US2115875A - Regenerative detector - Google Patents

Description

May 3, 1938.

W, VAN B. ROBERTS REGENERATIVE DETECTOR Filed Oct. 30, 1936 70 S/G/VA L w 4 6 I 2/ 20 V ll 7 24 5 TOSIGA/AZ |,z SOURCE 72] 1/ 7"Z3 fig W Y V V V I +8 9] II 40 .L L W9 Alf 11212 5p 4/ AMPL.

INVENTOR WALTER VAN B. ROBERTS ATTORN EY Patented May 3, 1938 PATENT OFFICE I REGENERATIVE DETECTOR Walter van B. Roberts, Princeton, N. J assignor to Radio Corporation of America, a. corporation of Delaware Application October 30, 1936, Serial No. 108,426

2 Claims.

My present invention relates to a regenerative detector, and more particularly to a new and improved type of regenerative detector circuit wherein audio amplification is simultaneously 51 secured.

In the prior art the regenerative detector is very well known, and it usually comprises a grid leak detector of the triode type wherein the plate circuit is regeneratively coupled to the tuned input circuit. It is known that such a regenerative detector circuit suffers the disadvantage that a large radio frequency current fiows in the plate circuit when strong signals are received. By virtue of the latter overloading occurs, since the plate circuit current variation that must be handled by the tube is equal to the sum of the audio frequency and radio frequency amplitudes. This operating disadvantage has discouraged the use of the regenerative detector circuit in situa- 20 tions where it may well be employed. It is pointed out that the recent trend has been toward use of a separate diode detector whose audio frequency output is filtered free of radio frequency components and impressed upon the grid of a tube used solely for audio frequency amplification.

Accordingly. it may be stated that it is one of the main objects of my present invention to provide a regenerative detector network wherein the tube employed in the network comprises a diode section and an audio amplifier section; the audio amplifier section being utilized for radio frequency regeneration by regenerative feedback from the output of the audio section to the tuned input circuit connected to the diode section, and such regeneration being secured without appreciably hastening the network overloading.

Another important object of the invention may be stated to reside in the provision of a detector network which comprises a tube constructed to furnish a diode section and an amplifier section, a signal input circuit being connected to the diode section to provide a diode detector circuit, the audio frequency component of the 45 detected signal current being impressed upon the control grid of the amplifier section whereby the latter functions as an audio amplifier, the plate circuit of the amplifier being relatively tightly coupled to the detector input circuit, and a relatively loose coupling being provided between the amplifier grid and the diode detector input circuit whereby the amplifier functions to provide regeneration of the signal current without carrying sufficient radio current to appreciably hasten overloading of the amplifier output circuit.

Still other objects of the invention are to improve generally the efiiciency and utility of regenerative detector circuits, and more especially to provide a regenerative detector circuit which is not only reliable in operation, but is economically manufactured and assembled in radio receivers.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into efiect.

In the drawing:

Fig. 1 shows a regenerative detector circuit embodying one form of the invention, and

Fig. 2 shows a detector circuit employing a modification of the invention.

Referring now to the accompanying drawing, wherein like reference characters in the different figures designate similar circuit elements, the numeral I denotes an electron discharge tube which may be of the well known 55 or 85 type. This type of tube essentially comprises electrodes arranged to provide a diode section and an independent amplifier section. Briefly, the tube comprises a cathode 2, a diode anode 3 disposed adjacent a portion of the cathode 2 so as to receive electrons therefrom. The diode anode 3 and plate 5 are arranged to receive independent stream of electrons from the common cathode 2. Those skilled in the art will readily realize that when using a tube of the duo-diode triode type, the two diode anodes will be strapped together, and thus furnish an effective single anode for the diode section. Furthermore, the amplifier section of the tube may be of the screen grid, or pentode, type as in the 85 type tube, if desired.

The signal input circuit 6 has its coil 1 magnetically coupled to the source of signal current, and the condenser 8 tunes the input circuit 6 at the desired signal frequency. If the receiving system is of the superheterodyne type, then the source of signal energy coupled to input circuit 6 will be the output of the I. F. amplifier. Since superheterodyne receivers are very well known to those skilled in the art it is not believed necessary to describe such a system in detail, except to point out that the input circuit 6 would be tuned to the operating I. F., and the condenser 8 would be of fixed value. If the receiving system is of the tuned radio frequency type, then one, or more, tunable radio frequency amplifiers precede the input circuit 6, and the variable condenser 8 would have its rotors arranged for unicontrol adjustment with the rotors of the variable condensers used in the preceding amplifiers.

The diode load resistor 9 is connected between the low alternating potential side of input circuit 5 and the grounded cathode, the by-pass condenser lll being shunted across resistor 9. The audio frequency component of detected signal current is impressed upon the control grid 4 by connecting the latter to an adjustable tap II.

The tap H is slidable along load resistor 9, and' is connected to control grid 4 through a path which includes condenser l2 and the coil 13. The latter is reactively coupled. to input coil 7, and the arrow through coils I and I3 denotes adjustability of the reactive coupling between the two coils. The junction of coil I3 and condenser l 2 is connected to ground through resistor l4, and the function of this resistor is to provide a definite direct current operating potential for grid 4.

The plate 5 of tube I is connected to the positive terminal of a source of direct current potential, which source is not shown, through apath which includes the feedback coil l5 and the headphones IG. Coil l5 and coil '1 are reactively coupled. If desired, the headphones l6 may be replaced by any other type of reproducer, such as a loudspeaker, and the audio output of the plate circuit of tube I may be amplified in one, or more stages of audio amplification.

In the circuit shown in Fig. 1, a relatively strong feedback coupling is provided between the plate circuit of tube I and the tuned input circuit 6. A variable coupling of the correct phase for regeneration is then provided between input circuit 6 and control grid 4. Since the feedback coupling is much tighter than customary in regenerative circuits heretofore used, it is only necessary to impress a small fraction of the radio frequency voltage across coil 1 upon the grid 4 to obtain suflicient regeneration, or even oscillation. Since the radio frequency voltage impressed upon grid 4 is very small there will be only a very small radio frequency current in the plate circuit, and accordingly this will not bring about overloading appreciably sooner than if regeneration were not used at all. For purposes of illustration, it is pointed outthat the coupling between coils l5 and 1 may be one such as would ordinarily be employed for amplification purposes where a plate circuit, or primary coil, is coupled to a tuned secondary circuit. The voltage step down between coils l and l3 is variable over a rangeincluding a step down that just compensates for the amplification action, which particular step down is the critical value for sustained oscillations.

In Fig. 2 there is shown an alternative circuit arrangement employing the same method of operation, but having its regeneration controlled by a variable capacity instead of a variable mutual inductance. In this figure any radio frequency component in the plate circuit is forced by choke coil 20 to flow through condenser 2| back into the tuned input circuit 6. The control grid 4 is connected to a point 22 which is at zero radio frequency potential when the adjustable condenser 23 is suitably adjusted. The tuning condenser 8 is connected in shunt to the adjustable condenser 23 and the fixed condenser 24, both of the latter condensers being connected in series. A slight variation of condenser 23 will impress a small radio frequency potential upon the control grid 4 and produce regeneration.

The diode detector has its audio frequency output connected through the condenser l2 and radio frequency choke coil 30 to the control grid 4. The grid leak resistor 3| is connected in series between the control grid 4 and the usual grid bias resistor 40. It will be understood that the voltage drop across resistor 40, the latter being shunted by the by-pass condenser 4|, provides the normal grid bias for control grid 4. The anode side of load resistor 9 is connected to the midpoint of input coil 1, and an automatic volume control connection (AVC) is shown connected to the anode side of resistor 9. The resistor-condenser network 50 filters the radio frequency components from the AVG bias, and, as is well known, the latter bias is applied to one, or more, radio frequency amplifiers for reducing the gain of the amplifiers as the signal amplitude increases thereby to maintain the carrier amplitude at the input circuit 6 substantially uniform over a relatively wide range of signal variation at the signal collector of the receiving system.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

1. In combination, in a detector network, an electron discharge tube provided with a diode section and an amplifier section, a tuned signal input circuit connected to the diode section and including means for rendering the diode capable of detecting signals, means for impressing the audio component of detected signals upon the control grid of the amplifier section, an audio utilization means in the plate circuit of the amplifier section, means tightly coupling the plate circuit of the amplifier section with the detector input circuit to provide strong regenerative feedback thereto, and a reactive coupling between the control grid of the amplifier section and said detector input circuit whereby the amplifier section functions to regenerate signal currents, said reactive coupling being substantially less than said tight coupling and to an extent such that only a very small radio frequency current flows in said plate circuit.

2. In combination, in a detector network, an electron discharge tube provided with a diode section and an amplifier section, a tuned signal input circuit connected to the diode section and including means for rendering the diode capable of detecting signals, means for impressing the audio component of detected signals upon the control grid of the amplifier section, an audio utilization means in the plate circuit of the amplifier section, means tightly coupling the plate circuit of the amplifier section with the detector input circuit to provide strong regenerative feedback, a reactive coupling between the control grid of the amplifier section and said detector input circuit whereby the amplifier section functions to regenerate signal currents, and said coupling between the plate circuit of the amplifier section and the detector tuned input circuit being relatively stronger than said other coupling to the amplifier control grid, the said reactive coupling being sufficiently small to prevent overloading of the said plate circuit by radio frequency currents.

WALTER VAN B. ROBERTS.

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