US2356201A - Frequency modulation signal receiving system - Google Patents

Frequency modulation signal receiving system Download PDF

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US2356201A
US2356201A US430588A US43058842A US2356201A US 2356201 A US2356201 A US 2356201A US 430588 A US430588 A US 430588A US 43058842 A US43058842 A US 43058842A US 2356201 A US2356201 A US 2356201A
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frequency
circuit
oscillator
frequencies
range
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George L Beers
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RCA Corp
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RCA Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D3/00—Demodulation of angle-, frequency- or phase- modulated oscillations
    • H03D3/02—Demodulation of angle-, frequency- or phase- modulated oscillations by detecting phase difference between two signals obtained from input signal
    • H03D3/24—Modifications of demodulators to reject or remove amplitude variations by means of locked-in oscillator circuits

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  • This invention relates to frequencvniodultion signal receiving systems of the typein which fie-A quency variations of the carrier' waive or ie'an' frequency of the signal ar eriiply'ed for the' re' ⁇ production of transmitted signals'.
  • An iinportant object of the invention isjto pro'- vide an ixnproved receiving system of the character referred to which achieves improved noise reduction, particularly in response to weak signals; and improved adjacent channel selectivity.
  • Another object of rfiy invention isA to provide anv improved vf'req'u'e'ricymodulation signal receiva ing system inA which the' frequency vdeviation of thev received signal is reduced b ⁇ y a predetermined ratio; such as 5 to 1, before dernodulation;
  • Another object of the invention is to provide n frequencyU niodulijtion signal receiv ng variations including, and substantially limited to, the range of frequencies of themodulate'd wave. I'he output of the oscillator is :fed to the discriminator network.
  • the locked-ln oscillator produces voltages at sub-harmonics Aor sub fr'nultixvzles Yof the A frequencies of the intermedlateor othersupplled the oscillator ls coupled to selective circuits in the dlscrimiriator network wlii ⁇ cn are re'sponslveto the band oi' sub-multiple frequencies produced ⁇ by the'y oscillator.
  • the sigf nal applied to the lo'ckedinloscillator may, in
  • Van' lrnproved frequency 25 modulatio eceivingsystenrln which a.' dynain'ic -irdueicy control isf provi'qeajiuc'criuecticii with the mduiation, sumciciit to lcckj in tiic cscilietcr for signals over afrequencv range corresponding' tion.
  • frequency modulation is used throughout the specification and claims, it should be understood to refer to any modulation wherein the instantaneous frequency of the transmitted waves is varied by thel application of modulating voltage of an alternating character such as music or speech. There are many possible functional relationsvbetween the instantaneous wave frequency and the modulating voltage, which are or can be used.
  • phase modulation because it is with equal correctness, and somewhat, more simply, definable as a modulation which causes the phase of the transmitted waves to shift in direct proportion to the instantaneous value of the modu-. lating voltage.
  • phase modulation and frequency modulation are tied together by the'fact that a changing frequency necessitates a changing phase and vice versa.
  • Fig. 1 is a schematic circuit diagram which illustrates one form of a frequency modulation signal receiving system embodying the invention
  • Fig. 2 is a schematic circuit diagram illustrating ⁇ another form of frequency modulation receiving system incorporating my invention and providing certain performance advantages over the system shown in Fig. 1,
  • Figs. 3 and 4 are graphs illustrating certain operating characteristics of the circuit o1' Fig. 2.
  • Fig. 5 depicts additional control means for the-v reactance tube employed in one embodiment of my invention.
  • the signal input circuits of my receiving system may be of any suitable type.
  • block diagrams are employed to represent the radio frequency amplifier 5, first detector C, local oscillator l, and intermediate frequency (I. F.) amplifier 8 of the usual superheterodyne type of vacuum tube receiver circuit.
  • I. F. intermediate frequency
  • a conventional dipole antenna is indicated at l as a suitable collector of signals for the radio frequency amplifler 5.
  • the intermediate frequency'amplifier l is pr0- vided with an output transformer IB having primary and secondary circuits resonant to the intermediate frequency.
  • the primary and secondary circuits of transformer I0 are suitably coupled and a variable resistor l l is connected in shunt with the secondary receiving circuit H to give the transformer a resonance curve of the desired breadth.
  • the intermediate frequency may be assumed to be 4.3 mc. (megacycles) and the transformer I0 is designed to pass the frequency band occupied by the modulated carrier wave with modulation.
  • the input circuits of the receiving system including the intermediate frequency transformer i0 with its secondary circuit Il, are constructed to receive a carrier wave with a total frequency swing of the order of kc. (kilocycles).
  • the devices 5, 6, and 'i are provided with the usual variable tuning means.
  • the input circuits of amplifieri and first detector 6 are each tuned to the mean or center frequency of the desired station channel, while the oscillator I is tuned to an oscillation frequency differing from said mean frequency by the value of the desired intermediate frequency.
  • the present frequency modulation (FM) band is 42 to 50 mc., with each transmitter station allotted a channel width of 200 kc.
  • the output circuit II is followed by a vacuum tube oscillator I2, which includes a tuned tank circuit I3, and a suitable frequency selective network, or discriminator, which as shown comprises tuned circuits I4 and I5 by which the applied signal is converted to amplitude modulation.
  • the signal is detected by suitable rectiers I6 and I1 coupled to said circuits I4 and I5 which are preferably shunted by resistors I4' and I5' respectively for reasons which will be hereinafter set forth.
  • the usual rectifier output impedance, or resistor is indicated at I8.
  • An output circuit I9 is connected thereto, one side of the output circuit being grounded as indicated at 20.
  • is coupled to the circuit I9 through a suitable capacitor 22.
  • the invention in its broader aspects and as set forth in some of the appended claims may be employed with a locked-in oscillator operating at the same frequencies as the modulated intermediate frequency wave.Y In its preferred embodiments, however, the oscillator I2 which immediately precedes the discriminator network produces voltages of frequencies less than the intermediate frequency and having ⁇ a frequency swing less than that of the intermediate frequency wave.
  • the oscillator tube envelope contains a grid 35'connected to the intermediate frequency secondary circuit II which in turn is connected to lground through a by-passcon-V denser I2.
  • the tank circuit I3f connected to the anode 40 of oscillator I2 comprises a variable magnetic core inductance 3I and a shunt tuning capacitor 32, and is tuned toa sub-multiple frequency of the intermediate oscillator I2 and the discriminator network is provided through a circuit lead 26, a resistor 25, and a variable coupling capacitor 21 connected to the anodeofthe oscillator and to the high potential sides of circuits I4 and I5.
  • the oscillator applies its output voltage to the discriminator whether a signal is being received or not, and since both the frequency and the frequency swing of the voltages which it produces are different from the intermediate frequency signal which is applied to the grid 35, it is apparent that the radio ⁇ frequency signal waves collected at the signalcollector device, such as the ⁇ usual antenna, do not themselves pass through the receiving system to the discriminator, but operate to control the frequencies of the voltages produced by the oscillator.
  • Grid current on grid 35 may be employed in place of the usual separate diode for automatic volume control (AVC) of the preceding tubes 5, 6, and 8.'
  • AVC automatic volume control
  • the AVC lead 62 is connected to ground 31.
  • the other end of lead 62 is connected to grid control circuits 63 through a Vsuitfrequency signal applied to the grid 35 to cause Y the tube I2 to produce oscillations of such submultiple frequency.
  • the 'I'he circuit I3 is grounded at 29 through a by-pass condenser 30 and is caused to oscillate ⁇ at the predetermined sub-multiple frequency by feedback through inductive couplings between the inductance 3I and an inductance indicatedr ai; 42. ⁇
  • the latter has a shunt tuning capacitor 43 included in a circuit 41 which is preferably shunted by a resistor 41' and is connected betweenv a second control grid 44 and ground, or cathode, through a suitable grid resistor shunted by a grid capacitor 46.
  • the normal oscillator frequency is primarily determined by the tuning of circuit I3.
  • the tube I2 may be a pentagrid tube of the 6SA7 type, and is preferably locked-in by the impression of the 4.3 mc.
  • the cathode Screen grids are arranged as circuit 41, comprising winding ⁇ 42 and condenser 43, hasa natural frequency of resonance higher than that of circuit I3.
  • the nductance 42 of circuit 41 was between one-fifth and one-sixth of the inductance of winding 3
  • a diode resistor connected in shunt cuit of the transformer Ill or at some other sultable point in the receiver system, could be used to provide the AVC potential in conventional manner.
  • the locked-in oscillator I2 operates at a submultlple of the instantaneous frequency of the modulated carrier impressed on grid 35, frequency division is obtained in which not only the and appropriate load with the primary cir- 1 mean-:carrier frequency is reduced, but also the frequency swing is correspondingly reduced.
  • the circuits I3, I4 and I5 may be made'responsive to a mean sub-'multiple frequency of 860 kc. thereby providing at 5:1 frequency reduction and a corresponding reduction in the frequency swingl For example, if at any instant, the received sigv nal has been heterodyned to an intermediate -frequency of 4.375 mc.
  • the frequency of the looked-in oscillator will then be 875 kc., (up .15 kc. from the mean subfmultiple frequency of 860 kc.) preserving the 5:1 ratio with the intermediate frequency on grid 35.
  • the circuits I3, I4 and I5 a frequency deviation from the mean frequency of kc. for full modulation, assuming that the applied signal has a maximum frequency deviation of i-75 this manner of eilect-V kc.
  • the maximum frequency swing of the signal applied to the discriminator is thus limited in this example to an audio frequency of 15 kc. on each side of the mean frequency.
  • the discriminator network may be of any suitable type for converting a frequency modulated signal into an amplitude modulated signal for detection by the rectiers I6 and I1. As shown, it comprises a selective system of the type more fully described in the application of John D. Reid, Serial No. 353,028, filed August 17, 1940, andincludes tuned parallel-resonant circuit I comprising inductance and capacity connectedv between the anode of rectifier I6 and that of rectifier I1.
  • the capacity existing across the electrodes of rectifier I1 is indicated in broken lines by capacity I5" and provides in combination with circuit I5 'a series circuit tuned to resonance at the lower frequency end of the admittance band of the discriminator which in this example of the invention is somewhat below 845 kc., while the parallel-resonant circuit I5 resonates at the higher frequency of the discriminator admittance band, i. e., somewhat above 875 kc.
  • This frequency selective network provides a linear operating characteristic for a frequency swing of 15 kc., as will be more fully described below.
  • Each of the coils of transformer IIl and the coils of circuits I4 and I5 may have adjustable cores composed of powdered magnetic material. A single core of such material may be used with coils 3
  • circuit I4 remote from condenser 21 is connected to a midtap on the resistor I8 in the output of rectiers I6 and I1.
  • a high frequency by-pass condenser 68 is connected across the upper half of resistor I8 and to the cathode of rectifier I6, and a similar condenser 61 is connected across the lower half of resistor I8 and to the cathode of rectifier I1.
  • the upper ends of circuits I4 and I5 are conductively connected together both for alternating and direct currents.
  • the capacity between anode and cathode of rectier I1 is represented by condenser I5" shown in broken lines. As more fully described in the said Reid application, Serial No. 353,028, the circuit I5 in combination with capacity I5", is series resonant to the lowest frequency of the admittance band of the discriminator, and the circuit I5 per se is parallel-resonant to the highest frequency of such admittance band.
  • the above circuits provide a direct current path from circuit I4 to the mid-tap on resistor I8, which is completed through the upper half of resistor I8, and rectifier I6 back to circuit I4 and a second direct current path which is completed through the lower half of resistor I8, rectifier I1, circuit I5, andci'rcuit I4 back to the mid-tap on resistor I8.
  • direct current in the first-mentioned path including rectifier I6 tends to make the upper end of resistor I8 posi-
  • the coil I4 need not be inductive with respect to ground. and that current e through the second direct current path including rectifier I1 tends to make the upper end of resistor I8 negative toground.
  • the circuit I4 functions mainly as a tuned circuit resonant in thevexample of the operation of the invention described hereinto approximately .860 kc. and interposedbetween the output o! the locked-in oscillator I2 and the input to the discriminator-rectifier. Itslower end is ellectlvelyy grounded at 20 through the highfreqnency by.- pass condenser 61.
  • Fig. 2 shows a discriminator-rectifier network somewhat different from that shown in Fig. 1.
  • the low potential side of the circuit I4 is connected directly to ground, as at 28, instead of to the center tap on resistor I8 and the circuits I4 and I5 are coupled by condenser 80.
  • the anode of diode I6 is connected to the center tap on resistor I8 to provide the D.C. path which in Fig. 1 is completed through circuit Il, and a single high frequency by-pass condenser 8
  • connection may be made with the anode of either of the rectiflers or to any point between them which provides a D.C. path to the diode plates.
  • the lock-in range may represent only la relatively small part, such las between 20 and 35 percent,.of the modulation frequency range.
  • the intermediate frequency signals impressed on the grid 35 in Fig. 2 can cause a, frequency shift of the voltage delivered from the oscillator I2 only of ⁇ the order of i5 kc. from the oscillator frequency determined by the tuning of circuit I3 before the oscillator falls out of control of the potentials on such grid.
  • the oscillator I2 is provided with autom-atie frequency control means as follows:
  • the circuit I3 which immediately precedes the discriminator, is associated with a reactance control tube indicated at 50.
  • the latter has a screen grid 50', a suppressor grid 50 and an anode 5I connected through a lead 50 to the high potential side of circuit I3 and through the inductance 3
  • the control grid 572 of reactance tube 50 is connected ⁇ through a control circuit lead 53, in-
  • the plate to cathode impedance of tube v5I is connected across the circuit I3, and the quadrature voltage on grid 52 causes the plate to cathode impedance of tube 50 to simulate an inductive reactance, as more specifically described in the application of- Charles Travis, Serial No. 19,563, filed May 3, 1935.
  • diate control reactance tube 50 inthe proper magnitude and phase to shift the tuning of the oscillator tank circuit I3 in the same direction as the frequency shift of the intermediate frequency. signals on grid 35.
  • the restricted lock-in range of the oscillator I2 is shifted back and forth so that it is always such as to permit the oscillator to lock in with the frequency of a desired modulated wave over a frequency swing corresponding to 100% modulation.
  • a system which is made very selective with respect to its response to interfering impulses is through the use of a reaictance tube feedback system made ⁇ fully responsive to the desired modulation. This operation maybe effected either by combined audio frequency and direct current potentials from potentiometer 55, when switch 10 is closed, or by audio frequency potentials through condenser 1I, when switch 'IU is open.
  • Fig. 3 The frequency reduction from the intermediate frequency to the sub-harmonic frequency is shown graphically in Fig. 3, to which attention is now directed along with Fig. 2.
  • the upper part of Fig. 3 shows the intermediate frequency of 4.3 mc. with the limits of its full frequency swing separatedby 150 Lkc. resulting from a frequency shift, or deviation, of i 'l5 k'c., and in comparison therewith the lower part of the figure shows the sub-multiple frequency of 860 kc. providing a frequency reduction in the ratio of :1 and a corresponding reduction in the frequency swing, or frequency deviation, to i 15
  • the limited frequency lock-in range of the oscillator in following the frequency swing of the controlling intermediate frequency is also indicated in Fig. 3.
  • the three, heavy vertical lines in the lower part -of the gure representrfrequencies to which the oscillator I2 may be adjusted by the reactances in or across circuit I3.
  • the oscillator may be adjusted to the frequency of .8 ⁇ 60 kc. indicated by the central vertical line, without reference to By ⁇ the reactance shunted across circuit I3 by the tube 5I), the oscillator I2 may be adjustedto a frequency of 15 kc. .lower than the central frequency of 860 kc. as indicated by the vertical line at the left, toa frequency of 15 kc. above the central frequency as indicated by the vertical line at the right, or -to any frequency intervening between slid limits.
  • the horizontal lines-in Fig. 3 denoted i5 kc. show that at any frequency to which the oscillator may be tuned, it has a lock-in range, ,for example, of the order of i5 kc. under the immeof frequency swingon grid 35.
  • the phase and magnitude of the potential impressed from potentiometer 55 on the control grid 52 of thereactance tube 50 controlits effect on the frequency ⁇ of the tuned circuit I3.
  • the amplitude of the control potential applied to the reactance tube is normally kept slightly below the value which would shift the oscillator to thecorrect frequency, assuming that the oscillator had no lock-in range. .In :other words, for 100 percent modulation the reactance tube shifts the oscillator frequency by slightly less than i-l kc., the discrepancy being cornpensated for by the oscillator lock-in action.
  • Vresponse range of the intermediate frequency transformer I0 may be impressed on the grid 35 of oscillator I2. If sub-multiples of these interfering frequencies are permitted to reach the demodulator,
  • the oscillator willnotfollow beyond its restricted lock-.in range frequencies, even though they are within the range of frequencies-impressed on the grid 35, which if demodulated would produce superaudible output potentials, because the feedback connections between the discriminator-rectifler circuits and the reactancetube are designed to pass only the desired modulation frequencies, and the frequency shift of the oscillator which the reactance -tube canproduce is therefore limited to the useful
  • the receiving system isfprovided with a circuit which is responsiveonly to small frequency variations
  • this restricted responserange is moved back and forth at a rate which follows the desired modulation of received signals but is not moved back and forth at a rate which will ⁇ follow superaudible noise impulses which may be present with the frequency swing limitation is provided for'superaudible noise frequencies, such frequencies being prevented from combining with the .carrier in the discriminatorrectifier system.” This increases the ratio of the carrier energy to the combined energiesof the side bands including the noise components.
  • Fig. 4 shows the demodulator, i. e., discriminatorrectier, voltage-frequency response characteristic.
  • the phase of the potentials applied to the reactance tube would be such that the effect of the reactance tube on the oscillator would beto reverse the direction of the voscillator I frequency change.
  • the reactance control tube cannot shift the oscillator frequencyfso thatvit will lock in with the signal Aon an adjacent channel because the circuit elements are so designed that if the frequency of the oscillator were to change beyond the Vuseful range of the'discriminator and towards the adjacent channel, the phase and magnitude of the potential applied to the reactance tube would shift in such a manner that the oscillation frequency would be shifted away from the adjacent channel frequencies. It will be noted further that the effect of the reactance tube on the frequency of the oscillator I2 for a signal discriminator characteristic is just the same as yand i' are not critical, ⁇
  • the reactancey tube provides an additional restriction which limits the frequency variations-of the lock-in i oscillator to the range represented bythe useful portion of the discriminator characteristic.
  • resistances I4 and Il' in shunt with circuits I4 and i5 respectively, be employed. They have,l however-,g been found to be desirable to broaden the resonance curves of the circuits and to increase the linearityl of the demodulator voltage-frequency response curve shown in Fig. 4.
  • the valuesof these resistors Il' In one'embodiment of my invention they were 560,000 and 130,000Y ohms respectively. Y
  • control grid 52 may by tact member 15 be connected through contact 16 and resistors and 18 to an adjustable contact 19 slidable along the resistor 3 9.
  • VThe resistors 1l and 10' and grounded condenser" are used to lter out any alternating current potentia which may be set up across resistor 38.
  • the oscillator may, if so desired, be de- 52 ofthe -reactance tube ling the oscillator frequency.
  • Fig. 5 Such an arrangement is illustrated in which the cathode 00 of intermediate frequency amplifier Iis conf nected to thel upper end of resistance I4 so that the current between anode 8,2' and'cathode Il of onev or more tubes in amplifier 0 also passes through resistance ,84 in a direction to make the cathode of tube 5,0.positive with respect to ground.
  • Figs. 1 and 2 indicate that the intermediatefrequency amplifier :8 is controlled by the-AVC.
  • resistance 85' provides negative grid bias both -to the grid 5220i tube l and to the control grids o1' one or Ymoretubes contained-in I-. ⁇ F. amplier 8.
  • the resistance 8,4 is therefore preferably chosen to give normal-bias as a Vvcathode :bias element for the intermediate frequency amplifier B in the absence of AVC action, while ⁇ the reactance 'tube 50 is so constituted that the same voltage drop impressed las negativebias on the grid 52 renders the reactance tube ⁇ 5l! ineffective.
  • the only leffector a received signal ⁇ is to shift the frequency of the locked-in oscillator in accordance with .the modulation, thereby causing the frewhen the switch 'I0 is discriminator characteristic.
  • a third, and likewise important, advantage of the invention lies in the improved adjacent channel selectivity obtained.
  • the adjacent channel selectivity is determined by the response curves of the radio frequency, intermediate frequency and discriminator circuits.
  • the signal on the channel adjacent to a desired signal is sufliciently strong to produce a voltage of a certain value at the discriminator-rectifier network, interference with the desired signal will be obtained even though the frequency deviations of the undesired signal do not operate-over the useful portion of the In the receiver of this invention the only signal which reaches the discriminator is represented by the frequency variations in the voltages produced by the lockedin oscillator.
  • the selectivity of the receiver is materially increased without resorting to the use of additional selective circuits.
  • vGfood reception has been achieved despite low signal to noise ratio, even with weak signals.
  • Automatic frequency control of the heterodyne oscillator 1 may be employed to improve the tuning of the receiver and to compensate for frequency drift of the oscillator 1.
  • the potentials developed across resistor I8 in Fig. l or resistor I8 and potentiometer 55 of Fig. 2 may control a reactance tube associated with the oscillator 1, as fully shown in the prior art including United States patents to G. L Beers, No. 2,203,857, granted June 11, 1940, and to S. W. Seeley, No. 2,121,103, granted June 21, 1938.
  • inter-station noise suppression systems such as the types described in United States patents to G. L. Beers, No. 2,135,557, granted Nov. 8, 1938; Jarvis, No. 2,115,813, granted May 3, 1938, Starrett No. 1,925,825, granted Sept. 5, 1933, can be used in conjunction with this receiving system. Since the locked-in oscillator I2 can be started and stopped by control of the potentials applied to grids 35 and 44 and noise suppression potentials derived as described in the above mentioned patents maybe applied to grid 35 or grid 4I or both, a simple means is provided for giving such noise suppression systems an ON/OF'F characteristic which cannot be obtained in asimilar manner in conventional receivers.
  • a circuit for receiving frequency modulated waves means for supplying frequency modulated signal waves to said circuit, a demodulator, selective circuits in the input of the demodulator for converting frequency variations to amplitude variations, and connections between said receiving circuit and said selective circuits, said connections including means for increasing the selectivity of the system and said last-named means including oscillation producing means locked in step with a desired frequency modulated wave over a range of frequency variations including, and substantially limited to, the range of frequencies of the desired modulated waves, whereby interference due to noise frequencies or-adjacent channel frequencies is reduced.
  • a circuit for receiving frequency modulated waves means for supplying frequency modulated signal waves to said circuit, a demodulator, selective circuits in the input of the demodulator for converting frequency variations to amplitude variations, and means connected between said receiving circuit and said selective circuits for improving the signal'to noise ratio of the system, said last-named means including an oscillator, means for coupling the output of the oscillator to said selective circuits, and means including said coupling means for causing said oscillator to lock in with a desired frequency modulated wave over substantially limited to, the range of frequencies of the desired modulated wave.
  • a circuit for receiving frequency modulated waves In a frequency modulation receiving system, a circuit for receiving frequency modulated waves,
  • vand means for varying the degree of coupling between the oscillator and the demodulator to Vcontrol the width of the frequency range over'which the oscillation'producing means will lockl in with the desired modulated wave supplied to said receiving circuit.
  • a circuit for receivingV frequency modulated waves means for supplying frequency modulatedsignal waves to said circuit, a demodulator, a vacuum tubecontaining an anode, cathodeland a pluralityof grids, means for impressing frequency modulated signal waves from said receivingcircuit on one of said grids, an oscillator havirigits output coupled to said ⁇ selective circuits and including said anode, another of said grids, a tank circuit connected to the anode and containing inductance and capacity, and a resistance shunted by a capacity in the circuit of said other grid together with vparallel-'resonant inductance ⁇ and capacity resonating at a frequencyhigherthan that of the tank circuit, and means including the inductance-capacity ratio of the oscillator tank circuit and the degree of coupling between the oscillator and said selective circuits for causassaaoi ⁇ multiple frequencies bear ing the oscillator tolock in with a
  • a receiving circuit means for supplying to said circuit waves modulated over a range of frequencies, a demodulator having an input network responsive to frequencies which are sub-multiples of the first-mentioned frequencies and having a'pass band of ⁇ a.
  • oscillation producing means interposed between the receiving circuit and said demodulator input network, said oscillation prociesand which vary over a Vsupplying to said circuit ducing means impressing voltages on the demodulator input network at frequencies of operation of the oscillation producing means and which are sub-multiples of the first-mentioned frequencorrespondingly reduced frequency range, and means for causing the oscillation producing means to lock in with a desired frequency modulated wave over a range including, and substantially of frequencies of such modulated wave.
  • a receiving circuit means for signal waves modulated over a range of frequencies, a demodulator having an input network responsive to frequencies which are sub-multiples of the lfirst mentioned frequencies and having a pass band of a width bearing substantially the same ratio to the width of said first-mentioned range of frequencies as lsaid sub-multiple frequencies bear to the first-v means including coupling elements between the output of the oscillator and the demodulator input network for causing the oscillator to lock in with a desired Afrequency modulated wave over a range including, and substantially Vlimited to, the range of frequencies of the modulated wave.
  • a frequency modulation receiving system la circuit for receiving frequency modulated waves, means for supplying frequency modulated signal waves tok said circuit, a demodulator, selective circuits in the input of the demodulator for converting frequency variations to amplitude variations and responsive to sub-multiples of the frequencysmodulated waves, a vacuum tube oscillator, devices including resistance and Vcapacity for ⁇ coupling the output of the oscillator to said selective circuits, and means including said coupling devices for causing the oscillator to deliver. to said selective circuits voltages at frequencies directly produced by said oscillator and which are sub-multiples of the frequencies of a desired frequency modulated wave supplied to said receiving circuit over aV range of frequency variations substantially restricted to the frequencies of said ⁇ wave.
  • a circuit for receiving frequency modulated limited to, the range waves means for supplying frequency modulated signal waves to'said circuit, said means including vacuum tube devices for increasingftlie strength of the modulated w'avesea de'rnodula'tor Vliaving an input network responsiveto sub-multiplfes of the frequency modulated "Waves, a vacuum,.tu be oscillator, including a control grid and ⁇ aplu ⁇ rality of oscillation-producing velectrodes, for vsupplying voltages of said sub-multiple frequencies to the demodulator, andmeans energizedbyiiow of current in the circuit of said control T(grid form automatically controlling the gain of said vacuum tube devices.
  • a circuit supplying signal waves modulatedover a range offfrequencies, a demodulator having an input network responsive to the fifth subfmultiplefrequencies of the range of frequencies of said applied wavesrvandhaving a pass band of a frequencyv widthapproximately equal to one-flftncf'the width of said range of) division means interposed frequencies,v frequency K between said supply circuit and v.saiddemodulator input network and controlled byy the signal waves over said range of frequencies, ⁇ said frequency divisionumeansbeingfconstructed to reduce said supplied frequencies to .said submultiple fre quenciesv and toreducesald range ofA frequencies to the narrower range to which-saidinput network is responsive, and circuits yassociated with the frequency division means for limitingits con-v trol substantially to the range a desired wave.
  • a circuit supplying signal waves modulated over a range offrequenciesyinof frequencies of cluding frequencies having sup,eraudible fre- Y quency differences .from tlie rneanfrequency of said rangeof frequencies, ademodulator having an input network responsive to sub-multipletf-requencies of the range ofrfrequenciesofsaid' applied waves and havinga pass vband off ai-fre quency width within the limits of ,audibilitypon each side of the mean frequencyand bearing approximately the same ratio to'tlie Width7 of ing in favor of a desired signal terrnenoiseand @desir 1: tema circuit f or rece ffeqeehieaccfresponding. fullfmcduistmn: a
  • said oscillator being constructed to produce oscillations of the range of frequenciesvto.
  • said demodulator input network is responsive-audio reduce said supplied. frequencies tof-said sub- Vmultiple frequencies andato reduce vthe ⁇ range off.
  • a receiving circuit'for wavesV modulated over a range of frequencies meansfor'r'eproducing the received signals and means fOr ld SiiIrlflfil'lreceiving Si ing 'oscillation'producing means and 1Vof itself 'to 110er inlwitntiiej l vcfa'desired'modulated) "j Y v'QI 'ltsrange' of frequ'e'ncifeaanda di'y tferrrfajcircuit 'for rece responsive automatically to changes in frequency of the modulated wave for causing said oscillation producing means to lock in with it over the whole of its range of frequencies.
  • a demodulator means inherently responsive to only small frequency variations in a received signal for supplying to the demodulator energy modulated in accordance with the signal, means controlled by the modulation of received signals y for shifting in frequency the narrow response range of said first named means Aincluding the mean frequency of said range so that wide frequency variations in received signals can be accommodated, and means for rendering the frequency shifting means normally ineffective in the absence of received signals.
  • a circuit for receiving waves modulatedv over a range of frequencies means including a demodulator for reproducing the desired signals, and interference preventing devices comprising oscillation producing means which, in the absence of other provisions, locks in with a desired modulated wave over a portion only of its range of frequencies, and additional means controlled by voltagesproduced in the output of the demodulator for extending the lock-in range of said oscillation producing means sufficiently to include the whole of the range of frequencies of the desired modulated wave but not enough to include frequencies substantially outside of said lastmentioned range.
  • a circuit for receiving waves modulated over a range of frequencies, means for reproducing the desired signals comprising a demodulator, and means for discriminating in favor oi' desired signals as against interfering frequencies, comprising a vacuum tube oscillator having a tank circuit and operating, in the absence of other provisions, to lock in with a desired modulated wave over a .portion only of its range of frequencies, a reactance tube connected across the tank circuit, and means for impressing voltages from the output of the demodulator on the reactance tube to change the tuning of the tank circuit in the direction of frequency change of the desired modulated wave.
  • a circuit for receiving waves modulated over a range of frequencies, means for reproducing the desired signals comprising a demodulator having an input network responsive to frequencies which are submultiples of the range of frequencies of the modulated waves and having a pass band of a width bearing approximately the same ratio to the width of said range of frequencies as the submultiple frequencies bear to the frequencies in said receiving circuit, oscillation producing means a desired modulated wave for causing the oscillation-producing means to produce voltages at sub-multiples of the frequencies of such modulated wave over the Whole of its range of frequencies.
  • a circuit for receiving waves modulated over a range of frequencies, means for reproducing the desired signals, and interference preventing means comprising a vacuum tube oscillator having an input circuit which receives signals from said receiving circuit and an output circuit which feeds alternating current to said signal reproducing means and having a tank circuit which, in the main, controls the frequencies of the voltages produced by the oscillator, said oscillator being constructed to lock in with a desired modulated wave on each side of the tank circuit frequency and over a portion only of the range of frequencies of the desired Wave, and means under the control of a desired modulated wave for automatically varying the frequency of the tank of its range of frequencies.
  • a receiving circuit responsive to a desired signal and to interfering frequencies which can beat either with themselves or the received signal to produce superaudible noise impulses
  • a demodulator means inherently responsive to only small frequency variations in the received signal for supplying frequency modulated energy to the demodulator, and means for shifting in frequency the narrow response range of said first named means including the mean frequency of said range so that wide frequency variations in the received signal can be accommodated, said lastnamed means including circuits controlled by the modulation of the received signal and unresponsive to said superaudible noise impulses.
  • a frequency modulation receiving system comprising means including a demodulator for reproducing the audio frequency modulations of received signals, and means for limiting the range the receiver is responof frequencies to which sive, said means comprising oscillation producing means, and means controlled by the demodulator for changing the frequency of the oscillations produced by the oscillation producing means in the direction of changes in the frequency of a desired modulated wave and at a rate corresponding with and substantially restricted to the audio frequency modulation of the wave, whereby interference from frequencies varying at a rate above audibility is suppressed.
  • a circuit for receiving modulated waves, means for reproducing the desired signals comprising a demodulator which produces a voltage varying substantially linearly with frequency over a range of frequencies necessary for reception of full modulation, a frequency division network connected between the receiving circuit and the demodulator for supplying to the demodulator sub-multiple frequencies of said first-mentioned range of frequencies, and means controlled by the demodulator for preventing the division network from supplying to the demodulator frequencies substantially outside of the range required for full modulation reception.
  • a circuit for receiving waves modulated over a range of frequencies means for reproducing the received signals including a demodulator con ⁇ - structed to produce voltages varying substantially linearly with frequency over a band ⁇ of frequencies which enables reception of said range of frequencies, and interference preventing means comprising a vacuum tube oscillator having a tank circuit, a reactance tube connected across the tank circuit, and circuits for impressing output potentials from the demodulator on the reactance tube to cause said tube to vary the frequency of the oscillator in the'direction of the frequency changes of a desired modulated wave over a desired operating range, said last-mentioned circuits being so constructed as not to pass demodulator output potentials of frequencies outside of the desired modulation frequency band.
  • a circuit for receiving frequency modulated waves means for supplying frequency modulated signal waves to said circuit, a demodulator, selective circuits in the input of the demodulator for converting frequency variations to amplitude variations, and connections between said receiving circuit and said selective circuits, said connections including tuned circuit means and thermionic means connected in cascade with the tuned circuit means for materially increasing the selectivity of the receiving system without altering the selectivity of the tuned circuit means, said thermionic means operating to produce oscillations locked in step with a desired frequency moduflated wave over a range of frequency variations including, and substantially limited to, the range of frequencies of the desired modulated waves, whereby interference duev to noise frequencies or adjacent channel frequencies is reduced.
  • a circuit responsive over a range of frequencies of a frequency modulated wave a second circuit responsive to a frequency swing substantially less than said range of frequencies, means interposed in direct path between said first circuit and said second circuit for reducing the range of frequencies of signals applied to said circuit to the narrower frequency swing to which the second circuit is responsive, said means. including a vacuum tube oscillator including an anode, a
  • cathode cathode, a plurality of other electrodes, and at least one tuned circuit operatively connected with certain of said electrodes to determine the approximate frequency of operation of said oscillator, and input signal means connected to an electrode of said tube other than said certain electrodes for varying the frequency of said oscillator within a range limited by constants of said tuned circuit or circuits.
  • a source of high frequency carrier energy which is frequency modulated over a range of frequencies
  • a circuit responsive to a frequency lower than said first-mentioned carrier frequency and to a frequency swing substantially less than said range of frequencies, and means interposed in direct path between said source and said circuit for dividing the carrier frequency to reduce it to the frequency of said circuit.
  • said means including a vacuum tube oscillator including an anode, a cathode, a pluralityA of grid electrodes, and at least one tuned circuit operatively connected with said anode and one of said grid electrodes to determine the approximate frequency of operation of said oscillator, input signal means connected to a grid electrode of said tube nearer the cathode than said first-mentioned grid electrode for varying the frequency of said oscillator within a range limited by constants of said tuned circuit or circuits, and a screen electrode interposed between said iirst-mentioned grid electrodes.
  • a tuned circuit having a substantially fiat response over a range of frequencies of a frequency modulated wave, said circuit being tuned to substantially the mid-frequency of the range, a second circuit having a fiat response over a band substantially less than the said range of frequencies, said second circuit consisting of a coil 'and a condenser connected in parallel and tuned to a submultiple of the frequency to which the first circuit is tuned, a vacuum tube having an anode, a cathode, a control grid adjacent the cathode, a suppressor grid adjacent the anode, an intermediate grid and a shielding 'grid adjacent the intermediate grid, said second circuit being connected to and between said anode and cathode of said tube, an inductanoe coil coupled to thel coil of said second circuit and connected to and between said intermediate grid and said cathode, means for developing and subjecting said intermediate grid to a negative potential with respect to said cathode, whereby said second circuit and the coil coupled thereto

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inductance-Capacitance Distribution Constants And Capacitance-Resistance Oscillators (AREA)
  • Stabilization Of Oscillater, Synchronisation, Frequency Synthesizers (AREA)
US430588A 1942-02-12 1942-02-12 Frequency modulation signal receiving system Expired - Lifetime US2356201A (en)

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FR955303D FR955303A (enrdf_load_stackoverflow) 1942-02-12
US430588A US2356201A (en) 1942-02-12 1942-02-12 Frequency modulation signal receiving system
GB2310/43A GB562993A (en) 1942-02-12 1943-02-11 Frequency modulation signal receiving system

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Cited By (28)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2429747A (en) * 1945-01-19 1947-10-28 Rca Corp Combined frequency divider and detector
US2440653A (en) * 1944-11-14 1948-04-27 Rca Corp Locked-in oscillator circuits
US2456915A (en) * 1945-05-22 1948-12-21 Rca Corp Angle modulated wave detector
US2457207A (en) * 1944-05-03 1948-12-28 Rca Corp Angle modulated carrier receiver
US2462759A (en) * 1942-06-13 1949-02-22 Philco Corp Apparatus for receiving frequencymodulated waves
US2488584A (en) * 1943-12-08 1949-11-22 Rca Corp Locked-in oscillator circuits
US2488585A (en) * 1945-05-29 1949-11-22 Rca Corp Frequency modulation receiver
US2488606A (en) * 1945-05-02 1949-11-22 Rca Corp Frequency modulation receiver
US2501416A (en) * 1945-02-28 1950-03-21 Philco Corp Muting circuit for frequency modulation radio receivers
US2507409A (en) * 1947-01-24 1950-05-09 Zenith Radio Corp Time modulated wave receiver
US2507730A (en) * 1946-05-16 1950-05-16 Rca Corp Frequency shift receiver
US2513763A (en) * 1945-01-04 1950-07-04 Rca Corp Locked-in oscillator circuit
US2539818A (en) * 1948-10-28 1951-01-30 Gen Electric Frequency modulation detector
US2561149A (en) * 1945-09-10 1951-07-17 Rca Corp Frequency modulation detector circuits
US2563243A (en) * 1949-05-10 1951-08-07 Joseph N Marks Indoor television antenna
US2604586A (en) * 1949-04-28 1952-07-22 Rca Corp Diversity reception
US2656465A (en) * 1948-05-12 1953-10-20 Zenith Radio Corp Synchronizing system
US2677059A (en) * 1951-03-06 1954-04-27 Rca Corp Signal generator
US2686221A (en) * 1949-11-03 1954-08-10 Rca Corp Simplified compbination fm and television receiver
US2721268A (en) * 1946-09-26 1955-10-18 Laddie T Rhodes Locked-in oscillator
US2790905A (en) * 1953-06-09 1957-04-30 Marconi Wireless Telegraph Co Automatic frequency control
US2817756A (en) * 1952-06-03 1957-12-24 Charles A Debel Variable bandwidth constant peak-amplitude discriminator
DE1040088B (de) * 1954-05-28 1958-10-02 Philips Patentverwaltung Empfangsgeraet fuer frequenzmodulierte Schwingungen
US2891105A (en) * 1953-09-23 1959-06-16 Rca Corp Automatic frequency control apparatus
US2922119A (en) * 1949-11-12 1960-01-19 Zenith Radio Corp Frequency halving synchronized oscillator
US2946960A (en) * 1956-05-16 1960-07-26 Motorola Inc Electronic circuit
DE1093429B (de) * 1956-07-07 1960-11-24 Koerting Radio Werke G M B H Demodulationsschaltung
US4068173A (en) * 1977-01-03 1978-01-10 Gte Automatic Electric Laboratories Incorporated Frequency stabilized microwave signal source

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE977600C (de) * 1952-12-24 1967-06-22 Koerting Radio Werke G M B H Mitnahmeoszillator fuer den Empfang frequenzmodulierter Wellen

Cited By (28)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2462759A (en) * 1942-06-13 1949-02-22 Philco Corp Apparatus for receiving frequencymodulated waves
US2488584A (en) * 1943-12-08 1949-11-22 Rca Corp Locked-in oscillator circuits
US2457207A (en) * 1944-05-03 1948-12-28 Rca Corp Angle modulated carrier receiver
US2440653A (en) * 1944-11-14 1948-04-27 Rca Corp Locked-in oscillator circuits
US2513763A (en) * 1945-01-04 1950-07-04 Rca Corp Locked-in oscillator circuit
US2429747A (en) * 1945-01-19 1947-10-28 Rca Corp Combined frequency divider and detector
US2501416A (en) * 1945-02-28 1950-03-21 Philco Corp Muting circuit for frequency modulation radio receivers
US2488606A (en) * 1945-05-02 1949-11-22 Rca Corp Frequency modulation receiver
US2456915A (en) * 1945-05-22 1948-12-21 Rca Corp Angle modulated wave detector
US2488585A (en) * 1945-05-29 1949-11-22 Rca Corp Frequency modulation receiver
US2561149A (en) * 1945-09-10 1951-07-17 Rca Corp Frequency modulation detector circuits
US2507730A (en) * 1946-05-16 1950-05-16 Rca Corp Frequency shift receiver
US2721268A (en) * 1946-09-26 1955-10-18 Laddie T Rhodes Locked-in oscillator
US2507409A (en) * 1947-01-24 1950-05-09 Zenith Radio Corp Time modulated wave receiver
US2656465A (en) * 1948-05-12 1953-10-20 Zenith Radio Corp Synchronizing system
US2539818A (en) * 1948-10-28 1951-01-30 Gen Electric Frequency modulation detector
US2604586A (en) * 1949-04-28 1952-07-22 Rca Corp Diversity reception
US2563243A (en) * 1949-05-10 1951-08-07 Joseph N Marks Indoor television antenna
US2686221A (en) * 1949-11-03 1954-08-10 Rca Corp Simplified compbination fm and television receiver
US2922119A (en) * 1949-11-12 1960-01-19 Zenith Radio Corp Frequency halving synchronized oscillator
US2677059A (en) * 1951-03-06 1954-04-27 Rca Corp Signal generator
US2817756A (en) * 1952-06-03 1957-12-24 Charles A Debel Variable bandwidth constant peak-amplitude discriminator
US2790905A (en) * 1953-06-09 1957-04-30 Marconi Wireless Telegraph Co Automatic frequency control
US2891105A (en) * 1953-09-23 1959-06-16 Rca Corp Automatic frequency control apparatus
DE1040088B (de) * 1954-05-28 1958-10-02 Philips Patentverwaltung Empfangsgeraet fuer frequenzmodulierte Schwingungen
US2946960A (en) * 1956-05-16 1960-07-26 Motorola Inc Electronic circuit
DE1093429B (de) * 1956-07-07 1960-11-24 Koerting Radio Werke G M B H Demodulationsschaltung
US4068173A (en) * 1977-01-03 1978-01-10 Gte Automatic Electric Laboratories Incorporated Frequency stabilized microwave signal source

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GB562993A (en) 1944-07-25
FR955303A (enrdf_load_stackoverflow) 1950-01-14

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