US2472218A - Radio reception - Google Patents

Description

W. LYON S RADIO RE'EPTIoN June 7, 1949.

Filed Feb.. 5. 1944 3 Sheets-Sheet 1 ATTORNEY June 7, 1949, w. LYoNs RADo RECEPTION 5 Sheets-Sheet 2 Filed Feb. 5, 1944 INVENTOR M4 nsf? Yon/s.

ATTORNEY w. LYoNs 2,472,218

RADIO RECEPTION June 7, 1949.

Filed Feb. 5, 1944 v3 Shets-Sheet 3 INENTOR Mz no? y0/VJ.

ATTORNEY kaf/42a,

Patented June 7, 1949 RADIO RECEPTION Walter Lyons, Wenonah, N. J., assignor :to Radio Corporation of America, a corporation of Deia? Ware Application February 5, 1944, Serial No. 521,174

(Cl. Z50-20) 3 Claims.

My present invention relates to the amplifical tion and translation or demodulation of high frequency waves. In particular, it relates to circuits for the translation of voice or code modulated high frequency waves.

For communication purposes it is desirable to have a radio receiver which is adapted :for the reception of either code or telephonie signals. One object of my present invention is to provide such a receiver which `operates for the efficient,

reception of either type of signal and which may be readily converted from code reception to voice reception or vice versa. Another .object is to provide a circuit arrangement which utilizes vacuum tubes in an eicient way whereby a small number L are employed with high utility in the reception of code and voice signals.

Other objects, advantages and features will .be self-evident from the more detailed description to be given later and also from the following overall brief description of my improved radio re.- ceiver.

Received high frequency waves bearing code or voice signals are amplied, heterodyned down to a convenient intermediate frequency and further ampliiied. For the reception of voice signals, the intermediate frequency waves are fed to the triode section of one tube acting as a detector. The detected waves ar-e fed to a triode section of a second tube which serves as an amplier. The amplified voice waves are utilized in any desired way. A diode section of the second `tube is used, as will be more fully explained hereinafter, for automatic volume controlling purposes in the R. F. and I. F. stages of the receiver. A second .diode section of the .second rtube is used as a gate to prevent the Iapplication of positive voltages to the -grids of earlier stages of the receiver despite the use of such yvoltages injected into a portion of the volume controlling circuits.

The volume control-ling diode circuit heretofore mentioned is also utilized for exciting certain amplifying and limiting tubes employed in the reception of code signals. When receiving `code signals a local oscillator is brought into play which feeds beating waves to the detector section of the rst tube. The resulting beat, adjusted to an audio frequency, is fed to the amplifying section of the second tube ymentioned above for monitoring purposes.

In the more detailed `description which follows, .reference will be made to `the accompanying drawings wherein:

Figure -1 is :a block .diagram .of l.the ,radio frequency and .intermediate .frequency-stages of a .radio reeeiyer suowlue port .of the automatic v01- iime Controlling eroiiits;

Figure 2, .consisting of Figures 2e eed 2b teken together, illiistrat s an arrangement of tubes and circuits for utilizing the intermediate frequency output of :the system shown Figure 1 fer reproducing the voice ,or code signals received on the antenne system of Figure `is .and

Fig-ure A3 is a more 1detailed illustration of a Coupling uni-t utilized iu the appurato-S of Figure 1.

In Figure :1, `pinoli :illustrates oiesremmetieelly the radio frequency arid intermediate frequency sieges of :the reoeiyer, the imonline ovaires ere picked up upon ari antenne p9 :arid fed to a rst radio frequency amplifier 262 VThe l output of the various radio frequency Sieges may be fed, :by plug-in coil .and :condenser circuits 64.1.6.6, ,te S110- oeedins R. ampi-iper etages .suoli as $8- The output of the radio rreoueney ampier stese 8 is fed to a first detector and oscillator stage '19 in which the amplified radio fr eouepey Wares are heterodyned down fte .a suitable intermediate frequency.

For example, the receiver may be `designed to receive waves in @the paudpongiog from 1.5 to .1 8 megacycles and the oscillator of thegl'rgt detector and I.oscillator 10 may be qz idjiusted in frequency so that the intermediate sfrequeney produced and amplified in .the ,intermediate frequency .amplifying stages 1.2 51A-and $16 fof ,the `.orcher .of $7.35 kilocycles.

In order to ,enable the roi-#pilier to loperate ,over such ,a wide range, plug-in .coil and condenser I- apparatus is provided for :the ooupliiisr between such stages las radio efreiiuencystages 6.2 and .6,8-

As shown in Figure 1, .typiealplug-.in .apparatus would consist .of a primary coil 1910 Atuned by a xedcondenser 592 and Variable iron core 9 4. The output of :circuit i90, $2 .-,woulozbe fed through :the link consisting of the small secondary .9.6 and coupling Icondenser .9.8 to the IieXt coupling condenser 0.0 ofthe plug-in arrangement o6. The waves fed :through ...coupling condenser ,we are then fed to :the small iprirnary :i102 which inductively feeds .the secondary M14. Secondar-y 11M is :tuned both by means .of a condenser 105 and variable iron core L08.

The mechanical l. aiurangement for plug-in coupling apparatus rsuch ias 6:4 :or .f6.6 of Figure 1 is illustrated in areatendetaiLin Figuren :Figurer3 illustrates itheiapparatus within either rectangle orof Figure f1. fReferringtogFigure 3, metal can @A Ais.o1,1nclied to the :insulating :base :200 in .any suitable Way. :Candid :helps .keep the paper form 202, cemented to the base 200, in place. That is, the under surface of the top of can 64 presses against the top of form 202. The large coil 90 is wound on the upper portion of the form 202 and the smaller secondary 9G is closely wound and arranged about 1/gth inch below the coil on form 202. Condensers 92 and 93 correspond to smaller condensers within rectangle 64 of Figure 1. Appropriate connections are brought out from the various elements within the can 64 to the prongs mounted beneath the base 200.

The iron plug 94 is mounted upon a screwthreaded shaft 205 in turn .screwed into an internally threaded opening in the key 208 also mounted on the base 200.

Turning now to Figure 2; that is, to both Figures 2a and 2b constituting Figure 2, amplified waves of intermediate frequency are fed from the tuned primary circuit 2 to the transformer secondary in the tuned circuit 4. The energy resonated in circuit 4 is divided into two paths. One path feeds a monitoring arrangement of tubes and circuits and the energy in the other path is rectified for A. V. C. purposes and for operation of -recording apparatus when code signals are being received.

For voice reception the output of tuned circuit 4 is fed through condenser 6 on to grid 5 of tube 8. Grid 5, cathode section and plate 9 of tube 8 operate as a detector, as a result of which the audio signal appears in the circuit of plate 9 of tube 8. This audio signa1 is fed through condenser I0 and potentiometer l2 to the grid |3 of tube |20. The amplified output appearing in the circuit connected with plate l5 of tube |20 is fed through transformer T| I3 to line terminals L and G of jack J |01. If desired, the voice output of transformer Tl i3 may be fed simultaneously to jack |06 and thence to earphones for monitoring purposes.

The bias on grid '5 of tube 8 is produced by cathode current flow through the cathode .3 of tube and biasing circuit BCI consisting of resistor R|35 and condenser C |55. Additional bias is provided by grid leak condenser R|3l and its condenser C |56.

It will be noted that while amplified intermediate frequency energy is fed through condenser 6 to the grid 5 of tube 8 for rectification and reproduction of the transmitted voice signal, another portion of the intermediate frequency waves is fed through lead |4 to the upper diode plate |'l of tube |20. This I. F. voltage operates on the electron stream from the cathode of tube |20 to produce a voltage drop across the resistor R|i29 (Fig. 2b). As illustrated in Fig. 1 this voltage drop across resistor R|29 serves automatically to control the volume or gain in the radio frequency and intermediate frequency amplifiers.

In this regard, point X of Figure 1 is connected to point X of Figure 2b and in this A. V. C. circuit, R|30 is an isolating circuitk resistor, and C|89 is a by-passing condenser. R|54 of Figure 1 is a variable bank of resistors for controlling the automatic gain control time constant.

Since the reception of C. W. code signals represents a substantial part of the service to which the present receiving system may be put, these variable A. G. C. time constant circuits have been provided. Three time constants have been provided by virtue of the R|54 circuit although two may suflce for most cases. As shown, with one resistor in circuit at |54 the time constant has a value of approximately one second; in another position of the switch the time constant has a value of one-tenth of a second; and in the third position one one-hundredth of a second. If two time constants are used it is preferable that they be made approximately one second and one-twentieth of a second. A fast time constant is required when recording signals that have a fast fading characteristic causing drop-outs and the A. G. C. is required to follow this. A slower time constant is desirable when noise occurring between code pulses is encountered.

Resistors 20, 22, 24 and 26 of Figure l are isolating resistors and may be one megohm each in value. Resistor 28 is another isolation resistor and may be, forY example, 100,000 ohms in value. Resistance R|24 of Figure 1 is a voltage dropping resistor and operates to apply a small positive voltage through a lead, as shown in Figure 1, to the automatic gain controlling circuit.

It will be noted, referring to Figure 2a, that diode plate I9 of tube |20 is connected through lead 32 to point X on the A, G. C. circuit. The action of this connection to the electrode |9 of tube |20 is to prevent excessive positive voltages from being introduced into the automatic gain controlling circuit. During operation with a workable signal, a negative voltage is, of course, developed across resistor |29 (Fig. 2b) of such value as to impress a resultant negative voltage on the grids of the various gain controlled stages through the resistors 20, 22, 24 and 26 of Figure 1.

One .purpose of applying the positive voltage through resistor R|24 of Figure l is to enable high negative voltages to be developed across resistor R|29 of suicient negative value to operate the keying circuits when code signals are being received. The positive voltage applied or injected through R|24 of Figure l, however, prevents the high negative voltage developed across resistance R|29 from being applied through the gain controlling circuits except in such values as to enable desired operation of the system over the automatic gain control range.

Also for diversity reception it is desirable to have as high as possible an E. M. F. on the diode I1. This high voltage will overcome the sum of the contact potential and rectified interference noise potential. Thus, with a relatively small signal on the antenna 60, say, one-half of one microvolt, a voltage of twenty volts may be built up across the diode resistor in circuit with diode plate The positive potential placed upon the A. V. C. string 20, 22, 24 and 26 delays the A. V. C. action and enables this voltage to be built up, as a result of which some twenty-two or twentythree volts may be secured for cutting off the other receivers of the diversity system. This high voltage also is useful for operation of the keying relay which requires high excitation.

In other words, development of high voltage across resistor R|29 enables efcient operation of the keying relay and recorder circuits and yet this high voltage is useful for A. V. C. purposes by virtue of the partial compensating action of the injected B voltage into the A. V. C. network through resistor RI24. Injection through RI24 does not mean that positive voltage is impressed on the grids, rather it means that the grids are fed with proper negative potentials for good operation. Should, for some reason, positive potential leak through to X (Fig. 1) conductor 32 will impress this voltage on I9 (Fig. 2a), thereby immediately and effectively grounding the grids 'connected to the A. V. C. string. When theI plate 195 is negative, conductor 32 is effectively open circuited. In this way I9 acts as a gatef preventing the grids in the A. V. C. string from going positive. Y 1

For voice reception, and also, if desired., 'for monitoring code signals, a bank of tone control condensers SI05 (Fig. 2a) may be provided as illustrated. The condensers of the bank SM5, as shown, may be selectively connected into circuit.

For monitoring code reception. and recording, switch S40 (Fig. 2b) is closed, which applies plate voltage through the isolating resistors RI45 and RIM to the plate 29 of vacuum tube 42.- It will be noted that plate 29, cathode 2l and grid 25 of tube 42 are connected to the tuned circuit 44 so as to provide a Colpitts type of oscillation generator. The tuning of this beat frequency oscillator may be controlled within limits by variation of condenser CII6. Output of the beat frequency oscillator portion of tube 42 is fed through condenser CI'II to the grid I of the detector section of tube 8 (Fig. 2a). As a consequence, audio frequency beat waves are produced in the plate circuit section, including plate 9, of tube 8 and are fed through condenser I0 to the grid I3 of tube |20 for amplification. The amplified tone so produced may be heard in phones connected with jack JIOB.

Typical examples of Waves to produce a suitable tone in the jacks for monitoring code signals are an intermediate frequency of 735 k. c. and a frequency for the local beat frequency oscillator 736 k. c., as a result of which the tone heard in the phones connected to the jack J IOB will be of the order of 1,000 cycles.

For detecting and recording code signals, as before, a part of the intermediate frequency waves are fed through lead I4 to the plate I1 of tube |20. The rectified voltage appearing across resistor RIZB (Fig. 2b) for code reception is not only used for automatic volume control, as before explained, but is also fed to the recording apparatus through switch SI04 when closed. Closure of switch SI04 impresses the voltage developed across resistance RI 29 upon the grid 23 of tube 42. Resistor RI43 is provided to connect the grid 23 to ground when switch SI04 is open and is of such value, as for example ten megohms, as not to interfere with operation when switch SI04 is closed.

Condenser CI58 is provided to by-pass high frequency noise voltages to ground without interfering With the relatively lower frequency code signals and to wipe out undesired modulations which may appear on the code signals. The amplified and limited voltage on plate 21 of tube 42, which amplified voltage is controlled by the input on the grid 23 thereof, is fed through condenser CI'I1 on to the parallel connected grids 3l and 33 of tube 50. It will be noted that the plates and cathodes of tube 50 are also connected in parallel, in this way effectively increasing the power output of the tube 50 which is to be applied to the recorder terminals. The output of tube 50 is fed to the recorder through condenser CI18, inductance coil LIZE and recorder jack J |08. CII9 is a shunting radio frequency bypassing condenser.

It will be noted that the signal sections of tube lf2 and tube 50 act as limiting amplifiers. This action is secured by virtue of the fact that grid 23 of tube 42 is operated at zero D. C. bias normally in the absence of signal and the grids of tube 50 are biased to plate current cut-oi-by virtue of voltage applied to the .grids .thereof through lead 34.

Because of the biasing circuit chosen for the tube 42, it is essential that the voltage developed across RI29 be large so as to quickly bring grid 23 of tube 42 to a value sufficient to produce limiting or plate current cut-off. As before explained, this voltage may be developed across RI20 and yet also may be employed for A. V. C. By the action of the circuit including the plate I9 of tube |20 any positive Voltage which might be vim-i pressed on the grids or otherwise due to tubes going gassy or due to other conditions, is immediately grounded and prevents the application of positive voltages to the grids of the automatically volume controlled stages. The grids may normally be maintained about three-quarters of a volt negative with respect to their cathodes under no signal condition. This follows for if a positive voltage is applied to I9, it effectively is reduced to cathode potential because of electron current flow.

Additional receivers may be provided for diversity reception. In this event, terminals D and A of the jack J |09 are connected in parallel. This will automatically connect a series of resistors R129 in parallel. However, if desired only one or more of such resistors may be left in circuit even though two, three or more receivers may be so connected in parallel. A good practical number of receivers for diversity action is three, although as many as six or seven may, if desired, be employed.

Having thus described my invention, what I claim is:

1. In combination, an amplifier amplifying high frequency waves modulated with code signals, a first tube having a detector section, a second tube having a relatively low frequency amplifier section and a diode detector section, a third tube having an amplifying section and an oscillator section, circuits for applying waves from the high frequency amplifier to the detector section of the first tube, circuits for applying waves from the oscillator section of the third tube to the detector section of the first tube, a circuit for applying the resultant relatively low frequency beat to the amplifying section of the second tube, means utilizing the amplified output of the amplifying section of the second tube for monitoring purposes, a circuit for supplying high frequency waves to the diode section of the second tube, a resistor across which voltages are developed by rectifying action of the diode section of the second tube, and circuits for utilizing said voltages to control the amplifying section of the third tube and to automatically volume control said high frequency amplifier, and a utilization circuit coupled to the output terminals of the amplifying section of the third tube.

2. Apparatus as claimed in the preceding claim, and including a voltage dropping resistor in said volume controlling circuit through which a positive voltage is applied in order to partially compensate the voltage developed in said resistor which is included in said diode detector section.

3. Apparatus according to claim 1 and including means for maintaining the grid of the amplifying section of the third tube at substantially zero potential with respect to the cathode, an additional amplifier complemented at least by triode electrodes, means for coupling the plate of said amplifying section in the third tube t0 said additional amplier and means normally effec- Number Name Date tive for applying a plate current cut-off bias to 2,144,244 vKoch Jan. 17, 1939 the grid of said additional amplier. 2,144,304 Braden Jan. 17, 1939 WALTER LYONS. 2,171,657 Klotz Sept. 5, 1939 5 2,196,248 Burnside Apr. 9, 1940 REFERENCES CITED 2,200,049 Van Loon May 7, 1940 The following references are of record in the 2207905 Weaga'nt July 16' 1940 me of this patent: 2,216,582 Barton Oct. 1, 1940 2,239,915 Hunt Apr. 29, 1941 UNITED STATES PATENTS 10 2,259,906 Neustadt` Oct. 21, 1941 u l. 2,281,693 Holst et al May 5, 1942 N mbe Name Date 2,296,921 Green sept. 29, 1942 2,135,599 Peterson Nov. 8, 1938

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