US2408644A - Combined amplitude-modulation and frequency-modulation receiver stage - Google Patents

Description

Oct. l; 1946. J. W.'HUFF 2,408,644

COMBINED MPLITUD'E-MODULATION AND FREQUENCY-MODULTION RECEIVER STAGE I v Filed'Jply 24, 1944 I E9n/.7% @mf/17W ATTORNEYS Patented Oct. 1, 1946 man CORIBINED ANIPLITUDE-MODULATION AND y FREQUENCY MODULATION RECEIVER STAGE John W. H ul, Chicago, Ill., assigner, by mesne assignments, to Belmont RadiofCorporation, Chicago, Ill., a corporation of vIllinois Application July 24, 1944,. Serial No. 546,298

Y 1 y A This invention relates to combined amplitudemodulation and frequency-modulation receiver stages and to a receiver embodying the same and particularly to a receiver of the type designed with a view to maximum simplicity for marketing in the lower price ranges.

In the prior art receivers designed for the reception of the standard broadcast band of approximately 500-1500 kilocycles and the frequency-modulation band of 41-50 megacycles, it has been the practice to provide an amplitude-modulation signal-transmitting channel including a diode amplitude-modulation detector, a frequency-m'odulationV signal-translating channel, at

least in part distinct from the amplitude-modulation channel and including one or more limiters followed by a frequency discriminator or detector, and an'audio-frequency system selectively energized fromk the amplitude-modulation channel or the frequency-modulation channel. This use of distinct amplitude-modulation and frequency-modulation channels increases` the complexity and cost oi the receiver and has limited the lower price ranges within which thisy Atype of receiver could be marketed.

` It is an object of the invention, therefore, to provide a new and improved combined amplitudemodulation and frequency-modulation receiver stage for selectively effecting detection of a received amplitude-modulation signal or acting as ajlimiter for areceived frequency-modulation` signal.

It is another` object of the invention to provide an improvedl receiver adapted selectively to receive amplitude-modulated signals or frequencymodulated'signals and including a combined am- In accordance with the invention, in a wave- 'i signal receiver4 adapted selectively to receive amplitude-modulated signals orfrequency-modulated signals, a dual-purpose signal-translating stage comprises a vacuum tuber having a plurality of electrodes, including a signal input electrode and a signal output electrode, and an input circuitior applying received signals to. the input electrode. The stage also includes a. frequency discriminator coupled to the output electrode of 7 claims. (erecto-,20),

operate as a frequency-modulation limiter. YThe stage. also includes switch means operable ina first position to establish the 'first-named circuit connections and to connect the output circuit to the amplitude modulation detector and operable in a second position to establish rthe secondnamedpcircuit connections and to connect the output'circuit to the discriminator.

Also in accordance with the invention, a wave signal receiver adaptedselectively to receive amplitude-modulated signals or frequency-modulated signals comprises, in the order named, a radio-frequency selecting and converting means for deriving from a selected received radio-frequency signal an intermediate frequency signal, a dual-purpose signal-translating stage of the type described, and a signal-reproducing means coupled to the signal-frequency output circuit of the stage. For a rbetter understanding of the invention, together, w'ithv other and further objects thereof, reference is" had to ythe following description taken in connection n with the accompanying drawing 'while'its scope will be pointed out in the appended claims. y n

vReferring now to the drawing, the single figure is a circuit diagram, partly schematic, of a com-v plete, superheterodyne receiver embodying the combined amplitude-modulation and frequencymodulation receiver stage of the invention.

, Referring now to the single figure 'of the drawing, there is represented, partially schematically, the circuit :of a complete superheterodyne wavesignal receiver adapted selectively to receive amplitude-modulated signals or frequency-modulated signals. This receiver comprises a. radiofrequency amplifying and selecting unit lll having its input circuit connected Ato an antenna circuit Il and itsoutput circuit connected to an oscillator modulator I2,these two units being effective to.. derive from a selected received radio-frequency signal -an intermediate-frequency signal from eitherthe amplitude-modulation range or the frequency-modulation. range. The units l0 and i2 may be of conventional design with suitable-range switches Illa, l2a, respectively, for selectively translatingV amplitude-modulated sign'alsv or-'frequency-modulated signals. The receiver also includes an"intermediate-frequency the vacuum tube, a signal-frequency output cirselector and amplifier, I3 coupled' to the oscillator modulator I2for translating'the intermediate-'- 3 cuits Ma, Illb tuned to transmit the frequencymodulated intermediate-frequency signal in series with the primary and secondary tuned circuits Mc, Id, respectively, tuned to the amplitude-modulation intermediate frequency. The series impedance of each of the component tuned circuits is negligible at the intermediate carrier frequency to which it is not intended to respond so that the tuned circuits eiectively comprise an automatic switching arrangement for selectivelyreceiving either the amplitude-modulated or the frequency-modulated intermediate-frequency signals.

The receiver also includes -a' dual-purpose signal-translating stage comprising a vacuum tube- I having a plurality of electrodes, including a signal input electrode or grid |5a andy `a signal output electrode or anode |5b. Specifically, the tube is illustrated as of the pentode type including also conventional screen and suppressor electrodes. The secondary circuit of the selector I 4 Vcomprises an input circuit for applying received intermediate-frequency signals to the input electrode I5a of tube l5 and includes a timeconstant circuit such as a series condenser I6 shunted by a leak. or load resistor I1 therefor. The anode |51) of tube I 5 and its screen are energized from a suitable source indicated as +B through a dropping resistor I8 by-passed' to ground by means of a condenser I9 shunted by a resistor 20.

The receiver also includes a frequency discriminator 2| coupled to the output electrode I 5b of tube l5. The discriminator may be of any conventional form but, as illustrated, comprises a primary tunedV circuit 2|a coupled to a secondary tuned circuit comprising an inductor 2lb shunted by two series-connected condensers 2|c and 2Id. The inductor 2lb is inductively coupledtothe primary circuit 2|a and, as indicated schematically, is adjustably tuned by means of a powdered. iron or-like ferro-magnetic core 2|Ic. The high. signal-frequency-potential terminal of the circuit 2|a is connected to thejunction between condensersZIc and 2|d. Terminals ofthe secondary tunable. circuit 2lb, 2|c, 2|d are connected` todiode rectiiiers 2|e and. 2| f shunted by load. resistors. 2Ig and 2I`h, respectively, the cathode Yof the diode V2 If being grounded. and the cathodev of the diode 2|e being by-passed to ground for intermediate-frequency signals through a condenser 2li. The signal-.frequency output is derived from the terminal-2li of the discriminator 2|. With the circuit connections forthe tube I5 as described, it operates as a conventional frequency-modulation amplifier and limiter.

The stage also includes circuit connections for the' electrodes of tube l5 such. that it operates with the time-constant circuit IB, l1 as an amplitude-modulation detector. To this end there is provided switch means operable in its first position to modify the normal tube electrode connections andto establish the amplitude-modulation detector circuit connections. Specifically, this means comprises a two-position switch 22 effective-in its first position, as illustrated, to connect the screen and output electrode or anode of tube I5 to ground, so that the input electrode |5 a and cathode ci the tube I5 `function as a diode. amplitude-modulationdetector with the timeconstan-t circuit I6, II as its load circuit. There is also vprovided a two-position switch 23 operable time-constant circuit I6, to a signal output circuit 24 of the receiver. The switches 22 and 23 are ganged for unicontrol with each other and with the switches Illa, I2a of the units I0 and I2 by means of a mechanism indicated schematically at U. The switch 22 is operable in its second or FM position to remove the ground connection from the screen and output electrodes of tube l5V and to restore the tube electrode connections to normal; that is, to establish the FM limiter circuit connections. Simultaneously, the switch 23 inA its secondr position is effective to connect the output circuitv 24 to the terminal 2li of the discriminator 2|y through a filter comprising a series resistor 25v and shunt condensers 2|z and 26. The values of the'resistor and condenser I6 of the time-constant circuit are chosen to impart a short time-constant of the order of 2 microsecondsy to this circuit, which is necessary both for good limiter action and for satisfactory amplitude-modulation detection. The negative bias developed across the circuit I6, is applied as an automatic ampliiication control bias to the control electrodes of lone or more of the tubes included within the units I0, I2 and I3 by way of the AVC circuit, as indicated.

The receiver also includes an audio-frequency amplifier 2l coupled to the signal-output circuit 24 and havingan output circuit connected to a signal reproducing means, such as a loud speaker 28.

The. operation of the complete receiver illustrated in the drawing will be readilyv understood from the foregoing description. In brief, however, the units I0 and I2 are effective to derive from a signal picked up by the antenna circuit. I I an intermediate-frequency signal having one value of intermediate carrier frequency for frequency-modulated signals and a substantially different, usually lower value, of intermediate carrier frequency for amplitude-modulated signals, as. determined. by the constants Aof the oscillator circuit which are adjusted b-y operation of the switch I2a.

When the switches |0a, |2a, 22 and 23 are operated to their right-hand positions for the reception of frequency-modulated signals, the intermediate-frequency signals derived therefrom. are selected by theportions Illa, Nb ofv selector I4 and applied to the signal-input electrode of tube l5.V Due to thev self-biasing, action of the grid circuit of this tube, including the time-constant circuit I6, I'I, and to the selection of its screen and anode potentials, the tube I5 operates in a conventional manner as a limiter to develop in its output circuit intermediate-frequency signals of substantially constant amplitude but frequency-modulated in accordancewith the transmitted signal. This intermediate-frequency signal 'is impressed upon the discriminator 2 which operates in a conventional manner to develop at its terminal 2 la' a signal-frequency output. While the operation of the discriminator 2| is conventional, its. circuit is not entirely conventional in that the primary voltage is fed into the. secondary circuit 2| b, 2Ic and 2|d at the junction between the condensers 2|c and 2id-...which effectively comprise a voltage divider, rather than at a midtap of the inductor 2lb as is conventional. This arrangementpermits the use of aninductor 2lb without an. electrical midpoint and therefore adapted for tuning by the. use of an. adjustable powderediron or other ferromagnetic core. Such an arrangement has well known. improved frequency stability characteristics.

The signal-frequency output fromy the terminal 2 Iy is-passed through the'carrier frequency 23 upon the audio-frequency ampliiier 21 from which it is delivered to the loud speaker 28 for reproduction. i .y v f VOn the other hand, ifL the switchesy Ia, I2a, 22 and 23 are operated to their-left-hand positions; as illustrated in the drawing, an intermediate-frequency `signalof lower carrier frequency is developedby unit I3 and `selectedin portions I4c, I4dbf selector 'I4 and impressed upon the signal-input electrode'v I 5a of Y-tube I5.

With this connection, the screen and anode electrodes of tube I5 are effectively grounded so that the vgrid and cathode of '.this'tubeioperate With the time-constant circuit I6; I1 as a'conventional diode peak detector, developing a signal-frequency output across the time-constant circuit This output is impressed through the switch 23 upon the audio-frequency ampliiier 21 from which it is delivered to the loud speaker 28 for reproduction. l

As is well understood in the art, the AVC connection from the time-constant circuit I6, I1 is effective to impress upon the control electrodes -of the tubes of the units I Il, I2 'and I3 a negative bias potential proportional tothe average intensity of the received carrier signal and thusV to control the amplification in these units in Suche. Way as to maintain the amplitude of the signal input to detector I5 within a narrow range for a wide range of received signal intensities.V

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

I claim:

l. In a wave-signal receiver adapted selectively to receive amplitude-modulated signals or frequency-modulated signals, a dual-purpose signal-translating stage comprising, a vacuum tube having a plurality of electrodes includin-g a signal input electrode and a signal output electrode, an input circuit for applying received signals to said input electrode, a frequency discriminator coupled to said o-utput electrode, a signa1-frequency output circuit, circuit connections for said tube electrodes to cause said tube to operate as a diode amplitude-modulation detector, circuit connections for said tube electrodes to cause said tube to operate a's a frequency-modulation limiter, and switch means operable in a iirst position to establish said rst-named circuit con-V nections and to connect said output circuit to said amplitude-modulation detector circuit and operable in a second position toV establish said second-named circuit connections and to connect said output circuit to said discriminator.

2. In a wave-signal receiver adapted selectively to receive amplitude-modulated signals or frequency-modulated signals, a dual-purpose signal-translating stage comprising, a vacuum tube having a plurality of electrodes including a signal input electrode and a signal output electrode, an input circuit for applying received signals to said input electrode including a timeconstant circuit, a frequency discriminator coupled -to said output electrode, a signal-frequency output circuit, circuit connections for said tube electrodes to cause said tube to operate with said time-constant circuit as a diode amplitude-modulation detector, circuit connections for said tube electrodes to cause said tube to operate-asa Ifrequency-modulation limiter, andv switch means operable in a iirst position to establish said iirstnamed circuit connections and to connectsaid output circuit to said time-constant circuit and operable in a second position to establishfsaid V second-'named circuit connections and to connect said output circuit to said discriminator.

3. In a wave-signa1 receiver adapted selectively to receive amplitude-modulated signals or irequency-modulated signals, a dual-purpose signaltranslating stage comprising, a vacuum tube having a plurality of electrodes including a signal input electrode and a signa1 output electrode,` an input circuit for applying received signals to said input electrode including a series condenser and a leak resistor therefor, a frequency. discriminator coupled to said output electrode, a signal-frequency output circuit, circuit connections for said tube electrodes to cause "said tube to operate with said time-constant circuit as a diode amplitudemodulation detector,l circuit connections for said tube electrodes to cause said tube to operate as a frequency-modulation limiter, andA switch means'operable ina iirst position to establish said iirst-named circuit connections and to connect said output circuit to said condenser and operable in a' second position to establish said secondnamed circuit connections and to connect said output circuit to said discriminator.

4. In a wave-signa1 receiver adapted selectively to receive amplitude-modulated signals or frequency-modulated signals, a dual-purpose signaltranslating stage comprising, a vacuum tube having a plurality of velectrodes including a signal input electrode and a signal output electrode, an input circuit for applying received signals to said input electrode including a time-constant circuit, a frequency discriminator coupled to said output 40 electrode, a signal-frequency output circuit, said to receive amplitude-modulated signals or fre-V quency-modulated signals, a dual-purpose signaltranslating stage comprising, a vacuum tube having a plurality of electrodes including a signal input electrode and a signa1 output electrode, an input circuit for applying received signals to said input electrode including a time-constant circuit, a frequency discriminator coupled to said output electrode, a signal-frequency output circuit, said tube electrodes normally being connected to operate as a frequency-modulation limiter, and switch means operable in a rst position to connect said signal output electrode to ground to cause said tube to operate with said time-constant circuit as a diode amplitude-modulation detector and for connecting said output circuit to said time-constant circuit and operable in a second position to restore said tube electrode connections to normal and to connect said output circuit to said discriminator.

6. A wave-signal receiver adapted selectively to receive amplitude-modulated signals or frequency-modulated signals comprising, a radiofrequencyselecting Vvandxconverting means for de.. riving' from a selected receiveclradio-irequency signal an intermediate-frequency signal, a dualpurpose` signal-translating stage including a Vacuum tube having'a plurality of electrodes includingza signal input electrode and a signaloutput electrode, an input circuit'for applying received signals to said input electrodev including a timeconstant circuit, a frequency discriminator'coupled to. said output electrode;` a. signal-frequency output circuit, circuit connections for saidtube electrodes to cause` said tube -tooperate with said time-constant circuit as a diode amplitude-modulation detector, circuit connectionsI for said tube electrodes to cause ysaid tube-to operate as a frefluency-modulation limiter, and switch means-operable in-a rst position toestablish said iirstnamed circuit connections and to connect said output circuit to said time-constant-circuit and operable in a secondposition to establish said second-named circuit connections and to connect said output circuit to said discriminator, anda signal-reproducing means coupled 4to saidoutput circuit.

7. A Wave-signal receiver adapted selectively to receiveamplitude-modulated signals or frequency-modulated signals comprising, a radiofrequency selecting and converting meansfor detime-constant circuit as a diode amplitude-modulationdetector, circuit connections for said tube electrodes toA cause said tube to operate as a frequency-modulation limiter, and switch means operable in a rst position to establish said firstnamed circuit connections and to connect said output circuit to said time-constant circuit and operable ina second position to establish said second-named circuit connections and to connect said output circuit to said discriminator, switch means included in said selecting and converting means for selecting signals from the amplitudemodulation range or the frequency-modulation range, unicontrol operating means for both of said switch means, and a signal-reproducing means coupled to said output circuit.

JOHN Wa HUFF.

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