US2212182A - Radio receiving apparatus - Google Patents

Description

Aug. 1940- L. PADDLE 2,212,182

RADIO RECEIVING APPARATUS Filed Aug. 27, 1938 Patented Aug. 20, 1940 UNITED STATES RADIO RECEIVING APPARATUS Leslie Harold Paddle, England, assignor to West, Norwood, London, Telephone Manufacturing Company Limited, London, England Application August 2'7, 1938, Serial No. 227,205

In Great Britain September 2, 1937 11 Claims. (01. 2 50-20) This invention relates to electrical communication systems, and more specifically to ultrashort wave radio systems employing super-regenerative receivers.

6 In receivers of this type, as is well known, a thermionic valve stage has input signals applied to a circuit thereof the resistance of which is made nearly zero or in some cases slightly negative, and the resistance of this circuit is then 10* cyclically varied-by means of a further oscillation-between a slightly positive and a slightly negative value. The operation of the circuit is not clearly understood, but it is generally accepted that during the one half cycle of the further oscillation, which for the sake of convenience may be identified as the quenching oscillation, the circuit has a negative resistance, during which time the amplitude of the input signals is building up to a limiting value determined by valve saturation and circuit conditions, during the succeeding half cycle of the quenching oscillation the stability of the circuit is restored by the resistance of the circuit being made positive. The output of the valve stage includes, however, a signal which is the original modulation frequency of the input signal.

While this may represent the operation of such a receiver on certain frequencies, it is believed that on ultra-high frequencies, that is above 30 megacycles per second, there is a secondary efiect which takes place and modifies considerably the operation of the stage.

Since the input circuit is invariably oscillatory it follows that the building up of the .voltage in the circuit to the limiting value occurs gradually with each cycle of the input signal during the half cycle of the quenching oscillation, and it seems therefore that the circuit does not reach the limiting condition of saturation sufliciently rapidly to destroy the characteristic modulation; it will be apparent that no modulation output can be obtained once this limiting value is reached. This is borne out by the observed fact that if too high a quenching voltage is used, causing saturation at an early point' in the quenching cycle, the output becomes distorted.

On the other hand, when using the super regenerative receiver on ultra short wavelengths it is believed that saturation is much more rapidly reached and that this accounts for the fact that when a super regenerative receiver is used on these wavelengths there is a diminished cute put whenthe input circuit is accurately tuned to the incomingsignal. It is found that there are two or more tuning points, separated from t the position of true resonance.

It is believed that in the ordinary receiver this saturation effect is normally allowed to appear, and the system operates by virtue of a 5 beat effect or heterodyne between the local quench oscillation and the input signal, the heterodyne being demodulated within the valve to obtain the desired signal and not, as is generally supposed, the signal itself. 14)

According to the present invention, therefore, there is provided a system which takes advantage of the true super regenerative effect on these ultra high frequencies, and the invention consists of a receiving device comprising a thermionic valve, 16 means for supplying a desired signal to a circuit associated with said valve, the resistance of said circuit being low or zero,means for cyclically varying the resistance of said circuit through zero, an output circuit from said valve responb sive at the frequency of the desired signal and a demodulator or the like fed from said output circuit.

With the present invention there is provided a receiver of the type in which one (or more) 5 valves are employed and which are brought to the point of oscillation by means of an external inductance or tuned circuit operating in conjunction with the internal capacity of the valves. Preferably two (or more) valves are employed 0 and are brought to the point of oscillation by the connection of an inductance between the two anodes and a small or preferably negligible inductance between the grids, or vice versa. Means are also incorporated whereby, through the Miller 35 effect in the valves, regeneration takes place; such means may consist of chokes or tuned circuits included in the cathode leads of the valves. An oscillating voltage is also impressed upon the valve or valves, this voltage for maximum sensi- 6 tivity being such that the circuit operates in a super-regenerative manner, that is the circuit is alternately caused to stop and start oscillating at signal frequency in accordance with the oscillating or quenching voltage of lower frequency. 45

According to a further feature of the invention, in a receiver of the type described, demodulation is obtained by electrodes associated with the detector stage itself, and preferably there is 50" arranged within the envelope of one or both of the two valves an auxiliary anode which operates with the cathode to form a demodulator; moreover this auxiliary anode is arranged with its circuit sothat the direct. current component of its rectified output, or a part thereof, is impressed upon the grid or grids of the valves.

According to another feature of the invention, in a circuit of this general type there is employed in conjunction with the valve stage two demodulating or rectifying devices, one of which is used to derive the demodulation component of an applied signal and the other is used for the purpose of controlling the grid potential in order to obtain an automatic gain control operation.

In the accompanying drawing there are shown circuit diagrams of radio receiving systems incorporating the present invention, 'which are given by way of example only as indicating some of the possible forms of the invention.

In the embodiment of the invention shown in Figure 1 use is made of thermionic valves which are arranged in the manner disclosed-in Patent No. 2,067,679, whereby the valves tend to oscillate. The anode-grid paths are in series, and an inductive element is included-in the series circuit so formed. In this specific example use is made of two valves V1, V2 having their anodes .joined to the terminals of an inductance L, tuned by means of a series or, as shown in Figure 1, a parallel variable condenser C, the grids of the valves being directly-joined. The cathodes of the valves are connected through impedances, preferably chokes RFC which permit them to oscillate relatively in' potential. The input circuit, for example the aerial, is coupled by means of the mutual inductance of a coupling coil LC adjacent the anode coil L. The regeneration which takes place in this valve stage is controlled by variation of the anode supply voltage from battery 3 by means of a resistance R, a byepass condenser C1 beingincluded. Also included in the anode supply circuit is a means,

T cal generator OSC may be such as the secondary winding of a transformer T1, by which a quenching oscillation from a loimpressed-upon the valve stage. Thus the valves may be brought to a condition of incipient oscillation and then periodically brought into oscillationand nonoscillation by the'app-lication of the quench signal.

The grid circuit of the valves is completed through an impedance such as RFC and a bias ba t y B2. v

The output from the stage is obtained by means of a transformer T2 arranged. between the cathodesofthe valves, the secondary winding of the transformer, tuned to the frequency of the desired signal by condenser C3 or not, as desired, feeding a grid leak demodulator valve V3 .fromwhich the modulations of the original signal are obtained by an output transformer T3.

It is found that, this circuit provides an excellent degree of automatic gain control, and one which is very satisfactory in operation. For example, it has been found possible to obtain an output constant to within half a decibel over an input range of 26 decibels.

In the embodiment of the invention shown in Figure 2b the receiver comprises two valves which are. arranged in the manner described above, one or both of the valves having an auxiliary anode A arranged in association with the cathode so as to, provide a diode rectifier therewith. v,Input is applied from a receiving aerial totheinductance arranged between the anodes 0 preferably, the received signal is applied to a buiferj amplifier valve V4 'of'the screen grid acorn type... Fiafia, the. output of which is applied across the choke RFC connected in the cathode lead of the valve V1.

The output from the valves V1 and V2 is applied from either the anode of the valves or from the grids to the auxiliary anode A, through a suitable condenser C4 if necessary, and a load resistance R1 is arranged between the auxiliary anode and an earthy point of the receiver. The auxiliary anode A may be fed from the anode of valve V2 by connecting condenser C4 to the anode by the lead D. Whether the auxiliary anode A is fed from the anode or the grid of valve V2, the unidirectional voltage produced across this resistance R1 or a part thereof is then fed back to the g ids of the valves with decoupling if necessary. The alternating voltage appearing across the load resistance R1 and representing the modulation component of the received modulated carrier wave signal is fed through a condenser 05 to the grid of a suitable amplifying valve V5 or other output circuit.

If desired, an auxiliary anode may be incorporated in each valve and push pull demodulation used. An example of such an arrangement is shown in Figure 3. This circuit is generally similar to that shown in Figure 2b except that a series tuned anode circuit is used and that the demodulating diodes are fed from the cathodes. With this circuit the two anodes A are joined together and the load resistance R1 is connected between the anodes and earth as before. It will be remembered that the cathodes of the valves V1 and V2 are out of phase. When one anode is positive with respect to its associated cathode (and is then passing current) the other anode will be negative with respect to its associated cathode and at that instant the anodecathode capacity of the passive diode will feed voltage to the conducting diode. At the next 1 half cycle the position will be reversed, but the current through the load resistance will be in the same direction at all times.

It will be appreciated that in some circumstances a direct electrical connection exists between the auxiliary anode and one ofthe grids for example, if the whole of the voltage across circuit may be connected between the cathodes as indicated in the fragmentary circuit diagram of Figure 4, the circuit forming the output impedance. This tuned circuit may conveniently. consist of a parallel tuned circuit L1, C6 in series with two small condensers C7, C8. Such a circuit may be adjusted to give a very sharply tuned output load. Figure 4 may be used either with a separate demodulator valve as shown in Figure 1, or with the-auxiliary anode demodulation described with reference to Figures 2b and 3.

Figure 5 illustrates an embodiment of the present invention in which there is provided a valve stage comprising two triode valves V1, V2 as before but each valve includes two auxiliary anodes A, A1 associated with the cathode thereof; Two of the auxiliary anodes, one in each valve, are joined and are returned through a load resistance R1 to an earthy point of the cathode circuits, for example to the common, low potential ends of the chokes RFC included in the cathode leads. One or both of the .second pair of anodes are connected to the grids and are also connected, through a second load resistance R2,

to a point of the circuit negative with respect to the mean potential of the cathodes; for example a variable resistance R3, shunted by a condenser Cs, may be arranged between the low potential ends of the cathode chokes and the negative terminal of the high tension supply B, and the second load resistance R2 is then returned to the negative terminal of the variable resistance.

The circuit is believed to operate in the following manner: The two valves are brought to the point of incipient oscillation by virtue of the anode-grid feed-back as previously described, and the oscillation is periodically initiated and quenched by the applied quenching oscillations, and a highly sensitive amplifying condition is thereby produced. When a modulated carrier wave signal is applied to the stage the first pair of anodes serves to produce the modulation component of the signal, which appears across the load resistance R1 and which maybe passed to a subsequent amplifier. As with the circuit of Figure 3 this demodulation occurs by virtue of the fact that the cathodes operate in opposite phase, and when one anode is not passing current the capacity between it and its cathode serves to feed the other anode, which is then passing current.

The second pair of anodes is directly connected to the grids and. these anodes operate to rectify the signal on said grids. The direct current component of rectification which appears across the associated load resistance R2 is impressed as a bias upon the grids, so as to provide automatic gain control. However, owing to the fact that the load resistance is returned to a point negative with respect to the cathode such rectification occurs only when the signal between grids and cathodes exceeds a figure determined by the value of the negative bias. The variable resistance R3 thus affords a means by which the initial gain of the system may be controlled (as it controls the grid potential) and it also controls the delay voltage of the automatic gain control system.

The second pair of anodes have been described as being directly connected to the grids, but if desired they may be fed from any appropriate point of the circuit, for example from a main anode or the grids through an isolating condenser, and the rectified voltage may be applied from the load resistance to the grids through a decoupling circuit.

In feeding a circu't of the type described from an open aerial it is sometimes found that the aerial constants are reflected into the stage, giving rise to certain small difficulties. To overcome these, there is arranged a buffer stage consisting of a pair of acorn pentode valves V6, V1 connected in a conventional push-pull amplifier circuit, between the aerial feeder and the superregenerative stage. The valves V6, V7 are fed from input terminals ANT through a tuned, balanced input circuit comprising inductances L2, L2 and tuning condenser C9. The grids of the valves are balanced with respect to earth by condenser C It, CH) and the direct current grid-cathode paths of the valves are completed through resistances R4. An output inductance L3 is coupled to the tuning inductance of the valves V1, V2.

With the circuit described it has been found that the anode current is very small--considerably less than one milliampere-and it has been possible to dispense with a high tension supply and to use only the applied quenching oscillation for producing the necessary anode current.

What I claim and desire to secure by Letters Patent is:

- 1. A radio receiver comprising at least two thermionic valves each having a grid and an anode electrode cooperating with a cathode electrode, circuit elements connecting the anode-grid paths of said valves in series in a circuit resonant at a desired signal frequency, a quenching oscillator circuit and a signal input circuit coupled to said resonant circuit, impedance connected between the cathodes of said valves to permit the development of an oscillatory potential between said cathodes, a signal frequency output circuit connected to the like electrodes of two valves, and a demodulator fed from said output circuit.

2. A radio receiving system as claimed in claim 1, wherein said output circuit is connected between the cathodes of the tubes.

3. A radio receiving system as claimed in claim 1, wherein said output circuit comprises a transformer tunable to the signal frequency and connected between the cathodes of the tubes.

4. A radio receiving system as claimed in claim 1, wherein said demodulator comprises an auxiliary anode within one of said valves and cooperating with the cathode electrode thereof to form a diode rectifier.

5. A radio receiving system as claimed in claim 1, in combination with means for automatically varying the bias on a grid electrode in accordance with the magnitude of the incoming signal.

6. In a super-regenerative radio receiver, a pair of thermionic valves each including a grid electrode and an anode electrode cooperating with a cathode electrode, an auxiliary anode in at least one of said valves and cooperating with the cathode thereof to form a diode rectifier, a circuit resonant at a desired signal frequency and including the grid-anode paths of said valves in series, a quenching oscillator circuit and a signal input circuit coupled to said resonant circuit, circuit elements of high impedance at signal frequencies connected between said cathodes, and an input circuit for said diode rectifier connected to one of the electrodes of at least one of said valves.

'7. In a super-regenerative receiver, the invention as claimed in claim 6, wherein said rectifier input circuit is connected to an anode electrode.

8. In a super-regenerative receiver, the invention as claimed in claim 1, wherein said rectifier input circuit is connected to a grid electrode.

9. In a super-regenerative receiver, the invention as claimed in claim 6, wherein said rectifier input circuit is connected through said circuit elements to both cathodes.

10. In a super-regenerative receiver, the invention as claimed in claim 6, wherein both of said valves have an auxiliary anode, and the auxiliary anodes are both connected to said rectifier input circuit.

11. In a super-regenerative receiver, the invention as claimed in claim 6, wherein there is an auxiliary anode in the other valve for cooperation with the cathode thereof to form a second diode rectifier, in combination with a signal frequency output circuit for both valves and working into said second diode rectifier, and means biasing the anode of the second diode rectifier negatively with respect to its cathode.

LESLIE HAROLD PADDLE.

CERTIFICATE OF CORRECTION.

Patent No. 2,212,182. August 20, who.

LESLIE HAROLD PADDLE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, seccnd column, line 514., claim 8, for the claim reference numeral read --6--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case inthe Patent Office.

Signed and sealed this 1st day of October, A. D. 191w.

Henry Van Arsdale,' (Seal) Acting Commissioner of Patents.

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