US2044745A - Receiving circuits - Google Patents

Description

June 16, 1936. C W. HANSELL 2,044,745

RECEIVING CIRCUITS Filed Aug. l, 1933 4 l0 Sheets-Sheet l f lNvENroR aw. AN SELL BY -M ATTORNEY l0 Sheets-Shet f5 c, w. HANsELL RECEIVINGv CIRCUITS` Filed Aug. l, 1935 lNvENToR C.W.

ATTQRNEY June 16, 1936.

nrw-

jHHn,

June 16, 1936.

C. W. HANSELL RECEIVING CIRCUITS Vl0 Sheets-Sheet 4 l INVENTOR c. w.

BY l

ANSELL.

ATTORNEYA Filed Aug. l, 1955 /S nl@ June 16, 1936 c. W. HANsELL IRECEI'VING cRcUITs Filed Aug. l, 1935 .10 SheetS-Sheet 5 `lune 161, 1936. c. W. HANSELL RECEIVING, CIRCUITS Filed Aug. l, 1933 l l0 Sheets-Sheet' lNvEN'roR C.W. HANS'ELL ATTORNEY June 16, 1936.

c. w. HANsELL 2,044,745

RECEIVING CIRCUITS Filed Aug. 1, 1933 fz//vf 70 fawn/#MM FHfQUfA/cy) oaf/w 7' l0 Sheets-Sheet 9 INVENTOR C.W.HAN5ELL ATTORNEY June 16, 1936.

HANsELl. 2,044;745

RECEIVING CIRCUITS Filed Aug. 1, 1953 l F FREE FROM M4465 5/6/1/415 l lO Sheets-Sheet 10 ,Etfgf'iz' mia.

L E aar/far AAAAAA ATTRNEY 1 Patented June 16, 1936 PATENT orties RECEIVING fon'to'urrs Clarence W. Hansell, Port Jefferson, N. Y., assignor to Radio Corporation of America, a co1'- poration of Delaware Application August `1, 1933, Serial No. 683,115 20 Claims. (C l.`2`5U0- 20) This invention relates to superheterodyne radio receiving circuits and, more particularly, to a method of and apparatus for suppressing image signals in such circuits.

One common and serious defect in high Vfrequency superheterodyne receivers which are designed and constructed to give good frequency circuits.

selectivity in the band aroundY a desired signal is the failure of such receivers to suppress the image band of frequencies symmetrically spaced on the opposite side of the beating oscillater frequency fromthe desired signal. Thus, for tuning adjustment, the receiver is known to admit two bands of frequencies separated by twice the frequency of the intermediate frequency For example, if such` a receiver were designed and adjusted to use a frequency of V million cycles per second from the rst beating oscillator and to have an intermediate frequency pass band around one million cycles, then it would receivefrequencies picked up by the receiver in bands around 19 million and 21 million cycles per second. This has been found to be` a very undesirable arrangement because of the probability of interference between signals in the two bands and the increase in noise engendered.

One of the reasons fordesigning a receiver with such an undesirable characteristicis the desire to reduce the cost of construction.. If the receiver were designed to use a higher intermediate frequency and there were provided sumcicnt high frequency selectivity `in circuits ahead of the first detector, the image band passed through the first detector might be effectively suppressed. However, when very highfrequencies are being received, the intermediate Vfrequency after the first detector might have to be made so high that the selectivity of the intermediate frequency circuits would not besuflicient to prevent image signals appearing in the circuits after the second detector. Then it would be necessary to provide a third detector with associated circuits and the receiver would have to be made much more complex and expensiver The present invention 'overcomes the abovementioned difficulty and provides a highly ecient and simple method of suppressing image signals; and this is effected, generally, by causing the output currents from two detectors used to receive the same signal to balance out substantially for frequencies on one side of the beating oscillator frequency and to add together Wholly or in part for frequencies on the other side of the beating oscillator frequency.` More specifically, it has been found that if the output .from a source of constant radio frequency is supplied to two separate detector circuits with a difference in the phase of the current in one detector input circuit with respect to the other by, say, degrees, and a radio signal frequency also applied-to both detectors in like phase, there will be obtained in the outputs of the separate detectors currents Ycorresponding to beats between the radiofrequency energies. Under these conditions there will be obtained from the two detectors outputs corresponding to the beat fre- `quency between the oscillator and the signal frequency, and the beat frequency outputs of the two detectors will have a phase relation corresponding to the difference in phase between the two radio frequency currents fed into the detectors from the oscillator. In such case the polarity of the beat frequency output from a heterodyne detector reverses as the frequency of o-ne of the vbeating currents is moved above or below the frequency of the other beating current. Also, if the same pair of currents are used to cause beats in two separate detectors under similar conditions, i; e., they are applied to the detectors with a shift' in relative phase, then the two detector outputs will have a difference in phase equivalent to a polyphase power system. Then if one beating frequency were applied aboveV or below zero beat Vwith the'other there will be produced a reversal `on one side of the beating oscillator frequency and to add together wholly or in part for frequencies on the other side of the beating oscillator frequency. There is thus obtained a hetero- `dyne detector system which has little or no output for frequencies below that of the beating oscillator and full output for frequencies above Ythe beating oscillator, or vice versa.

The invention is more adequately described in `connection with the accompanying drawings wherein `Figures la andl 1b show, merely for purposes of illustration, different ways of obtaining detector outputs according to the principles of the present invention; Figures 2o to 2f show vector diagrams which represent the different detector voltages and currents in the detector circuits when effected in accordance with the pres- `'ent invention; and Figures 3 to 8 inclusive illustrate, by way of example only, various image supure la..

pressing receiver arrangements embodying the principles of the present invention. Figures 9 to 13 inclusive show various circuit schemes whereby oscillators may be made to give a degrees phase relation over a wide band of frequencies.

Referring to Figures 1w and 1b, there are shown simple diagrams of the image suppressing heterodyne detector system of the present invention wherein two detectors I and 2 are supplied with high frequency energy from any source of re`` ceived energy, such as an antenna 3 and also from a local beating oscillator 4. The energies supplied to the detectors I and 2 from local beating oscillator 4 are applied to the detectors with a difference in phase of preferably 90 degrees. A phase shift apparatus has been indicated in Fig- In actual practice, it is probable that the two output circuits, designated a and b, from the oscillator will be tuned and that the phase shift will be obtained by simply adjusting one above and one below the output frequency so that one carries current of leading phase and the other carries lagging current with respect to the oscillator output voltage. Since the frequency will be constant, it is entirely practical to depend upon the tuning of the circuits to produce the phase shift. Of course, if preferred, some other form of phase shifting device, as indicated, which may comprise a radio goniometer or articial transmission line, may be used to shift the phase. The oscillator may be variable in frequency or it may comprise a crystal unit such as is known to be capable of supplying extremely constant frequencies through the use of a piezoelectric crystal, It will be apparent, of course, from the foregoing that, if desired, the phase of the received energy may be applied 90 degrees differently in phase to the detectors I and 2 instead of a difference in phase of the currents from the outputs of the oscillator 4.

The beats between the received signal energies and the local oscillator give outputs from the two detectors I and 2 which differ in phase by 9'0 degrees. The output from detector I can be made 90 degrees leading in phase with respect to output from detector 2 for received energizes below the frequency of the local oscillator. Then, for received energy frequencies above that of the local oscillator the output of detector I will lag that of detector 2 by 90 degrees. Now, if there are employed circuits, such as 5 and 6, after the detectors which cause an additional 90 degrees phase shift between the two detector outputs either the higher or lower received frequency output components from the detectors can be made to add while the other components are suppressed. Then, if the detector outputs are equal in amplitude there is received one band of frequencies above or below the local oscillator lfrequency while there is suppressed the image band below or above the local oscillator frequency. Y

An analysis of the principle upon which the present invention is based follows, for which the vector diagrams of the currents and voltages are shown in Figures 2a to 2f inclusive. These figures are believed to be self-explanatory.

Let the high frequency incoming signal:

where wa and wb are audio frequencies, Kh and KZ the modulation factors, etc.

wh=high frequency, wl:low frequency. Let wi:intermediate frequency and wo:osclla tor frequency. Let Ao:amplitude of oscillator and assume very large compared to AZ and Ah, of incoming Waves, that is: Al Ao and Ah Ao call E: m and Ao 'I'hen m( 1 and n 1 This is the normal condition in a superheterodyne receiver.

NOW w0=wi+wh=wlwi Assume phase ofwo on #2 rst detector shifted by 90 leading #1. Then we have impressed on the two rst detectors:

4The rectied component is given by the absolute Value of thefollowing complex expressions: Then rectified current from #1:

yThen rectified current from #2:

because m 1 and q1 The inter-frequency 'currents are then #1 Aolm cos wt-I-n cos wit] #2 Ao[m sin wit-n sin wit] YCall the second detectors a and b connected in circuits from 1 and 2.

Therefore Ydepending upon connections one may eliminate either m or n. If n is eliminated there `is left 2m= 2 [1 -I- Kh cos wat] or the audio modulation of the higher incoming radio frequency.

With this type of detector it is possible to beat l "Il Cil i of the firstdetector.

directly down to audio frequencies or down to oscillator'frequency and perfect addition of waves l000'cycles above. If the pass band for the audio frequency circuits were made V500 cycles wide then the suppression of waves plus and minus 250 cycles from the perfectly suppressed wave would still be fairly good. .Also by adjusting the relative amplitudes and phases of currents in detector inputs or outputs or both, any particular interfering wave might be almost perfectly balanced out without much change in the strength of reception for the Vdesired wave. If the audio selectivity is made greater, or the output frequency is made higher, keeping the same selectivity, the need for and difliculties in balancing any particular undesired frequency become less. In practice, it is possible to beatdirectly down to audio frequencies in a very cheap mobile receiver, but it is preferredfor high class receivers to beat down to` an intermediate frequency and use a second detector in order to more perfectly balance out all image reception. V-Where an intermediate frequency is useid, the final band passed by the receiver may be small as compared `to the intermediate frequency and almost pervfect balancing can be obtained for the whole image frequency band. In some cases, it may be desirable to utilize circuits for holding constant amplitudes and relative phase differences over 5 over an antenna 'I whichis coupled to a high frew quency amplifier 8 through an electrostatic shield 9 in a well known manner. The output from amplier 3 is `applied to the two tubes I9 and I l of the first heterodyne detector.

In addition, there is provided an oscillator Iii, the output of which'is applied to a phase splitting circuit designed preferably to give a shift ofabout 90 degrees between the twoinputs i 2 and I3 to the two tubes Ill and I I, respectively,

K This phase splitting circuit is supplied with trimmer or Vernier adjustments I4 and I5 for exactly balancing undesired image frequencies.

The tuned circuits of the high frequency amplifier 8, oscillator I6 and detector input circuits are assumed to be variable, but unicontrolled .by

-one mechanism. Plug-in coils or circuits may be4 employed to adapt the high frequency circuits to any one o-f several desired bands of frequencies. The high frequency circuits assigned to marine service, for example, `are divided up into-rather small percentage bands so that it` should be entirely practical to provide wave change from one band to another by means of switches or plug-in circuit elements and have these elements adjusted for balancing out image signals in their respective bands.

The currents from the two detector tubes Ill and I lare shown applied to their individual output circuits Il and I8, respectively, which are phase shift will be 90 degrees.

tuned to frequencies above andV below the desired intermediate beat frequency from the first detector system. The detuning of these circuits should be such as to cause a shift in relative phase `of currents setup in them equal to the phase 1 shift provided by the phase splitting circuit in the output of the oscillator. In this case the As a result, the detector outputs corresponding to one band .of high frequencies will oppose one another and those due to the other band will add in the conimon output circuit I9 which is coupled to both detector output circuits Il and I8.

Output circuit I9 carrying a desired band is shown applied to an intermediate frequency amplifier having two stages 20 and ZI, the circuits of which provide selectivity around the desired signal to any desired degree. The intermediate frequency amplifier is shown followed by a second detector 22 and an audio amplifier 23. The circuits illustrated in Figure 3, as so far described, are suitable for reception of telephone signals, but may be made suitable for continuous wave telegraph signals by providing a locally generated beating frequency input, as shown in Figure 3A, to the second detector 22. By providing means to turn the second beating oscillator on and off the receiver may be quickly adapted to either modulated phone or continuous wave telegraph reception. figure, it should be noted that, if desired, the capacity of the condensers of the circuits II and I8, as indicated by the dash connecting line, may vary oppositely as their common shaft or control Yis turned in one direction. Other ways are, of course, known of constructing differently variable condensers.

The intermediate frequency circuits may be fixed and do not require changes or tuning to tune the receiver from one desired signal frequency to another'. However, if desired, a differential condenser or other adjustment may be provided for the two detector output circuits to` provide more exact adjustment for balancing undesired image signals.v Y

Figure 4 illustrates a modification of Figure 3 wherein the output circuit for the first amplifier 8 is coupled directly to the grids of detectors I 0 and I I through blocking condensers 50 in order to eliminate the two tuned input circuits for the detector tubes. In this case, if indirectly heated vacuum tube cathodes such as shown at 5I are instead of the grids. A simplification of this sort is great aid in providing unicontrol tuning.

In this gure there is also shown an arrangement for simplifying the phase splitting circuits of the oscillator to the detectors, and this is accomplished by passing the oscillatcrvcircuit radio frequency current, or a portion of it, through a resistance and condenser in series, as shown. The

In connection with this vii el L1 voltage drop across the resistance and condenserV willawaysbe 90 degrees different in phase. If

the condenser in series with the resistance is will be small compared with the impedance of the main resistance and coil of the oscillator circu1t.

Figure 5 is a further modification and illustrates a receiver arrangement for high frequency telephone signals which eliminates the first beating oscillator by making the circuits of the first; detector self-oscillating to hold the two tube circuits on the same frequency and at the proper phase angle by suitably controlled coupling between them. In this circuit two detectortube circuits 24 and 25 are held at 90 degrees phase relation by means of reactive coupling between them which is provided by a small amount of inductive or capacitive mutual reactance. In practice, a small amount of mutual inductance would be preferable because the percentage of mutual inductance would remain constant even though the frequency of oscillation be varied over a large range by means of unicontrol variable condensers.

Referring in more detail to this figure, there is shown an antenna 'l coupled to a screen grid high frequency amplifier 26. Amplifier 26 serves to prevent energy from the oscillators in the receiver from reaching the antenna and being radiated in a manner to produce interference in other receivers. A capacity neutralized amplifier might be used although it is preferred to employ the screen grid tube amplifier, with appropriate shielding, as shown.

The output of screen grid high frequency amplifier Z6 is coupled to both of the two high frequency detectors 24 and 25 through coils 21, 28, 29 and 30. The mutual inductance introduced through these coils not only couples the output of the amplier 26 to the two detector tubes 24 and 25, but may also provide all or part of the inductive coupling between the two oscillating detector circuits. By virtue of this inductance coupling between the two oscillators, which are assumed to be electrically identical or similar, they are held in synchronism with a constant phase difference of substantially 90 degrees when correct adjustments have been made. Consequently, beats between the two detector oscillations and amplified energies from the antenna 'l result in detector output beat frequency energies substantially 90 degrees different in phase.

The tuned circuits of the high frequency amplifier 26 and self-oscillating detectors 24, 25 may be electrically similar and all tuned by three similar condensers on the same rotatable shaft or, at any rate, mechanically operated by a single tuning arm. If desired, plug-in coils may be used in some cases to adapt the receiver to reception in different bands.

The oscillating detector tubes as shown in this particular diagram are assumed to have grid bias and regeneration such that the strength of oscillations is held to something 0n the order of half maximum amplitude and the amplitude left quite sensitive to small amounts of helping or opposing energy fed in from the amplifier. At the same time the anode current is made sensitive 4to the amplitude of oscillation and all these factors contribute to making, the detectors very sensitive.

The intermediate frequency outputs from the two detectors are shown applied to two tuned circuits. These circuits are similar except that one is tuned above and one below the middle of the intermediate frequency pass band by such an amount as to cause opposite shifts of 45 degrees in the currents set un in the circuits. If

desired, the tuned circuits might be replaced by reactance-resistance phase splitting circuits, artificial lines, radio goniometers or any other known phase shifting devices.

The tuned detector output circuits shown in the diagram are equipped with condensers which may be varied differentially for controlling the relative phase shifts in the currents in order to obtain most perfect cancellation of any particularly strong interfering image signal.

The two circuits are shown coupled to the input of an intermediate frequency amplifier. The relative coupling to the two circuits should be differentially variable for exactly balancing the amplitudes of any undesired image signals. If preferred, means may be provided for varying the detector sensitivities, instead, by varying the electrode potentials, regeneration, circuit losses, etc.

The output circuit of the intermediate frequency amplifier is shown coupled to a second detector through a coupled circuit band pass filter. The output of the second detector is amplified and passed to the loudspeaker or any other suitable utilization device.

To obtain automatic volume control there is shown a resistor in series with the anode supply to the final detector. The Voltage drop in this resistor varies in accordance with the strength of average input to the detector. The changing voltage tends to decrease the detector sensitivity for increasing input and also varies the screen grid voltage on the amplifier tubes in a direction to decrease their amplification.

Although, in the diagram there has been shown only one source of voltage for each of the grid bias, screen grid and anode potentials it will be understood that, in practice, different voltages may be used on electrodes of different tubes.

To illustrate one way in which the receiver may be utilized we might assume that the signals from a telephone transmitter operating on a carrier frequency of 40,000,000 cycles per second is to be received. If this is a high quality transmitter its carrier may carry modulating frequencies from about 25 to '7500 cycles.

In the first detector we may employ an oscillating frequency of 39,600,000 cycles which will produce an intermediate frequency carrier of 400,000 cycles. The image band which we wish to eliminate is one having a midband at 39,200,000 cycles, which is only about one part in 50,000 removed from the desired band so that it is not appreciably reduced by the selectivity of the circuits ahead of the -rst detector.

Assuming all adjustments are correct we may balance the 400,000 cycle image energy almost perfectly to zero in the input to the intermediate frequency amplifier. The intermediate frequency circuits eliminate energies of frequency more than plus or minus 7500 cycles removed from the 400,000 cycles. Energies which are l7500 cycles removed will not balance quite perfectly because they are nearly 2% removed from the balanced frequency. The amount of unbalance in this case will amount to` possibly as much as 2 to 2.5 degrees in angle and 2.5% to 3% in amplitude which may produce an unbalanced amplitude of undesired image energy as much as 2% of the sum of the desired detector outputs. In the case assumed, the maximum interfering eifect from any part of the image band will then be about 2% of normal amplitude, 0.04% of normal power or 25 decibels reduced. Assuming that the desired carrier is reasonably strong the chief resulty of unbalance image energy would be to were produce audio noise of maximum. intensity .at 7500 cycles, but which would decrease very-.rapidly at lower audio frequencies.'

. Another circuit similar to that of wherein two detector tubes are used with the ordinary type of regeneration or oscillation may be employed for marine or similar equipment.; Such an arrangement is shoWnin'Figure 6, wherein the high frequency Waves are beat'down to relatively low intermediate frequencies and the sec ond detector made regenerative for phone and modulated wave reception or self-oscillatingfor reception of continuous waves. By carefulfattention to obtaining maximum sensitivityin the self-oscillating detectors there is thusA obtained an extremely simple and inexpensive receiver which has substantially the same` performance" characteristics as themore elaborate superhet erodyne receivers. Y A ,Y

`Figure 7 shows an image band suppressing receiver system wherein ,no phase `shifting is re-V balanced out.` Preferably, a 'low intermediate frequency is used. lI-ligh frequency and intermediate frequency amplifiers and many other refinements may be added, gif desired', VReversing relative polarities of., thei'p'rimaryfwindings 35 and 36 ofthe audio transformer 31 allows selection of the band either above or below the high frequency oscillator. s f

Figure 8 shows an arrangement for ultra high frequency reception fwherein the two first 'detector tubes are adjusted and used as Barkhausen oscillators locked in stepwithma, difference phase between the oscillations.. TheBarkhausen eect maybe used, if desired, only forregeneration to obtain increased high frequency sensi-v tivity and selectivity. Y ,L Figure 9 shows ascheme for holding' `he os cillators in synchronism withl a phase're'lat'in of substantially 90 degrees, regardless 'of variations in their frequency. This arrangement'gives the oscillators a fixed 90 degrees phaserelation over any range of frequencies by coupling the two oscillators H and 4l insuch manner that their second harmonics are always held substantially` 180 degrees out of phase. Y In way; their fundamental frequencies, ofA necessity, are always at and ground, or the negative side of the anode circuit power supply system. Preferably, the 'cou-f pling `between the 'oscillators 'atfthe fundamental frequency is a minimum, though 'some coupling is permitted. Theeffect of 'd the circuit'shownj tuned tothe second harmonie` (or any other. even harmonic,gif desired)` is to insert a strong degenerative effect at ,the second harmonic frequency into each oscillator circuit taken alone. In other words, it tends strongly to -i reduce the; strength of oscillation in eachosc'illator. I-Iowever, when both oscillators are active they'balance out second harmonic currents in .thecircuit tuned to the harmonicand thuseach permits the other to oscillate full strength, without. second harmonic degeneration.;v This full [strength os Figure V Y phase relation, which corresponds to 90 degrees phase lrelation from the fundamental.

It is preferred in the circuit arrangement just described thatV all variable condensers shown `be controlled by one shaft or knob.

It will be noted that the accuracy of phase control between the two oscillators is only slightly dependent upon the tuning of the second harmonic circuitjit only being necessary that the circuit develop considerable harmonic frequency impedance. .i As a result, the system has no criticalv adjustments and is quite practical to construct and operate. Obviously, other detailed circuit arrangements may be used instead; for example, vthe, harmonic frequency tuned circuit may be inserted in series with the positive or anode end of the power supply circuit instead of in the negative or cathode end. Also, any other known type ofV oscillator circuit may be used.

If theoscillators 4!! and di are used directly as detectors, the high frequency input may be coupled to them and intermediate frequency circuits inserted in series with the anode supply leads.

An' alternative to the arrangement of Figure 9 may be set up with two relaxation oscillators or frequency dividers having their frequency controlled by a double frequency oscillator, output from which would be applied to the frequency dividers `1180 degrees `out of phase. If tripping tube or glow tube, condenser, resistance frequency dividers are used the resistance can be unicontrolled with the oscillator. condenser to hold correct relative adjustments over a large range of frequencies.

HFigures 10 to 13 utilize auxiliary electrodes for second harmonic synchronization of oscillators at the 90 degree phase relation.

. Figure 10 shows two oscillator circuits in which thescreen grids of four electrode tubes are used asanodes. In the circuit the plates of the tubes arev connected in parallel and then placed Vin series with a circuit tuned to the second harmonic Qffthe Aoscillator frequency. In order that the second harmonic circuit may lock the oscillators in step at 90 degree phase relation it is necessary Yfor thersecond harmonic circuit to cause a reduction in oscillator power except when the second harmonics are 180 degrees out of phase. In other words, the building up of oscillations in the secondzharmonic circuit must reduce the current flow` to the screen grids. Since the second harmonic circuit, Ywhen oscillating, Vreduces the anodelvoltage, simultaneouslyv with reduction in screen grid` voltage from the fundamental frequency oscillation we must have conditions which cause a reduction in screen grid circuit with reduction in anode voltage. We may obtain this condition bymaking the anode D. C. voltage positive, but much less than the screen grid D. C.

d voltage so that, due to dynatron effect a conlation condition, if the circuits are correctly` adjusted, and so the fundamental frequency oscil-` lations are held at degree phase relation.

Figure 11 shows another circuit in which the plates are maintained at a considerably higher D. C. potential than in Figure 1 so that secondary emission currents returning from anodes to screen grids is prevented. In this case the anode potentials tend to draw the electrons through and away from the screen grids in a way to greatly reduce the screen grid current and the strength of oscillations at fundamental frequency.

The second harmonic circuit in this' case is connected between the plates in push-pull fashion. Now if second harmonic oscillations are set up in the circuit, when electron currents flow, the plate potentials are reduced and allow a greater flow of current to the screen grids. Then the stronger the second harmonic currents become the greater will be the power developed at the fundamental frequency in each oscillator. The second harmonic currents normally will be maximum when they are degreesv out of phase on the two plates. Therefore, the system normally holds the second harmonics at 180 degrees and the fundamental frequency oscillations at 90 degrees phase relation.

Figure 12 shows schematically a diagram of a system in which two high frequency oscillators are held in synchronism at 90 degrees phase relation by means of a second harmonic tuned circuit connected in series with the paralleled connections to the screen grids of two four electrode tubes. In this case, unless the oscillators hold the second harmonics at 180 degrees phase relation, oscillations are set up in the second harmonic tuned circuit which exert a strong degenerative effect, a condition which the tube circuits automatically avoid.

In this same gure there is shown an input coupling fora high frequency to be detected. There is also shown the intermediate beat frequency output circuits arranged to provide 90 degrees relative phase shift in the two intermediate frequency outputs. Coupled to these two cirsuits is an intermediate frequency output circuit after which may include amplifiers, detectors, loudspeakers, recorders, etc., the operation of which will have been made relatively free from image band interference.

Figure 13 shows schematically a self-oscillating detector system using five electrode tubes. It will be noted that there is also shown a high frequency input to the first pair of grids from the cathode. The input grids are shielded by the next set of grids which are tuned for the second harmonic of the self-oscillation frequency and are effectively grounded back to the cathodes for the fundamental frequency. Of course, appropriate circuit shielding would be used in addition.`

The third pair of grids and the anodes are used to produce the high frequency self-oscillations held 90 degrees diiferent in phase due to locking by the second harmonic developed in the circuit to the second pair of grids.

The final output is obtained from two oppositely detuned circuits, tuned on either side of the beat frequency between the local oscillations and the incoming signal which is to be received.

It will be apparent that many modifications may be made in the circuits above described without departing from the present invention. For example, in the oscillator circuits shown, various trimmer adjustments may be provided forbal'- cally adjust themselves to this maximum oscil-v ancing" exactly the undesired image frequency' energies. The trimmers for adjustment of phase may operate on the tuning of the high frequency' oscillating circuits differentially or upon the tuning' of the. two intermediate frequency output circuits differentially. Relative amplitudes may be adjusted accurately by differential variation ofY high frequency input or intermediate frequency output couplings or by differential adjustments o f vacuum tube electrode potentials.

In practice, since the intermediate frequency circuits may always operate in a fixed or relatively fixed" frequency band they do not require adjustments in operation other than perhaps some' trimmer adjustments of phase and amplitude for exactly balancing image band interference. The high frequency circuits, including the second harmonic circuit should preferably be controlled by a single tuning dial.

The circuits of Figures 10, 12 and 13, and others like them where a single ended, or unbalanced second harmonic circuit is used which requires no transformer action, may very well operate well enough for many practical purposes by inserting a resistance in place of the tuned circuit. In cases where this can be done the tuning system will be simplified through the elimination of one variably tuned circuit.

Obviously, the image suppressing detector systems Vmay be combined with nearly all the known circuit elements and features necessary to produce'an economical and efficient receiving system for any useful purpose. For example, the detector may be combined with reflex circuits in which a single tube may simultaneously perform several different and distinct functions.

It is toV be distinctly understood that the present invention is not limited to radio reception, but may be utilized in carrier telegraph, telephone, or other communication systems over wires, beams of 1ight,'sound waves, or any other form of radiation or guided Wave energy transfer, signaling or control system.

I claim: 1. 'I'he method of suppressing the effects of undesired bands of frequencies which includes receiving signal energies, generating local energies, beating the undesired energies with locally generated energies of like frequency but of different relative phases so as to produce beat frequency energies of different phases, then shifting the relative phases and combining the beat frequency energies in such a manner that they substantially balance out.

2. The method of receiving desired bands of frequenci'es which includes receiving energies including the desired bands, generating local energies, beating the desired energies with the locally generated energies of like frequency but different relative phases so as to produce beat frequencyenergies of different phases, then shifting the relative phases and combining the beat frequency energies in such manner that they add together wholly or in part.

3'. The method of suppressing the effects of undesired ban-ds of frequencies but utilizing desired bands of frequencies which includes generating energies of like frequency but different phases, beating both with the locally generated energies of like frequency but different phases so as to produce beat frequency energies in such manner that the undesired energies aire substantially balanced out while the desired energies add togetherV wholly or in part.

4. The method of suppressing image band re- 75 ception in' asup"er-heterodyner receiver having `two detectors which includes supplying the two detectorswith-radio frequency energies of like frequencies but different phases, to produce beat frequency energies of different relative phases, then shifting the'relative phases and combining the detector output energies so that image frequency band energies are substantially balanced out whileV the desired-frequency band energies are added together wholly or in part.

5. In a signal receiver comprising two detectors whose input circuits are arranged toreceive the signal energy simultaneously, the method of operation which comprises combining in said detectors signal energy and locally generated energy, one of which has a difference in phase in said input circuits of substantially Y90 degrees, obtaining from said detectors energy having substantially an additional 90 degrees phase shift, and combining energies obtained from both of said detectors whereby there is effectively suppressed an image band of frequencies differing by a predetermined amount from the frequency of the locally generated frequency.

6. In a super-heterodyne receiver comprising a signal collecting circuit coupled to two detectors having separate input and output circuits and `whose input circuits are arranged to receive the signal energy simultaneously, the method of operation forobtainingriniage signal suppression which comprises generating local oscillatory en-l ergy of substantially constant frequency, supplying one of said energies to said detectors with a difference in phase of substantially 90 degrees,

combining said signal energy and locally generated roscillatory energy in each of said detectors, obtaining in said detector output circuits substantially an additional 9) degrees phase shift between the, kenergies insaid output circuits, and

combining the energies in both of said output circuits whereby energies of frequencies above said local oscillator frequency substantially Vadd and energy below said oscillator frequency substantially `balance each other.

7. In combination in a receiver, a first detector and a second detector, each having input and output circuits, a source of signal energy and a source of locally generated oscillations both sources being coupled simultaneously to said in- `put circuits, means coupling sai-d sources to said input circuits designed to shift the relative phases of the energies Vfrom said sources on said respective input circuits by substantially 90 degrees,

i means in said detector output circuits for shifting the phase of the output energies 90 degrees with respect to each other, and a utilization circuit coupled to said last means.

8. In combination, in a super-heterodyne radio receiver, a first detector and a secondY detector each having input and output circuits, a source of signal energy coupled to both input circuits of said detectors, and a local beating oscillator also coupled ,to both input circuits, means for shifttenna coupled to both input circuits of said'detectors, and a local beating oscillator so coupled as to supply leading currents to one ofsaid detector input circuits and lagging currents substantially 90 degrees out of phase With said leading currents to the other of said detector input circuits, phase shifting means in each of said output circuits for providing substantially 45 degrees leading phase in one of said outputs and 45 degrees lagging phase in the other of said outputs, and a tuned utilization circuit coupled to both of said output circuits.

10. In combination, in a super-heterodyne receiver, a first detector and a second detector, each having input and output circuits, an antenna coupled to both input circuits of said detectors, and a local beating oscillator so coupled as to Supply leading currents to one of said detector input circuits and lagging currents which are substantially 90 vdegrees out of phase with said leading currents to the other of said detector input circuits, phase shifting means in each of said output circuits for providing substantially a 90 degrees phase shift between said two detector outputs, said detectors being arranged to provide output energies which are substantially equal in amplitude, and a utilization circuit coupled to both of said output circuits.

11. In combination, in a super-heterodyne radioreceiver, a rst detector and a second detector, each having input and output circuits, an antenna, a high frequency amplifier arranged to receive signal energy from said antenna coupled toboth input circuits of said detectors, circuit means for causing Athe flow of local oscillatory energy in both input circuits of said detectors with a phase difference of substantially 90 degrees, and phase shifters in the Ioutput circuits of said detectors for effecting an additional 90 degrees phaseshift between vthe two detector outputs, and a utilization circuit coupled to both of said detector output circuits.,V

12. In combination, in a super-heterodyne radio receiver, a first detector and a second detector each having input and output circuits, an antenna, a screen grid radi-o frequency amplifier coupled to said antenna through a transformer and arranged to receive signal energy from said antenna and to supply said signal energy to both input circuits of said detector, shielding means between the windings of said transformer; circuit means for causing the ow of local oscillatory energy in both input circuits of said detectors with a difference in phase of substantially 90 degrees, phase Shifters in the output circuits of said detectors for effecting an additional 90 degrees phase shift between the two detector outputs, an intermediate frequency amplifier coupled to bothV detector output circuits, a third detector, and a band pass filter between said intermediate frequency amplifier and said last detector, an audio frequency amplifier coupled to said last detector, and a translation device in circuit with said audio frequency amplifier. f

13. In combination, in a receiver, afirst oscillator detector and a second oscillator detector 14. In combinati-on, in a receiver, a first oscillator detector and a second oscillator detector having input circuits inductively coupled to each other for effecting an approximate 90 degrees phase relationshipv between the oscillatory energy in said input circuits, means for supplying signal energy to said input circuits, output circuits for said detectors, individual tunable phase Shifters in each output circuit for obtaining an additional 90 degrees phase shift between the two detector outputs, unicontrol means for said tunable phase Shifters, and a utilization circuit coupled to both of said output circuits.

15. In combination, in a receiver, a first oscillator detector and a second oscillator detector, having input circuits inductively coupled to each other for effecting an approximate 90 degrees phase relationship between the oscillatory energy in said input circuits, unicontrol tuning means in said input circuits, means for supplying signal energy to said input circuits, output circuits for said detectors, individual tunable phase Shifters in each of said output circuits for obtaining an additional 90 degrees phase shift between the two detector outputs, and unicontrol means arranged to control said individual tunable phase Shifters differentially, and a utilization circuit coupled to both said output circuits.

16. An image signal suppressing receiver system including two self-oscillating electron discharge tube detectors and controllable means coupling said detectors so arranged as to maintain their oscillations at the same frequency but different in phase by substantially 90.

17. In a superheterodyne receiver, the combination of a first detector and a second detector, each having input and output circuits, a source of high frequency signal energy, means coupling said source to the input circuits of said detectors, adjustable means for tuning said input circuits to the signal frequency, a local oscillator having an output circuit including a phase splitting circuit provided with a Vernier control means for regulating the current in said output circuit, connections between said detector input circuits and spaced apart points of said phase splitting circuit, means for tuning one of said detector output circuits to a frequency higher than the frequency difference between the signal and oscillator frequencies, means for tuning the other detector output circuit to a frequency lower than said frequency difference and a utilization circuit coupled to both said detector output circuits.

18. The combination defined in the preceding claim in which said Vernier control means comprises a variable condenser in series with an adjustable resistor.

19. In a superheterodyne receiver, the combination .of a rst detector and a second detector each having input and output circuits, Variable condensers connected to said input circuits to tune them to the same resonant signal frequency, unicontrol operating means for adjusting said condensers, a local beating oscillator coupled to said input circuits to supply potentials thereto which differ in phase in said respective input circuits by substantially 90 degrees, adjustable means in the output circuits of said detectors for causing a phase shift of substantially 90 degrees in the said output circuits and a utilization circuit coupled to each of said output circuits.

20. In a superheterodyne receiver, the combination of a rst detector and a second detector, each comprising an electron discharge tube having a cathode, control grid and plate, means for imp-ressing signal voltages on said control grids which are in phase, a local oscillator having an output circuit so arranged that the phase difference between two points thereof is substantially 90, a connection between each of said points and the respective cathodes of said tubes, circuits connecting said cathodes and plates including means for causing a phase shift of more than in said circuits and a common output circuit coupled to said last named circuits.

CLARENCE W. HANSELL.

Images