US2497605A - Wave length modulating device - Google Patents

Description

Patented Feb. 14, 1950 WAVE LENGTH MODULATING DEVICE Gerard Hepp, Eindhoven, Netherlands, assignor to Hartford National Bank & Trust Company, Hartford, Conn., as trustee Application May 13, 1947, Serial No. 747,778 In the Netherlands May 23, 1946 Claims.

1 The invention relates to a device for producing oscillations modulated in frequency or in phase by sound oscillations, more particularly for being used as a communication transmitter. In transmitters of this kind the carrier frequency must be very constant, whereas the frequency sweep is allowed to be comparatively small, since the frequency range occupied by the communication to be transmitted is comparatively small.

The'object of this invention is to provide a means to frequencyor phase-modulate a given constant oscillator frequency in accordance with some desired transverse audio wave. According to the invention, this modulation may be made to vary in a predetermined manner as a function of the frequency of the impinging transverse audio wave by a manipulation of the physical properties of certain circuit elements.

In a well-known circuit-arrangement phase modulation is effected by supplying a carrier oscillation of constant frequency, for example, originating from a crystal-controlled oscillator, to a phase-displacing network, in which the phase displacement depends on a modulating quantity, for example, a modulating current, which varies the inductance of coils included in the network, the phase-shifting being subsequently materially increased with the aid of frequency multipliers.

According to the invention, phase displacement is effected by including reactances in the phase-displacing network, which are mechanically varied by sound oscillations.

It is known per se to include reactances varied by sound oscillations in the tuning circuit of a generator of frequency-modulated oscillations but such a generator exhibits the limitation in that the central frequency is not constant.

To constitute variable reactances use may be made in particular of condensers; these variable condensers can readily be united to form a single condenser microphone by dividing one of the electrodes of such a microphone into a plurality of relatively insulated sectors.

In order that the invention may be more clearly understood and readily carried into effect, it will now be explained more fully with reference to the accompanying drawing.

Figure 1 illustrates one embodiment of the invention;

2 which produces the oscillation to be modulated and 2 a phase-shifting network, in which the capacities C are each constituted by the capacity of each sector of the subdivided electrode of a condenser microphone relatively to the other nonsubdivided electrode.

By suitable choice of the mechanical constants the characteristic curve of the microphone may be given such form that the low notes of the sound oscillations to be transmitted bring about a materially larger capacity variation than the high notes. This device produces frequencymodulated oscillations, while dispensing with the customary integrating network which is otherwise essential to produce frequency-modulated oscillations with the aid of phase-modulators and transforms the modulating sound oscillations in such manner thatthe modulated oscillation exhibits a frequency deflection which is proportional to the sound oscillations. In general, however, the characteristic curve of the microphone will be given a considerably less marked form than corresponds with complete integration in order to ensure at the same time the preemphasis of the high notes.

Fig. 2 illustrates the frequency characteristic curve of a microphone of this kind.

Fig. 3 shows a cross-section of the variable reactance elements referred to in Fig. 1. Each of the reactive components marked C are shown with external leads on one side and a common plate or diaphragm on the other forming both the electrical terminal and the diaphragm upon which the sound oscillations impinge. Such impinging will cause a relative displacement of the diaphragm and, therefore, the reactance between the common terminal and the individual lower terminals will vary as a function of the sound oscillation.

The frequencyor phase-modulated oscillations set up in the output circuit of the phase-shiftingnetwork 2 may be fed, as indicated in Fig. l, to a frequency multiplier 3 in order to increase the frequency or phase deflection.

What I claim is:

1. A wavelength modulating circuit arrangement; comprising a source of oscillatory potential, an output circuit coupled to said source and means to vary the phase of said potential, said means comprising an electro-acoustical capacitative transducer responsive to sound waves impinging thereon and having a first electrode and a second electrode comprising a plurality of electrode elements} in capacitative relationship with said first electrode and defining a plurality of distinct capacitors with said first electrode, one of said electrodes being in the form of an acoustically vibratory diaphragm and the capacity of each of said capacitors being individually variable in proportion to the magnitude of the sound waves impinging on said diaphragm, an impedance element interconnecting two of said second electrode elements to form therewith and with said first electrode a phase shifting network, and means to connect said network to said source to vary the phase of said source in proportion to the magnitude of the sound waves impinging on said dia phragm.

2. A wavelength modulating circuit arrangement, comprising a source of oscillatory potential, an output circuit coupled to said source and means to vary the phase of said potential, said means comprising an electro-acoustical capacitative transducer responsive to sound waves immeans to connect said network to said source to vary the phase of said source as a function of the magnitude of the sound waves impinging on said diaphragm.

3. A wavelength modulating circuit arrangement, comprising a source of oscillator potential, an output circuit coupled to said source and means to vary the phase of said potential, said means comprising an electro-acoustical capacitative transducer responsive to sound waves impinging thereon including an acoustically vibratory conductive diaphragm, a plurality of electrodes, each electrode in conjunction with said diaphragm defining a distinct capacitor, the capacity of each of said capacitors being variable in magnitude in proportion to the magnitude and in inverse proportion to the frequency of sound oscillations impinging on said diaphragm, a plurality of impedance elements interconnecting said electrodes to form therewith a phase shifting network, and means to connect said network to said source to vary the phase of said source in proportion to the magnitude and in inverse propor-- tion to the frequency of the sound waves impinging on said diaphragm.

'4. A wavelength modulating circuit arrangement, comprising a source of oscillatory potential,

an output circuit coupled to said source and .an electro-acoustical capacitative transducer responsive to sound waves inpinging thereon for translating sound energy into electrical energ and for coupling said source of oscillator potential to said output circuit including a first electrode and a second electrode comprising a plurality of electrode elements in capacitative relationship with said first electrode and defining a plurality of distinct capacitors with said first electrode, one of said electrodes being in the form of an acoustically vibratory diaphragm and the capacity of each of said capacitors being individually variable in proportion to the magnitude of the sound waves impinging on said diaghrag-m, an impedance element interconnecting two of said second electrode elements to form therewith and with said first electrode a phase shifting network, and means to connect said network to said source to vary the phase of the source in proportion to the magnitude of the sound waves impinging on said diaphragm.

5. A wavelength modulating circuit arrangement, comprising a source of oscillatory potential, an output circuit coupled to said source and an electro-acoustical capacitative transducer responsive to sound waves impinging thereon for translating sound energy into electrical energy and for coupling said source of oscillatory potential to said output circuit including an acoustically vibratory conductive diaphragm, a plurality of electrodes, each electrode in conjunction with said diaphragm defining a distinct capacitor, the capacity of each of said capacitors being variable in magnitude as a, function of the magnitude of sound oscillations impinging on said diaphragm, a plurality of impedance elements interconnecting said electrodes to form therewith and with said diaphragm a phase shifting network and means to connect said network to said source to vary the phase of said source as a function of the magnitude of the sound waves impinging on said diaphragm.

GERARD HEPP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,615,645 Nyman Jan. 25, 1927 2,077,223 Crosby Apr. 13, 1937 2,262,468 Percival Nov. 11, 1941 2,418,842 Kinsburg Apr. 15, 1947

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