US2167605A

US2167605A - Intermediate frequency amplifier system

Info

Publication number: US2167605A
Application number: US180490A
Authority: US
Inventors: Wendell L Carlson
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1937-12-18
Filing date: 1937-12-18
Publication date: 1939-07-25
Anticipated expiration: 1956-07-25

Description

July 25, 1939. w. l.. cARLsoN INTERMEDIATE FREQUENCY AMPLIFIER SYSTEM 2 Sheets-Sheet 1 Filed Dec. 18, 1937 Snnentor Gttorneg July 25, 1939. w. 1 CARLSON 2,157,605

INTERMEDIATE FREQUENCY AMPLIFIER SYSTEM :7 l Filed Dec. 18, 1937 2 Sheets-Sheet 2 zo-@Mc 65 7i Ffn/ /g 67 60 i u l ll 55 v -E E I mei/l -CL B B FWEQ. 77 d3 /57 E 72 Vi 9/ 73 i l i l Osc.

Low was@ 3nventor Bg I Gttorneg Patented July 25, 1939 UNITED STATES mTERMEDIATE FREQUENCY AMPLIFIER SYSTEM Wendell L. Carlson, Haddonleld, N. J., assignor to Radio Corporation ol' America, a corporation of Delaware Application December 18, 1937, Serial No. 180,490

14 Claims.

'I'he present invention relates to an intermediate frequency amplifier system for radio receivers, and has for its primary object to provide an improved amplifier system of that character for multiple wave band radio receiver systems having a frequency coverage in at least one ultra high frequency band.

By way of example, the invention may be considered to relate Ito a multiple wave band receiver of the type covering a frequency range of from substantially 500 to '70,000 kilocycles and divided into the present standard broadcast, medium short wave, short wave. and `ultra high frequency bands, which are commonly known at present as the A, B, C and D bands, respectively, for broadcast receivers and the like, the D or ultra high frequency band being in the range above 20,000 kilocycles.

It is a further object of the present invention to provide an intermediate frequency amplifier system which permits a frequency response or channel width for the higher frequency bands greater than the present five kilocycle range on each side of resonance, and to permit the same to be extended to as wide as from 10 to 50 kilocycles on each side of the resonant or main frequency response of the signal receiving channel. With this arrangement, the intermediate frequency channel may have a response characteristic which is from two to five times as wide as is now used.

It is an object of the invention to provide covering the same number of broadcast or signal channels as in the present broadcast range, in a wider frequency range corresponding to the increased band width of the receiving system. For example, with the present broadcast tuning range covering substantially 1000 kilocycles, from 540 to 1600 kilocycles, it is proposed that an ultra high frequency tuning range cover at least 2000 kilocycles, for example, between 40 and 42 megacycles. With the same number of channels for an even wider band width of the response characteristic of the tuning system, the ultra high frequency or D band range may cover from 20,000 to 60,000 kilocycles.

It is also an object of the present invention to provide an improved intermediate frequency amplfier system for a multiple wave band receiver having an ultra high frequency band, with two intermediate frequency channels responsive to different intermediate frequencies so related and separated that a harmonic of the lowerintermediate frequency does not fall within the response range of the higher intermediate fre- (ci. o- 20) quency amplifier channel, whereby the same amplifier tubes and circuits may be used for both channels and the switching from one channel to another may be effected in a simple manner.

It is also a further object of the present invention to provide an improved intermediate frequency amplifier system for a multiple wave band receiver having a high intermediate frequency amplifier channel designed to pass double side band modulation frequencies-in a band width several times as wide as used for a low intermediate frequency amplifier channel in the same system, whereby in the higher frequency'tuning bands higher fidelity of reproduction may be obtained, a higher image ratio may be provided, less acoustic feedback is encountered, and there is less tendency for signals to drift out of tune.

In carrying out the invention, a low intermediate frequency amplifer channel is provided for the A, B and C bands, while a separate high frequency intermediate amplifier is provided for the D or high frequency tuning band and may be used for the C band, if this is also in a relatively high frequency range. The switching from the low intermediate frequency channel to the high intermediate frequency channel is effected by a simple switching arrangement preferably in conjunction with the band change control means.

It has been found that it is sometimes desirable to change 'the frequency converter, including the type of oscillator Aused for receiving signals in differing frequency bands, that is, one type of oscillator and converter is more effective and stable at ultra high frequencies, while another type of oscillator and converter may produce a uniform signal output over the tuning range of another signal receiving band.

Accordingly, it is an object of the present invention to provide an improved intermediate frequency amplifier system wherein the two amplifier channels may be provided as hereinbefore referred to, and may include different frequency converters and oscillators in conjunction with each channel, arranged selectively to be rendered effective by simple switching means, and effectively coupled to the respective amplifier channels with which they operate.

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

In the drawings, Figure 1 is a schematic circuit diagram of a multiple wave band radio receiving system embodying the invention;

Figure 2 is a curve showing the relative response characteristic between two amplifying channels in the circuit of Fig. l;

Figure 3 is a schematic circuit diagram of a portion of the circuit shown in Fig. 1 and embodying the invention; and

Figure iis a further schematic diagram of a radio receiving system embodying the invention, and providing a further modification of the system shown in Fig. 1.

Referring to Fig. 1, the radio receiving system shown may comprise any suitable multiple wave band tuner and oscillator, as indicated at 5. having a tuning indicator 6 and a tuning control means 1, whereby it is tunable through each of the various wave bands selectable by a band change control means indicated at 3. This band change control may be assumed to cover the usual number of wave bands, such as the A, B, C and D bands referred to hereinbefore.

The tuning means and oscillator are coupled to a converter or frequency changer comprising a multiple grid tube 8, having a grid I0 for receiving oscillations and a grid II for receiving the incoming signal, whereby the oscillations and signal are mixed at the output circuit indicated at I2. The output circuit I2 is the output anode circuit of the mixer tube 9 in the present example, and this is arranged to be selectively connectable to either one of two amplifying channels indicated at I3 and Il, both of which are arranged to use common amplifier tubes indicated at I5 and' I6 and a common rectifier or detector indicated at I'l.

In providing the circuit and tube arrangement referred to, the ampliier channel I3 is provided with interstage tuned coupling transformers I8, I9 and 20, all tuned to the same intermediate frequency, which may be a high intermediate frequency such as 2500 kilocycles, for example, while the channel I4 includes corresponding interstage coupling transformers indicated at 2|, 22, and 23, tuned to the same low intermediate frequency, such as 460 kilocycles, for example.

The circuit arrangement 0f the amplier is such that, from the converter tube 9, the intermediate frequency signal passes through the output circuit I2 to a simple two-point switch indicated at 25 and selectively through the switch to the tuned primary 26 of the transformer I8 or to the tuned primary 2l of thetransformer 2| ,thetwo primaries being tuned to 2500 kilocycles and 460 kilocycles, respectively. The tuned secondaries 28 and 29, respectively, of the transformers I8 and ZI are connected permanently in series between the input grid 30 of the rst amplier tube I5 and the cathode circuit 3I through a suitable bias potential source indicated at 32. Each of the pn'- maries may be connected to a suitable B potential source, as indicated.

The remaining secondaries of the other interstage coupling transformers IS-ZZ and 20--23 are similarly connected with the succeeding tubes i6 and I'l and the primaries of the said transformers are likewise connected in series as indicated so that, between the successive tubes of the amplifier, the primaries and secondaries of the interstage coupling means are connected in series and are rendered effective to couple the amplier tubes in cascade relation to each other as an intermediate frequency ampliiier responsive to two intermediate frequencies or narrow bands of frequencies about two mean widely separated intermediate frequencies.

The secondaries 28 and 28 are tuned respectively to the frequencies of their corresponding primary winding and, together, form an input circuit for the first amplifier tube which passes two bands of frequencies, that is, the amplifier is a double frequency amplifier with only one intermediate frequency signal impressed on the amplifier at a given time, determined by the position of the switch means 25, which may be coupled to the band change control, as indicated by the dotted connecting line 35. In a four-band tuning system of the type referred to, the connection is such that the switch means 25 is moved from an output connection with the'low frequency channel I4 to the connection shown with the high frequency channel I3, when the band change control is moved to provide tuning in the highest frequency range, such as the D band, and even in both the C and D bands,if the C band is arranged to include relatively high frequencies, such as frequencies above 20,000 kilocycles, for example.

Each of the succeeding amplifier stages and the detector I'I are similarly coupled for response in the two frequency bands or intermediate frequencies, the low frequency channel I4 being responsive in a narrower band about the 460 kilocycle mean frequency and the channel I3 being responsive in a broad band about the 25,000 kilocycle mean frequency, whereby high fidelity operation is obtained in the high frequency channel.

The channel I3 may be made responsive to a high intermediate frequency, for example, of 4000 kilocycles. However, it is desirable that with the remaining amplifier stages and detector permanently coupled by the series connection between the two channel coupling means, the relation between the two intermediate frequencies be such that the harmonic of the lower intermediate frequency does not fall within the present range of the higher intermediate frequency amplier.

The relative frequency response of the two channels is indicated in Fig. 2, to which attention is now directed, along with Fig. l, and in which the response peak at 38 is the characteristic response of the amplifier channel I 4, while the response peak at 39 is that of the amplifier channel I3. The 460 kc. peak may have a band width of, for example, 5 or 10 kilocycles at or near resonance, and the 2500 kc. peak may have a band width, for example, of 10 or 20 kilocycles at or near resonance. The several transformers LC ratios may be so proportioned as to amplify equally through the various stages at both frequencies or the design may be arranged so as to increase the amplification of one channel more than the other.

With this response characteristic and spacing of the two frequencies of the amplifier, the switching between the two channels may be effected by the simple switching means in connection with the separate primary windings 0f the initial or input coupling transformers of each channel, as shown. If desired, the switching means may be extended to include the secondary windings as well as the primary windings of transformers I8 and 2I. The transformers are preferably tuned by movable magnetic cores in connection with fixed capacitors, as indicated.

It will be noted that the interstage coupling transformers for the two channels in the inter* mediate frequency amplifier are arranged in such a manner, serially in circuit with the tubes, that the high frequency channel coupling transformers are connected in circuit adjacent to the tube plate and grid elements, whereby they are located at the high potential ends of the input and output circuits for the various tubes, while the low frequency channel coupling elements are located in the low potential sides of the responsive input and output circuits for the tubes and more adjacent to the cathode and plate supply for the respective grid and plate circuits. The transformers I8 and 2| may be in a common shield container or in separate containers. This also applies to transformers I9 and 22 and t0 transformers 20 and 23.

In order to place the simple switching arrangement involving a two-point switching change more adjacent to the low potential side of the input coupling means of the amplifier, and thereby avoid regeneration due to capacity coupling between the switch and other parts of the amplifier system, the circuit shown in Fig. 3 may be used between the converter 9 and the first amplifier tube I5.

Referring to Fig. 3, the output circuit I2 is connected permanently to a low frequency tuned primary winding 40 and a high frequency tuned primary 4I in series, while the input grid 30 of the tube I5 is connected permanently to a high frequency tuned secondary winding 42 and a low frequency tuned secondary winding 43 in series. The primarywinding 48 is coupled to the secondary winding 43, while the primary winding 4I is coupled to the secondary winding 42, as indicated.

`The two transformers thus provided are electrostatically and electromagnetically separated by space or by suitable shielding means, as indicated at 44. It is important that 460 kc. signals be highly attenuated when the switch is set for reception of 2500 kc. signals. Likewise, 2500 kc. signals must be highly attenuated when the switch is set for reception of 460 kc. signals. Therefore, coupling between coils 48 and 42 should be avoided.

In this input coupling circuit, the switching for selecting the two channels is provided at the low potential or anode supply end of the primary circuit and at the bias or low potential side of the secondary circuit, by a selector switch means having one section indicated at 45 which may be closed, as shown, when the other section, indicated at 46, is open, and when the section 46 is closed the section 45 opens. 'I'he switch sections are utilized to connect in circuit the tuning capacitors for the primary winding 4I and the secondary winding 43, as indicated at 41 and 48, respectively.

When the switch section 46 is closed, the high frequency primary 4I is tuned to apply energy to the tuned secondary 42 at 2500 kilocycles, and the tuned secondary winding 43 is rendered ineffective to respond in the 460 kilocycle range because of the opening of the switch section 45. which disconnects the tuning capacitor 48.

When the switch section 45 is closed, the secondary winding 43 is tuned to respond to signals in the 460 kilocycle range, and receives energy .from the low frequency primary 40. Since the switch section 46 in then open, the primary 4I is untuned and is rendered ineffective to transfer energy to the secondary 42. In switching the low frequency secondary winding 43, it will be seen that the winding is open-circuited by the switch section 45, and this is desirable in reducing the response from this winding when operating the amplifier in the high frequency range. In order to supply biasing potential to the grid 30 when the winding 43 is open-circuited, a bias supply resistor is provided, as indicated at 49. to complete the grid circuit around the capacitor 4I. This is a relatively high resistance and provides no appreciable load on the capacitor while at the same time conveying the biasing potential to the grid 38.

0n the primary side, anode current is permitted to flow through the untuned winding 4I when the switch section 46 is opened. Both switch sections 45 and 46 are connected to operate alternately in connection with the band change means, as indicated by the dotted connections 50.

From the foregoing description, it will be seen that for an al1-wave receiver of the superheterodyne type, a double intermediate frequency amplifier may be provided with one intermediate frequency signal passing therethrough at a given time, and selective control may be provided by a simple two-position switch coupled to the band change means, to operate when the band change means is-moved to provide ltuning in the ultra high frequency or D band. Furthermore, it will be seen that switching may be provided at low intermediate frequency potentials, so that the switch means has no substantially high potentials thereon which might cause regeneration coupling with other portions of the amplifier, such as the output of the amplifier.

In the embodiment shown in Fig. 3, the 460- kilocycle primary and secondary are preferably located in aseparate shield from the 2500-kilocycle primary and secondary windings. It will also be noted that the high frequency secondary is connected in circuit adjacent to the input grid of the rst amplifier tube I5, with the low frequency secondary more adjacent to ground or the bias supply connection.

The switching of the input circuit of the two channels of the amplifier may be arranged so 1 that no high alternating current or intermediate frequency potential is provided at the switch terminals, while at the same time providing for using separate converter tubes for each of the two channels, as shown in Fig. 4, to which attention is now directed.

Referring to Fig. 4, the superheterodyne receiving system shown is adapted for receiving signals in two different frequency ranges, one of which is a relatively high frequency range, for example, above 20 megacycles. In this system, an intermediate frequency amplifier arranged for double frequency response is provided, and comprises two

amplier channels

55 and 56, utilizing common amplifier tubes indicated at 5'I and 58. .The amplifier tubes are connected in cascade relation through interstage coupling transformers indicated at 59, 60, 6I and 62, the rst two being tuned to respond to a relatively high intermediate frequency, such as 2500 kilocycles, and the latter two being tuned to respond to a lower intermediate frequency, such as 460 kilocycles, for example.

The secondaries of the transformers 59 and 6I are connected permanently in series as shown, to form the input grid circuit for the input amplif'ler tube 51, and the output circuit of the tube 51 includes the primaries of the

transformers

60 and 62, connected in series as shown. The input or grid circuit of the tube 58 is provided by the tuned secondaries of the transformers Bil and B2, permanently connected in series. This follows the same arrangement as previously described in connection with Fig. 1, and places the windings of the higher frequency coupling transformers in circuit adjacent to the tube elements. The

detector is not shown, but may be coupled as preu viously shown and described in connection with Fig. 1.

'I'he input circuit of the two-channel amplifier comprises a tuned primary winding 68 for the high frequency transformer 59, and a tuned primary winding 8| for the low frequency transformer 6I. Each of these primary windings is connected to a separate converter or mixer tube, the primary 88 being connected to the output circuit of a mixer tube indicated at 55. and the primary winding 64 being connected to the output circuit of a mixer tube 55. 'I'his arrangement permits a different type of mixer or frequency converter tube to be used for the productionof the two intermediate frequencies.

For the high frequency channel 55, the converter tube 65 is of the type having two control grids indicated at 51 and 58, the first named grid receiving signals through a iixed tuned band pass filter indicated at 68, from a signal source such as an antenna circuit 18, and the grid 58 receiving oscillations through a coupling capacitor 1l, from the tuned circuit 12 of a separate oscillator tube 13.

The converter or mixer tube 88 is of the combined oscillator and mixer type. adapted to provide self-oscillations through the inclusion therein of oscillator electrodes 1I coupled to a tuned oscillator circuit indicated at 15. Signals are introduced into the tube through a control grid 18 and a tuned signal input circuit 11, also coupled to the signal energy supply circuit 10, as indicated by the tuned primary winding 18.

The three tuned

circuits

12, 15 and 11 are arranged to be variably tuned by means of a multiple unit tuning capacitor providing uni-control and comprising a variable tuning section connected across the circuit 12,' a second variable tuning section 8| connected across the circuit 15, and a third variable tuning section 82 connected across the circuit 11. 'Ihe uni-control operation of the three sections is indicated by the dotted connection 83.

The low frequency channel 55 of the amplifier receives signals at the intermediate frequency from the frequency converter 55 which converts the incoming signals timed in by the circuit 11 under control of the variable capacitor section 82. The oscillations are introduced electronically into the electronic stream of the device 55, as is well known, and the oscillations are controlled in frequency by the variable tuning capacitor 8| simultaneously with the tuning of the circuit 11, the circuits 11 and 15 being arranged to provide the desired frequency difference throughout the tuning range of the circuit 11. This type of oscillator and mixer is suitable for use in connection with low frequency circuits such as the standard broadcast and medium short wave bands, and reduces the number of tubes employed and the circuit connections thereto. In the present example, the tuned circuit 11 may be considered to respond to the broadcast band of 540 to 1600 kilocycles, and to produce an intermediate frequency of 460 kilocycles.

The tube 66 is energized under control of a switch 85 in the cathode circuit indicated at 86, and in the present example is shown in the closed position, for causing the tube 56 to operate as a converter of the detector-oscillator type. When the receiver is operating in the low frequency range, the oscillator 13 and the mixer 55 are deenergized by suitable switching control means, which in the present example comprises a switch 81 located in the cathode circuit 88 of the tube 65, and a switch 89 located in the anode circuit 80 of the tube 13.

The switches 81 and 88 are shown in the open position and are arranged to be open, as shown, when the switch 85 is closed, also as shown, The switches 85, 81 and 8! may form sections of a common switch means, and are. in any case, arranged for uni-control operation, as indicated by the dotted connection Il, whereby. when the switches 81 and 89 are closed, the section 85 opens, and vice versa.

When the switches 81 and 88 are closed, the oscillator 13 and the mixer tube l5 are energized and signals from the oscillator 18 are applied to the mixer tube 58, to beat with incoming signals on the grid 81, received through the band pass filter 69. If the band pass filter is tuned to a fixed frequency band in the range of ultra high frequencies, such as from 40 to 41 megacycles, for example, the tuning of the system within that band may be effected by tuning the oscillator alone by the variable tuning capacitor section 80, and this arrangement is followed in the present example, although it should be understood that the input circuit for the grid 51 may be tuned by uni-control means in the same manner that the control grid 15 of the mixer tube 56 is tuned by the circuit 11.

The oscillator 13 is tuned through a. frequency range to beat with the incoming signals through the band pass filter 58, to produce the desired intermediate frequency of 2500 kilocycles, for example, which passes through the channel 55. The channel 55 is rendered ineffective by deenergizing the converter or mixer tube 55 by the opening of the switch section 85.

The circuit of Fig. 4 has the advantage that no intermediate frequency potentials are applied to the switch terminals 81, Il or 85, and provision is made for utilizing separate converter tubes for each of the frequency bands, each having advantages not possessed by the other for the particular use. For example, at ultra high frequencies, ,the converter tube 85, with separate mixer grids and a separate oscillator, operates with more uniform output and frequency stability than with a combined oscillator and detector tube of the type -shown at 85.

The superheterodyne receiverl circuits herein disclosed include two intermediate frequency channels, one having characteristics suitable for use in connection with reception of radio frequencies in the order of 1000 kc. and 10,000 kc. having channel allocations with approximately 10 kc. separation, and the other one having characteristics suitable for use in connection with reception of radio frequencies in the order of 50,000 kc., for example, having channel allocations with about 50 kc. separation.

Means are provided for combining the two in termediatefrequency channels into one cascade amplier employing common intermediate frequency amplifier tubes, with selecting means, restricted to the input circuits preceding the iirst intermediate frequency amplifier tube, resonant for effectively passing only signals in one or the other of the intermediate frequency channels.

I claim as my invention:

l. An intermediate frequency amplifier system for multiple wave band receivers, comprising means providing two intermediate frequency amplifying channels, means for tuning said channels to a lower and a higher intermediate frequency, the higher. intermediate frequency falllng between two of the harmonics of the lower intermediate frequency, and a plurality of amplifier tubes connected to operate jointly with both of said channels.

2. An intermediate frequency amplier system for multiple Wave band receivers, comprising means providing two intermediate frequency amplifying channels, means for tuning said channels to a lower and a higher intermediate frequency, the higher intermediate frequency falling between two of the harmonics of the lower intermediate frequency, a plurality of amplifier tubes connected to operate jointly with both of said channels, means providing selective input circuits for said channels resonant for passing signals at said lower and higher intermediate frequencies, and wave band change means having an element movable to select one of said input circuits.

3. An intermediate frequency amplifier system for multiple wave band receivers comprising means providing two intermediate frequency amplifying channels, means for tuning said channels to a lower and a higher intermediate frequency, the higher intermediate frequency falling between two of the harmonics of the lower intermediate frequency, a plurality of amplifier tubes connected to operate jointly with both of said channels, and means for introducing an intermediate frequency signal into each of said channels selectively at the input ends thereof comprising a selector switch, and means providing wave band change control for operating said selector switch.

4. An intermediate frequency amplifier system for multiple wave band receivers comprising means providing two intermediate frequency amplifying channels, means for tuning said channels to a lower and a higher intermediate frequency, the higher intermediate frequency falling between two of the harmonics of the lower intermediate frequency, a plurality of amplifier tubes connected to operate jointly with both of said channels, and means for introducing an intermediate frequency signal into each of said channels selectively comprising a tuned input circuit for each channel resonant for effectively passing only signals at the lower and the higher intermediate frequencies, a selector switch connected with said input circuits for rendering one or the other effective to respond to signals, and means providing wave band change control for operating said selector switch.

5. In a superheterodyne receiver, the combination of means providing two intermediate frequency signal channels, tuning means in one of said channels for passing intermediate frequency signals in a narrow lower frequency band and tuning means in the other of said channels for passing signals in awider and higher frequency band lying between two adjacent harmonics of the mean frequency of the lower frequency band, circuit means including common amplifier tubes for combining the two intermediate frequency channels into one cascaded amplifier circuit, means providing selectable tuned input circuits for each of said channels preceding the first intermediate frequency amplier tube, said circuits being resonant and selective for effectively passing only signals in one of the intermediate frequencies through said amplier circuit.

6. An intermediate frequency amplifier system for multiple wave band receivers, comprising means providing two intermediate frequency amplifying channels, means for tuning said channels to a lower and a higher intermediate frequency, the higher intermediate frequency falling between two f the harmonics of the lower intermediate frequency, a plurality of amplifier tubes connected to operate jointly with both of said channels, and means for introducing an intermediate frequency signal into each of said channels comprising a sepalate converter tube and means for selectively energizing said tubes.

7. An intermediate frequency amplifier system for multiple wave \band receivers, comprising means providing two intermediate frequency amplifying channels, means for tuning said channels one to a lower and the other to a higher intermediate frequency, the higher intermediate irequency falling between two harmonics of the lower intermediate frequency, a plurality of ampliner tubes connected with said last named means to operate jointly with both of said.channels, means for introducing an intermediate frequency signal into each of said channels comprising a frequency converter for each channel, a tunable high frequency oscillator coupled to the frequency converter for the higher intermediate frequency channel, means for introducing signals within a predetermined high frequency band into the last named converter, means tunable conjointly with the high frequency oscillator for introducing signals and oscillations into the other of said converters, and means for selectively energizing said last named converter with respect to energization of the first named converter and oscillator.

8. An intermediate frequency amplifier system for multiple wave band receivers, comprising means providing two intermediate frequency amplifying channels, means for tuning said channels one to a lower and the other to a higher intermediate frequency, the higher intermediate frequency falling between two harmonics of the lower intermediate frequency, a pluralityof amplifier tubes connected with said last named means to operate jointly with both of said channels, means for introducing an intermediate frequency signal into each of said channels comprising a tube having two signal input grids and output circuits, one coupled to each of said channels to provide separate frequency converter means for said channels, a tunable high frequency oscillator coupled to one of the input grids of the converter tube for the higher intermediate frequency channel, means for introducing signals within a predetermined high frequency range into the last named converter tube connected with the other of the signal input grids thereof, means tunable conjointly with the high frequency oscillator for introducing signals and oscillations into the other 'of said converter tubes connected with one of ,the signal input grids thereof, and means for selectively energizing said last named converter tube with respect to energization of the first named converter tube and oscillator.

9. In a superheterodyne receiver, means providing a multiple wave band tuner and oscillator, tuning control means therefor, wave band change control means therefor, and an intermediate frequency amplifier providing two intermediate frequency amplifying channels therein and a series .of cascaded amplifier tubes common to and connected with both said channels jointly, one of said channels having frequency response characteristics for the reception of signals in the tuning means and oscillator in a frequency range below 10,000 Akilocycles with signal channel allocations permitting approximately 10 kilocycle separation and the other of said channels having response characteristics for the reception of signals in the tuning means and oscillator in a frequency range above 10,000 kilocycles with signal channel allocations permitting from 10 to 50 kilocycle separation, means providing selectable tuned input circuits for said channels preceding the rst intermediate frequency amplier tube, said circuits being selectable and resonant for effectively passing only signals in one or the other of said intermediate frequencies to which the separate channels are responsive.

10. In a superheterodyne receiver, the combination of means providing two intermediate frequency signal channels, tuning means in one ofsaid channels for passing intermediate frequency signals in a narrow lower frequency range and tuning means in the other of said channels for passing signals in a wider and higher frequency range lying between two adjacent harmonics of the mean frequency of the lower requency range, circuit means including common amplifier tubes for combining the two intermediate frequency channels into one cascaded amplifier circuit, means providing selective tuned input circuits for each of said channels preceding the first intermediate frequency amplifier tube, said circuits being resonant and selective for effectively passing only signals in and through one of the intermediate frequency amplifying channels to the exclusion of the. other, said last named means including a high frequency tuned secondary winding and a low frequency tuned secondary winding of two separate intermediate frequency coupling transformers serially in the input circuit of the rst intermediate frequency amplifier tube, a tuned primary Winding for each of said transformers, and means for selectively detuning the high frequency primary winding and the low frequency secondary winding concurrently with selective change in the tuning response of said receiver.

11. An intermediate frequency amplier system for multiple wave band receivers, comprising means providing two intermediate frequnecy amplifying channels, means for tuning said channels to a lower and a higher intermediate frequency, the higher intermediate frequency falling between two of the harmonics of the lower intermediate frequency, and a plurality of amplifier tubes each connected with both of said channels to operate jointly therewith, and means responsive to wave band change for selectively applying signals at said intermediate frequencies to said channels.

12. In a multiple wave band superheterodyne receiver, the combination of means providing two intermediate frequency signal channels, tuning means in one of said channels for passing intermediate frequency signals in a narrow lower frequency range and tuning means in the other of said channels for passing signals in a wider and higher frequency range lying between two adjacent harmonics of the mean frequency of the lower frequency range, circuit means including common amplifier tubes for combining the two intermediate frequency channels into one cascaded amplifier circuit, and meansproviding selective tuned input circuits for each of said channels preceding the first intermediate frequency amplier tube, said input circuits being resonant and selectable in response to change in wave band for effectively passing signals in each of the intermediate frequencies selectively through said amplifier circuit.

13. In a superheterodyne receiver, the combination of means providing two intermediate frequency signal channels, tuning means in one of said channels for passing intermediate frequency signals in a narrow lower frequency range and tuning means in the other of said channels for passing signals in a wider and higher frequency range, circuit means including common amplifier tubes for combining the two intermediate frequency channels into one cascaded amplifier circuit, means providing selective tuned input circuits for each of said channels preceding the first intermediate frequency amplifier tube, said circuits being resonant and selective for effectively passing only signals in and through one of the intermediate frequency amplifying channels to the exclusion of the other, said last-named means including a high frequency tuned secondary winding and a low frequency tuned secondary winding of two separate intermediate frequency coupling transformers serially in the input cir- Y cuit of the rst intermediate frequency amplier tube, a tuned primary winding for each of said transformers, and means for selectively detuning the high frequency primary winding and the low frequency secondary winding concurrently with selective change in the tuning response of said receiver.

14. In a multiple wave band superheterodyne receiver, the combination of means providing two intermediate frequency signal channels, tuning means in one of said channels for passing intermediate frequency signals in a narrow lower frequency range and tuning means in the other of. said channels for passing signals in a wider and higher frequency range, circuit means including common amplier tubes for combining the two intermediate frequency channels into one cascaded amplifier circuit, and means providing selective tuned input circuits for each of said channels preceding the first intermediate frequency amplifier tube, said input circuits being resonant and selectable in response to change in wave band for effectively passing signals ineach of the intermediate frequencies selectively through said amplifier circuit.

WENDELL L. CARLSON.