US2180736A - Phase modulation receiver - Google Patents

Description

Nov. 21. 1939. c. w. HANsELL 2,180,736

YHSE MOULATIQN RECEIVER Filed May 5, 1956 2 sheets-sheet 1 REC; l

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INVENTOR CLARENCE Wl HANSELL n BY gg i- "'III" I /iATl-m ,QE/IMP. /sr [,757: I E AMP I Nov. 21, 1939.y V c, w, HANSELL 2,180,736

PHASE MODULATION RECEIVER y I Filed May 5, 19:56 '2- sneeze-sheet 2 2,26.,- i: Li: v :i PHASE Mao. f i: 1:

WAVE 7- l ATTORNEY l i lNvr-:N'roR I I CLARENCE W. HANSELI.

Patented Nov. 21

2,180,736 PHASE MoDULA'rIoN REcEIVER Clarence W. Hansell, Port Jeerson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application May 5, 1936, Serial N0. 77,978

Claims.

It is quite well known that an electron tube oscillator, coupled to another source of alternating current energy of very nearly the same frequency, can easily be held at exactly the same frequency as the other source. In this case, if the natural frequency of the oscillator and the frequency of the other source are made different by varying amounts then the anode current to I, n the oscillator tube will vary approximately in of phase modulated signals detected with frequency modulation detectors it is only necessary to distort the audio output by making the audio circuits respond with a relative strength which is inversely proportional to the modulating, frequency.`

Such a means for correcting the output of a frequency modulated wave receiver on which phase modulated Waves are impressed is. shown in Crosbys United States application #618,154 led June 20, 1932.

My present invention involves a new and simplified phase modulation receiver which gives substantially correct values of output for all modulating frequencies without the use of correction circuits of the type used in Crosbys application #618,154 filed June 20, 1932.

In the present invention I cause oscillating detectors of a type somewhat similar to those disclosed in my Patent #1,867,567 to respond correctly to phase modulated signals, without the use of audio frequencyA response distorting circuits. 'I'his is accomplished by tuning the anode circuit of a pair of push-pull oscillating detector tubes by means of a circuit of such low power factor vthat it will not respond or appreciably change its current at a rate higher than the lowest audio frequency on the modulation wave. This circuit is preferably tuned to the frequency of the carrier wave carrying the phase modulated signal. In a preferred embodiment, this carrier wave is derived from the output of the first de- `rtector in a heterodyne receiver and is of a frequency of the order of an intermediate frequency.

In describing my novel system reference will be Amade to the drawings in which Figures l1 to 3 inclusive each show the essential elements of a phase modulating receiver of the oscillating de- (Cl. Z50-20) tector type arranged in accordance with my inv vention. The circuit of Figure 1 also includes a radio frequency amplifier, first detector, and an intermediate frequency amplifier of a heterodyne receiver which feeds the phase modulated wave to the novel demodulating circuit of the present invention. The heterodyne receiver here also includes frequency or phase control means. Each `of the figures includes different types of low power factor circuits connected between the anodes of the oscillating detectors,

Referring to the drawings, each phase modulation receiver comprises two electron discharge devices IIJ and I2, having their control electrodesconnected in push-pull relation as shown by a reactance 26 and grid leak and condenser units 6 and 8 and their anode electrodes connected by a radio frequency circuit I4, I4', and I4, in

Figures 1, 2, and 3 respectively, of low power factor. The anode electrodes of the tubes are also connected with a modulation. frequency output circuit comprising a transformer 24 having two primary windings PI, P2r connected by way of blocking condensers 23 and 25 between the anodes and cathodes of tubes I0 and I2 respectively. The tubes II) and I2 when energized, produce oscillatory energy which appears in 20. These voltages excite the control electrodes in displaced phase relation as indicated by the arrows at the right of 2U. Oscillation generation in these tubes may be due in part to external circuit tuning and impedance and inner electrode coupling as in Figures l and 2 or to external coupling circuits as in Figure 3, by means of which energy is supplied from the anode circuits to the grid circuits in the proper phase relation to produce regeneration.

The oscillators I0 and I2 are in a sense, entrained and produce oscillations of a frequency determined by the reactance 20 and low power factor circuits I4, I4', and I4".

Phase modulated waves are applied to a tuned circuit I8 from any source and from I8 in like phase to the control electrodes of tubes I0 and I2 as indicated by the arrows at the left of '20. The relation between the average phases of the waves applied from I8 to the control electrodes of tubes Ill-and I2 and the phase of the oscillations produced in I0 and .I2 and applied through 20 to the electrodes may vary through a wide range. In a preferred embodiment, a phase quadrature relation is produced.

If the circuit I8 is excited by a first detector andan intermediate frequency amplifier, as in Figure l, I8 is tuned to the intermediate frequency, I8 may be coupled toa radio frequency amplier. In any event, provision must be made to insure that the phase modulated Waves in I8 are of a frequency as near as possible equal to the frequency of the oscillations produced in III and l2 so that the phase displaced oscillations and modulated wave energy on the control electrodes may combine properly.

The low power factor or high Q circuit in Figure 1 comprises a piezo-electric crystal I4 connected as shown between the anode electrodes. lll has a natural period of vibration equal to the mean frequency of oscillation of IB and l2, which is also the mean frequency of the applied phase or frequency modulated wave. In other words, this circuit is highly selective to the selected frequency. The low loss power factor circuit in Figure 2 comprises a portion or section of a large size transmission line. This section including lll and its enclosing member l5 is preferably as shown of an electrical length equal to one-half the length of the wave produced in l and l2 and of the signal carrying wave applied in i8. The anodes as shown are connected as shown to spaced points on this line and the line is, in effect, a parallel tuned circuit of very low power factor connected between the anodes of I ll and l2. The line lll and enclosing member are preferably large in diameter and of highly conductive material. The line is dimensioned and connected in the circuit so that it forms sured in this modification by virtue of feedback between the electrodes of the tubes. Constant frequency operation is insured by virtue of the high Q or 10W loss characteristic at the line and circuit. The line control oscillator of this olisclosure is in some respects similar to that shown in Lindenblads United States application #6,814 led February 16, 1935. In Figure 3 the low power factor circuit comprises a magnetostriction oscillation control element lll". This element comprises a mechanical vibrator in the form of a metallic member i3 and magnetizing windings W and W' on each end thereof connected in the anode circuits of tubes IU and l2 respectively. The member i3 may be permanently magnetized or, if preferred, may be magnetied by a direct current circuit. The rod v1- brates or distorts in the presence of a field such as produced by W and W'. If the natural period of the member i3 is coordinated properly with the frequency change or reversal of the field produced by W or W- strong vibrations are set up in the rod i3. The circuit including W and W and member i3 forms a resonant circuit of high Q or low loss or low power factor at the frequency of oscillation which is the mean frequency of the impressed phase or frequency modulated wave. For further information concerning magnetostriction oscillations as illustrated in Figure 3, see pages 270 to 273 of Radio Engineering by Terman, first edition.

In describing the operation of my phase modulated wave receiver, reference will be made to Figure 1 of the drawings. Here the two tubes l0 and I2 form a push-pull piezo-electric crystal controlled oscillator in which the crystal is connected between the ltwo anodes and forms the equivalent of a tuned anode circuit if distributed inductance and capacity of tubes, connections, etc., arey taken into account. A phase modulated carrier is applied to the grids of the two tubes in parallel or push-pull relation. Normally I prefer to have the average phase of the input about different from the phase of the locally produced oscillations on the grid of either tube and to have the self-produced oscillations in synchronism with the -input energy except for said phase displacement.

To obtain synchronism I first adjust the first heterodyne of the receiver to the frequency of the oscillations produced in the oscillating detectors lll and l2. Under certain conditions the grid leak and condenser units 6 and 8 in the grid circuits of l0 and l2 produce direct current potentials. Now, if the relative phase of the oscillating energy produced by IG and l2, and the signal modulated energy changes, the two voltages on one grid will more nearly add in phase and those on the other grid will more nearly oppose. Thus, the radio frequency or carrier frequency input to the two oscillating detector grids will vary differentially as the phase of the oscillations produced and the applied signal wave varies around the selected average values. Due to the grid leak action of 6 and 8 the average bias potential on one tube will gol up and the other go down when the phase of the incoming wave changes and will result in unbalancing oi' anode currents. If the relative phases vary rapidly the anode current will Vary rapidly and cause output current to flow in the secondary of transformer 24. Thus the desired modulation of phase of the wave applied at i8 is caused to produce corresponding and linear current changes in the output of 24.

The large size transmission line lll' of Figure 2 and the magneto-striction oscillator control means l of Figure 3 also provide low power factor anode circuits for the tubes lll and I2 and serve in a manner which will be apparent to control the oscillating detectors Ill and l2 in a manner such that phase modulations on the input electrodes of said tubes produce corresponding direct current modulations or variations in the output circuit. In fact, if a sufficiently low intermediate frequency is used an ordinary tuned circuit will be of sufficiently low power factor for carrying out the present invention and in many practical cases will be used.

In each case, the radio frequency potentials may be prevented from reaching the audio frequency circuits by means of choking inductances RFC connected as shown between the low power factor circuits and audio frequency circuits in each figure.

Proper biasing potentials for the oscillating detectors lll and l2 may be supplied by a condenser by-passed source I6. In practice I may omit the grid leak and condenser units 6 and 8 and utilize the non-linear tube characteristic obtained by proper biasing potentials to obtain the unbalance in the anode currents when the relative phases of the applied currents shift.

Anode potentials may be supplied to the tubes I0 and l2 in any manner but preferably are supplied by way of resistances 25 connected as shown.

If the relative phases of the signal carrying wave and the locally produced oscillations tend to drift apart for a longer time than the time of phase deviation due to signal modulations there will be produced a steady unbalance o-f anode currents. This steady unbalanced current in the anodes of IU and l2 may be caused to produce differential potentials at 26 which may be used through a phase or frequency control circuit to control the phase or frequency of the local oscillato-r connected with the rst detector. This control circuit forms no part of the present invention and need not be described more in detail here. A similar control circuit has been described in` detail and claimed in orosbys United YStates application #616,803 rfiled June 13, 1932,

pendent upon the phase of alternating electrical energy which includes the steps of locally converting direct current energy into alternating current energy of va fixed frequency equal to the mean frequency lof the alternating electrical energy and of a phase different thanrthe phase of `the alternating electrical energy, superposing the n alternating electricall'energy on the alternating current to vary the eiciency of said conversion, and producing a response corresponding to the magnitude of the direct energy converted as an indication of the phase of the alternating energy.

2. The method of securing a response dependent upon the phase of alternating electrical energy which includes the steps of, locally converting direct current into alternating current' vof a Xed frequency equal to the frequency of the alternating electrical energy but of a phase different than the phase of the alternating electrical energy, combining the alternating electrical energy with the alternating current to. control said conversion, producing a response characteristic of the intensity of the direct energy converted, and producing an indication` charac- .teristic of said response.

3. The method of securing a response dependent upon the phase of alternating electrical energy by means of a low power factor oscillator which includes the steps of, locally converting direct current energy into alternating current in said oscillator of low power factor, adjusting said oscillator to a xed frequency equal to the mean frequency of the alternating electrical energy and of a phase different than the mean phase of the alternating electrical energy, applying the alternating electrical energy to said oscillator to control the character of said conversion, and

, producing a response corresponding to the mag- .nitude of the direct current energy supplied to the oscillator as an indication of the phase of the alternating energy.

4. The method of 'detecting phase modulations on oscillatory energy which includesthe steps of, converting direct current energy into alternating current of afrequency equal to the mean frequency of the oscillatory energy and of a phase different than the mean phase of the phase modulated oscillatory energy, simultaneously converting direct current energy into other alternating current of a frequency equal to the mean frequency of the modulated oscillatory energy and of a phase different than the mean phase of the phase modulated oscillatory energy, combining phase modulated oscillatory energy with each of the said alternating currents to control said conversions, and utilizing the differential of the direct current energies converted for producing indications.

5. The method of detecting phase modulations on oscillatory energy which includes the steps of, converting direct current energy into alternating current of. a frequency equal to the mean frequency ofthe phase modulated oscillatory en-v oscillatory energy, entraining said alternating currents, impressing said phase modulated oscillatory energy on said entrained alternating currents to control the efliciency of said conversions nating current in the other of said oscillators of low power factor, adjusting said second low power factor` oscillator to the mean frequency of the oscillatory energy and to a phase different than the mean phase ofthe oscillatory energy,

applying the phase modulated oscillatory energyv in like phase to the said oscillators to control the operation thereof and utilizing the` differential of thevdirect energies supplied to said low powerv factor oscillators for producing indications. ,l

7. In a system for demodulating phase modulated oscillatory energy, a pair of electron discharge tubes each having a control grid, a cathode and an anode, a circuit resonant at the mean frequency of said oscillatory energy and of low power factor connecting the anodes of said tubes in push-pull relation, an alternating current circuit tuned to the mean frequency of said oscillatory energy connected with the control grids of said tubes, means for energizing the electrodes of said tubes whereby oscillatory energy of substantially constant phase is produced in said tubes and circuits, means for applying -phase modulated oscillator energy the mean frequency a natural `period equal tothe frequency of said phase modulated oscillatory energy connecting the anodes of said tubes in push-pull relation, an alternating current circuit connected with the control grids of said tubes, means for energizing the electrodes of said tubes whereby oscillatory energy is produced in said tubes and vcircuits of a frequency equal to the natural period of said crystal, means for applying phase modulated energy the mean frequencyv of which is equal to the frequency of the produced oscillatory energy in phase to the control grids of said tubes and a utilization circuit connected with the anodes and cathodes of said tubes.

9. In a system for demodulating phase modulated oscillatory energy, a pair of electron discharge tubes each having a control grid, a cathode and an anode, a low power factor transmisysion line connecting the anodes and cathodes of saidV tubes in push-pull relation, said line having a natural frequency equal to the mean frequency of said kphase modulated oscillatory energy', .an

alternating currentl circuit connected to they control grids of said tubes, means for energizing the lil() electrodes of said tubes wherebyoscillatory energy is produced in said tubes and circuits, means for applying phase modulated energy the mean 'frequency of which is equal to the frequency of the produced oscillatory energy in phase to the control grids of said tubes and a utilization circuit coupled with the anodes of said tubes.

10. In a system for demodulating phase modulated oscillatory energy, a pair of electron discharge tubes each having a control grid, a cathode and an anode, a magneto-striction oscillation control circuit of low power factor connecting the anodes and cathcdes of said tubes in push-pull relation, said magneto-striction circuit being resonant at a frequency equal to the mean frequency of the phase modulated oscillatory energy a circuit connected with the control grids and cathodes of said tubes, means for energizing the electrodes of said tubes whereby oscillatory energy is produced in said tubes and circuits, means for applying phase modulated energy the mean frequency of which is equal to the frequency of the produced oscillatory energy in phase to the control grids of said tubes and a utilization circuit coupled with the anodes of said tubes.

11. In a system for demodulating phase modulated wave energy, a pair of electron discharge tubes each having a control electrode, an anode and a cathode, circuits connecting said control electrodes and cathodes in push-pull relation, a biasing impedance in each of said circuits, reactive means connected with the control electrode of each tube for applying phase modulated energy in phase to said control electrodes, a circuit of low power factor connecting the anodes of said tubes in push-pull relation, saidA circuit being resonant at the mean frequency of the wave energy, a signalling circuit connected with the anodes of said tubes and means for energizing the electrodes of said tubes to produce sustained oscillations in said tubes and circuits.

12. In a system for demodulating phase modulated wave energy, a pair of electron discharge tubes each having a control electrode, an anode and a cathode, alternating current circuits connecting said control electrodes and cathodes in push-pull relation, a biasing impedance connected with each of said circuits, reactive means connected with the control electrode of each device for applying phase modulated wave energy in phase to said control electrodes, a circuit tuned to resonance at the mean frequency of the phase modulated wave energy and of low power factor connecting the anodes and cathodes of said tubes in push-pull relation, a signalling circuit connected with the anodes of said tubes and means for energizing the electrodes of said tubes to produce sustained oscillations in said tubes and circuits.

13. In a signalling system, an oscillator, means for causing said oscillator to oscillate in synchronism with phase or frequency modulated wave energy to be demodulated including a frequency selective circuit incapable of responding fully to wave energy variations of the frequency of modulation of said phase or frequency modulated Wave energy to be demodulated, means for supplying direct current to said oscillator to operate the same, and means for controlling the value of the supplied direct current in accordance with phase differences between the modulated wave energy to be demodulated and the wave energy set up in said frequency selective circuit by virtue of oscillation of said oscillator.

14. In a phase modulated Wave demodulating system, an oscillator, means associated therewith for causing said oscillator to oscillate substantially in synchronism with the carrier of phase modulated wave energy to be demodulated, means including said first named means for causing said oscillator to have an output substantially proportional to the phase difference vbetween the oscillations produced by said oscillator and the said phase modulated wave energy, and means for imf pressing said phase modulated wave energy on said oscillator.

15. A phase modulated wave demodulating system as recited in claim 1,4 including means for automatically holding the carrier of the phase modulated wave energy to be demodulated at a substantially constant phase relation with respect to the oscillations produced by said oscillator.

16. A phase modulated wave demodulating system according to claim 14 where the said oscilto operate substantially in synchronism with the f carrier of the phase modulated wave energy of intermediate frequency, means including said rst named means for causingv said oscillator to have an output substantially proportional to the phase difference between the oscillations pror duced by said constrained oscillator and the phase modulated Wave energy yof intermediate frequency, and means for impressing the phase modulated wave energy of intermediate frequency on said constrained oscillator.

i8. A system as recited in claim 1'? including means for automatically holding the carrier of the phase modulated wave energy of intermediate frequency at a substantially constant phase relation with respect to the oscillations produced by said constrained oscillator.

19. A system as recited in claim 17 wherein said constrained oscillator and means includes circuits so selective that oscillatory energy stored in them cannot change in amount substantially at rates corresponding to the modulation fre-y quencies of the intermediate frequency Wave energy.

20. In a system for demodulating wave energy modulated in phase, a local oscillator including an oscillatory circuit tuned to the mean frequency of said wave energy and having a power factor sufliciently low that the current iiow therein will not change in intensity substantially at a rate higher than the lowest modulation frequency on the wave energy to be demodulated, direct current supply means for energizing said local oscillator for producing oscillatory energy in said oscillatory circuit of a frequency equal to the mean frequency of said phase modulated wave energy, means for impressing said phase modulated wave energy on said oscillator to modify its oscillation in accordance with the relation between the normal phase of the oscillatory energy and the phase of the modulated wave energy, and means for utilizing the changes of intensity of the direct current supplied to said local oscillator as an indication of the phase modulation on said wave energy.

CLARENCE W. HANSELL.

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