US2171148A - Superregenerative receiver - Google Patents

Description

1939- I I w. s. PERCIVAL 2,171,148

SUPERREGENERATIVE RECEIVER Filed Nov. 1'7, 1936 INVENTOR P AL W. S RCIV BY din/v I A'ITORN EY Patented Aug. 29, 1939 UNETED STATES PATENT OFHQE SUPERREGENERATIVE RECEIVER pany of Great Britain Application November 17, 1936, Serial No. 111,231 In Great Britain November 20, 1935 10 Claims.

The present invention relates to wireless and like receivers, and more particularly to receivers of the'kind in which use is made of the principle of super-regeneration.

A known super-regenerative receiver comprises a thermionic valve having its anode circuit coupled back to its control grid circuit, the nature and magnitude of the back-coupling being such that an oscillation applied to the control grid circuit tends to build up in amplitude; the valve is also arranged to generate quenching oscillations, which serve to quench the oscillations which build up in the input circuit, so that the valve generates trains of oscillations of the frequency to which the input circuit is resonant, the trains occurring at the quenching frequency; the valve is arranged to operate as a detector, and if the applied oscillation is amplitude modulated, the modulation frequencies appear in the anode circult.

Such a super-regenerative circuit, although the amplification of which it is capable may be high, is found to have grave disadvantages; more particularly, it is very susceptible to carrier wave vinterference, and the level of noise (due, for

example, to the Schrott and Johnson effects) is high, both these faults being due to lack of selectivity. Furthermore, in cases in which it is necessary to use a high quenching frequency, for example, in the case of the reception of television signals, it may be found that the amplification of the circuit is undesirably low. It has also been found that the power output at the modulation frequency from a circuit such as that described is also low, that is to say, the valve operates inefficiently as a detector.

It is an object of the present invention to provide an improved wireless or like receiver of the super-regenerative type, in which the disadvantages mentioned above are reduced.

According to one feature of the invention, for the purpose of improving selectivity, a super-regenerative receiver is provided, comprising a valve including a cathode, control grid and anode and having a resonant circuit associated with its con,- trol grid circuit and with its anode circuit coupled to its control grid circuit in such a manner that a positive feed back can occur and a source of quenching oscillations, the arrangement beingsuch that for a considerable portion of a cycle of the quenching oscillations the effective selectivity of said resonant circuit has a value not greatly difierent from that corresponding to the condition in which the dynamic resistance of the resonant circuit is substantially infinite. In other Words the effective resistance of the resonant circuit for a considerable portion of a cycle of the quenching oscillations is at a minimum and hence the selectivity of the circuit is considerably increased. The circuit during this period thus permits the signal to build up at its own frequency when the resonant circuit is at substantially optimum selectivity, thus providing discrimination against noise and interference. The desired result may be achieved by suitably choosing the magnitudes of the positive feed-back and of the amplitude of the quenching oscillations.

Preferably, however, the source of quenching oscillations is arranged to generate trains of oscillations of a wave form such that in the interval between a quenching period and the subsequent burst of oscillation the amplitude of the quench ing oscillation has a value corresponding closely to critical reaction for a time which is a substantial portion of a cycle of the quenching oscillation. By critical reaction is meant the condition in which the dyanmic resistance of the input resonant circuit is infinite, and the circuit resistance during such conditions may be substantialiy zero, or even slightly negative. Suitable wave forms for the quenching oscillation will be described hereinafter.

For the purpose of improving the power output from a super-regenerative valve the quenching frequency oscillations are given a wave form such that between a burst of oscillation and the subsequent quenching period the amplitude of the quenchingoscillation has a value corresponding closely to critical reaction for a time which is a substantial portion of a cycle of the quenching oscillation.

In order to improve amplification, the present invention provides a super-regenerative receiver comprising two thermionic valves in cascade, each having a cathode, control grid and an anode and an additional electrode or electrodes if desired, and means for feeding back energy derived from the output circuit of the second valve to the input circuit of the first valve in the positive sense, and means whereby the two valves are separately quenched. In such an arrangement, more than one resonant circuit will normally be provided, in which case it is necessary to damp both of the tuned circuits. If the natural damping of these circuits is not sufficient, diodes may be provided, one for each circuit which are caused to pass currents and hence to damp the circuits during the quench period.

The trains of oscillation generated in the superregenerative stage of a receiver according to the invention are preferably applied, to a separate detector, which is preferably constituted by a diode valve of the low impedance type, and from which modulation frequency oscillations can be derived.

It has been found that the voltage across the resonant circuit associated with the superregenerative valve contains not only a carrier of the original frequency with its. own modulation, but also the original carrier frequency modulated with the quench frequency, which in turn is modulated with the original modulation.

Hence according to a further feature of the invention, the voltage developed across the resonant circuit is applied to a separate first detector, and the modulated quench frequency component, which is derived from the first detector, is applied (after amplification if desired) to a second detector, from which the modulation-frequency component is derived.

In an arrangement such as that last described, embodying two detectors, the eificiency of the second detector, and the quality of its output, may be improved by feeding quenching frequency oscillations thereto in suitable phase; the second detector may, in such an arrangement, be arranged to operate as a form of homodyne detector.

The chief advantage arising from the use of a separate detector is that owing to the low impedance of its input circuit to frequencies other than the original carrier frequency only this frequency and the carrier modulated by the quench frequency will be applied thereto and hence for example, the quench frequency is prevented from passing to the subsequent amplifiers. Furthermore the wave form of the high frequency oscillations exhibits sharp peaks, and hence a rectifier of the low impedance diode type is more emcient. Again, where the modulation frequency output is taken from the super-regenerative valve several stages of low frequency amplification are often necessary and as its well known low frequency amplification tends to introduce.

hum andinstability. Where, however, two detector stages are used, the whole or a part of the desired amplification can take place at high frequencies. Where two detectors are employed with the first detector followed by a resonant circuit tuned to the quenching frequency it has been found that the modulation frequency output of the second detector is frequently greater than the output that can be obtained from the first detector at the same frequency. A further advantage of using double detection is that a quenching frequency amplifier can be introduced between the two detectors, thus increasing the available voltage to the second detector and increasing its linearity and power output.

In order that the said invention may be clearly understood and readily carried into effect the same will now be more fully described with reference to the accompanying drawing in which:

Fig. 1 shows a super-regenerative receiver according to the invention.

Fig. 2 illustrates various wave forms which the quenching oscillations may have, and

Fig. 3 illustrates a modified form of superregenerative stage according to the invention.

Referring to Fig. 1, an inductance coil I has one end 2 grounded, and the other end 3 thereof connected to a receiving aerial and is tuned by a variable condenser l. The cathode of a triode valve 5 is connected to a point 6 in coil I, and. the control grid of valve 5 is connected to a point 1 therein through a condenser as shown. The anode of valve 5 is connected through a radiofrequency choke coil 8 and a filter resistance 9, with which are associated by-pass condensers l and i i, to the positive terminal 12 of a source of anode current, not shown.

Valve serves, in a manner which will be described hereinafter, as a super-regenerative valve, and quenching oscillations are derived from a valve N3, the anode of which is connected, through the primary winding of a transformer M, to the positive terminal l2 of the anode current source. The cathode of valve I3 is grounded, and its control grid is connected to ground through a grid condenser l5 and the secondary Winding of transformer M. The latter winding is shunted by a condenser i0, and by a circuit comprising a condenser Ill and a potentiometer l8 in series. Grid condenser it has a leak resistance i9, and the valve It operates as a relaxation oscillation generator of the blocking oscillation type, which type is known in television technique. In the operation of valve i3 and its associated circuit the grid condenser 65 is charged by the flow of grid current from the valve to such an extent, during the first half cycle of oscillation, that further oscillation becomes blocked. The charge of condenser i5 leaks. away through resistance H! at a relatively slow rate until the grid potential reaches such a value that sufficient anode current fiows again for oscillations to recommence. This action gives rise to positive pulses of potential across the grid coil of the transformer M at a frequency determined by the values of the condenser l5 and resistance l9 and the potential of the direct current source in the anode circuit. By means of a high pass filter constituted by the condenser I! and potential divider resistance I8 a wave form of the kind shown in Fig. 2b is applied to the grid of the valve 5 superposed on the bias voltages determined by the potentiometer 20. Other forms of oscillators in which the flow of current is periodi- 'Fig. 1 of the drawing the circuits l1, I8, 20, 22,

and 25 function as a high pass filter and the first of these components may have the value 0.0002 microfarad and the second component 50,000 ohms, the condenser I5 may have a capacity of 0.002 microfarad, the resistance IS a value of 50,000 ohms, and the condenser IS a capacity of 0.002 microfarad. Instead of employing a relaxationor blocking oscillator for obtaining the desired wave form, a multivibrator system may be employed which may, if desired, be associated with a'high pass or similar filter for generating the preferred wave form. Wave forms suitable foruse in the invention will be hereinafter more particularly referred to.

The control grid of valve 5 is given an adjustable negative bias from a tapping point on a potentiometer 20 associated with a source 2| of bias potential, through resistance 25. Quenching oscillations of the form shown in Fig. 2b are applied to valve 5 as aforesaid from an adjustable tapping point on potentiometer [8 through condenser 22 and radio-frequency choke coil 23 in series, a high frequency by-pass condenser 24 being connected as shown.

As previously stated the cathode and grid of valve 5 are tapped into the aerial tuning circuit I, 4, at points 6 and I and the valve then operates 7 to generate oscillation at the frequency to which this circuit is tuned.

By arranging that for a considerable portion, for example a third or more of the cycle of quenching oscillations, the wave form of the quenching oscillations has a substantially flat portion which is arranged to correspond with critical reaction the effective selectivity of the circuit is greatly increased since during this portion the effective resistance of the circuit is substantially zero.

Three suitable wave forms for affording this condition are shown at a, b and c in Fig. 2; in each case, the amplitude of the oscillationv is plotted against time as abscissae, and parts of the oscillations above the abscissae correspond to burst of oscillation in the super-regenerative valve, while during the parts below, the superregenerative valve is quenched. In Fig. 2a, which represents an ideal wave form, the parts d are arranged (for example in the case of the receiver of Fig. 1, by adjustment of the bias. of valve 5 and hence of the amount of reaction) to correspond to critical reaction. Fig. 2b shows, as already stated, the wave form of the oscillation generated by a practical quench frequency oscillator.

In a receiver, using a quench wave form of the kind illustrated in Fig. 2b and operating at 44 megacycles per second, it was found possible to obtain a selectivity corresponding to a pass band of 100 kilocycles, with again of from 300 to 1000 times greater than that obtainable from an ordinary detector with critically adjusted reaction. It was also found that sensitivity could be ad justed by varying the amplitude of the quenching input by potentiometer IS, the reaction control (potentiometer 20) being left at a fixed adjustment thus maintaining selectivity at a high value. A suitable quenching frequency was found to be one between about 10 and 80 kilocycles per second.

In Fig. 2c is illustrated a wave form which may be employed if it is desired to increase the power output of the super-regenerative valve; the wave form includes, in addition to the parts at of Fig. 2a, further parts e, one of which follows each train of oscillation in the super-regenerative valve, and enables the signal to persist for a short time before it is quenched. The parts e are shown as corresponding to critical reaction, but they may if desired correspond to a condition of rather less reaction; in either case, these parts of the wave form result in an improvement in the load factor of the super-regenerative valve, that is, the

ratio of the fraction of the operating time during which that valve is loaded to the maximum desirable load. The parts d of the wave form of Fig. 20 may be omitted if desired.

The upper end 3 of coil I is. connected through condenser 26 to the anode of a diode 21, the oathode of which is earth-ed; the trains of oscillation from valve 5 are thus applied to, and are detected by, diode 21. The latter is shunted by a radiofrequency choke coil 28 in series with a circuit comprising a condenser 29 and an inductance coil 3% in shunt, tuned to the quenching frequency.

The oscillations at the quenching frequency are amplified by means of a high-frequency amplifier valve 5| which has a grid leak 32 and grid condenser 32%, and has a resonant circuit 3:? tuned to the quenching frequency arranged in its anode circuit. Potential differences set up across circuit 36 are fed through condenser 35 to the anode of a second diode detector valve 36, the cathode of which is earthed. The diode 36 is connected through a quench frequency choke coil 31 to its load resistance 38; across which modulation frequency potential differences are established and which are fed through a filter 39 to the control grid of a low-frequency amplifier valve 40.

The output of detector 2! is found to consist of substantially saw-tooth oscillations of the quenching frequency, these oscillations being modulated with the modulation of the received signal, and disappearing when no signal is being received. Amplifier 3| is accordingly not loaded when no signal is present.

Certain features of the invention can be employed without utilising the wave forms shown in Figures 2a, 2b and 20. For example the valve l3 may generate quenching oscillations of sinusoidal wave form, in which case means are preferably provided for adjusting the amplitude of the quenching oscillations applied to the super-regenerative valve to a value such that, over a sub stantial part of the quenching cycle, conditions of approximately critical reaction exist in the superregenerative valve.

Reference is now directed to Fig. 3, in which is illustrated a modified form of super-regenerative stage according to the invention. A screen grid valve 4| has a resonant circuit comprising an inductance coil 42 and a variable condenser 13 connected in shunt arranged in its control grid circuit. The anode of valve 4! is connected through a further resonant circuit comprising an inductance coil M in shunt with a variable condenser to the positive terminal 46 of a source (not shown) of anode current, the negative ter" minal of which is earthed; in operation, both resonant circuits are tuned to a wanted signal frequency.

The anode of valve M is coupled through a condenser 41 to the control grid of a further screen grid valve 48, the anode of which is connected through a radio-frequency choke coil $0 to the positive terminal 46 of the anode current source. The control grids of valve i! and 48 are biased by means of biasing resistances 5t and 5| respectively.

The anode of valve 43 is connected through a condenser 52 both to one of two output terminals 53 and to the control grid of valve 4!. Terminals 53 may be connected to a detector (not shown) such as detector 27 of Fig. l, and the connection to the control grid of valve ii serves to provide reaction.

Quenching oscillations of any suitable waveform and amplitude are applied from source 54 to the control grids of valves ll and 43 through radio frequency chokes 55 and 5% respectively; in this way, both valves M and it are separately quenched. The two resonant circuits 32, t3 and M, 45 are arranged to have such damping that they are self-quenching when valves GI and 48 are quenched; in other words, the damping is such that the oscillations which build up in these circuits die away sufliciently quickly during the quenching periods. Additional damping may be provided if desired by means of thermionic discharge devices arranged in shunt with the tuned circuits and made conductive, during,

quenching periods, by the quenching oscillations.

As is well known (see, for instance, the textbook Wireless Principles and Practice by L. S. Palmer, 1928 edition, pages 357-3) the amplification of a super-regenerative receiver is of the form aewherein B is a factor which is large as compared to unity and proportional to the mutual conductance of the valve. When an ordinary high frequency amplifier stage is employed, the factor a only is increased, but where two valves are employed in cascade as shown in Fig. 3, the factor B is approximately squared and although there is some reduction in the factor a this is relatively unimportant. Hence the arrangement in accordance with this feature of the invention is capable of making the best use of two valves from the point of view of amplification, particularly if the factor B is large as, for example, 6 or more.

The invention is not to be limited to the specific' details described, as many modifications can be made within the spirit and scope of the appended claims.

I claim: r

1. In a super-regenerative receiver an electronic tube including a cathode, control grid and anode, external connections between said tube elements forming an anode circuit and a control grid circuit, a resonant circuit associated with said control grid circuit, means for coupling the anode circuit to the control grid circuit in such a manner that a positive feed back can occur, a source of quenching oscillations, said source of quenching oscillations being provided with means for generating trains of oscillations of a Wave form such that between a burst of oscillation and the subsequent quenching period the amplitude of the quenching oscillation has a value corresponding closely to critical reaction for a time which is a substantial portion of a cycle of the quenching oscillation.

2. In a super-regenerative receiver, a first thermionic tube having an input circuit and'an output circuit, a second thermionic tube having an input circuit and an output circuit, means for connecting the output circuit of the first tube to the input circuit of the second tube, means for feeding back energy derived from the output circuit of the second tube to the input circuit of said first tube in a positive sense, a source of quenching oscillations, coupling means between the source of quenching oscillations and each of said tubes for applying the quenching oscillations to each of said tubes and thereby separately quench each thereof.

3. In a receiver of the super-regenerative type, an electronic tube provided with an anode, a cathode and a grid electrode, external circuits connecting said tube electrodes so as to produce regeneration in the operation of said tube, a signal energy interceptor coupled to one of said circuits, a resistive voltage dividing circuit, means for applying a substantially constant potential acrosssaid last named circuit, a contact selectively movable over said circuit, means for connecting saidgrid electrode to said contact, a second resistive voltage dividing circuit, a source of quenching frequency for the receiver comprising, a relaxation oscillation generator of the blocking oscillation type, means for applying the quenching frequency energy across said second resistive voltage dividing circuit, a contact selectively movable over said last named circuit, and means for connecting said grid electrode to said contact.

i. In a super-regenerative receiver, an electronic tube provided with an anode, a cathode and a grid electrode, external circuits connecting said electrodes so as to produce sufiicient regeneration in the operation of said tube to cause the generation of oscillations, a tunable circuit coupled with said external circuits for controlling the frequency of the generated oscillations, a signal energy interceptor coupled to the tunable circuit, means for biasing the grid electrode with respect to the cathode comprising, a connection between the grid electrode and the cathode, said connection including a source of potential and a variable resistance, a source of quenching frequency for said receiver comprising, a relaxation oscillation generator, a voltage dividing circuit, means for applying the quenching frequency energy across said last named circuit and means including a condenser for connecting the grid electrode of said tube to a point of said voltage dividing circuit.

5. In a super-regenerative receiver, an electronic tube providedwith an anode,a cathode and a grid electrode, external circuits connecting the tube elements so as to produce oscillations, a tube circuit coupled with said external circuits for controlling the frequency of the generated oscillations, a signal energy circuit coupled to the tunable circuit, means for biasing the grid of said tube with respect to the cathode thereof, a source of quenching frequency for said receiver comprising an oscillation generator including an electronic tube, a voltage dividing circuit, means for applying the quenching frequency oscillations across said last named circuit, a connection between the grid electrode of said first named tube and a point of said voltage dividing circuit, a diode rectifier for said receiver having an input side and an output side, means for connecting the input side acrosssaid tunable circuit, a tunable circuit tuned to the frequency of the quenching oscillations, means including a radio frequency choke coil for connecting said last named tuned circuit across the output side of said diode rectifier, an amplifier circuit for amplifying the output of the diode rectifier and a second rectifier connected across the output of said amplifier, and a utilizing circuit connected across the output of the last named rectifier.

6. In the operation of a super-regenerative receiver of the type which is provided with an oscillation generator circuit, including a regeneratively connected tube, tunable to oscillate at any signal frequency within a band of frequencies and in which the generation of oscillations is intermittently quenched by application thereto of quenching oscillations of predetermined frequency during operation of the circuit, the method of greatly increasing the effective selectivity of the receiver which consists in controlling the wave form of the quenching oscillations so that during substantially a third of the cycle of the quenching oscillations the Wave form thereof has a substantially fiat portion winch is arranged to keep the tube during this interval at critical reaction.

7. In a super-regenerative receiver, an electronic tube provided with an anode, a cathode and a grid electrode, external circuits connecting said tube elements so as to produce positive regeneration causing generation of oscillations, a tunable circuit coupled with said external circuits for controlling the frequency of the generated oscillations, a signal energy interceptor coupled to the tunable circuit, means for biasing the grid electrode of the tube with respect to the cathode thereof comprising a connection between the grid electrode and the cathode, said connection including a source of bias potential in series with a variable resistance element, a source of quenching frequency for said receiver comprising a relaxation oscillation generator, a voltage dividing circuit, means for applying the quenching frequency oscillations across said last named circuit, a contact selectively movable over the last named circuit, means including a reactive device for connecting the grid electrode to the contact, a diode rectifier for said receiver and means including a coupling capacity for connecting the diode rectifier across said tunable circuit.

8. In a super-regenerative receiver, an electronic tube provided with a cathode, a control grid and an anode, external connections between said tube elements forming an anode circuit and a control grid circuit, a resonance circuit coupled with said control grid circuit, means for coupling the anode circuit to the control grid circuit in such a manner that positive feed-back can occur, a source of quenching oscillations, said source of quenching oscillations being provided with means for controlling the generated quenching oscillations so that the trains of oscillations are of a wave form such that between a burst of oscillation and the subsequent quenching period of the receiver the amplitude of the quenching oscillation has a value corresponding closely to critical reaction for a time which is a substantial portion of a cycle of the quenching oscillation.

9. The method of amplifying varying electric currents which includes the steps of impressing the varying potential of the current to be amplified upon a feedback system, generating a train of oscillations the wave form of which have a substantially fiat portion over a substantial part of each cycle thereof, periodically damping the feedback system by applying the generated train of oscillations thereto whereby the varying electric currents and the generated oscillations are effectively combined, detecting the resulting energy, deriving therefrom energy of the quenching frequency modulated by a component of the varying electric currents, amplifying the derived energy and detecting the amplified energy to derive therefrom the amplified varying electric currents.

10. In a super-regenerative receiver, a first thermionic tube having an input circuit and an output circuit, a second thermionic tube having an input circuit and an output circuit, means for electrically connecting the output circuit of the first tube to the input circuit of the second, a source of signal energy, means for connecting said source to the input circuit of the first tube, a utilizing device connected to the output of the second tube, means for feeding back energy derived from the output of the second tube to the input of the first tube in a positive sense to thereby produce regeneration, a source of quenching oscillations and coupling means between the source of quenching oscillations and each of said tubes for applying oscillations from said source to both said tubes simultaneously.

WILLIAM SPENCER PERCIVAL.

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