US2440320A - Modulation system - Google Patents

Description

N. H. YOUNG, JR 2,440,320

MoDULA'TIoN SYSTEM Filed Marh 13, 1944 2 Sheets-Sheet 1 INVENroR.

Amm/v H. rou/VG, Je, BY i ATMP/vm April 27, 194s.

April 27,1948. N. H. YOUNG, JR 2,440,320

MODULATIN SYSTEM Filed March 13, 1944 2 Sheets-Sheet 2 5455 WHVE INVEN TOR. NORMA/v H. You/VG, Je.

Patented Apr. 27 1948 -'MonULA'rIoN SYSTEM Norman H. Yoiiiig, Jr., Jackson Heights, N. Y.,

assgnor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application March 1a, 1944, serial No. 526,264

(oi. 17e-171.5)

6 Claims.

The present invention relates to pulse generation, and more particularly to a system for generating pulses which are time-modulated in accordance with the characteristics of speech or other intelligence.

It is an object ofthe present invention to provide a system for generating time-modulated pulses.

Itis a further object of the invention to provide a time-modulation system in which a base wave is caused to be raised or lowered with respect to the normal zero axis thereof.

It is a still further object of the invention to provide means for applying to a base-Wave displaced relative to its normal zero axis, a signal Wave representing speech or other intelligence, so that the position of the base wave will be further laterally displaced toward or away from its normal zero axis in accordance with the characteristics of the modulating wave. It is an additional object of the invention to provide means for translating this speech-modulated laterallydisplaced base wave into relatively narrow pulses the time displacement of which is a function of the modulating intelligence.

Other objects and advantages will be apparent from the following description of a preferred form of the invention and from the drawings, in which:

Fig. 1 is a schematic diagram of a time-modulated pulse generator embodying a preferred form of the present invention; and

Fig. 2 is a set of curves useful in explaining the operation oi' the invention.

In Fig. 1 is shown a high-frequency oscillator 4 producing a base wave of conventional sinusoidal character, such as indicated by the waveform 6. Oscillator 4 is connected to the primary of a coupling transformer 8. A source of speech current or other intelligence, represented by the amplifier I0, is connected to the primary of a second coupling transformer I4. The speech current from amplifier l ll may be as indicated by the waveform I2 as compared to base wave 6.

The secondary windings of coupling transformers 8 and I4 form parts of a series circuit,

ent invention is designed to become saturated at a level considerably below the peak amplitude of the base wave 6. The B--H, or saturation curve for the core to be preferred is shown in Fig. 2.

Referringagain to Fig. 1, three electron discharge devices consisting of triodes V1, V2 and V3 are illustrated. V1 is an amplifier tube having a grid-cathode circuit including the coil L. The grids of V2 and V3 are respectively connected to the anode and cathode terminals of Vithrou'gn suitable coupling condensers. Each of triodes V2 and V3 is provided with a grid bias of such a value that only the positive portions of a re ceived wave will be conducted. A further amp1ier 22 is connected in the common output circuit 0f V2 and V3.

Considering now the operation of the system of Fig. I, it will be observed that the coupling transformers 8 and I4 are connected in series'with the source of polarizing voltage I8. As a result, the base wave, the speech current, and the constant direct current'will be mixed algebr'aically one with the other. However, to simplify the description, each of these currents and its effect on the remainder of the system will be considered separately.

When current from the oscillator 4 is passed through the coil L, surges of voltage are produced across'it at about the instants the current passes through zero. This mode of operation is illus* trated by the curves of Figs. 1 and 2, in which the wave 6 is shown applied to the saturation curve 24 of the core of coil L. The resulting projection illustrates the rate of change of flux in the readily saturable core of the coil. Since the satue ration level is quickly reached, the ux density is, in effect, clipped at that point and remains constant at such Value for a greater part of that particular alternation of the wave.

Since the voltage developed across coil L due toits reactance is a. function of the rate of change of ilux, and does not depend upon the instantaneous density of the flux, the output voltage produced in the cathode-grid circuit of triode V1 will take the form of a series of pulses 28, curve A, Fig. 2.

Pulses 28 have a width determined by the time required Lby the core of coil L to reach saturation level, This saturation time determines in turn the shape of the curve 26 representing the rate of change of flux, as the shorter the saturation time the nearer the curve 26 will approach a rectangular pattern and the narrower willbe the pulses 28 produced during the time the flux Abiased to pass only positive pulses.

3 in the core is varying between its maximum limits.

As can be seen in Fig. 2, the pulses 28 are spaced apart equally in time due to their derivation from the sinusoidal wave 6. As a result of the alternating nature of the flux as shown by the rate of change curve 26, successive pulses 28 are of opposite polarity. The pulses 23 appear on the grid of tube V1, and as a result of the inherent phase reversal in an electron discharge tube, output pulses 28a. of similar nature but displaced 180 in phase will be obtained in the anode circuit of the tube. These pulses 28a are illustrated in curve B.

The grid of triode V3 is Connected to triode V1 by a cathode-follower arrangement, so that the pulses appearing on the cathode of V1, which are of the same polarity as pulses 28, are received on the grid of Vs. The grid of V2 is connected to the anode of V1 to receive the phase-reversed pulses 28a. However, each of the triodes V2 and V3 is After phase reversal through V2 and Vs, the pulse outputs .28o and 28e of these tubes are shown in curves C and D respectively, the negative portions of lpulses 28 and 28a being clipped oif. Since the anodes of V2 and Vs are joined at point 29, the pulses appearing at that point are a combination of those shown in curves C and D, this combination being indicated by curve E. An additional 'amplier 22 inverts the pulses shown by curve E so that they are of positive polarity as shown by curve F.

The above description has assumed a sinusoidal carrier wave 6 being passed through coil L. If now a polarizing voltage or potential of substantially constant value :from source I8 be applied to base wave 6 as indicated by broken line 4l in Fig. 2, the wave will in effect be displaced laterally relative to its normal zero axis 34 to assume a new position 38 such as indicated by the points 132 displaced relative to points 40 on the normal zero axis '34. These new points 42 will be alternately to one side and the otherof the corresponding points Bil. Consequently when the wave ii in its new position 38 is passed through coil L,

the voltage pulses 28 produced as a result thereof will be time displaced along the-time axis, and following the positioning of the points Li2 will be grouped together in pairs. grouping of the pulses after the D. C. bias has been added to the wave 6, and after the pulses of curve E have been inverted by their passage through amplier 22. These new biased pulses are indicated at 28d.

If now speech current from source lil, such as shown by waveform I2, be superposed on the D. C. biased wave 38, wave 38 will be again displaced laterally with respect to the normal zero axis 34 within the limits of the audio range. The points 42 will accordingly be again longitudinally shifted along the axis 34 in push-pull manner according to the instantaneous value of the speech or other signal energy.

Ifthe D. C. bias voltage is properly chosen, one limit of the audio range may be made to coincide with the position of the pulses 28D and 28e as indicated in curve E before their position is shifted by laddition of the polarizing voltage. This preferable limit is indicated at 30 on curve F. The opposite limit of the audio swing is shown at 32 on the same curve. The output of amplifier 22 will thus be pulses which are time-modulated in respect to their relative spacing in accordance with the characteristics of the curve l2 repre- Curve F shows the senting the intelligence which it is desired to transmit.

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

I claim:

l. In a pulse time-modulation system, a source of alternating current, an electron discharge device having an anode, a cathode and a grid, a saturable reactor element, a circuit connecting said source across the cathode and grid of said electron discharge device, said element being a part of said circuit and receiving current from said source to produce clipped voltage alternations, said grid and said cathode acting to conduct alternations of opposite polarity respectively to result in pulses of opposite polarity in the respective cathode and anode circuits of said device, a source of direct current of substantially constant value, means for introducing said direct current into said connecting circuit whereby the normal zero axis of said alternating current will in eiiect be displaced relative to the amplitude limits thereof, means for segregating the pulses of a given polarity appearing on the anode and cathode of said electron discharge device, and means for combining the segregated pulses of said given polarity to form a train of pulses.

2. A system according to claim 1, in which said connecting circuit includes a choke coil between said source of alternating current and said reactive element.

3. A system according to claim l, in which said reactive element comprises a coil having a'core of readily saturable material.

4. A system according to claim l, in which said segregating means includes two additional electron Adischarge devices respectively connected to be controlled by energy from the anode and cathode circuits of said rst-mentioned electron discharge device, and bias means for controlling the conductivity of each of said two additional electron discharge devices so as to pass only those received pulses which are of a given polarity.

5. In a pulse time-modulation system, a source of alternating current, an electron discharge device having an anode, a cathode and a grid, a saturable reactor element, a circuit connecting said source across the cathode and grid of said electron discharge device, said element being a part of said circuit and receiving current from said source to produce clipped voltage alternations, said grid and said cathode acting to conduct alternations of opposite polarity respectively to result in pulses of opposite polarity in the respective cathode and anode circuits of said device, a source of direct current of substantially constant value, means for introducing direct current from said source into said connecting circuit whereby the normal zero axis of said alternating current will in effect be displaced relative to the amplitude limits thereof, a source of speech current, means for superposing said speech current onto the alternating current in the circuit formed of said element, said cathode and said grid whereby the amplitude of the combined alternating and speech currents will vary with respect to the said effectively displaced zero axis in accordance with the modulating characteristics of said speech current, and means for mixing the pulses of a given polarity appearing on the anode and cathode of said electron discharge device so as to form a, train of pulses grouped together in pairs, a variation in the amplitude of said speech current acting to cause a change in the time interval between pulses of each of said pairs.

6. In a pulse generating system, a source of V alternating current, an electron discharge device having an anode, a cathode and a grid, a saturable reactor element, a circuit connecting said source across the cathode and grid of said electron discharge device, said element being a part of said circuit and receiving current from said source to produce clipped voltage alternations, said grid and said cathode acting to conduct alternations of opposite polarity respectively to result in pulses of opposite polarity in the respective anode and cathode circuits of said device, means for segregating the pulses of a given polarity appearing on the anode and cathode of said electron discharge device, the means for segregating including two additional electron discharge devices respectively connected to be controlled by 6 energy from the anode and cathode circuits of the first-mentioned electron discharge device, and bias means for controlling the conductivity oi each of said two additional electron discharge' devices so as to pass only those received pulses which are of a given polarity.

NORMAN H. YOUNG, JR.

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

UNITED STATES PATENTS Number Name Date 1,438,988 Espenschied Dec. 19, 1922 1,597,323 Massole Aug. 24, 1926 2,027,054 Miessner Jan. 7, 1936 2,061,734 Kell Nov.. 24, 1936 2,284,401 l Manley May 26, 1942 2,284,444 Peterson May 26, 1942 2,289,564 Wrathall July 14, 1942 2,311,796 Wrathall Feb. 23, 1943

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