US2250862A - Combination amplitude-modulationfrequency-modulation receiver - Google Patents

Description

y 1941. .1. F. FARRINGQTON 2,250,862

COMBINAT ION AMPLITUDE-MODULATION- FREQUENGY-MODULAT I ON RECEIVER Filed July 16, 1940 V AL I0 vvvv INVENTOR J HN F. FARRINGTON ATTORNEY Patented July 29, 1941 COMBINATION ANNE-MODULATION- FBEQUENCY-MODULATION RECEIVER John F..Farrington, wom n. 11., minor to Hazeltine Corporation, a corporation of Delaware .11 Claims.

' This invention relates generally to modulated- Application July 16, 1940, Serial No. 345,726

carrier signal receivers for receiving and repro-- ducing both amplitude-modulated and frequen- -cy-modulated carrier signals and. particularly,

to such a receiver in which a single carrier-' frequency signal-translatingstage is utilized as a limiter when receiving a frequency-modulated signal and as an amplitude-modulation detector when receiving an amplitude-modulated signal.

Certain units of a modulated-carrier wave-signal receiver for receiving an amplitude-modulated signal are identical with, or very similar to, corresponding unitsof a receiver for receiving and reproducing a-frequency-modulated carrier signal. It has previously been proposed to usecertain of suchunits as common elementsin a combined amplitude-modulation and frequency-modulation receiver. However, the circuits which have heretofore been used are somewhat more complicated or less satisfactory in operation than is desired. Certainreceivers for receiving a frequency-modulated carrier wave require a separate stage in the signal-translating channel of the receiver, the function of which is to limit the translated signal to eliminate therefrom any amplitude-modulation components and amplitude variations. However, if parts ofa frequency-modulation receiver circuit are to'be used also in the circuit of an amplitude-modulation receiver in which alimiting action is not,

as an amplitude limiter over a given carrier-.

1 wave corresponding to a signal within the given tolerable, the limiter stage of the frequencymodulation receiver is generally used simply'as a carrier-frequency amplifier in the circuit of the amplitude-modulation receiver. However. sufficient carrier-frequency amplification for all purposes must also be provided for the frequencymodulation receiver circuit so that the additional amplification provided by using the limiter stage as an amplifier in the circuit of the amplitudemodulation receiver really serves no useful purpose. Furthermore, a different type of detector circuit is required in a frequency-modulation receiver than in an amplitude-modulation receiver. Therefore, it is very desirable to be able to use the limiter stageof a frequency-modulation receiver as an amplitude detector in an amplitude-modulation receiver.

It is an object of the invention, therefore, to providean improved receiver circuit for receiving either an amplitude-modulated carrier wave or a frequency-modulated carrier wave in which one ormore -of the above-mentioned disadvantages of prior art circuits are eliminated.

I It is still anotherobject of the invention to provide a combination amplitude-modulation- 551i and 32, respectively, to either the frequencyfrequency modulation receiver in which a single carrier-frequency signal-translating stage serves as a limiter when the apparatus is being utilized to receive a frequency-modulated carrier signal and as an amplitude detector when the apparatus is being utilized to receive an amplitudemodulated signal.

In accordance with the invention, a modulatedcarrier wave-signal receiver comprises a carrierirequency signal-translating stage and means included in the stage for causing the stage to act frequency range, so that amplitude modulation is removed from translated signals within'the given carrier-frequency range. Means are also included in the stage for causing the stage to act as 'an amplitude-modulation detector over the above-mentioned carrier-frequency range. a

Means are further provided for selectively utilizing a first signal output from the stage to reproduce a received frequency-modulated carrier frequency range or a second signal output from the stage to reproduce a received amplitudemodulated carrier wave corresponding to a signal within the given frequency range. For a better understanding. of 'the invention,

together with other and further objects thereof,

reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims;

The single figure of the drawing represents a modulated-carrier wave-signal receiver of the superheterodyne type for receiving either an amplitude-i'nodulated carrier signal are. frequency ing, the system illustrated comprises a receiver modulated carrier signal.

Referring now more particularly to the drawof the superheterodyne type including an antenna circuit H), II connected to a radio-frequency amplifier l 2 to which are connected in cascade, in the order named, an oscillator-modulator l3, an intermediate-frequency amplifier l4, and a carrier-frequency signal-translating stage 15 which acts as a limiter when frequency-modulated carrier signals are being received and which acts as an amplitude-modulation detector when amplitude-modulated carrier signals are being received. A frequency-modulation detector I6 is coupled to one output circuit of carrier-frequency signal-translating stage l5, while an audio-frequency amplifier ll is selectively connected, by means 101 a switch It and coupling condensers modulation detector I. or to an output circuit of carrier-frequency signal-translating stage II for receiving detected amplitude-modulation components of adesired received signal. A signal-reproducing device I. is coupled to the output circuit of audio-frequency amplifier II. It will be understood that frequency-modulation detector I. may be of a conventional type and, as shown, is of the type comprising a transformer having a primary winding 20,'tuned to the mean frequency of the intermediate-frequency channel of the receiver by a condenser 2|, and a secondary winding 22, also tuned to the mean frequency of the intermediate-frequency channel of the receiver by a condenser 23. Damping is provided in the tuned primary winding of transformer 20, 22 by means of a resistor 20'. Diodes 24, 25 are provided having load circuits therefor including resistors 26 and 21, by-passed for carrier-frequency currents by a condenser 28. In order to supply a voltage proportional to the vector sum of the voltages of the primary and secondary windings of transformers 2|, 22 to one of the diodes and to provide a voltage proportional to the vector difierence of the voltagm of the primary and secondary windings to the other of the diodes, a coupling condenser 29 is coupled between one side i of winding 20 and a mid-tap on winding 22, while the mid-tap of winding 22 is coupled to the com mon junction of resistors 26 and 21'. Automatic frequency control potentials are derived from frequency detector I 6 and applied by means of the conductor designated AFC -to an automatic frequency control unit 30 which is coupled to oscillator-modulator I3 to control the frequency of the oscillator section thereof in a manner well understood in the art.

The stages or units I to I4, It to I8 and 30 may all be of conventional well-known construction so that detailed illustration and description thereof are deemed unnecessary herein. Refer ring briefiy, however, to the operation of the system described above, a desired received carrier signal, which may be either frequency-modulated or amplitude-modulated, is intercepted by antenna circuit III, II and is selected and amplifled in radio-frequency amplifier I2 and coupled to the oscillator-modulator I3 wherein it is converted into an intermediate-frequency signal which, in turn, is selectively amplified in the intermediate-frequency amplifier I 4 and coupled to the carrier-frequency signal-translating stage I5. If the desired received signal is a frequencymodulated carrier signal, the switch I9 is thrown so that audio-frequency amplifier I1 is connected to an output circuit of frequency-modulation detector I6. The desired intermediate-frequency signals are, therefore, limited in carrier-frequency signal-translating stage I5 and detected in frequency-modulation detector I6, the detected components thereof being supplied through audiofrequency amplifier I! to signal reproducer I8 for reproduction.

If the desired received signal is an amplitudemodulated carrier signal, the switch I9 is thrown so that audio-frequency amplifier I1 is coupled to carrier-frequency signal-translating stage I5 in order to supply to audio-frequency amplifier I I the desired amplitude-modulation components for reproduction.

In either case a voltage varying in accordance with the degree of mistuning of the receiver is derived from unit I 6 and applied to-t'he automatic frequency control unit 30 over the conductor labeled A. F. C. to control the tuning of the receiver in a manner which is, per so, well understood by those skilled in the art.

Coming now to the portion of the system embodylng an essential feature of the present invention, there is included in the carrier-frequency signal-translating stage I5 a vacuum tube 35, the circuit of which includes means for causing the stage to act as an amplitude limiter over a given carrier-frequency range so that amplitude modulation is removed from translated signals within a given carrier-frequency range. Means are also included for causing the stage to act as an amplitude-modulation detector over the given carrier-frequency range. To this end, input circuit of vacuum tube 35 includes a parallel-resonant circuit comprising an inductance 36 inductively coupled to an inductance 31 which is, in turn, coupled to the output terminals of intermediate-frequency amplifier II. The secondary winding 38 of the transformer 31, 38 is tuned to the intermediate-carrier frequency of the receiver by means of a condenser 38, the tuned circuit being damped by a resistor 36'.

In order to cause the input circuit of tube 35 to act as an amplitude-modulation detector, there is provided in series with tuned circuit 36, 38 a suitable load circuit including a resistor 39 and a resistor 40 by-passed for carrier-frequency currents by condensers II and 42. The output circuit of tube 35 comprises tuned circuit 20, 2| of frequency-modulation detector I6. The unidirectional voltage developed across resistor III is applied through a suitable audio-frequency filter, including a series resistor 43 and a shunt condenser and the conductor labeled AVC, to one or more tubes of radio-frequency amplifier I2, the oscillator-modulator II, and intermediatefrequency amplifier II to maintain the amplitude of the signal input to stage I5 within a relatively narrow range for a wide range of received signal amplitudes. Resistor 39 and condenser 42 are proportioned to have a suitable time-constant and the screen grid of tube 35 is maintained at a relatively low potential so that a quickly-responsive limiting action is effected in signals translated to the anode circuit of tube 35.

In considering the operation of the portion of the circuit Just described, it will be seen that resistor 40 forms a suitable load circuit so that amplitude-modulation components of the received carrier signal are detected in the input circuit of tube 35. Specifically the input circuit of tube" acts as a diode detector, the intermediate-frequency signals of the receiver being applied thereto through tuned circuit 36, 38 and amplitude-modulation components of the signal being derived across resistor 40. Elements 3! and ll effectively comprise a carrier-frequency filter which aids in eliminating carrier-frequency signals from the output to condenser I2 or to the AVG circuit. Therefore, switch I9 is included in a means for selectively utilizing a first signal output from stage I5, derived through frequencymodulation detector I 6, to reproduce a received frequency-modulated carrier wave corresponding to a signal within a given frequency range, or for utilizing a second signal output from the stage, derived from load circuit 40, II, to reproduce a received amplitude-modulated carrier signal corresponding to a signal within the given frequency range. When operating as a frequency-modulation receiver the elements I9, 42 efiectively comprise a fast time-constant circuit so that the grid of tubeIll,,-ln addition to the usual limiting action thereo provided by thetime-constant circuit in r cluding elements to, 4 l is made substantially less responsive to higher-frequency components such as noise components. 7

While it is not intended to limit the circuit of the invention to any particular circuit values,

there follows a list of circuit values whicli'have been found to be particularly efiective in the circuit of Fig. 1. a

Tube as Type 6831 Condenser 4| 400 micro-microfarads Condenser 42 50 micro-microfarads Condenser l4 0.02 microfarad I Resistor 38 50kilohms. Resistor 40---. 250 kilohms Resistor l3 1 megohm Resistor 36' lrilohms Resistor 20' 20 kilohms Tuned circuits 36-38, 20,

2|,and 22, 23 Tuned to a frequency of 2900 kilocycle's I While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and amplitude modulation is removed from translated signals-within said given carrier-frequency range, means for detecting amplitude-modulation components in said input circuit and for deriving a signal output therefrom, and means for selectively utilizing a signal output from said output circuit to reproduce a received frequency-modulated carrier wave corresponding to a signal within said given frequency range or said detected amplitude-modulation components to reproduce a received amplitude-modulated carrier wave corresponding to a signal within said given fre-' quency range.

4. A modulated-carrier wave-signal receiver comprising, a carrier-frequency signal-translating stage including a vacuum tube having input and output circuits, means included in said stage forv causing said stage to act as anamplitude limiter over a given carrier-frequency range so that amplitude modulation is removed from translated signals within said given carrier-ire quency range,- means comprising a tuned'circuit and a time-constant circuitin said input circuit for detecting amplitude-modulation components and for deriving a signal output therefrom, and

modifications as fall within the true spirit and;

scope of the invention.

What is claimed is:

1. A- modulated-carrier wave-signal receiver comprising, a carrier-frequency signal-translating stage, means included in said stage for causing said stage to act as an amplitude limiter over a given carrier-frequency range so that amplitude 'modulation is removed from translated signals within said given carrier-frequency range, means included in said stage for causing said stage to' act as an amplitude-modulation detector over.

said given carrier-frequency range, and means a given carrier-frequency range so that amplitude modulation is removed from translated sigmeans for selectively utilizing a signal output from said output circuitto reproduce a received frequency-modulated carrier wave corresponding to a signal within said given frequency range, or said detected amplitude-modulation components to reproduce a received amplitude-modulated carrier wave corresponding to a signal within said given frequency range.

5. A modulated-carrier wave-signal .receiver comprising, a carrier-frequency signal-translat- ,ing stage'including a vacuum tube having input and output circuits, means including a tuned circuit and a time-c'onstant circuit for'causing said stage to, act as an amplitude limiter over nals within said carrier-frequency range, means included in-said stage for'causlng said stage to act as an amplitude detector over said givencar- '-rier-frequency range, andmeans for selectively utilizing a first signal output from. said stage 'to reproduce a received frequency-modulated carrier wave corresponding to a signal within said .given frequency range, or amplitude-modulation componentsderived from said stage to reproduce and output circuits, means included in said stage for causing said stage to'act as an amplitude limiter over a given carrier-frequency range so that amplitude modulation is removed from translated signals within said given carrier-frequency range, means included in said stage for causing said stage to act as an amplitude-modulation detector over said given carrier-frequency range, and means for selectively utilizing a signal output from said output circuit to reproduce a received frequency-modulated carrier wave corresponding to a signal within said given frequency range, or

a signal output fromsaid input circuit to reproduce a received amplitude-modulated carrier wave corresponding to a signal within said given frequency range.

3. A modulated-carrier wave-signal. receiver comprising, a carrier-frequency signal-translating stage including a vacuum tube having input a received amplitude-modulated 'carrier wave corresponding to a signal within said. given fre- I quen'cy range.

6. A modulated-carrier wave-signal receiver comprising, a carrier-frequency signal-translating stage including a vacuum tube having input and output circuits, means including is. tuned circuit-and a time-constant circuit in said input circuit for causing said stage to act as an amplitude limiter over a given carrier-frequency range so that amplitude modulation is removed from translated signals within said given carrier frequency range, means included in said stage and including said tuned circuit and said timeconstant circuit for causing said stage to act as an amplitude detector over said given carrier- I frequency range,and means for selectively utilizing aflrst signal output from said stage to reproduce a received frequency-modulated carrier wave corresponding to a signal within said given 7 frequencyrange, or the amplitude-modulation components developed in said time-constant cirand output circuits, means included in said stage cuit to reproduce a received amplitude-modufor causing saidstage to-act as an amplitude Jim-'- iter over a given carrier-frequency range so that lated carrier wave corresponding to a signal within said given frequency range.

, 7. A modulated-carrier wave-signal receiver comprising, a carrier-frequency signal-translat-' ing stage including a vacuumtube having input and output circuits, means including a tuned circuit and a time-constant circuit in said input circuit for causing said stage to act as an amplitude limiter over a given carrier-frequency range so that amplitude modulation is removed from translated signals within said given carrier-frequency range, means included in said stage and including said tuned circuit and said time-constant circuitfor causing said stage to act as an amplitude detector over said given carrier-frequency range, means ior selectively utilizing a first signal output from said stage to reproduce a received frequency-modulated carrier wavesponsive to higher-frequency modulation components when the receiver is acting. as a frequency-modulation receiver.

8. A modulated-carrier wave-signal receiver comprising, a carrier-frequency signal-translating stage including a vacuum tube having an input circuit and an'output circuit, means included in said stage for causing said stage to act as an amplitude limiter over a given carrier-frequency range so that amplitude modulation is removed from translated signals within said given carrierirequency range, means included in said stage for causing said stage to act as an amplitude-modulation detector over said given carrier-frequency range, means included in said input circuit for deriving an automatic amplification control voltage for said receiver, and means for selectively utilizing a first signal output from said stage to reproduce a received frequency-modulated carrier wave corresponding to a signal within said given frequency range, or a second signal output from said stage to reproduce a received amplitudemodulated carrier wave corresponding to a signal within said given frequency range.

9. A modulated-carrier wave-signal receiver comprising, a carrier-frequency signal-translating stage, a frequency-modulation detector coupled to said stage, means included in said stage for causing said stage to act as an amplitude limiter over a. given carrier-frequency range so that amplitude modulation is removed from translated signals within said given carrier-frequency range, means included in said stage for causing said stage to act as an amplitude-modulation detector over said given carrier-frequency range, and means for selectively utilizing a first signal output derived from said stage through said frequency-modulation detector to reproduce a received frequency-modulated carrier wave cor-. responding to a signal within said given frequency range, or a second signal output from said stage to reproduce a received amplitude-modulated carrier wave corresponding to a signal within said given frequency range.

10. A modulated-carrier wave-signal receiver comprising, a carrier-frequency signal-translating stage, a frequency-modulation detector coupled to said stage, means included in said stage for causing said stage to act 'as an amplitude limiter over a given carrier-frequency range so that amplitude modulation is removed from translated signals within said given carrier-irequency range, means included in said stage for causing said stage to' act as an amplitude-modulation detector over said given carrier-frequency range, means for deriving a voltage from said frequency-modulation detector to provide an automatic-frequency control for said receiver, and means for selectively utilizing a first signal output derived from said stage through said frequency-modulation detector to reproduce a received frequency-modulated carrier wave corresponding to a signal within said given frequency range, or a second signal output from said stage to reproduce a received amplitude-modulated carrier wave corresponding to a signal within said given frequency range.

11. A modulated-carrier wave-signal receiver comprising, a carrier-frequency signal-translating stage, means included in said stage for causing said stage to act as an amplitude limiter over a given carrier-frequency range so that amplitude modulation is removed from translated signals within said given carrier-frequency range, means included in said stage for causing said stage to act as an amplitude-modulation detector over said given carrier-frequency range, a signal reproducer, and means for selectively deriving a first signal output from said stage and applying it to said signal reproduced to reproduce a received frequency-modulated carrier wave corresponding to a signal within said given frequency range, or a second signal output from said stage and applying it to said signal reproducer to reproduce a received amplitude-modulated carrier wave corresponding to a signal within said given frequency range, said last-named means comprising means for disconnecting the circuit for translating each of said signal outputs to said signalreproducer during the time when the other of said signal outputs is being supplied to said signalreproducer.

JOHN F. FARRINGTON.

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