with suitable variable tuning capacitors 33 and 35 for the radio frequency or high frequency amplifier and the first detector or mixer tube respectively and these are in turn interconnected for gang operation by suitable means as indicated by the dotted connection 31.

For a further understanding of the wide frequency range covered by the system shown, the

} medium frequency range quency, medium frequency and high frequency ranges.

In the present example, in the high frequency or'D range, the first tube or radio frequency amplifier isremoved fromthe circuit, and signals from the antenna are directed from the contact B of the switch 2| through a lead 39 to the circuit wiring associated with the contact.D of the grid switch 21 for the detector mixer tube f3. The wiring comprises a connection lead 1 between the ground 43 and a tap 45, a second connection lead 47 between the tap 45 and thecontact D of the switch 21 and a third circuit lead or wire 49 from the switch arm 21 through to a point of connection 5| with the tuning capacitor 35 for the grid or input circuit of the first detector 13.

In the D band or high frequency range, the inductance'of the wiring alone is utilized inconjunction with the tuning capacitor to provide an auto transformer for coupling the antenna directly to the grid of the first detector l3, the primary of the auto transformer comprising the wire 4| and the secondary comprising the wire 4| and the wires 41 and 49 which, in the physical arrangement of a receiver, are connection leads of sufficient size to be rigid and cut to the proper length to provide the desired inductance to tune through the indicated range with the common tuning capacitor 35, in the high frequency hand.

For the C band, which is within the medium frequency range, the coils or transformer I and II are utilized to couple the antenna with the radio frequency amplifier 5, and the latter'with the detector l3 through the switching contacts C -of the switches 2|, 23, and 21, the inductance of the transformers being such that the same tuning capacitors 33 and may be utilized to tune through the C range as above indicated. The remaining bands B, A and X are similarly arranged and for the-purpose of simplifying the drawings the inductances therefor have been eliminated since such switching connections, are

I grid 5| is connected through an input lead 53 with the switch 23, then through the coil system to a common lead 55 in which is provided a filter Cand D bands, the connections for the c and n comprising a series resistor 51 and bypass capacitor 59. Through the filter, the lead 55 is connected with a lead 6| providing a suitable source of automatic volume control potential as indicated. The connections for the various bands for the lead 55 are indicated in connection therewith.

The radio frequency amplifier 5 is provided with a self -bias resistor 33 to establish an initial bias 'in addition to the automaticvolume control potentials received through the lead 6|.

The first detector or mixer tube I3 is of the multiple grid type, termed a pentagrid-mixeramplifier and may be of the type 'now to be known commercially as RCA-6L7. This is a new commercial type of tube having a grounded metal envelope 65. It is provided with an equipotential cathode 61, a control grid 69 and an output anode H. In addition, it is provided with a suppressor grid 13 connected with the cathode, and three additional grids 15,11 and l8,'the latter two being screens on either side of the grid 15 and interconnected, whereby the latter grid is shielded from the control grid 69 'and the output anode H by the grid |'|'|8 as well as by the suppressor grid 13.

The grids ill and 18 provide a screen structure which maybe termed a screen grid or screen for anode 1|, signals applied thereto are mixed to provide a desired intermediate frequency signal from the output anode H and thence through the intermediate frequency amplifier transformer l8.

The cathode 61 of the detector is provided with a self-bias resistor 19 and the inductances for the D andC bands are connected to ground, the

ground for the C band being indicated at BI and for the'D band at 43, whereby the signal control grid 69 is self-biased for the said bands. For the remaining X, A and B bands,-additional automatic volume control bias is obtained from the supply lead 6| through a filter comprising a series resistor 81 and bypass capacitor 89. The bias supply is taken through taps 85 as shown for the X band which is shown complete with the coil 83. With this arrangement, the first detector is provided with automatic volume control in certain of the lower medium frequency and low frequency ranges. It has been found that this arrangement tends to provide a more uniform output from the detector as is desirable, and prevents varying load conditions from affecting the oscillator on the higher frequency bands.

It will be noted that the radio frequency amplifier 5 is provided with an additional series resistor 9| in the cathode lead 93 and that this is controlled by a tap switch 95 having contacts corresponding to the contacts of the switches previously described. The contacts B, C and D are connected to ground as indicated at 91, while the contacts X and A are open circuited, thereby providing means for short-circuitlng the additional resistor 9| in the B, C and D bands only. It will be seen that in the X and A bands the negative bias on the radio frequencytamplifier is thereby increased by the amount of the potential drop in the resistor 9|. The sensitivity of the receiver for the A and X bands is, therefore, simultaneously decreased with wave band change. The operating connection for the switch 95 is indicated by the dotted line connection 99.

In connection with the radio frequency amplifier stage it should be noted that the contact D for the grid control switch 23is connected through a lead IOI with the bias supply lead 55 whereby the tube is under control of the bias supply system although not in directoperation for the transmission of signals. Likewise, the D contact for the anode switch 25 is connected with the contact C whereby plate potential is maintained on the tube for the D band. Anode supply for the tube 5 is provided through the supply lead I03 and in turn is connected, through a filter resistor I35 provided with a bypass capacitor II", to a potential supply lead I33.

In connection with the detector tube I3, the

cathode is connected to ground for radio frequency potentials through suitable bypass capacitors III and H3 and the screen grid 11 is likewise grounded at radio frequencies through a bypass capacitor II5. Both the screen grid and anode leads are provided with suitable series re- The radio frequency amplifier tubemay be of the type known commercially as the RCA 6K7, triple-grid control amplifier. The oscillator I5 is also preferably of the metal enclosed type comprising a grounded metal envelope I29, an equipotential cathode I3I, a control grid I33, a screen grid I35, and suppressor grid I31. 'The main, anode is indicated at I39. This may be of the type known commercially as RCA-6J7. The oscillator is of the grid leak and capacitor type, the control grid I33 being connected through a grid capacitor I4I- to the variable tuning capacitor I43 to the contact arm of a grid switch M5 andis also connected to ground I41 through a grid leak I49 and thus through the coil to the cathode. I

The cathode of the oscillator is directly coupled or connected to the second or outer control grid I5, of the detector I3, through a connection lead I5I and a grid or coupling capacitor I53. a grid leak connection I55 is provided between the grid I5 and the cathode 81. Both the oscillator grid. I33 and the oscillation grid I5 are, therefore, grid leak and capacitor coupled to their respective sources of signal potential. The oscillation grid I5 receives oscillations from the cathode of the oscillator.

heretofore been possible: Furthermore, because of the location of the grids and relatively high degree ofscreening in the mixer tube I3, the reaction between the signal and oscillator circuits has been reduced, that is, the reaction between circuits connected with the grids 69 and I5. This is a material advantage in aligning the various circuits connected with the oscillator and detector.

Because of the electronic coupling of the secondcontrol grid I5 which is connected with the oscillator I5, as hereinafter described, and because the grid I5 is well shielded, the direct coupling to the oscillator circuit and the capacity coupling [therewith is relatively low. This results in less change of amplitude or frequency because of changes in load caused by tuning the circuit connected to the grid 69.' r

The radio frequency amplifier 5 may be of any suitable type, but is preferably of a type comprising a metal grounded shield "9 containing an equipotential cathode I2I, an output anode I23 in association with the control grid, together with a suppressor grid I25. and a screen grid I21. It will be noted that like the screen grid and anode of the detector I3, the screen grid I2! is provided with a seriesresistor I23 and the anode I23 is provided with the series resistonllli.

In connection with the automatic volume control lead 6|, the same automatic volume control potential is applied to all tubes and the control of gain is regulated by the operation of the anode and screen grid series resistors, which, in operation, tend to raise the electrode potentials as the control grids are caused to become more negative in response to increased signal strength. By properly relating the resistance in the screen and anode circuits, the gain maybe controlled without resorting to a-voltage divider resistor for the automatic volume controlcircuit. This obviates the necessity for applying differing automatic volume control potentials to the various controlled tubes As a miner tube or first detector, it has been found thatthe electrode arrangement best adapted for a high frequency range of operation in a broad frequency. range, is with the inner grid asthe signal control grid while the second or outer control grid is utilized as the oscillation grid. As fhereinbefore described, it is provided preferably with a grid leak and capacitor type of bias supply. The inner or control grid is provided with an automatic volume controlled or a fixed negative bias.

It has been found that this grid connection prevents degenerative action in the mixer tube as encountered heretofore in muitigrid devices when the outer grid is utilized as the signal grid.

With the present arrangement, having the outer grid connected to the source of oscillations and to the cathode through a grid leak resistor, while the inner grid is utilized for the signal, the degenerative effect is not present and. the device provides signal amplification instead. In this connection, therefore, the inner control grid will be referred to as the signal grid and the outer control grid-as the oscillation or oscillator grid.

The control grid I33 of the oscillator is colt" 1 nected with the various wave band circuits conand simplifies the automatic volume control 5375- I tern.

trollable by the switch I45 and a second switch I51 is provided to change the cathode connections with said circuits. "The latter switch may be termed the cathode coil-selector switch while the switch I45 is the grid coil selcctor switch.

The grid coil-selector switch arm is CCIl'il'li ted with the tuning capacitor M3 through a 1 connection or lead indicated at Mill. flYhe iii on is provided with contacts corresponding in ltllJllil ber to the number of wave bands to be covered, in this case five bands, and the switclizl contacts corresponding thereto are indicated it. Wt, C and D for the wave or frequency h ids hare inbefore indicated, and reprcsentirl a morality of bands covering a wide frequen en tending into a relatively high fre liency range.

The contact D of the grid col selector switcizl is connected to ground icated at it'd in or lead cont tin llfltiillil'ififti the contact D of the cathode selector switch I51 whereby, when the switch I51 is in the position shown, the cathode of the oscillator is connected to the tap I61.

The combined length of the lead wires I59 and I63 is such that, with the-switch I45 in the position shown, suflicient inductance is included therein to form a grid inductance for the oscillator while the lead I65 to ground forms the anode inductance ofa Hartley type oscillator, the total inductance being tuned by the capacitor I48.

The oscillator I5 utilizes'both the main anode I39 and the screen grid I35 as anode electrodes, with the suppressor grid I31, between the two anode electrodes, connected to ground as indicated at "I.

The oscillator suppressor grid may be tied to the screen grid of the detector, bypassed to ground, and both grids may then be series fed from the positive +B supply source. This is of advantage when automatic volume control is applied to the detector as the screen voltage regulation is then such that the voltage change of through the common series resistor II1.

In order to decouple the two electrodes, a filter is provided in the lead I68, comprising a series resistor I12 and bypass capacitor I14.

It has been found that variations in screen grid current causing variation in the drop in the resistor II1, provide potential changes in the proper direction on the suppressor grid of the oscillator to maintain its plate or anode impedance at the proper values to counteract the load change of the detector tending to change the oscillator output amplitude and frequency.

The anode circuit for the screen grid I35 is completed to the ground I6I through a by-pass capacitor I13 and a ground connection I15 from the anode screen grid lead I11. A series resistor I19 is provided in the lead I11 between the screen grid and the source of anode or screen grid potential represented by the supply lead I8I. This resistor has a desirable regulating function on the oscillator which will hereinafter be described.

The main anode I39 is connected through an output anode lead I33 to a feed back coil or winding I85, thence through a lead I01 to a second feed back coil I89 and is connected to a source of anode potential provided by the supply lead I09, through a series regulating and filter resistor I9I provided with a bypass capacitor I93. The function of the resistor I9I in regulating the osciliator and in-conjunction with the resistor I19 will hereinafter be described.

With this arrangement, the'screen grid I35 as an anode, is coupled in the oscillator circuit through the inductance of the lead I65, with the cathode connected to the tap I61, and grid connected to the end terminal of the inductance represented by the lead I59 and the lead I63 in pling is provided through the main anode I39 and the feed back winding I85 which comprises a few turns coiled adjacent to the'grid switch I45 -in inductive coupling relation to the wires I63 v and I65. An anode circuit switch having a three element movable contact arm I95 is provided with contacts corresponding to the selected wave bands X, A, B, C and D and, in addition, two spaced contacts I91 and I99, the latter contacts and the contact B being engaged by the three element contact and connected to ground 20I, in

the position shown. In this position, through the contact I91, the main anode circuit is shunted to ground through a bypass capacitor 203 on the low potential side of the feedback winding I85. The alternating current path from the main anode to cathode therefore, includes not only the feed back winding I85 but also the lead I65 or anode inductance, through the ground connections 20I and I6I.

The contact C of the switch I95 is connected through a bypass capacitor 205 to the lead I83 and thereby to the anode I39 for connecting the anode directly to ground through the switch arm when the switch arm is moved to the left as viewed in the drawings to engage the contact C,

and because of the triple arm, the contact C is connected to ground for the positions B and A of the switch I95. Since the contacts B, A and X are blank in the position X, the ground 20I is each connected through series capacitors 221, 229

and HI, respectively, to corresponding contacts C, B and A on the grid coil selector switch I45 through suitable grid leads 233, 235 and 231.

The inductance for the X band as indicated at 239 is an inductance without tap having the grid end connected to the contact X of the switch I45 to a lead 24I and having the opposite end connected. to ground 243 through a series adjustable capacitor 245. Each of the inductances for the X, A, B and C bands is provided with shunt terminal capacitors indicated at 241 and the series capacitor 23I for the grid circuit of the A band is also provided with a shunt trimmer capacitor indicatedat 249.

With this arrangement it' will be seen that the cathode I3I of the oscillator and the oscillation grid 15 of the first detector or mixer tube may be connected to differing tap points on the various inductance elements for the various wave bands to be covered, while the control grid connection may be made to the grid ends of the inmain anode series through the switch 145. Additional cou- 7'5 ductances for the bands C, B and A through series capacitors 221, 229 and 23I, respectively. The grid connection for the band X is made directly to the inductance 239. The inductance of the lead I59 between the switch I45 and the tuning capacitor I43 for the oscillator has a negligible effect in the lower frequency bands, such inductance having less than one percent of the inductance in the B band coils.

For the C, B and A bands, the oscillator anode connections for both the screen grid I35 and the I39 are completed through the grounded ends of the inductances and the bypass capacitor 205, directly from the anode lead I33 and through the bypass capacitor I13 from the screen grid lead I11, both anode electrodes being thereby effectively coupled through the inductances of the C, B and A band.

band A is connectedthrough a lead I" with the Q contact X are'blank. ;The main movable contact 1 said inductances are ineffective tointer! the operation of the D'band inductance It will be noted that to; the x receives oscillator Also. it will be seen that for theC -Bfand A 2 bands theseriescapacitors 221, 22! and!!! are for the X band is included in the alternating cur- 5 rent path from the anode I. In thiscase the screen grid I35 is ineffective to set up voscillations.

It will be noted that the lead 225 from the intermediate tap iii of the inductance III for the.

contact D of the anode short-circuiting switch Iii. This is for the purpose of short-circuiting to ground the anode portion of the inductance 2H for the bands C and D aswell as tl' 1e'- band* .8 since this is the largest of the solenoid in-'-, ductances and it has been found that thesarne tends to break up into portions which resonate at certain of the higher frequencies; tuned through on the C and D bands unless thesame j is soshort-circuited. i The grid ends of the inductances-for-the B, and (Hands are also short-circuiti-tofmund' thereby to render the .inductances ineffective to resonate at frequencies in the; next adjacent, lower bands, by a grid I short-circuiting Iii having contacts D, C, B, A, x and two additional contacts Ill adjacent to the contact]! in sequence-of operation. which contactsr withthe 25! comprises three fingers for engagingthree adjacent. contacts simultaneously in a similar manner to the switch I. .The contact D of the switchm it connected t the .{lead m through alead-QI" and similarly the contacts C and B;are. connected through leads if with the; leads 235 and 231., respectively rangementfbeing such that in. the

for 3 the D band, the" inductances for} g c. n and'A are V efbands short circuited to groundthr'ough a lead 2" and .a groundconnection illgfwhe eby 40 try.

by the rigid wiring i5! and lif -ill .As th switch "I is moved in a clockwies directionfas viewed in" the drawings, the short-circuit is progressively removed from the C, B and-Akband inductances until the contact reachesthe'posltion! with the extreme left hand contact. arm as viewed in the drawings, at the contact'X,-;when

all short-circuiting of the inductances is removed forthe x band operation.

- The grid and cathode coil selector switch its and in together with the anode andglld coil short-circuiting switches it! and iii arsprefer ably interconnected for simultaneous operation in the relation shown and as indieated by the dotted connections fill.

anqoperationthe cathode switch lllis connected@tl rougli the contact X, thence-through theentird coilifofthe band A to ground, whereby the inductahce'ioffthe coil is included in the cathode circui which coil a portion of the oscillator v, appear and will-thus be transferred f lation grid IS. I In all of the other cillatlon grid 1! is connected ac portion of the oscillatorcoil or ind V voltage therefrom directlyr,

included in circuit with the tuning capacitor n and in the high potential side of the circuit. This arrangement forthe A', B and 0 bands has the effect of changing the grid excitation over the This useof age developed is least at the low frequency ends of the bands but the grid is effectively shifted toward the cathode at the low frequency and by virtue of the'ratio between series. and tuning capacitors so thatta larger percentage of. the oscillator voltage appears from cathode to ground;- l0

On the highest frequency range D, a low frequency winding I8! is provided in the plate circult of the pentode oscillator 15 to obtain oscillation over the low frequency end of the D band.

It will be noted that this winding is provided with a shunt tuning capacitor 261. This is for the purpose of tuning the winding l8! below the tuning'range of the D band, but adjacent thereto. The winding and shunt capacitor'fl'l constitute a tuned circuit in the main anode circuit which isresonant to a frequency preferably below the lowest frequency to which the oscillator is tunable in the D band. Therefore, atany'frequency within the tuning range of the D band this circuit will act capacitively and the value of the capacitive reactance will increase with decrease infrequency. The arrangement is such that the circuit is, therefore, eflective only in the lower. frequency portion ofthe D band of theoscillators. This circuit is also used to regulate the rate of changeof frequency as the oscillator is tuned over the D band, show up thl'soscil vlator at the low frequency end, so that the oacillator will track with the antenna circuit without the necessity of including a series capacitor. In

order that the oscillator circuits may inore readily be understood the simplified circuits representative of the. low frequency, medium frequency and high frequency connections have been redrawn without the switching, bypass and other elements, in Figs. ,2, 3 and 4, Fig. 2, j showing the general circuit arrangement for the medium frequency or A, B and. Chanda, Fig. 3 showing the circuit arrangement for the high frequency or D band,

and Fig.4 showing the circuit arrangement 'for.

the low frequency or 3 band. The same refer ence numerals have been usedthroughout in referring to the corresponding circuits and elements thereofas in Fig. l.-

Referring to ;2, it will be seen that the screen grid "I and the main anode ifl'of the oscillator i are each bypassed to ground through bypass capacitors 2.5 and I'll, respectively. here by being connected through the ground lit-to the anode end of the inductance 2 across which is connectedthe tunlngcapacitor I. The cat ode I is connected to the intermediate tap Ill .and to the lead -l5l-for the'ili'stdetector oscillation grid. The controlTgrld III is coupled through its grid leak and capacitor lit-4M, to the grid and of the inductance 2i 1, thereby providinga Hartlfil' y e oscillator. The suppressor; grid I31 provides an effective screen between the twoanode electrodes "I and ISL g H Y a pentode device as an oscillator has been found to beeifective in providing im- I provedoscillator stability and uniform oscillator output. Additional means for stabilizing the output comprises-the series resistors 'lll'and" iii between the supply meana'indicated at 2"; and) the-anode electrodes. The power supply means 1",; represents any suitable power supply for the receiving system, operated from a variable source of power such as alternating current and arranged to supply heating current to the apparatus.

The two series resistors in the anode circuits prevent the internal impedance of the oscillator tube and, therefore, the frequency of the oscillator system from varying appreciably from a predetermined adjustment. The voltage on the two electrodes is maintained substantially constant since the tendency to increase the B supply voltage tends to provide an increasing current and an increased drop in potential. This is further made more effective by the fact that the heater current is derived from the same source and simultaneously with an increase in B potential, the heater current is correspondingly increased, thereby causing an increased plate current and an increased drop in potential through the resistors I19 and I'9-I.

By way of example, if the B voltage is 200 volts and assuming the resistors I9I and H9 to be so chosen as to provide a 40 volt drop, the anode potentials will thus be 160 volts. If the B voltage were to increase 10% to 220 volts, the plate and screen current would be increased approximately 10% causing a 10% rise in voltage across the resistors to a total of 44 volts and r the new anode and screen potential would then be 176 volts.

However, because of the increased filament voltage of 10%, there will .be an increase in 29% or to a value of 53 volts. Subtracting 53.

volts from the 220 volts B supply will provide a potential of 167 volts at the two anodes which is only slightly more than a 4% increase 7, over that with normal B supply voltage although the supply voltage has increased 10%.

The effect of the combination oflvthese teatures is to cause the plate resistance of the oscillator tube to remain substantially constant regardless of the voltage impressed thereon and, therefore, the oscillatory system tends to maintain the same frequency throughout very widely varying conditions of supply voltage.

It will be seen ,that both anodes, that is, the screen grid and the main anode are provided with a return circuit to cathode through the anode portion of the inductance 2| I thereby providing an oscillator of the Hartley type having two anode electrodes separated by a grounded screen electrode and with the cathode and output connection floating above ground.

It will be noted that the A band inductance is selected for illustration in Fig. 2 as representing the other circuits of the medium frequency bands. In this connection the series capacitor 23I between the inductance and the tuning capacitor is shown. As has been pointed out hereinbefore, this is also a compensating c'apacitor for causing the output of the oscillator to be more uniform, thereby to apply to the first detector substantially the same output voltage for the high frequency and low frequency ends of the band. It will further be noted in Fig, 2 that the bypass capacitor for the anode I39 is the capacitor 205, this connection being provided by the switch I95 in the A, B and bands as will be seen by referring to Fig. 1 thereby eliminating both feed back windings I85 and I89 from the alternating current circuit.

Referring now to Fig. 3, the connections for the high frequency or D band are shown in connection with the oscillator I5, the inductance of the rigid bus wiring being shown in conventional manner as inductances at I and at I58- I63. It will be seen from an inspection of Fig. 3, that the change in connections effected therein includes removing the series compensating condenser 23I (Fig. 2) from the high side of the tuned circuit and adding the tuned feed back winding I which is tuned adjacent to and below the frequency band covered by the oscillator circuit in order to maintain the strength of the oscillations constant over the entire tuning range of the oscillator. This is done by boosting the low frequency end of the range by added feed back provided by the coil I85. It will also be noted that the bypass capacitor 203 is now effective in the main anode circuit caused by operation of the switch I thereby bypassing the feed back winding I89 shown in Fig. 1. The compensating resistors I9I and I19 are effective in the anode electrode circuits to maintain the plate impedance of the oscillator substantially constant as described in connection with Fig. 2.

Additional stability is obtained at the high frequency end of the D band by so proportioning the value of grid, anode and tuning capacltors and of the grid and anode inductances that the oscillator is effectively stabilized as to variations in voltages and load. The grid and anode capacitors may be made of equal value, and the grid and plate inductances I63 and I55 are of equal value without magnetic coupling between this provides an additional stabilizing feature which is used to advantage over the higher frequency portions of the D range.

. The first detector receives energy from the oscillator across the inductance I65 or the anode portion of the oscillator inductance as in the medium frequency range of the circuit shown in Fig. 2. This method of coupling the oscillator cathode with the second control grid of the mixer tube provides a relatively low load on the oscillator.

As in the preceding figure, and in the Ine-' dium frequency ranges, both oscillator anode electrodes I35 and I39 include the anode inductance portion I65, the connections between the anode electrodes and the cathode comprising the capacitors 203 and H3 to ground, the ground IBI of the main tuning inductance, thence through the inductance element I65 t0 the oathode I3I from the tap I6'I on the main tuning inductance. Both anode electrodes are thereby effective to maintain oscillations which are reinforced in the low frequency end of the tuning range of the oscillator by the feed back winding I85.

It will be noted that the anode electrodes I35 and I39 are shielded by the suppressor grid I31 which is connected to ground as in the medium frequency range.

Referring now to Fig. 4, the connections for the low frequency or X band range of operation are 51102711.

In this circuit the first detector is supplied with oscillations from the inductance 2I I of the A band introduced into the cathode circuit between the cathode 3I and ground '2 I3 and is shunted merely by the trimmer capacitor'241. Accordingly, it is tuned to a relatively highfrequency above the tuning range of the oscillator for this band and operates .as an inductance to. provide coupling with the first detector throughthe lead II.

The oscillation are set up wholly by feed back from the coil I89 and the main inductance 239 is not tapped but is utilized entirely in the grid circult of the oscillator. Since the oscillator is required to cover. a relatively narrow frequency range (1.42) the output may be maintained constant without special means other than provided by the coil introduced in the cathode circuit.

It will be noted that the inductance of the feed back winding I85 of Fig. 1 has been omitted since its inductance is negligible in this range and the bypass capacitor for the main anode I39 is indicated at I93.

The suppressor grid I31 is utilized as a screen between the anode electrodes I35 and I39 as in the other frequency bands and the compensating resistors HI and I19 operate in the same manner to stabilize the oscillator frequency with variations in supply potential.

In the low frequency range it will be seen that K the oscillator system is changed from the Hartley circuit to the feed back circuit with the screen grid I35 effective to control the internal impedance of the oscillator and the main anode I39 utilized for setting up oscillations by feed back.

The oscillator inductance is a single winding without taps. The feed back-arrangement shown with its absence of taps is therefore decidedly advantageous in eliminating absorption circuits which would fall in a higher frequency band.

Furthermore, the inductance in the cathode lead which is coupling means for the detector, provides an impedance from which to take the detector load without tapping into the tuned circuit. The inductor 2 being in the cathode lead is in a circuit common to the grid, screen and plate.

Therefore, while the screen grid is not provided with a return circuit through the main tuning inductance it is nevertheless coupled with the control grid and with the main anode through the inductor 2| I.

Referring again to Fig. 1 along with Figs. 2 to 4 inclusive, it has been pointed out that the oscillator circuit is arranged to cover a relatively wide frequency range of operation in a series of separate bands, while providing improved frequency stability and uniformity of output over the various tuning ranges. The oscillator operates on fundamental frequencies which are supplied to the first detector on an auxiliary mixing grid which in this case is the second control grid. The oscillator generates signals which, in all bands, are above the frequency of the incoming signal by the amount of intermediate frequency which,

in this case, is chosen at 460 kilocycles.

As shown in the drawings, the cathode of the oscillator is above ground potential for high freformer or coil being provided by the circuit wiring. Four selector switches are provided, the switch I95 being the anode coil short-circuiting switch, the switch I being the coil short-circuiting switch and the switches I45 and I51 being the grid coil and cathode coil selector switches respectively. The witch I45 serves to connect the grid of the oscillator and the main tuning capacitor I43 to the proper coil for the range to which the switch is adjusted. The switch I51 serves to connect the cathode and the first detector to the appropriate part of the circuit being the plate or anode portion of the inductance for all bands except the X band when it introduces an inductance in the cathode circuit for coupling with the detector.

The switch I95 serves to bypass the inductance I85 which is the D band feed back coil when the A, B or Cl ranges are used. However, as this coil has such .low inductance it is not necessary to bypass it when the long wave length band X is in use. The switch I95 also serves to ground quency oscillations while the anode or plate is effectively at ground potential. This arrangement together with the plateand screen series resistor causes the circuit to be substantially independent of power supply variations in regard to stability and uniformity of output.

Separate coils or transformers are used for each of the tuning ranges. The switching of the different bands is such as to short-circuit certain unused coils which would absorb energy from the circuit in use.

The overall oscillator circuit comprises five separate transformers or coils, the D band transbands B, C or D are being used. The switch 25I serve to detune the coils of the three bands immediately below the one-being used. This detuning is accomplished by connecting the series condensers for the A, B and C bands across the coil, thus tuning it to a low frequency and avoiding any possibility of interference with the higher frequency bands in use by the absorption of v energy.

In the case of the A band coil, since it is divided into a large and small section by the tap there is a tendency for the lower or plate section of the coil to resonate in band C and D although the whole coil is detuned. Therefore, the plate portion is short-circuited also in addition as above described, through the switch I95.

The coil for the 1) band comprises merely a piece of rigid wire extending from the ground to the switch l5 and thence, when theswitch is thrown to the position D, through to the tuning capacitor I43. The capacitor tune the piece of It is,

rigid wiring to the proper frequencies. therefore, necessary that the length of the wire and. the location of the same be maintained in position after adjustment.

Because of the extremely high frequency to which the oscillator responds it is necessary that exceedingly short ground connections be used at certain points. For example, as shown in Fig. 1, the heaters and the cathodes are preferably bypassed directly to ground at the tube terminals except at the'oscillator, the cathode 'of which is used for coupling purposes. In this connection it 'direct ground connection as indicated at 28I ad- 'jacent to the tube terminals.

Likewise the shield or metal envelope of the oscillator is directly connected to ground, a rninimum length of lead being used. Th se direct connections are of importance in order to prevent spurious osc llations or responses at the h h frequency end of D band, as the circuits within the detector tube, i. e. the elements thereof have na ural periods corresponding to frequencies of 480-220 megacycles. The harmonics of the oscillator that fall in the range of 180-220 megacycles so excite the detector tube that responsesdenoted by hiss output at intermediate frequency are obtained. In order to prevent these spurious responses, it is necessary to have the filaments,

minimum of impedance at 200 megacycles. In some cases it may be desirable to include a trap in the oscillator coupling lead tuned in the neighborhood of 200 megacycles to prevent the oscillator harmonics from reaching the detector. Such a circuit is shown at I52, and may consist of a 9 micro-microfarad capacitor I54 connected across several inches of the lead ll providing an inductor I56 between the oscillator cathode and the detector coupling condenser I53.

This trap may also be inserted at I58 in the detector cathode lead to provide degeneration at 200 megacycles.

From the foregoing description it will be seen that an oscillator, first detector or frequency 'changer system is provided wherein Ta) Minimum reaction is. obtained between the oscillator andthe radio frequency or signal input circuits and minimum loading of the oscillator.

the D band alone.

(e) The oscillator output voltage delivered to the first detector or mixer tube is uniform throughout the various wave bands covered thereby improving the emclency of conversion in the flrst detector or mixer tube. The automatic volume control is simplified, sincethe screen grid and anode circuits are controlled by suitable series compensating resistors regulating the gain of the system in response to strong signals of high amplitude.

While the combination has been shown and described in connection with a 5'band superheterodyne receiving system, it should be understood that it may be applied to similar systems having fewer or a greater number of wave bands for wide frequency range coverage.

I claim as my invention: 1. In combination, an electron discharge device including an input electrode, an output electrode and a pair of additional electrodes, a resonant circuit connected to said input electrode and tunable over a range of frequencies, and feedback means for supplying energy to said resonant circuit, said means including a pair of paths coupled respectively between said output electrode and said circuit and between said pair of additional electrodes and said circuit, said feedback paths being connected in aiding phase relation and having reactive constants so proportioned that saidpaths are individually effective primarily over different complementary portions of saldfrequency range and provide a preselected and substantially uniform feedback of energy throughout said'frequency range.

2. The invention as set forth in claim 1 wherein one of said additional electrodes is a screen shields and cathodes of the first detector and oscillator tubes grounded by paths which have a this includes a range of 17.8 to 73 megacycles for grid interposed between said input electrode and said output electrode and is effectively grounded for high frequency currents.

3. The invention as set forth in claim 1 wherein said additional electrodes are interposed be-' tween said input and output electrodes and are eflectlvely grounded for high frequency currents.

4. In combination, an electron discharge device including an input electrode, an output eleconant circuit, said means including apair of paths coupled respectively between said output electrode and said circuit and between said additional electrode and said circuit, said feedback paths having reactive constants so proportioned that said paths are individually effective primari- 1y over different complementary portions of said frequency range and provide a substantially uniform strength of oscillations throughout said frequency range. 5. In combination, an electron discharge de vice including an input electrode, an output electrode, a cathode and an additional electrode effectively grounded .for high frequency currents, a resonant circuit connected at its high potential end to said input electrode and tunable over a range of frequencies, a connection from an intermediate point on said circuit to said cathode, and feedback means for supplying energy to said resonant circuit, said means including a pair of paths coupled respectively between said output electrode and said circuit and between said additional electrode and the low potential'end of said circuit, said feedback paths having reactive constantsso propertioned that said paths are individually effective primarily over din'erent complementary portions of said frequency range.

6. The invention as set forth in claim 5 where- I .in said output electrode path is primarily effec tive in' the lower end of said range.

7. In combination, an electron discharge de vice including an input electrode, a output electrode and an additional electrode, a resonant circuit connected to said input electrode and tunable over a range of frequencies, and feedback means for supplying energy to said resonant circuit, said means including a pair of paths coupled respectively between said output electrode .and said circuit and between said additional electrode and said circuit, said feedback paths having reactive constants s0 proportioned that said paths are individually eflective primarily over difierent complementary portions of said fre-' quency range. v

8. The invention as set forth in claim 7 wherein the feedback path from said output electrode resonates adjacent the low frequency end of said range. I

9. The invention as set forth in claim 7 where in said additional electrode is a screen grid disposed between sald input and output electrodes.

10. The invention as set forth in claim 'I ftrodea pair of additional electrodes, a resonant circuit including an inductor element connected at its high potential end to said input electrode and tunable by a variable capacitor element over a range of frequencies, and feedback means for supplying energy to said resonant circuit, said means including a pair of paths connected respectively between said output electrode and said circuit and between one of said additional electrodes and said circuit, the other of said addi tional electrodes being effectively grounded for high frequency currents, said feedback paths having reactive constants so proportioned that said paths ar individually effective primarily over different complementary portions of said frequency range, said output electrode feedback path including an inductor and capacitor in parallel resonant relation below said frequency range and coupled inductively to said resonant circuit.

12. The invention as set forth in claim 11.

wherein said cathodeis connected to an intermediate point on said inductor element,'the low potential end of said inductor element being effectively grounded for highfrequency currents.

13. The invention as set forth in claim ll wherein said inductor element consists. of two substantially equal inductance portions, the

i said second circuit being coupled to said first cirtween said output electrode and said additional electrode in shielding relation therewith, and regulating means connected to said output electrode and additional electrode.

18. The invention as set forth in claim 7 wherein the feedback path from said output electrode resonates adjacent the low frequency end of said range and regulates the rate of change in frequency of said tunable circuit, by slowing up the rate toward the low frequency end of said range.

19. In an oscillator for a superheterodyne receiving system, an electric discharge device including a cathode, an input and a plurality of output electrodes, a first circuit tunable over a band of high frequencies connected to said input electrode, to said cathode, and to one of said 0114 put electrodes for feeding back energy to cause' said circuit to oscillate, a second circuit tuned to resonate adiacent the low end of said band,

cult to regulate the rate of change in frequency of said tunable circuit by slowing up the rate cathode being connected betweensaid portions,

- and regulating means are connected to said output electrode and one of said additional elecl4.*The invention fas setiforth in claim 11 1 wherein said [inductor element consists of two substantially equal, and uncoupled inductance portions, said cathode .saidportions. a

being connected between l5. Theinvention asset forth in claim 11 wherein, 'saidinductor element consists of two substantially; equal and uncoupled inductance portions, said cathode'being connected between gportionsfand individualregulating resistors I r connected between a positive potential supply frailty of output electrodes, a first circuit contoward the low frequency end.

20. The invention as set forth .in claim 19 wherein said second circuit is connected to one of said output electrodes and to said cathode for feeding back oscillatory energy'to said first circuit.

21. In an oscillator for asuperheterodyne receiving system, an electric discharge device including an input electrode, a cathode and a plunected to said input electrode and to said cathode and tunable over a band of frequencies, a

connection from one of said'output electrodes to said circuit for feeding back energy to cause said circuit to oscillate, a second circuit fixedly tuned adjacent and below the low frequency end of said tuning range connected to another of said output electrodes and to said cathode whereby said second circuit reacts capacitively, the capacity reactance increasing with decrease in frequencyv of'said tunable circuit, said second circuit being coupled to said first circuit and characterized by a regulating effect upon the rate of change of frequency as the tunable circuit is tuned toward the low frequency end of said range. I

JOHN D. REID.

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