US1937785A - Wireless communication apparatus - Google Patents

Description

Dec. 5, 1933.

w. P. PLACE 1,937,735

WIRELESS COMMUNICATION APPARATUS Filed Sept. 15. 1932 INVENTOR, ll zllal'd P. Place.

BY mm HIS A TTORNEY.

Patented Dec. 5, 1933 PATENT OFFICE WIRELESS COMMUNICATION APPARATUS Willard Place, Wilkinsburg, Pa., assignor to The Union Switch & Signal Company, Swissvale, liaJ, a corporation ofPennsylvania Application September 15, 1932 7 Serial N8, 633,273

12 Claims.

The present invention relates to the art of wireless communication, and comprises a novel circuit arrangement utilizing a solid rectifier of appreciable rectifying area, such as a metal oxide or internal boundary type of rectifier, as a detector of high frequency electric waves. This application is a continuation in part of application Serial No. 540,348, filed May 2'7, 1931.

.Metal oxide or internal boundary rectifiers have voltage resistance characteristics which make them ideal for use as detectors in radio receivers but for reasons that will be apparent as the description proceeds, no eiiicient radio receiver utilizing this type of detector has heretofore been developed.

An internalboundary rectifier may be considered as a capacity reactance in parallel with a resistance. In the high resistance direction, the capacity reactance is so much lower than the resistance that the resistance may be neglected. In the low resistance direction the capacity reactance, while large compared to the resistance, is not so high that its efiect can be neglected. The rectifier then consists essentially ofa capacity reactance in the high resistance direction and of a similar capacity reactance in parallel with a very much lower resistance in the low resistance direction. As long as the resistance in the low resistance direction is small compared 30' to the capacity reactance, the unit will function as a rectifier, because in that case the impedance in one direction is greater than it is in the opposite direction. At radio frequencies the capacity reactance is so low that it is necessary to make special arrangements to provide that the resistance in the low resistance direction shall be low enough to produce satisfactory rectification.

Since the resistance in the low resistance direction decreases with increasing current density,

one way to improve this condition is to arrange that the power input to the rectifier is great enough to maintain a relatively high current density through the discs. This is accomplished bythe use of two different expedients. One is to make the rectifier discs very small, the other is to connect the rectifier, together with additional capacities used for adjustment, in parallel with an inductance on the alternating current side so that the whole output circuit of the vacuum tube which feeds it consists of a parallel tuned circuit. This provides a relatively high impedance as a load on the vacuum tube and allows the inductance to furnish the capacity current in the rectifier, thereby increasing the current density considerably above what would be possible with the same vacuum tube if the parallel tuned circuit were not used. Thehighimpedance, which is a characteristic of this parallel tuned circuit, also enables us to. get a greater amplification from a given tube than could be (3-9 obtained if the rectifier were connected across the tube without any auxiliary apparatus.

This circuit arrangement may be used in two ways to eliminate distortion. In the first place, the high currentdensity used in the rectifier es eliminates the curved part of its characteristic allows it to operate altogether as a linear rectifier. In the second place, such a parallel tuned circuit can be given sucha high impedance compared to the impedance of the plate circuit of the vacuum tube that any variations will have an entirely negligible effect on the amplification and therefore will produce no distortion as between high and low voltages coming through the tube. The circuit arrangement just described [5 also has the effect that the rectifier is operated at high efficiencies. 1

Other features of the new circuit which makes possible the efiicient use of an internafboundary type of rectifier as a detector will be discussed in connection with the description of the accompanying drawing to whichreference should now be had.

Fig. 1 illustrates diagrammatically a radioreceiver utilizing a metal oxide rectifier as a detector and departing as little as is practicable from the usual type of receiving circuit and Fig. 2 illustrates the preferred embodiment of the invention in which no stage of audio amplification is required. i

The rectifier illustrated in each of Figs. 1 and 2 is of the bridge type. Preferably, as hereinbefore discussed, each element of the rectifier is as small asit can be made diagrammatically at 1 in order to minimize the capacity and increase l the current density. Each arm of thebridge includes several rectifying elements; the number depending upon the rectifying area of each and the plate resistance of the radio frequency amplifier with which the rectifier is to be used. No 199 exact indication of the proper number of discs to use can be given, but in general, the smaller the rectifying area, and the lower the plate resistance of the preceding tube the fewer discs are required. With a triode such as the type 27 used as a radio frequency amplifier, four discs in each arm of the bridge, each with a diameter of about 0.08 inchea'have been found to give excellent results in either of the circuits of Figs. Ior 2'. The number of discs should be such that the of no fective impedance of the rectifier is large compared to the plate resistance of the amplifier.

In Fig. 1 the rectifier l is coupled to the last tube 2, preferably a triode as illustrated, of a radio frequency amplifier by a choke coil 3. The plate of tube 2 is connected to one end of the choke 3 and through a capacity 4 to one input terminal of the rectifier l and one end of a variable inductor 5. The cathode of tube 2 is connected through a grid biasing resistor 6 and capacity 7 in parallel to ground. Any other suitable means for providing grid bias to the tube could be used if desired. The other input terminal of the rectifier 1 and the other end of the inductor 5 are connected to ground througha capacity 8. The inductance coil 3 is of such a value as to offer high impedance to alternating current of radio frequency while offering substam tially negligible resistance to direct. current, thus forcing the alternating component of the plate current to take the path to ground through capacities 4 and 8 and through coil 5 and rectifier 1 in parallel; capacities 4 and 8 being so chosen as to offer negligible reactance to the high frequency current. Inductance 5 and rectifier 1 form a parallel tuned circuit connected across the output terminals of tube 1. Such a circuit, as heretofore discussed, insures a high voltage across the rectifier and when the area of each disc of the rectifier is small, as described, insures that the current density through the rectifier will be high.

For simplicity a battery 9 for applying positive potential to the plate of tube 2 through the coil 3 is indicated, and a battery is indicated as supplying heating current to the tube but any other suitable sources of electromotive force could be employed.

One end of a resistance 10 is connected through a condenser 11 and inductance 12 with one output terminal of the rectifier 1 and the other end of the resistance 10 is connected to ground and through an inductor 13 with the other output terminal of the rectifier. Directly across the output terminals of the rectifier are connected a choke 14 and resistance 15. A condenser 16 parallels the resistance 15. The choke 14 is of such value as to offer high impedance to alternating current while the inductors 12 and 13 and the capacity 11 are so chosen as to offer low impedance to audio-frequency current but high impedance to currents of radio frequency. The steady direct current corresponding to the mean value of the unmodulated carrier wave is thus dissipated through the choke 14 and resistance 15 while the audio-frequency alternating component of the rectified wave corresponding to the modulation current passes through the coil 12, capacity 11, resistance 10 and coil 13 back to the rectifier. The inductor 12 serves to prevent alternating voltage of radio frequency due to any unbalance in the inherent capacity of the four legs of the rectifier from being impressed on the grid of the audio-frequency amplifier tube 17; and grid of this tube being connected to a variable contact on resistance 10 for the application of a controllable percentage of the low frequency alternating voltage thereto. Inductor 12 also serves to prevent the second harmonic of the radio frequency carrier wave from reaching the grid of tube 1'7. 7

The inherent capacity of the coil 14 together with the capacity 16 serves to smooth out the radio frequency ripple and should be correct for this purpose but not so large as to pass an appreciable amount of the higher audible frequencies. If the inherent capacity of choke 14 is small, a condenser could be added in parallel therewith. The inherent capacity of the rectifier 1 may itself be sufiicient under some circumstances to serve the purpose of these capacities. Inductor 13 is not essential but insures sensibly complete full wave rectification by forcing currents of radio frequency to go to ground through the opposite leg of the rectifier. Without inductor 13, a part of this current would pass through one leg of the rectifier, coil 14 acting as a capaci ty, and through capacity 16 to ground without going through the other leg of the rectifier.

The cathode of tube 1'7 is connected through resistance 18 and condenser 19 in parallel to ground. The plate of tube 17 is indicated as connected through a load device 20 with a battery 21 the negative terminal of which is connected to the positive terminal of battery 9. Device 20 may represent a loud speaker, earphones, a meter or any type of coupling to succeeding tube or tubes for further amplification as desired.

The operation of the above-described circuit will be clear from the description already given. The alternating component of the modulated carrier wave amplified by tube 2 and preceding tubes, if any, is completely rectified by the rectifier l; the steady direct current from the rectifier being lay-passed through the inductance l4 and resistance 15 while the pulsating portion corresponding to the modulation current is passed through the resistance 10. A controllable percentage of the alternating voltage across resistance 10 is then impressed upon the grid of the audio-frequency amplifier tube 17 and the amplified audiofrequency current delivered to the device 20. With this arrangement adjustment of volume may be efiected by varying the position of the sliding contact on resistor 10 without the accompaniment of objectionable noise which might occur if the steady current component of the rectified current were to take the path through resistor 10.

Tube 2, being a triode, has a plate resistance which is small compared to the effective alternating current impedance of rectifier 1 when each arm thereof is composed of a plurality of discs of relatively small rectifying area. Thus, when the constants of the above described circuit are suitably selected, the rectifier will operate efficiently with a high ratio of applied to delivered voltage and with substantially no distortion due to change in the amplification factor of the radio frequency amplifier.

In Fig. 2 a circuit is illustrated which is similar in some respects to the circuit of Fig. 1, but is preferred thereover because of simpler and more economical construction and because including fewer elements which produce frequency distortion. In instead of providing two separate inductors, one for coupling the radio frequency amplifier with the rectifier and one for balancing out the inherent capacity of the rectifier, a single inductor 22 is provided to serve both purposes and a variable capacity 23 is connected .1 4

across the rectifier input terminals for tuning the circuit to parallel resonance. One end of inductor 22 is connected to the plate of tube 2 and to capacity 4 and the other end isconnected to battery 9 and, through a capacity 24 with the cathode of tube 2. In the output circuit of the rectifier a simple resistance 25 is substituted for the series branch including inductor l4 and resistance 15 of Fig. 1, and a potentiometer resistance 10a, of a value large compared with that of lot resistor "25 is substituted forthe lowered value resistor 10 of Fig. 1. A controllable portion of the potential drop across resistor 10a in the alternating branch of the rectifier output circuit is impressed upon the input terminals of a power output tube 26 without the intervention of the usual stage of audio-frequency amplification. Tube 26 isspecifically illustrated as a pentodehaving control, screen and cathode grids. Suitable batteries 29 and 30 areindicated for supplying positive, potential to thescreen grid and plate respectively of tube 26 and biasing means for the control grid of the tube are indicated at iii-and 19. Any other well known type of power tube could be substituted therefor. A loud speaker 27 orother load device is coupled to the output circuit of tube 26 by means of a transformer 28. I

In the preferred circuit of 2 there are'but few elements, namely, the grid biasing devices, the output transformer and the elements in the alternating current branch of the rectifier out put circuit which could impair, the 1 frequency characteristic of the circuit. Each of these elements may be readily designed in accordance with well known methodsto avoid frequency distortion to any desireddegree. In so far as the metal oxide rectifier is concerned tests have shown that it will follow modulation frequencies without distortion. 1

Two circuits embodying the invention have now been described.

In each circuit a bridge type metal oxide recti fier operates as a detector of modulated high frequency current. In each circuit the rectifier is. located in a circuit tuned to parallel resonance and in each the rectifier has been indicated as being so constructed asto have a very small capacity reactance. In each circuit a high voltage is impressed across the rectifier and in each the impedance of the load upon the preceding amplifier is high compared to the plate resistance of the .tube with the result that the circuit operates and from the drawing that the underlying feature of the invention which makes possible the use of an internal boundary rectifier as a detector is the fact that all parts are so arranged and so constructed as to insure a high current density through the rectifier. Increasing the current density, decreases the forward resistance and consequently decreases the losses in the rectifier and decreases the effect of the capacity. Neutralizing the capacity of the rectifier by placing the rectifier in a parallel tuned circuit insures a high voltage across the rectifier compared to that which would be obtained with a lower impedance circuit, and consequently, when each arm of the rectifier comprises a plurality of discs each having a small rectifying area, insures a high current density. Thus, ineffect, a construction which tends to in crease the current density tends also to reduce the capacity effect of the rectifier and an arrangement which tends to neutralize the capacity tends also to increase the current density. In each case impedance.

In each of the circuits illustrated direct coupling is provided between the rectifier and the preceding amplifier; substitution of transformer coupling for, the direct coupling illustrated is possible but the resulting arrangement is inferior because less efiicient due to the unavoidable losses introduced by the transformer. In each circuit the' preceding high. frequency amplifier is illustrated as a triode. ,Any other tube could be used, but to avoid distortion at the higher frequency, a tube having a relatively low plate resistance is preferably employed. When a tube havingqa high, plate resistance. is used, an eiIective impedanceof the rectifier sufiicient to avoid distortion considerably decreases the efficiency of the circuit.

In the above description and in the appended claims the term metal oxide rectifier is intend ed to include only rectifiers having appreciable rectifying area as distinguished from rectifiers, such ascrystal detectors, where rectification occurs at point contacts only.

The following is claimed: 1

1. A radio receiver including as a detector a metal oxide rectifier, the forward resistance of which is small compared to itscapacityreactance, the input circuit of said rectifier including means for balancing out the input capacity of the rectifier, thereby increasing the impedance across the rectifier and increasing the current density through the rectifier. M

2. A radio receiver including a high frequency amplifier, a metal oxide rectifier coupled thereto to serve as a. detector, and means connected across the input terminals of said rectifier for balancing out the inputcapacity thereof.

3. Aradio receiver including in combination, a high frequency amplifier, a source of plate potential for said amplifier, an inductance connected between said source and the plate of said amplifier, a full wave metal oxide rectifier, and a pair. of capacities connected in series across said inductance, and a variable capacity connected. across said inductance for tuningto parallel resonance the output circuit of said amplifier whereby the capacity of said rectifier may be neutralized and a higher voltage impressed 120 across the input terminals thereof.

-, 4. A radio receiver according to claim 3 including a pair of parallel branches in the output circuit of said rectifier, one for the steady direct current component corresponding to the carrier wave and one for the alternating component corresponding to the modulation current and including a power output tube, the alternating voltage across a controllable portion of said alternating current branch being impressed across said output tube.

5. A detecting circuit for insertion between successive stages of a radio receivercomprising in combination a metaloxide rectifier, means for coupling the same to the preceding stages of the receivenmeans including a resistance in series with the rectifier for coupling the same to succeeding stages of the receiver, means associated with said resistance for adjusting the volume of current transmitted to the succeeding stage of the receiver, and a by-pass about said resistance for the passage therethrough of the steady direct current corresponding to the mean value of the unmodulated carrier wave whereby substantially noiseless adjustment of volume may be effected, said by-pass including elements oifering a high impedance to currents of the frequency to be transmitted to the succeeding stage of the receiver.

6. A detecting circuit for insertion between 0 succeeding stages of a radio receiver comprising in combination, a full wave metal oxide rectifier, means for coupling the same to the preceding stages of the receiver, means including a resistance in series with the rectifier for coupling the same to succeeding stages of the receiver, means associated with said resistance for adjusting the volume of current transmitted to the succeeding stage of the receiver, and means in series with said resistance for preventing transmission of high frequency current thereto and for insuring sensibly complete full wave rectification.

7. A detecting circuit for insertion between successive amplifiers of a radio receiver comprising in combination, a full wave metal oxide rectifier having two input and two output terminals, a condenser in series with each of said input terminals to prevent the passage of direct current thereto, said condensers and rectifier being connected in series across the preceding amplifier of the receiver, a choke coil in series with a source of potential being also connected across the output terminals of said preceding amplifier, and means connected to said output terminals of the -I rectifier for coupling said rectifier to the succeeding amplifier of the receiver.

8. The combination according to claim 7 including means connected across said input terminals of the rectifier for balancing out the inherent capacity of said rectifier.

9. A detecting circuit for insertion between the last radio frequency amplifier and the first audio-frequency amplifier of a radio receiver which comprises a metal oxide rectifier, means I connected across the input terminals of said rectifier for balancing the inherent capacity thereof, means for coupling the rectifier to the last radio frequency amplifier of the receiver, and means for coupling the rectifier to the first audiofrequency amplifier of the receiver, said lastmentioned means including a resistor adapted to have a controllable percentage thereof connected across the first audio-frequency amplifier.

10. The detecting circuit according to claim 9 including means connected with said rectifier and said resistor for preventing the passage through said resistor of the steady direct current corresponding to the mean value of the carrier Wave.

11. A radio receiver having a high frequency amplifier, a full-Wave metal oxide rectifier, a coupling between the output circuit of said amplifier and said rectifier comprising an inductance, means included in the input circuit of said rectifier for balancing out the input capacity of said rectifier, an output circuit for said rectifier including two branches, one for the steady direct current corresponding to the carrier Wave and one for the alternating component corresponding to the modulation current, and means for impressing across the following circuit of said receiver a controllable portion of the voltage across said alternating current branch of the rectifier output circuit.

12. A radio receiver including a metal oxide rectifier operating as a detector, a high frequency amplifier, and an output circuit for said amplifier comprising a parallel tuned circuit one branch of which includes said rectifier, whereby the effective impedance of the amplifier output circuit may be made large compared with the plate resistance of said amplifier, said rectifier being of the bridge type each arm comprising a plurality of series connected elements, the number of elements and the rectifying area of each being such as to insure a high current density through the rectifier and to make the forward resistance thereof low compared to the parallel capacity re actance.

WILLARD P. PLACE.

LEE.

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