US2141426A - High fidelity receiving system - Google Patents

Description

n Dec. 27,

P. WEATHERS HIGH FIDELITY RECEIVING SYSTEM Filed Aug. 29, 1936 FIL TER lBY INVENTOR Paul Weathers yPatented Dec. 27, *1938 K HIGH FIDELITY RECEIVING SYSTEM Paul Weathers, Audubon, N. J., assignor to Radio Corporation 'of America, a corporation of Delawarel Application August 29, 1936, serial No. 98,435 is claims. (ci. 25o-zo) The present invention yrelates to high fidelity radio receiving systems, and has for .its object to provide an improved receiving system of `that character. It is also an object of the invention to provide an improved control circuit for noisek suppression and automatic'volume controlv which operates to improve the fidelity of the sound output from said receiving system when operating in response to strong carrier waves;

It is a further object of the present invention to provide a superheterodyne receiver having a plurality of intermediate frequency amplifier circuits or amplifying channels, each of which functions to provide a certain operatingcharacter- 1li;k istic, resulting in an over-all improved audio frequency output'characteristic or higher fidelity sound output. f

It is also a further object of the present invention to provide a high fidelity superheterodyne receiving system having three intermediate frequency amplifier channels, all of which conduct the modulated carrier wave and one of which is Y utilized for control purposes, such as automatic volume, noise suppression and fidelity control.

It may also be considered to be an object of the present invention to provide a superheterodyne receiver, wherein the functions of receiving strong modulated carrier waves, the reception of modulated carrier waves of normal strength, and

l the control of the system are provided in separate amplifying channels .associated with the intermediate frequency amplifier.

s Theinvention will Vbe better `understood from the following description when considered in connection with the accompanying' drawing, and its s'copewill4 be pointed out in the appended claims. In the drawing: Y Figure 1 is a schematic circuit diagram of an .intermediate frequency amplifier in a receiving Y 40. system embodying the invention,. and f l quency circuit 5, which may be connected with a first detector (not shown), is coupled through a tuned intermediate frequency input transformer E with an intermediate frequency amplifier tubek 1, in turn coupled through a second intermediate frequency coupling-transformer V8 with a `second detector 9 and an audio frequency amplifier Iii which supplies the loud speaker device II. The amplifying channel described, forms the main amplifyingchannelof the receiving system and represents any suitable sharply tuned intermediate frequency amplifier for a superheterodyne receiver.

The intermediate frequency input transformer IiA comprises a primary winding I2 and a secondary Vwinding I3, each tuned by a capacitor I4 to a predetermined intermediate frequency, and the transformer 8 is similarly tuned to provide a comparatively sharply tuned amplifying channel responsive to a predetermined intermediate frequency.

The primary-circuit, comprising the winding I2 and the capacitor'I, is coupledto a second intermediate frequency signal amplifying channel comprising a first stage amplifier tube I6. The coupling connection'isprovided through a. coupling Vcapacitor I-'I, and a coupling resistor I3 in circuit with the control grid indicated at I9. The connection to the coupling capacitor is made through a lead 20 with a terminal 2l on the tuned input or primary circuit, and the opposite terminal of the circuit, indicated at 22, is connecd through a capacitor 23 vto ground or chassis The cathode ofthe amplifier device I6 is indi-` cated at 25 and is connected through a cathode lead 26 Vto groundV or chassis 21. A series, voltagedrop producing'resistor 28 provided with a loy-V pass capacitor-29 at vintermediate frequencies is connected in series with the 'cathode lead. The cathode'rend of the .resistor I8 is likewise bypassed to the cathode lead 26 through a by-pass capacitor 30.

The remainder of .the'second signal amplifying v channel of which the tube I6 is the first amplifier device,'comprises a detector tube 35 of the diode rectifier type, having a pair of diode anodes 36 associated with a cathode 3'I in conjunction'with Vamplier electrodes 38. The output anode 39 is connected with a tuned circuit 4D and a coupling capacitor 4I to provide coupling with an audio frequency volume control potentiometer 42. The volume control device` is followed lin circuit by an audio frequency amplifier tube 43, coupled to a loud speaker device 44.

lI n the amplifying channel the various cou- CII pling circuits are pro-vided with filter means for improving the audio frequency .amplifying char--v acteristic of the channel, such as in the output circuit of the amplifying portion of the detector l35 a tuned circuit 40 is provided as a couplingr kilocycles, to operate degeneratively in the anode.

circuit, thereby to reduce the audio frequency response sharply at approximatelyftenkilocycles.`

Each of the devices 35'and 43 is provided with suitable sources of bias potential, comprising, in the present example, self-bias Vresistors 53 and 54, provided With by-pass capacitors 55 in connection with the chassis or groundr.'

The sharp amplifying channel first stage amplifier 'I is provided with a control grid 60; which' is connected through an input lead 6| and the Secondary I3, with a bias potential supply lead 63, in which is provideda filter comprising' aA series resistor 64 and by-passcapacitor; 65. The 'amplifier isalso provided witha suitable self-bias resistor 66, providing a connection between theY cathode, indicated at 61, and ground 6B.

A third. amplifyingr channel, comprises" a rst stage intermediate frequency amplifier device having a control grid |I connected togroundl 'I2 through a grid resistorV T3, and coupledV to the highrside 6I of the tunedinput circuit for the tube l, through a coupling'capacitor 'Iibetween the resistorr`|3 and .the lead 6I. The amplifier device 'Ill is provided with a cathode 15, and an outputV anode '|6, and ispreferably of the high gain type as indicated. In the `present example, like the other amplifier tubes it' is represented-as a pentode amplifiery device.

The cathode 'I5` is connected to ground 'H- through a self-bias resistor 18; 'Ihe amplifier device 'I8 is followed Vin* circuit in the amplifying channel by a control tube 89'having a plurality of functions, and in the present example including a cathode 8|, a pair of` anode electrodes 82 and 83 associated therewith as diode rectifier anod'es, a control grid 84, and amain output anode 85, whereby thertube comprises a suitable amplifier and a double diode rectifier. Y

The device 'functions as a-:combined diode-A signal biased amplifler and as an'automatic. vol'` ume control rectifier, and is coupled'to" the pre`` ceding intermediate frequency amplifier deviceV 'I8 through the primary winding 88 andathevsecondary winding 89 of an intermediate. frequency coupling transformer 9D. The primary windingis located in the output anode circuit' 9|V of the amplifier device '|01 and is coupled. atV itsv anode end through a lead 92 and a coupling capacitor. 93 with the diode anode 83 which' operates as a shunt connected automatic volume control diode.` in conjunction with the cathode 8|. The' diode output resistor for the diode-anodeV 83:'isindicated at 94, 95 and 96 comprising three 'resistor' sections in series between the diode anode 83"andf ground indicated at 91. The sections- 95V andV 963 are provided with suitable by-passcapacitors 98.

From the ground 9?-, the diode output Vcircuit is completed through the ground 2-1, the cathode resistor 28 of the first stage amplifier I6`in the broad channel, and a connecting return-lead-v |00- to the cathode 8| whereby the cathode resistor 28 is included in the output circuit.l The resultingv automatic volume-control potential derived from the resistors 94, 95'and 96 is takenfroma tappoint IDI between the resistor sections 95 and 96 through a lead |02 tothe bias supply terminal end |03 of the grid resistor I8 whereby the biasing potentials from the automatic volume control diode 83 are applied to the control grid I9.

Since the diode 83 is coupled directly to the primary winding 88 which is tuned more broadly than the secondary, Ythe automatic volume control response is broader than that of the main amplifying channel and'serves to reduce the response in the broad channel in the presence of received adjacent channel signals. Automatic volume controlpotentials are also applied to the first stage amplifier I of the sharp channel through the' bias supply lead 63 which is connectedl with the tap'point IllI. It may also selectively be connected with a higher negative voltagertapspointl Iithrough a suitable selectorswitch |051 as indicated.

The normal anode current flow through the resistor 28 of the rst amplifier stagev I6 of the broad channel is sufficiently large with Vrespect to the rectified signal current from the diode 83', that the main` control potential is derived from the resistor section 96 for controlling, the grid I9` of` the intermediate frequency amplifier I6 after ,the`

gain of the broad channel and of the sharpfchan-A nel is controlled by the automatic volume-control means,.in such mannerl that the gain variesinversely with the carrier Wave strength. This is particularly true for the relatively strong carrier Waves which would cause overloading ofthe receiving system anddistortion in the output system. f

For normal carrier wave amplitudes, however,

the Vautomatic volume control Vmeans, comprisingY the diode rectierV 83, operates'to reduce the gain' as thecarrier wave strength increases, thereby reducing the signal output, through the sharp channel;r For relatively WeakA signals orlow carrier Wave strength, the broad channelis cut off or prevented from operatingto transmit signals to the output device, thus eliminating noises and interference when receiving weak signals.

The meansprovided forsuppressing the broad signal comprisesfthe second diode anode 82 which is connected across the tuned circuit comprising the secondary 89, and is provided with a diode output resistor III) across which is connected an intermediate frequency by--passl capacitor III. Thediode. circuit 89:"for the diode82 is, therefore, much more sharply responsive than thev automatic volume control circuit which is connectedV with the primary 88.

The direct current biasing potentials derived from received'signals andappearing in the diode output resistor I IIJ, are appliedY to the controlj grid .84 through a lead I VI 2 having a movable con-- tact I I3 in connection with the resistor I I 6. The grid 84 is, therefore, diode signal-biased and, in response to increasing signal strength or carrier wavestrength, receives an increasing negative lpolarities as indicated, and is supplied to the anode 85 through a vseries variable resistor II5. The anode circuit is completed through ground connection I0 and ground connection 21, resistor 28, and lead I 00, thereby returning to the cathode 8|.

It will be seen that the anode current from the device 80 is caused to flow through the cathode resistor 28 in the amplifier I6 for the broad channel, and the current flow is in such direction that the potential across the resistor 28 has a polarity as indicated, conforming to the flow of anode current in the device I6.

The grid I9 of the intermediate frequency amplierdevice I6 in the broad channel, receives the biasing potential set up in the, resistor 28, through the ground connection 21, thence to the resistor .98, through the lead |02, and the grid resistor I8.

It will be seen that, in response to increase in the signal strength which causesv a reduction in the anode potential through the anode 85, Vthe potential drop through the resistor 28 is reduced, thereby reducing the negative biasing potential on the grid I9 and, at a predetermined point determined by the biasing potential, permitting the broad-channel to operate to receive signals to be amplified.

As the carrier wave amplitude further increases, the gain of the broad channel amplifier will thus further increase and, up to a certain point where the automatic volume control potential'from the anode 83 becomes effective, the gain of the high frequencyv or broad channel varies directly with the carrier wave strength.`

By varying the resistor I|5 in relation to the resistor 28, the voltage drop in the anode circuit may be proportioned to permit the broad channel to function at any predetermined, desired signal strength.

The adjustment of potentiometer I|3 toward positive end causes less rectified signal voltage to reach grid 84 which increases the plate current of tube 80 for a given intermediate frequency l voltage which, in turn, reduces the gain of pentode Y I 6 by Virtue of the increased current through v resistance which confines all of the external volt-v age drop due to the plate current of tube 80 to the cathode resistor 28, to some high value of resistance which causes more of the external voltage drop to Aoccur in resistor |I5. Thus the ap- Vproach to the operating condition of pentode I6 may be made gradual or abrupt by suitable adjustment of resistor II5. f

If it is desired to utilize a single audio frequency channel for receiving the output 'of the two signal amplifying channels, the same may be arranged as Shown in Fig. 2, to which attention is now directed.

Referring to Fig. 2, only the second detectors, |20 for the sharp channel, and |2| for the broad channel, are shown in the system. Each detector receives intermediate frequency signals through an input circuit.

In connection with the detector |`2|, Van inputV circuit |22 is shown, and in connection with the detector |20 an input circuit |23 is provided. The circuit |22 and the .broad amplifying channel which it represents, are adapted to pass signals having an audio frequency fidelity up to 800i) cycles, and the sharp channel, represented by the circuit |23, is adapted to pass signals having an audio frequency fidelity up to 4500 cycles.

The sharp channel is, therefore, used for receiving signals from weak or distant signal sources, while the channel |22 responds to local or strong signals for higher fidelity operation under control of a suitable third channel, in the manner and as described in connection with Fig. l. As this does not concern the mixing system shown in Fig. 2, and is fully described in connection with Fig. 1, the drawing has been simplified bythe omission of the control system.

The detectors |20 and |2| may be of any suitable'type, and in thepresent example are in the form of diode rectiflers of the double diode, full wave type, the diode output resistors being indicated at |24 and |25 for the detectors|2| and |20, respectively, and coupled `to control grids |26 for the amplifying portions of the detectors for applying to the output circuits |21 and |28 the audio frequency signals rectied in the detectors.

'Ihe output lead |21 for theV broad channel is coupled through a coupling capacitor |29 with a high frequencyv filter |30, which is adapted to remove any ten kilocycle beat note, and the filter is followed by a suitable audio frequency amplifier |3| and loudspeaker device |32. In the absenceofa strong carrier wave suflicient to put into operation the broad channel |22, the sharp channel |23 is adapted to deliver audio frequency signals, throughthe output circuit |28, to an output lead |33 which is connected with the lead |21,

whereby both channels may jointly operate to supply audio frequency signals thereto, at .the junction point indicated at |34. Y

For the purpose of causing the amplifier channels to accentuate or compensate certain portions of the audio frequency range, suitable flltersare included in the detector output circuits, which may be described as follows: f

-In the broad channel |22, following the detector, a 7500 cycle filter |35 is included in the cathode lead |36 of the detector |2I, and serves to accentuate the audio frequency range in the high frequency end thereof, to compensate for wide band cutting in the tunning system. Like- Wise, in the output circuit and connected in the lead |33, is a similar filterv |31 which is broadly responsive to 7500 cycles, to further accentuate the high frequency end of the audio frequency range, while the upper limit thereof is sharply cut off by the high frequency filter |30. By this arrangement, thei broad channel |22 provides high audio frequency fidelity and a vdesirable high frequency response up to the limit permissible because of inter-channel interference. I

In the main amplifier channel, or sharp channel |23, the cathode lead of the rdetector |20 is indicated at `|38 and includes a pair of tuned filters |39 and |40, which are tuned, respectively, to l0 kilocycles and 4.500 cycles, the former to cut off. Y

|31 is also in-fseries withthe. lead; |33 from'ltheY sharp channel and `interposed between thez sharp.

channel detector and the audio frequency'output circuit |21, whereby audio. frequency signals in'l the range of the lter |31, forexample about 7500:

bination, a mainsignal amplifying channel and;

two additional signal amplifying channels, one only of said. additional amplifyingV channelsincluding means providing variable gain control potentials forV the other amplifying channels in response to variations in carrier wave amplitude, certain of said amplifying channels including means wherebyV the frequency responseY characteristic of said channels are altered;

2. A superheterodyne radio receiving system having an intermediate frequency amplifier comprisingv a main signal amplifying channel and two additional signal amplifying channels, one only of said` additional signal amplifying channels including meansV providing variable gain control potentials for the other amplifying channels in response to-variations in carrier'wave amplitude, and means in the other of said additional` signal amplifying channels andV the main signal amplifying channel for imparting thereto differing frequency response characteristics.

3. A radioreceivingsystem in accordance with claim 1, further characterized byY the fact thatV means are provided in' connection with the' variable gain control potentialsupply channel and in connection with the other amplifying channels, whereby the. gain' of. one ofthe additional amplifying channelsvarieswithin predetermined' limits directly with variations in the strength ofr a receivedi carrier wave and the gainof the main 4. A radio receivingsystem comprising in com-- bination, a main signal amplifying channel and two additionalsignal amplifying, channels, one

of said additional amplifying channels including means providing variable gain.A control potentials for the other amplifying channels in response to variations in. carrier wave amplitude, and oneV of said last named amplifying channels including means forr passing modulation frequencies in a wider frequency range than the mainv signal'amplifying channel, and means foi'r applying said control potentials to said widerfrequency range and main amplifying channels to control the gain thereth'roughin opposite sense.

5. A superheterodyne receiving system, as definedby claim 4,1 furthercharacterized in that-it includes means Yproviding a common audio frequency amplifier, an output circuit for the broadto attenuate high frequencyA signalstherefrom and `iszinfshunt relationfto the'broadly responsive signal.amplifyingchannel Wherebyit operates to accentuate the high frequency response therefrom.' Y

6; A. superheterodyne radio receiving system comprising in combination, means providing intermediate frequency signals in response to a receivedmodulated carrier wave,.intermediate frequency amplifier means broadly responsive to said signals, intermediate frequency amplifier means more sharply responsive to said signals, a third intermediatefrequencyamplifier means for said signals, andmeans providing gain controlling potentials for vsaid rst'and secondnamed amplifier means. connected with said third amplifier to receive amplified signals therefrom.

7; Asuperheterodyne radio receiving-system in accordance with claim 6, further characterized by theV fact that the broadly responsive amplifying .means includesfan electric discharge amplifying device having a control grid and a cathode, a biasing resistor in circuit between the control grid and the cathode, and that the gain controlling potential supply means includes an amplifier device responsive to carrier wave amplitude having an output anode circuit including a control resistor and said biasing resistor, thereby to vary theV gain in the broadly responsive amplifying means directlyfin accordance with carrier wave strength.

8. In a superheterodyne receiving system, the combination of an intermediate frequency amplier providing three signal amplifying channels connected in parallel relation to eachother, common meansfor supplying intermediate frequency signals to said amplifyingchannels, means in two ofA said-amplifying channels for'varyirig the gainV of"saidV channels in response to variations in control potentials applied thereto, means connected with a thirdcliannel for deriving said control potentials from signals amplied therein, and

Vmeansfor` applying said'control potentials to said two amplifying channels in opposite sense whereby the gain in one channel varies directly with signal strength and the gain in the other channel varies inversely with signal strength.

9. In asuperheterodyne receiver, the combination .of means providing a plurality of intermedia-te frequency signal amplifying'channels, sound output means connected with each of said channels, means for impartingto one ofsaid channels a higher degreeV of audio frequency fidelity than another. of said channels, and control'means cori-Y nected with a third of said amplifying channels for controlling the first and second namedY chann'els.` to provide an over-all uniform audio frequency output characteristic for Vhigh fidelity operationin response to" carrierv waves having a predetermined'. high amplitude.

l0. A high fidelity superheterodyne receiver having three intermediate frequency amplifier channels, means in each of said channels for amplifying. a modulatedintermediate frequency carrier wave, demodulating means for said signals in connection with two .of said amplifying channels, and means in connection with' the third offsaid amplifying channels only for deriving from an amplified carrier wave gain control potentials for the first and second named amplifying channels.

l1. A highfidelity superheterodyne` receiver having three intermediate frequency amplifier channels, means in each of sa-id channels for amplifying a modulated intermediate frequency carrier wave, demodulating meansA for said signals in connection with two of said amplifying channels, means in connection with the third of said amplifying channels for deriving from an amplified carrier wave, gain control potentials Yfo-r the first and second namedamplifying channels,

l2. In a radio receiving system, means provid-I ing a plurality of modulated carrier wave amplifying channels, means in one of said amplifying channels providing .a high degree of fidelity in response to a received modulated carrier wave, means in another of said channels providing a lesser degree of fidelity in response to said carrier wave, means in a third channel providing automatic volume and suppressor control potentials in response to said carrier wave, means for applying said automatic volume control potentials to the second named amplifying channel, means for applying said suppressor potentials to the first named amplifying channel, and means for adjusting the operation of said potential supply means whereby the first named amplifying channel operates in response to received signals having a predetermined high amplitude.

13. A superheterodyne radio receiving system comprising, in combination, an intermediate frequency amplifier providing three signal amplify-VV ing channels in parallel relation to each other, demodulator means terminating each of said amplifying channels, an audio frequency amplifier for demodulated signals connected with two of said channels for receiving theaudio frequency output therefrom, said channels having differing frequency response characteristics, an amplier tube connected with the demodulator of a third channel for receiving a biasing potential therefrom, said last named demodulator including a diode signal rectifier and an output resistor for said rectifier, means providing a variable bias ,potential supply connection for said control grid with said resistor, means connected with said third channel for deriving a Ycontrolling potential responsive to variations in the strength of received carrier waves for one of said signal amplifying channels, an electric discharge amplifier device in another of said signal amplifying channels having a cathode, a resistor in series with said cathode, and means for causing anode current from said first named amplifier device to flow through said cathode resistor, thereby to provide a suppressor control potential for the channel in which said electric discharge amplifier is connected.

14. A superheterodyne radio receiving system as defined in claim 13, further including means for causing the gain in the amplifying channel in which said last named electric discharge amplifier device is connected to vary directly with variations in carrier wave strength and the gain of said one of said amplifying channels to vary inversely with variations in carrier wave strength.

15. A superheterodyne radio receiving system comprising in combination, an intermediate frequency amplifier providing three signal amplifying channels in parallel relation to each other, means connected with one of said channels for controlling the gain inthe other two channels,

. demodulating means terminating said other two amplifying channels, anaudio frequency amplifier for demodulated signals connected with each of said last named channels for'receiving the audio frequency output therefrom, high frequency filter means connected in series between one of said demodulators and the audio frequency kamplifier for attenuating high frequency signals from said one of said demodulators, and said filter being connected in parallel relation to output circuitofl the other" of said demodulators in connection with said audio frequency amplifier, to accentuate the high frequency response of signals from said other demodulator.

16. A superheterodyne receiving system including in combination, means providing an intermediate frequency amplifying channel having a relatively broad frequency response characteristic, means providing a second intermediate frequency amplifying channel having a relatively sharp frequency response characteristic for passl ing audio frequency signals in a frequency range substantially lower than the frequency range of the first named channel, means providing a third intermediate frequency amplifying channel,

' broadly responsive automatic volume control means in said last named channel connected with the secondy amplifying channel to provide a controlling potential therefor whereby the gain.

varies inversely with variations in carrier wave strengthVand more sharply responsive means providing in connection with said third channel a diode signal-biased amplifier having an anode output circuit including a bias control resistor in the first named amplifying channel for varying the gain thereof directly with variations in carrier wave strength.

17. A superheterodyne receiving system including in combination, means providing an intermediate frequency amplifying channel having a relatively broad frequency response character- 'istic, means therein for effecting an audio frequency response throughout a frequency range uniformly below substantially ten kilocycles, means providing a second intermediate frequency amplifying channel having a relatively sharp frequency response characteristic for passing audio frequency signals in a frequency range substantially lower than the frequency range of the first named channel,.means providing a third intermediate frequency amplifying channel, broadly responsive automatic volume control means in said last named channel connected with the second amplifying channel tol provide a controlling potential therefor whereby the gain varies inversely with variations in carrier wave strength, means providing in connection with said third channel a diode signal biased amplifier having an anode output circuit including a bias control resistor in the first named amplifying channel, and sharply tuned transformer means having a tuned secondary for applying signals to said diode-biased amplifier to control the anode current thereof, thereby to vary the gain of the first named amplifying channel directly with carrier wave strength.

18. A superheterodyne receiving system including in combination, means providing an intermediate frequency amplifying channel having a relatively broad frequency response characteristic, means providinga second intermediate frequency amplifying channel having a relatively sharp frequency response characteristic for passing audio frequency signals in a frequency range substantially lower than the frequency range of the first named channel, means providing a third intermediate frequency amplifying channel,

for varying the gain. thereof directly With variations in carrier Wave strength, means for varying the diode bias potential on said amplifier,- and means including asecond resistor in said anode circuit for proportioning the potential drop in 5 said bias control resistor With vrespect to the potential drop through said anode circuit.

PAUL WEATHERS.

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