US2300394A - Pulse modulation system - Google Patents

Description

Nov. 3, 1942. w, E TTY ETAL 2,300,394

PULSE MODULATION SYSTEM Filed Aug. 22, 1940 SWEEP WHVE SOUIPCE 50 15 1 555? 31 3 l2- -J I 18 I firm-Mars I Attorney Patented Nov. 3, 1942 PULSE MODULATION SYSTEM William Arnold Beatty and Charles Thomas Scully, London, England, assignors to International Standard Electric Corporation, New York, N. Y.

Application August 22, 1940, Serial No. 353,688 In Great Britain October 13, 1939 4 Claims. (Cl. 179-1715) This invention relates to methods of producing a radio frequency carrier signal'which is modulated by time modulated pulses.

In high frequency transmitting systems utilising time modulated pulses, it is possible to first generate the time modulated pulses and to then utilise these pulses for the purpose of modulating the carrier wave. There are certain disadvantages in this procedure in that should a large pulse voltage be required for high power modulation, it becomes necessary to amplify the pulse by means of a high quality amplifying system which does not distort the initial shape of the pulse.

The present invention resides in a system for producing a carrier wave, amplitude-modulated by time-modulated pulses wherein an electron beam, which is deflected across a target in such a way as to set up time-modulated pulses, is modulated in intensity at carrier frequency.

One advantage thereby achieved is that the necessity of amplifying a time-modulated D. C. pulse signal is obviated.

The invention is a development of the method of generating pulses described in pending U. S.

patent application Ser. No. 312,645, filed January 8, 1940, and U, S. Patent 2,256,336, issued September 16, 1941, the development being the radio frequency modulation of an electron beam which is being repeatedly deflected across oneor more targets under the control of a wave of constant form and which'is deflected transversely of the first deflection under the control of a sound or the generation of time modulated pulses as de-' scribed in the aforementioned patent application and patent.above identified. The tube elements are indicated as follows,'cathode H, control grid l2, focussing anode l3, final anode l4, deflector plates 15, aquadag ring anode l6, and two target electrodes l1 and 18. The various D. C. operat- .ng voltages and circuits are not shown as these follow well known cathode ray tube practice.

The deflector plates are shown as excited by.

sweep wave source 30 and speech wave source 3!, respectively, In the aforementioned patent applications, the electron beam is assumed to have a constant value while it is being "deflected across the target plates, except during the fly back period when preferably it is completely suppressed, this being achieved by the application of a negative voltage between the cathode H and the control grid I2.

It is now proposed that the beam be modulated at a radio frequency during such time as it is not suppressed in the fly back period. A source of radio frequency I9 is coupled bythe tuned circuit 20, 2| to the control grid l2 and cathode II, the control grid by means not shown being normally biassed to cut off. The effect of the radio frequency drive is to give an electron beam modulated at radio frequency. :The target plate I1 is coupled by means of tuned circuit 22, 23 to the final anode it, which is at cathode potential for the carrier frequency. During such time as the beam strikes the target plate ll, a radio frequency at the same frequency as supplied by the input 19 is present in the circuit 22, 23. Sincethe period of time during which the beam can strike the target plate I1 is a function of the amplitude of the modulating signal it follows that the radio frequency signal is present in the circuit 22, 23 for periods of time which are functions of the amplitude of the modulating signal applied to one of the pairs of deflecting plates l5. The circuit 22, 23 is coupled to an output circuit 25, 26, the output being utilised in any desired manner. I

Targets I1 and I8 may have any of the shapes disclosed in the application and patent previously mentioned (e. g. application Ser. No. 312,645 and Patent No. 2,256,336). Fig. 2 illustrates one suitable form for such targets, the two targets 81 and It being in this case connected together so as to form one V'-shaped target.

In caseswher it is desired toobtain a pulse signal of the type described in the aforementioned patent application Serial No. 312,645, i e., a signal having one edge of an amplitude different to the remainder oi the pulse, the second target it can be connected to the final anode M by ,another tuned circuit 21, 28, this circuit being also tuned to the frequency of the supply l9.

Fig. 3 illustrates suitable forms for targets l1 and 18 for such a case.

If the circuit 25, 26 is suitably "coupled to the circuit 22, 23 and 21, 28 different amplitudes of cycles.

v During the fly back period the output can be suppressed either by back biassing the grid I! or by suppressing the generation of the radio frequency at source l9. This can be done in any known manner.

What is claimed is:

1. Ap aratus for producing a carrier wave amplitude-modulated by time-modulated pulses coml g'reaching said target, 'a source of carrier wave producing a beam of electrons, a target for receiving said electrons having at least two portions insulated from each other whose effective shapes determine the wave form of said pulses, first deflecting means for deflecting said beam in a first direction across said target, second deflecting means for deflecting said beam in a direction at an angle to saidflrst direction, control means for regulating the number of electrons energy connected to said control means for modulatingsaid beam, a source of sweep voltages connected to said first deflecting means, a source of modulating voltages connected to said second deflecting means, and an output circuit connected to said target.

3. Apparatus according to claim 2 wherein said target comprises a triangular effective portion, the legs of said triangular portion being parallel prising a cathode-ray tube having a source of 20 to said two directions, and a thin strip-like eifecelectrons, a target for receiving said electrons, whose effective shape determines the wave-form of said pulses, means for deflecting said electrons across said target, control means for regulating the number of electrons reaching said tartive portion, parallel to the hypothenuse of said triangular portion.

4. Apparatus according to claim 3 wherein said output circuit comprises a first circuit connected to one of said target portions, a second circuit connected to the other of said target portions, and a third circuit coupled to said first and second circuits, the coupling between said flrst and third circuits being different from the coupling between said second and third circuits.

.WILLIIAM ARNOLD BEA'I'IY. CHARLES THOMAS SCULLY.

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