US3007120A

US3007120A - Modulation system

Info

Publication number: US3007120A
Application number: US772480A
Authority: US
Inventors: Robert C Ferrar
Original assignee: Deutsche ITT Industries GmbH
Current assignee: TDK Micronas GmbH; International Telephone and Telegraph Corp
Priority date: 1958-11-07
Filing date: 1958-11-07
Publication date: 1961-10-31
Anticipated expiration: 1978-10-31

Description

R. c. FERRAR MODULATION SYSTEM Oct. 31, 1961 Filed NOV. '7, 1958 1 muxb 1 .0.3K QQ. n. kboubo .$152 mv m wwvbo; "Q U Inventor R085 7' C FRRAR- ...015% .wht Sagt Attorney .mbkbb ited States This invention relates to a carrier modulating system and more particularly to a system for producing double sideband suppressed carrier signals.

In t-he usual methods for suppressing the carrier in suppressed carrier systems a balanced modulator is employed using either vacuum tubes or diodes. A carrier is introduced in such a way that it does not appear in the output but the sidebands do. This is accomplished by introducing the audio signal in push-pull and the carrier in parallel and connecting the output in push-pull. It can also be connected with the carrier and audio inputs in push-pull and the output in parallel. These methods, however, require relatively expensive components and circuitry.

It is an object of this invention to replace the relatively expensive balanced modulators normally used for accomplishing the modulation process in a single sideband system for voice communication by a simple and inexpensive device.

It is a further object to provide a modulating system that completely suppresses the carrier without depending on critical balance of any of its elements.

A feature of this invention is a modulating system which comprises means for producing two forces one opposed to the other and varying these forces in intensity in accordance with a first modulating energy. There are provided also means for varying the resistance to each of said forces inversely in accordance with a second modulating energy and means for extracting from the forces a modulated wave which is the product of the iirst and second modulating energies.

A further feature of this invention is the provision in a modulating system of a magnetically permeable structure having pole pieces disposed on both sides of an air gap and means for producing simultaneously opposing magnetic elds in the pole pieces which vary in intensity in accordance with a modulating signal energy. Means are provided within the air gap for varying inversely the reluctance of the magnetic circuit of each magnetic iield sinusoidally at a constant rate and means are provided within the magnetic elds to derive therefrom a signal voltage varying in amplitude in accordance with the intensity of the magnetic iield and reversing in phase in accordance with reversal of the magnetic iield and with the frequency at which the reluctance of the magnetic circuit is varied.

Still a further feature of this invention is the provision of a magnetically permeable U-shaped structure having pole pieces disposed on both sides of an air gap and primary inductor means disposed on both legs of the structure to produce simultaneously opposing magnetic elds in both of the pole pieces but varying in intensity and in polarity in accordance with a modulating signal energy. A transducer is excited by a second modulating signal energy of a higher frequency than the first modulating signal energy and the transducer moves a magnetically permeable member within the air gap in a to and fro motion at the frequency of the second modulating energy. This movement of the member within the air gap varies inversely the reluctance of the magnetic circuit of each magnetic field and introduces in secondary inductor atent 3,007,120 Patented Oct. 31, 1961 ice coils wound in the legs of the U-shaped structure a signal which is the product of the lirst and second modulating signals.

A further feature is that the primary inductor coils having the first modulating signal energy are wound in the same direction to produce magnetic fields of the same polarity in both pole pieces. One of the secondary inductor coils is wound opposite to the direction of winding of the other secondary coil and t-he primary coils so that any signal of the first modulating energy that would be induced in the secondary coils is cancelled out and the product signal energies induced in the secondary output coils are added together at the output thereof.

Still a further feature of this invention is the method of generating the modulated wave which comprises the steps of producing two magnetic fields one opposed to the other which Vary in intensity and in polarity in accordance with a modulating signal, varying the reluctance of the magnetic iields inversely in accordance wit-h the harmonic motion of magnetic material disposed within the magnetic fields and extracting from the magnetic fields a signal which is proportional to the product of said modulating signal and said harmonic motion, and containing no signals having frequencies corresponding to those of said modulating signal and said harmonic motion.

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. l is a schematic diagram of the modulating system of this invention;

FIG. 2 is a graph of the curves of the input and output signals of the system without a carrier signal; and

FIG. 3 is a graph of the input and output signals of the invention with a carrier signal.

Referring to FIG. l, there is shown a magnetically permeable U-shaped structure 1 which has two pole pieces 2 and 3 disposed on the ends of the legs 4 and 5 of the U-shaped structure and opposite each other on both sides of the air gap 6. Primary coil 7 is wound on leg 5 and primary coil 8 connected in series to coil 7 is wound on leg 4, and are connected to the modulating voltage input. Primary coil 8 is wound in the same direction as coil 7 so that when coils 7 and 8 are excited by an audio signal similar magnetic poles on both sides of the air gap 6 are produced. Secondary coil 9 is Wound on leg 5 in the same direction as coil 7. Secondary coil 10 connected in series to secondary coil 9 is wound on leg '4 in a direction opposite to the Winding of secondary coil 9 and primary coils 7 and 8. A transducer 11, which may be a crystal transducer or any similar device, is connected to a source of carrier signal. Coupled to the crystal transducer 11 and movable thereby at the frequency of the carrier signal is a magnetically permeable member 12, such as an iron vane, disposed within the air gap 6 and free to move in a to and fro motion within the air gap. The carrier signal is a single tone having a frequency in the range 8-36 kc. It is understood, however, that the frequency may be greater and is limited solely by the ability of the iron vane to move at the given frequency. The member 12 is disposed almost the entire length of the inner space of the U-shaped member 1 and it is understood that the clearance between the end 13 of the member 12. and the base 14 of the U-shaped member 1 is held as small as possible so that a minimum air gap is produced in order to keep the reluctance of the magnetic circuits as low as possible at that point. The air gap 6i, on the other hand, is relatively large to provide a relatively large fluctuation in the reluctance of the magnetic paths as the member 12 is moved in agreement with the carrier signal. When the primary coils 7 and 8 are excited by an audio signal similar magnetic poles are produced on both sides of the air gap and magnetic paths are produced within the U-shaped member 1 and the member 6 as illustrated by the broken lines 15 and 16 which illustrate opposing magnetic fields. At any instant pole pieces 2 and 3 are both north or both south or the magnetic field is Zero. The magnetic iiux which is effective on the secondary coils 9 and 10 is modulated sinusoidally by the mechanical motion of the iron vane 12 which is driven at the desired carrier frequency by the crystal transducer 11. Modulation takes place because of the change in reluctance of the magnetic paths of both magnetic circuits as the iron vane 12 successively assumes different positions within the magnetic field in accordance with a sine law.

It ca n =be seen that if the secondary coils 9` and 10 are so wound as to produce additive voltages with respect to the motion of the iron vane 12 voltages induced in coils 9 and 10 from primary windings 7 and 8 will cancel, thus producing no modulating voltage at the output terminals if all coils are previously balanced. An approximate balance between coils 7 and 8 and between 9 and 10 is desirable in order to keep the modulating frequency component at the output terminals small. However, the carrier output amplitude will be proportional to the instantaneous current in coils 7 and 8 and the phase of the output will reverse when the exciting current in coils 7 and 8 reverses. To produce a fiat frequency response coils 7 and 8 must be driven from a constant current source.

The waveforms of FIGS. 2 and 3 illustrate the conditions occurring in the modulation system of this invention without carrier and with carrier produced by the motion of the iron vane. In FIG. 2, the input modulation voltage having the waveform A has the same form B and C in coils 7 and 8. The induced voltage D in coil 10 is of the same phase as the voltages B and C, due to double reversal obtained from the 180 phase lag of the induced voltage, together with the reversal of the winding. The induced voltage E in the secondary winding 9 is 180 out of phase from the impressed voltage of coil 7. The output voltage F therefore has zero voltage due to the cancellation of the oppositely phased currents in windings 9 and 10. In FIG. 3 the modulating voltage G is of the same form as A and the voltage in windings 7 and 8 shows the waveforms H and I which are the product of the modulating voltage and the modulation of the magnetic fiuxes in both circuits with the carrier amplitude proportional to the intensity of the magnetic field as produced by the modulating voltage. In the waveform H it is assumed for reference that the iron vane is moving in such a direction that the reluctance of the magnetic path of the magnetic circuit 16 is decreasing so that the carrier voltage has an increasing positive magnitude. Conversely, the reluctance of the magnetic path 15 is increasing so that the carrier phase in the winding 8 is rotated 180 from that in winding 7 as shown in waveform I. The induced voltage then in secondary winding 10 shown as the waveform J is of the same phase and same amplitude as the waveform of waveform H. The waveform K illustrates the induced voltage in the secondary winding 9 with the phase of the modulating voltage reversed 180 from the voltage of the waveform of I. It should be noted with reference to the waveforms of H, I, J and K that the carrier component phase reverses each half cycle of modulating signal due to reversal of ux polarity. rI`he output voltage is then the sum of waveforms I and K and since the carrier phases are opposite in coils 9 and 10, and the coils are connected in polarity opposition, the voltages are additive. There is thus produced as the output of the secondary windings 9 and 10 a voltage which is proportional to the product of the input modulating voltage and the carrier voltage. This is, in effect, a double sideband suppressed carrier wave. There is negligible audio output if the windings are balanced. There is no output of carrier since the injection of the carrier is fully mechanical and therefore there is no induced unmodulated carrier in the output windings.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A modulating system comprising a magnetically permeable structure having pole pieces disposed on both sides of an air gap, modulating signal energy means for producing simultaneously similar and substantially equal magnetic fields in said pole pieces varying in intensity in accordance with said modulating signal energy, means disposed within said air gap for varying the reluctance of the magnetic circuit of each said magnetic field sinusoidally at a constant rate and means disposed within the magnetic fields to derive therefrom a signal voltage varying in accordance with the intensity of said magnetic fields and with the frequency of said sinusoid.

2. A modulating system comprising a magnetically permeable structure having pole pieces disposed on both sides of an air gap, first modulating signal means for producing simultaneously similar and substantially equal magnetic fields in both said pole pieces varying in intensity in accordance with said first modulating signal, means disposed within said air gap for varying the reluctance of the magnetic circuit of each said magnetic fields at the frequency of a second signal, and inductor coils disposed in said magnetic fields to derive therefrom a signal which is proportional to the product of said first and second signals.

3. A modulating system comprising a magnetically permeable structure having pole pieces disposed on both sides of an air gap, first modulating signal means for producing simultaneously similar and substantially equal magnetic fields in both said pole pieces varying in intensity in accordance with said first modulating signal energy, inductor coils disposed within said magnetic fields, means disposing a magnetically permeable member within said air gap between said pole pieces, means coupling a source of a second modulating signal energy to said member whereby said member, when said coupling means is excited by said second signal, will move to and fro within said air gap at the frequency of said second signal to vary the reluctance of the magnetic circuit of each said magnetic field and induce thereby in said inductor coils a signal which is proportional to the product of said first and second modulating signals.

4. A modulating system comprising a magnetically permeable structure having pole pieces disposed on both sides of an air gap, first modulating signal means for producing simultaneously similar and substantially equal magnetic fields in both said pole pieces varying in intensity in accordance with said first modulating signal, first and second secondary coils disposed in said magnetic fields, a transducer, means coupling a magnetically permeable member to said transducer and disposing said member within said air gap between said pole pieces, means coupling a source of a second modulating signal energy to said transducer whereby said transducer, when excited by said second signal, will move said member to and fro within said air gap at the frequency of said second signal to vary the reluctance of the magnetic circuit of each said magnetic field yand induce thereby in said first and second secondary coils a signal which is proportional to the product of said first and second modulating signals.

5. A modulating system comprising a magnetically permeable structure having pole pieces disposed on both sides of an air gap, first modulating signal means for producing simultaneously similar and substantially equal magnetic fields in both said pole pieces varying in intensity in accordance with said first modulating signal energy in- :recargo cluding first and second primary coils, means disposing said primary coils about said structure in the same direction of current flow therethrough, and means coupling a source of said first modulating signal energy to said first `and second primary coils; first and second secondary coils disposed in said magnetic fields, said first secondary coil being wound in the same direction as said first primary coil and said second secondary coil being wound in a direction opposite to said second primary coil and to said first secondary coil, a transducer, means coupling a magnetically permeable member to said transducer and disposing said member within said a-ir gap between said pole pieces, means coupling a source of a second modulating signal energy to said transducer whereby said transducer, when excited by said second signal, Will move said member to and fro within said air gap at the frequency of said second signal to vary the reluctance of the magnetic circuit of each said magnetic field and induce -thereby in said first and second secondary coils a signal which is proportional to the product of said first and second modulating signals.

6. A modulating system comprising a magnetically permeable structure having pole pieces disposed on both sides of an -air gap, first modulating signal means for producing simultaneously similar and substantially equal magnetic fields in both said pole pieces varying in intensity in accordance with said first modulating signal energy including first and second primary coils, means disposing said primary coils about said structure in the same direction of current iiow therethrough, and means coupling a source of said first modulating signal energy to said first and second primary coils; first `and second secondary coils, said first secondary coil being wound adjacent said first primary coil, said second secondary coil being wound on said structure adjacent said second primary coil, means coupling said first secondary coil to said second secondary coil in series, said first secondary coil being wound in the same direction as said first primary coil and said second secondary coil being wound in a direction opposite to said second primary coil and to said first secondary coil, a transducer, means coupling a magnetically permeable member to said transducer and disposing said member Within said air gap between said pole pieces, means coupling a source of a second modulating signal energy to said transducer whereby said transducer, when excited by said second signal, will imove said member to and fro Within said air gap at the frequency of said second signal to thereby vary the reluctance of the magnetic circuit of each said magnetic field and induce thereby in said first and second secondary `coils a signal which is proportional to the product of said first and `second modulating signals.

7. A modulating system comprising a magnetically permeable U-shaped structure having pole pieces disposed on both sides of an air gap, first modulating signal means for producing simultaneously similar and substantially equal magnetic fields in both said pole pieces varying in intensity in accordance with said first modulating signal energy including first and second primary coils, said first prima-ry coil being wound on a rfirst leg of said U-shaped structure and said second primary coil being wound on a second leg of said structure, means coupling said first primary coil to said second primary coil in series, said first and second primary coils being wound in the same direction, and means coupling a source of said first modulating sign-al energy to said first and second primary coils; first and second secondary coils, said first secondary coil being wound on said first leg adjacent said first primary coil, said second secondary coil being wound on said `leg adjacent said second primary coil, means coupling said first secondary coil to said second secondary coil in series, said first secondary coil being wound in the same direction as said first primary coil and said second second-ary coil being wound in a direction opposite to said ysecond primary coil and to said first secondary coil, -a transducer, means coupling a magnetically permeable member to said transducer and disposing said member w-ithin said `air gap between said pole pieces, means coupling a source of a second modulating signal energy to said transducer whereby said transducer, when excited by said second signal, will move said member to and fro within said air gap at the frequency of said second signal to vary the reluctance of the magnetic `circuit of each said magnetic field and induce thereby in said first `and second secondary coils a signal which is proportional to the product of said first and second modulating signals.

References Cited in the file of this patent UNITED STATES PATENTS 1,841,459 Taylor Jan. 19, 1932 2,419,573 Lawlor Apr. 29, 1947 2,863,124 Misek et al. s- Dec. 2, 1958 FOREIGN PATENTS 487,016 Germany Nov. 30, 1929