US2021692A - Short wave receiver - Google Patents

Description

Nov. 19, ,31.9357 ."HjM. LEWIS- l SHORT'WAVE RECEIVER original Filedse'pt. 25, 1951 3 Sheets-Sheet l Y WM.. n .M MA Y W, k um pm NOV- 19, 1935. H. M. LEWIS SHORT WAVE RECEIVER original Filed sep. 25,` 1931 Y I 3 Sheets-Sheet 2 Nov. 19, 1935. H. M. LEWIS 2,021,692

SHORT WAVE RECEIVER original Filed sepi. 25, 1931 5 sheets-sheet s INVENTOR ATTORNEYS Patented Nev. 19, 1935 UNITED STATES l 2,021,692 SHORT WAVE RECEIVER Harold M. Lewis, Douglaston, N. Y., assighor to Hazeltine Corporation, a corporation of Delai,-v

Ware

Original application September 25, 1931, Serial No. 565,024. Divided and this application April 27, 1934, Serial No. 722,614. In Germany September 21, 1932 1o claims.

The present invention relates to a tuning system, or, more particularly, to such a system for use in a short wave receiving apparatus. Exemplary of such a system is that used in a short Wave converter.

This application is a ydivision of my copending application Serial No. 565,024, led September 25, 1931, now Patent No. 2,001,277, dated May 14, 1935.

A short Wave converter is an apparatus which, when used in conjunction with any broadcast receiver, permits the reception of short wave signals by the said broadcastv receiver. The converter comprises an oscillator and modulator, by which the short wave'signal currents are converted in'to currents of a frequency within-the tuning range of the broadcast receiver. The current of this frequency, which frequency will be referred to hereinafter as the intermediate frequency, is amplified, detected and reproduced by the broadcast receiver.A

The frequency range covered by the short wave band is approximately from 1500 kc. (200 meters) to 20,000 kc. (15 meters). This range of frequencies is so great that it is not practical to tune a circuit through the entire range by the variation of a single tuning element. Some arrangement must be provided for changing both of the frequency determining elements; that is, both the inductance and the capacity. In accordance with the usual practice the tuning is actually done by varying the capacity of a variable condenser, and the inductance is changed in steps to permit the condenser to tune the cirk cuit throughout the various portions of the range.

It is common practice to divide the short wave band into several bands which will be referred to in this application as the short wave band, the middle wave band, andthe long wave band. v

The inductances used in tuning the radio-frequency circuits of the short wave receiver, or theV radio-frequency circuit and oscillator circuits of a converter, are usually wound on removable 'l forms commonly known as plug-in coils, which coils are changed when desiring to go from one of the short wave bands toanother. A system of this type has the disadvantages that it is eX- pensive to manufacture and requires shifting of coils when operating.

Various systems have been proposed by which the inductance of the tuning coils is changed in steps by means of switches. However, the leads and switch mechanisms introduce capacities which considerably lessen the range of the tuning (Cl. Z50-20) condensers, and usually the resulting large number of points to be switched has condemned this system;

Furthermore, considerable difficulty is experienced in constructing an oscillator capable of covering such a broad range of frequencies, as there is a considerable difference in the feedback coupling needed at the two ends of the short wave band.

It is the object of the present invention to overcome the above noted difficulties and provide a system in which the inductance values of a single winding maybe varied in'steps by providing a system in which the leads required for changing the inductances are relatively short and have negligible capacity effects. It is a further object of this invention to provide an oscillator coupling system having a simple structure, not involving the use of moving parts, by which the coupling effect may be simultaneously altered as the frequency determining inductance is changed, to permit the oscillator to oscillate eifectively throughout the entire short wave band.

These and further objects of this invention will become apparent from the following specification taken in connection with the appended claims and drawings. A

In accomplishing the objects of the present invention the inductance of the frequency deter-v mining circuit of the converter oscillator is provided with a switch for short-circuiting the long wave portions thereof and long wave and middle wave portions thereof, when operating the oscillator to receive signals in the middle wave lband and short wave band, respectively. Dual mage netic and capacitative feedback couplings-'fare provided between the plate circuit of thehzosc'zil'# lator and the grid coil when operating within' the middle wave band.V Whenoperating'in the long wave band the inductive coupling is negligible, and the feedback is essentially through the capacitative coupling between. the plate and grid circuits. When operating in the short wave band the capacitative coupling effect becomes negligible, Whereas the coupling between the circuits due to the inductive coupling, is considerable.

Provision is also made for obtaining a uniform coupling between the antenna circuit and the input of the modulator. A straight inductive coupling is utilized when receiving signals within the short wave-and middle wave band.` When operating in the long wave band an auto-transformer effect is obtained by connecting the antenna circuit to include a portion of the long wave section of the .grid inductance.

`The modulator and oscillator windings are so arranged relative to the switches for short-ciry cuiting their unused portions and relative to the grids of the modulator and oscillator tubes that the leads, particularly when the converter is operating in the short wave band, are as short as possible.

In order to permit the continuous rotation of the tuning dial in either direction to progressively tune the converter through the entire band, the condensers used in both the modulator input and oscillator circuits are each provided with double stators and double rotoi's so constructed that when the capacity between one of the pair of rotors and stators is maximum, that between the other pair of rotors and stators is minimum.

Switching means are provided, operated simultaneously with the switches for short-circuiting the unused portions of the tuning inductances, for connecting the appropriate sections of the condenser-s.

Series condensers are provided for connection in the oscillation circuit for each of the bands and are appropriately connected in circuit by a switch operated together with the previously mentioned switches, when the range of the converter is shifted from one band to the other. The padding condensers for the section of the oscillator tuning condenser, which is used for the middle wave band, is provided in shunt with ihis section. A condenser is connected from the middle wave band tap of the inductance to the stator of the condenser, so that when the entire tuning inductance is in use this condenser may act as a padding condenser for the long wave band. This condenser is then essentially in shunt with the section of the variable condenser in use. When the long wave section of the inductance is shortcircuited, however, as when operating in the middle wave band, this condenser is in parallel with the series condenser in use at that time.

The condenser shaft has an indicator ldial geared thereto so arranged that it rotates a complete revolution for each half revolution of the condenser shaft. 'I'his dial has thereon three indicating scales, the outer scale being for indicating the frequencies in the' short wave band, and the inner scale being for indicating the frequencies in the long wave band. The scales pass by indicator lights placed behind the dial within a compartment which permits illumination of but a single scale by each lamp, and a switch operated simultaneously with the wave changing switches operates to light the appropriate scale. A full description of this feature of the present invention is given in an application of Harold Miller Lewis for Tuning scale, Serial No. 565,027, tiled September 25, 1931, now Patent No. 1,987,857, dated January l5, 1935.

In order to permit the operation of a single control knob to control the frequency of reception, regardless of which of the three bands the converter is operating in, there is provided a gang switch mechanism operated by the condenser control knob at the appropriate instant as the dial is rotated from'one to the other of the frequency bands. 'I'his feature of the presen, invention is fully described in an application of Harold Miller Lewis for Switching arrangement, Serial No. 565,026, filed September 25, 1931.

It can thus be seen that an arrangement has been provided by which the set can be tuned through the entire short wave band by the operation of a single control, and by which the frequency for which this apparatus is set to respond is automatically indicated at all times as the set is tuned.

In order to prevent the reception of broadcast signals by the receiver used in conjunction with the converter, the leads between the converter, as well'as the converter itself, are completely shielded. The anenna input of the converter contains a trap circuit to prevent currents of undesired frequency being impressed upon the input of the modulator and amplified thereby. The plate supply of the modulator contains a tuned radio-frequency choke which is tuned roughly to the intermediate frequency and thereby tends to by-pass currents of frequencies differing greatly therefrom which have been received in the converter. The full details of this portion of the present invention are given in an application of Harold Miller Lewis for Short wave receiver arrangement, Serial No. 565,025, filed September 25, 1931, now Patent No. 2,000,084 dated May 7, 1935.

Attention is now invited to the accompanying drawings in which:

Fig. 1 is a circuit diagram of the converter embodying the present invention;

Fig. 2 is a simplified circuit diagram of the converter circuit as connected when the switch is in the long wave position;

Figs. 3 and 4 are elementary diagrams for use in explaining the opera-tion of the oscillator circuit;

Fig. 5 is a simplified diagram of the modulator circuit;

Fig. 6 is a diagram of an alternative modulator circuit;

Figs. 7 and 8 represent the secondary and primary windings respectively of the antenna coupling transformer used in the converter comprising the present invention; and

Figs. 9 and l0 represent the secondary and primary respectively of the oscillator coll.

Referring now to Fig. l, the antenna circuit includes the antenna I0, the ground II, the trap circuit I2, comprising the inductance I3 and condenser I4, the primary winding I5, and a portion of the secondary winding I6. 'I'he inductance I3 and the condenser I4 of the trap circuit I2 are so proportioned that said circuit is resonant to the intermediate frequency produced by the short wave converter. The input circuit of the converter is connected to the grid of modulator device I1, which may be any thermionic tube, though that shown is of the screen-grid type.

The input circuit is tuned by means of the condenser 2|, which may be a double condenser employing, as shown, a single rotor and two stators so arranged that the capacity obtained between the rotor and one stator is maximum, when the capacity between the rotor and the other stator is minimum. The connections to the stators arc controlled by means of the switch 23. The actual condenser includes two stator-s and two rotors, so arranged that when one rotor is entirely within its stator, the other rotor is entirely out of its stator. The function of the condenser and switch arrangement will be explained later.

The tapped secondary I6 is connected by means of switch 24, so that any of the tapped portions of the secondary may be included in the input circuit. The switch is so connected that the unused portions of the winding are short-circuited.

For producing the hetcrodyne frequency for combining with the incoming signal and thus producing the intermediate frequency, there is provided the oscillator 25. This oscillator tube is of the single grid type and includes 1n its grid circuit the secondary 40 of the oscillation transoscillation circuit is completed through the biasing resistor 21, which is connected to the cathode of the tube 25. The frequency of theA oscillation circuit is determined by means of condenser 3|,which is similar to condenser 2|, and is connected to be operated therewith in a unl- `control manner by means of the control knob 22 associated with the indicator dial 26.

The connections to the two continuously variable portions of the condenser 3| are controlled b-y means of switch 33.

Padding condensers 4|M and-4|S are provided across the two portions of condenser, as shown, for the purpose of aligning the oscillation circuit with the input of modulator I1 in thernid-l dle wave range and short wave range, respectively. Padding condenser 4|L is connected across the long wave portion of the inductance winding 40, so that when the switch 34 is on contact L this condenser is practically in shunt with the condensers 3| and 4|S for adjusting the alignment in the long wave range. When the switch 34 is on contact M, the condenser 4|L is in shunt with condensers 31 and 31', and the total series capacity is at that time the sum of these three condensers.

In series with condenser 3| is provided a series capacity which is variable in steps, comprising condensers 36, 31 and`38, the connections to which are controlled by means of lthe switch 35. Each of these condensers is provided with the padding condenser 36', 31', or 38', respectively, for the purpose of correcting the alignment of oscillator circuit with the modulator input in the various frequency bands. In the middle frequency band, as hasy just been stated, the condenser 4|L is in shunt with 31 and 31'. Coupling coils 44 and 45 coup-led to the middle and long wave portions of the secondary 40, respectively, are included in the cathode circuit of the modulator I1. 'I'his circuit also includes the biasing resistor 46 shunted by by-pass condenser 41 for the purpose of causing tube I1 to act as a modulator.

'I'he plate and screen-grid potential are provided by means of the power supply source 20 which, as shown, is of the ordinary doublewave rectifier and lter type. This power supply also provides heater lighting current for' heating the cathodes of tubes I1 and 25. A resistor 29 is included in the plate lead of the oscillator 25 for the purpose of reducing the plate potential thereof.

As shown, the dial 26 includes three scales, 26a, 26-b, and 26c, these scales covering the short wave band, middle Wave band, and long wave band, respectively.

It is in be noted .that in order to get better spacing of the frequency indicato-rs, the short Wave scale is placed in the outer position on the dial 26, as the condenser motion to get the frequency separation required to separate the various stations is less in the short wave band than it is in the long wave band.

For the purpose of indicating in which of the frequency ranges the converter is operating, eachof the scales is provided with one of the illuminating lights 1I-a, 1 |-b, or 1 |c, controlled by means, of switch 39 to light them when tuning through the short wave band, middle waveband, and long wave band, respectively.

Switches 23, 24, 33, 34, 35 and 39 are so ar- 5 ranged as to be simultaneously operated and also to be actuated by the control knob 22 as'the condensers are tuned through the limiting ca pacities for one of the frequency bands.- Thus,

the rotation of the control knob 22 results in the 10 actuation of the switches 23 and 33, resulting in switching of theconnections to condensers 2| and 3|, respectively, to give the opposite capacity extreme for the modulator and oscillator circuits. Switch 39 is simultaneously operated changing 15 the lighting of the indicating lights and thus indicating the change in the frequency band by changing the indication from one to lanother of the scales. The specific means for actuating the switches constitute no part of the present 20 invention, but are described fullyin application of Harold Miller Lewis, for Switching arrangemen Serial No. 565,026, iiled September 25, 1931.

Included-in the plate supply to the modulator 25 I1 isthe inductance 50. This inductance may have a high inherent capacity as indicated by capacity 5|, or an actual condenser may be placed in shunt therewith. The inductance and capacity, however, are so proportioned that fre- 30 quencies other than the desired intermediate frequency will be by-lpassed.

A connection from the output of modulator I1 is made through condenser 52 and lead 53 to the antenna binding post of the receiver 51. connection is made through a shielded cable 54, which may, for. example, be a BX cable, from the Walls of which the lead 53 is spaced by means of bakelite spacers 56. Also'connected through the cable 54 is the ground connection 55, which 40 is connected to the ground binding post of receiver 51. The capacity 52 and the inherent capacity between the leads 53 and 55 are so proportioned that they constitute a dummy antenna to properly load the modulator I1, and to prevenl misalignment of the input of receiver 51. Switch 59 is provided between the antenna I0 and the lead 53 by means of which the antenna may be directly connected to the input of the receiver 51 wheny it is desired to receive signals in the broadcast band directly on receiver 51.

The receiver 51 may be of any well known type, and is provided with the usual sound reproducing device 58. The specic details of neither 51 nor 58 constitute any part of the present invention. 55

The receiver is tuned to theintermediate frequency vwhich it is desired to utilize, preferably 1,000 kc. The direct reception of signals of 1,000 kc., when the set is being operated to receive short wave 'signals by means of the converter, is 60 prevented by means of the shielded cable 54. The modulator is prevented from acting as an amplier of signals of 1,000 kc. frequency by means of trap circuit I2. Any signals. of a frequency other than 1,000. kc. in the output of modulator 65 I1 would be by-passed through the inductance A5I). It is thus seen that a number of provisions have been` made to prevent the interference of broadcast signals with the short wave signals being received by means of the converter. In Fig. 2, to which attention is now invited, the circuit shown in Fig. 1 is again represented, except that the switches have been eliminated the connections being made as if the converter were tuned to some frequency within the long wave ed as 83 is fed to the cathode lead of the modulator I1 which, as has been described, is biased for grid bias detection. The incoming signal is fed through the oscillatory circuit 84 to the input of tube I1, which by means of the biasing resistor 46 operates as a rectifier or modulator, and thereby produces in its output circuit a distorted wave form from which a current of the intermediate frequency can'be selected and supplied through the condenser 52 to the terminals A and G of the radio broadcast receiver.

It is to be noted thatfrequencies other than the intermediate frequency for which the radio broadcast receiver is to be adjusted are by-passed through the inductance 50, whereas this inductance and its inherent capacity form a high impedance path relative tocurrents of the intermediate frequency.

As previously stated, the circuit I2 acts to prevent currents of the intermediate frequency being received over the antenna I and amplified by the modulator I1, and the shielding of the lead 53 prevents a direct pick-up between the output of the device I1 and the input of the radio broadcast receiver.

The oscillator circuit 83 contains, as can be seen, the usual series condenser 38 in series with the tuning condenser 3l, by means of which the circuit 83 is made to respond to a frequency continuously differing from the frequency to which circuit 84 responds by the amount of the intermediate frequency as the circuits are tuned in a uni-control manner. l

Figs. 3 and 4 illustrate the means by which the single oscillation transformer is made to cover the considerable frequency range required of this type of equipment. The various portions of the inductance 40 are tuned by the respective parts -of the condenser 3| and thus constitute a 4tuned grid circuit.

In order to provide the offset frequency and thus permit alignment between the condensers 3| and 2| to permit ganging, a series condenser 36, 31 or 38 is provided. This condenser has the dual function of assisting the alignment and of permitting capacitative feedback action. The introduction of this capacity in the grid return requires a resistor 21 to prevent the grid from floating and to act as a grid bias resistor.

More specifically, Fi'g. 3 shows the action on the circuit when it is operating in the short wave and middle wave band. The used portion of the inductance 40 in these bands is relatively small` and there is considerable coupling effect between the feedback inductance 42 and inductance 40.

This is particularly true in the short wave band.

In the short wave band the capacitative feedback coupling is negligible. In the middle wave band, however, the capacitative feedback action is considerable. The inductive feedback action between 42 and 40 is less within this range, and the two couplings are so arranged as to give practically uniform operation throughout the middle frequency band.

Referring particularly to Fig. 4, in which the circuit represents the action of the oscillator circuit when operated in the long wave band, the inductive coupling between the coils 42 and 40 is negligible, and the oscillator is of the capacity coupled type utilizing the series capacity 38. l

Fig. 4 also represents the padding capacity arrangement. As can be seen from Fig. 1, the same section of the condenser 3l is utilized throughout the long and short wave bands. This complicates the arrangement required for thepadding capacity of these two bands. The usual padding condenser 4|M, however, is provided for the middle frequency band. The usual padding condenser 4|S 10 is also shunted across the section of the condenser used for the long and short wave bands. This capacity is adjusted for the short wave bands, and it has been found that it should have a very low value. For paddingthe condenser 3| for opera- 15 tion in`the long wave band, the condenserl 4|L is shunted across that portionvof the coi1` which is in use only during operation in the long wave band. The few turns of -winding 40, not shunted by this condenser, are negligible when operating within the long wave band, so that the condenser 4|L is lessentially in parallel withthe condenser 3|. However, as can be seen from Fig. 1, when the switch 34 is on contact M for operation in the middle frequency band, the condenser 4|L is 25 in parallel with the condensers 31 and 31', the capacities of which are, therefore, adjusted to form the total series capacity which is required for producing alignment within the intermediate frequency band.

It can thus be seen that a substantially uniform feedback coupling is obtained throughout all three of the wave bands.

An important feature of the presentinvention is that as there is but a single tuning stage in 35 fil the input to the modulator device, the oscillator frequency is the principal determinate of the frequency to which the converter is set to respond. This, it can be seen, increases the tuning range of the converter somewhat beyond what would be the case if the condenser 2| determined the range. As an example, when using a 1,000 kc. intermediate frequency and tuning the oscillator between 3,000 and 9,000 kc., which is a 3:1 ratio, the incoming frequency which can be received will vary between 2,000 and 8,000 kc., giving a receiving frequency ratio of 14:1.

Fig. 5 shows the modulator of Figs. 1 and 2 arranged for comparison with the circuit shown in Fig. 6.

Fig. 6 shows an alternative form of modulator circuit in which the grid-leak type of detection is used. This type of circuit gives slightly better sensitivity than that shown in Fig. 5, which latter is the usual grid bias arrangement and gives a better noise level but less sensitivity.

In Fig. 6 the low resistance grid "biasing resistor 46 and its shunt condenser 41 have been removed, and the grid leak 46 and grid-leak condenser 41' in the grid circuit of the tube I1 have 60 been substituted therefor.

Although it is clear that the specific coils for use in a converter constructed in accordance with the present invention will depend upon the characteristics of various other elements and upon the 65 frequency ranges to be considered, the inductances used in covering the frequency ranges from 1,740 kc. to 19,400 kc. are shown in Figs. 7-10, and will now be described.

Fig. 7 illustrates the antenna coupling secondary. This secondary is wound on a 1% inch form and comprises 69% turns of No. 18 B & S gauge enameled wire wound 20 turns per inch. The terminal 6I is connected to the grid of the tube I1 and the terminal 62 is connected to the 75,

ground Il. The tap 64 is taken to include 5% turns and is connected to contact S of switch 24. The tap 65 is taken'to include 20% turns and is connected to contact M of switch 24. The terminal 63 is connected to the antenna coil I5 and is taken turns from terminal 62.

The primary of the antenna coupling transformerv is wound on 3A inch form 61 and is placed inside the form 60 of Fig. '1, and spaced therefrom byA means of spacer 68. The winding I5 comprises 18 turns of No. 26B 8: S gauge enameled wire wound 24 turns per inch.` The terminals 69 and are connected to the trap circuit I2 and terminal 63 of winding I6, respectively.

The-oscillator secondary winding 40,- shown in Fig. 9, comprises 43% turns of No. 1.8 B & S gauge (enameled wire wound on 11A inch form 12. 20

, turns per inch. The terminal 13 is connected to contact L of switch 34 and -the contact 14 is connected to the grid of' oscillator tube 25. The tap 15 is taken 51/8 turns from the end of coil and the terminal 15 is connected to contact S of switch 34. The terminal 16 is tapped 155/4 turns from the end of the coil and is connected to contact M of switch 34.

The feedback coupling coil 42 and the modulator coupling coils 44 and 45, shown in Fig.v l0,

are all wound on a inch form 11 which is placed inside of form 12 and spaced therefrom by means of spacer 18. Thewinding 42 comprises 41/2 turns of 30 B & S gauge enameled wire close wound. Terminals 8l and 82'of winding 42 are connected to the contact L of switch 34 and the oscillator plate .condenser 43, respectively. Windings 44 and 45 comprise 5 Iand 41/2 turns. respectively, of No. 30 B & S gauge enameled wire close wound. Winding 45 is spaced 1A; inch from Winding 42, and windings 44 and 45 are spaced approximately 21/2 inches apart. These coils are connected in series and are connected by terminals and 86 to the cathode of modulator I1 and the modulator bias resistor 46, respectively. The condensers used have a maximum capacity of microfarads and a minimum capacity of 19 microfarads.

Using the coils just described, the calibrated range of the converter is:

Kilocycles Meters 1740-4180 (163-72 3800-9075 (79-33. l Short wave band... 8650-19, 400 (34. 8-15. 5

Certain other constants which have been found satisfactory are included:

Although any appropriate tubes may be used a UY224 has been found appropriate for use as modulator i1 and UY227 has been found to be appropriate -for use as the oscillator 25. The power supply device may be provided with the usual Uxzso, although it is to he understood that any appropriate power supply arrangement may be substituted for that shown.

I claim:

i. A superheterodyne receiving system forreceiving signals covering a plurality of 4wave length bands, comprising' a modulator input circuit, and an oscillation circuit tunable by ganged condensers, said input circuit includingv an inductance and one of said condensers, said oscil- 5 lation circuit including an inductance, a series condenser, and another'of said ganged condensers, and a feedback circuit comprising an inductance magnetically coupled to said oscillation circuit, and also including saidA series conlo denser and means for simultaneously varying the inductance of saidmodulator input and oscillation circuits, and the series condenser of said oscillation circuit for determining the wave length band to' be received. 15 2. A superheterodyne receiving system for rel ceivlng signals covering a plurality of wave length bands, comprising a plurality of ganged condensers, modulator-input and oscillator circuits tunable by said ganged condensers; said input 20 circuit including one of said ganged condensers, an inductance, means for short-circuiting portions of said inductance to permit wide variations in the response of said circuit, an antenna transformer coll coupled to a portion of said inductance 25 and connected through a second portion of said inductance to ground, whereby the coupling of said input circuit is varied as portions of the inductance are short-circuited; and Isaid oscillator circuit including an oscillation circuit having 30 an inductance, a series condenser, and'another of said ganged condensers, and a feedback circuit comprising an inductance magnetically coupled to said oscillation circuit, and also comprising said seriescondenser and means for simul- 35 taneously varying the inductance of said modulator input and oscillation circuits, and the series condenser of said oscillation circuit for determining the wave length band to be received.

3. In a superheterodyne receiver adapted to 40 receive signals covering a broad b'and of frequencies by continuous tuning through a plurality of steps in said band, a tunable input circuit for said receiver, an oscillation generator of the thermionic vacuum tube type, including a 45 grid circuit. a frequency-determining network in said circuit, comprising a variable inductance, a

- condenser variable in steps, and a continuously variable condenser tuning said circuit, and a feedback` circuit including an inductance magnet- 50v ically coupled to the first-mentioned inductance and including said condenser variable in steps, said condenser variable in steps being adjusted for each step to set the frequency of the oscillation generator uniformly higher in frequency 55 than the input tuning frequency of said receiver.

4. In a heterodyne radio frequency apparatus designed to permit continuous tuning through a plurality of contiguous wave bands which comprises a modulator and a tunable input circuit 60 therefor, and an oscillator, including grid andplate circuits, said grid and plate circuits each including an inductance, the inductance of said circuits being inductively related, said grid circuit including means for short-circuiting portions of said inductance, two inversely varying condensers selectively connected in shunt'with said inductance, a series alignment condenser for each of said bands selectively connected in series 70 with said inversely varying condensers for assisting the coupling of said grid andplate circuits as well as the alignment of the modulator and oscillator circuits, a padding condenser in lshunt with each of said inversely varying con- 75 densers', and a capacity so connected that it is alternatively in parallel with the series` alignment condenser coupling said grid and plate circults.-and connected as a padding condenser in shunt with the inversely varying condenser then in the circuit, whentuning in a selected wave band and the contiguous longer wave band, respectively. A

5. In a heterodyne receiving arrangement a receiver input circuit, an oscillator circuit in which .the coupling between the grid and plate circuits thereof is maintained substantially constant throughout a broad band. said oscillator circuit including grid and plate circuits, an inductance in said grid circuit, means for shortvcircuit a portion of the inductance of the grid circuit to vary the effective inductance thereof to make large changes in the frequency of said oscillator, a connection common to said grid and plate circuits, whereby the coupling between said circuits is simultaneously varied as the portion vof the grid inductance is short-circuited, said grid and plate circuits each including a commonl condenser, which condenser has the dual function of causing the alignment of the receiver input andoscillator circuits to permit uni-control tuning of said circuits, and assisting in the coupling of the two circuits.

6. Ina heterodyne receiving system, an oscillator circuit adjustable to produce oscillations covering a broad wave length band, subdivided into a short wave band. a middle Wave band and a long wave band, said oscillator comprising an oscillator tube, grid and plate circuits-for said tube, said grid circuit comprising a tuning inductance, a switch connected so as to short-circuit a portion of said inductance to cause said oscillator to respond to frequencies throughout a plurality of wave length bands, a condenser shunted across said inductance, a series alignment condenser for each of the wave length bands, switching means for connecting the appropriate alignment condenser in the circuit, and

said plate circuit including a stopping condenser,

an inductance, ,andl the series alignment condenser, said last-mentioned inductance being inductively related to the short wave band portion of said tuning inductance and connected to the low potential end thereof, and a modulator circuit for said receiving system including a modulator tube, an input circuit for said tube, including a tuning inductance, a variable condenser for tuning said inductance, an antenna circuit inductively related to said tuning inductance and connected thereto, switching means for short-circuiting portions of said tuning inductance `to alter the wave band through which the modulator is adapted to operate, a cathode circuit inductively related to the oscillator tuning inductance, and means for simultaneously operating all of said switching means.

7. In a superheterodyn receiving system, a

converter for producing a predetermined difference frequency between any received frequency and a locally generated frequency in any of a plurality of bands of frequency, including a iirst tuned circuit for selecting the received frequency and a second tuned circuit for determining the locally generated frequency, said first circuit comprising inductance variable in steps and a continuously variable condenser; said second tuned circuit comprising inductance variable in steps, a condenser variable in steps and a continuously variable condenser; switching means for simultaneously varying said inductances and said condenser variable in steps for operation in any one of said bands and uni-control means for simultaneously tuning with said continuously variable condensers to receive a desired frequency and produce said diiference frequency.

' 8. In a heterodyne receiving system for reception in a plurality of bands of frequency, a frequency selecting circuit for tuning in said plurality of bands comprising inductance variable in steps and a continuously variable condenser, an oscillating circuit to provide in each of said bands a local frequency differing from said selecting circuit frequency by a predetermined frequency, said oscillating circuit including a frequency-determining circuit comprising inductance variable in steps, a condenser variable in steps and a continuously variable condenser, and switching means for simultaneously changing both of said inductances variable in steps and said condenser variable in steps.

9. In a heterodyne receiving system in accordance with claim 8, a vacuum tube generator for generating the local frequency and including said oscillating circuit to determine the locally generated frequency and having plate and grid circuits, said condenser variable in steps being included in b oth plate and grid circuits to provide a feedback path between said plate and grid circuits, the values of capacity of said last-mentioned condenser being such that the mutual capacitive reactance of said path becomes larger when the frequency band in use becomes lower.

10. In a heterodyne receiving system, an oscillation generator of the thermionic vacuum tube type and a frequency-selecting circuit, said oscillation generator including grid and plate circuits, a frequency-determining network to tune one of said circuits, said network including a variable inductance, a first condenser adjustable in steps, and a second condenser which is va- L riable; feedback means between said grid and plate circuits including inductive reactance; unicontrol means for simultaneously modifying said variable inductance and the value of capacity of said rst condenser whereby the effective cou-

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