US2572707A - Pulse generator - Google Patents

Description

Oct. 23, 1951 M. ELIE 2,572,707

PULSE GENERATOR Filed June 20, 1947 l'igJ MINT-I'M '"lllllltll mm liweiwor fiu/eics 215 {axis UNITED STAT Patented Oct. 23, 195i ES PATENT OFFICE PULSE GENERATOR Maurice Elie, Paris, France, assigiior' to Compagnie Generale de Telegraphic Sans Fil, a corporation of France Application- June-20, 1947 Serial N6. 755,874,

In France September 19, 1939 Section 1, Public Law 690, August 8, 1946 Patent expires September 19, 1959 "forms of oscillator having characteristics (to be cuit when it is placed in a suitable magnetic field.

' These oscillations can cover an extremely extensive frequency spectrum. The invention is more particularly applicable to the case of very short-waves, but it can also be applied in the whole range of frequencies allowed by these oscillators.

Figure 1 represents diagrammatically a magnetron comprising anodes I and a filament 2 in a 'magnetic field I-I. Only one anodepair is shown but obviously there may be more. The filament is heated from a. source U and the anodes are fed with positive voltage from a source Up. The anode current Ip is indicated by a milliammeter. The oscillating current, for example, in aerial current loop connected to the anodes, is designated by IA.

, The characteristics of an oscillator as represented in Figure 1 are'shown graphically in Figure 2, in which (for a given field strength), the variations of Ip and IA, are plotted as ordinates against Up. It will be seen that if the field is kept constant, when the plate voltage Up increases from zero, the current Ip, which at first is nil, commences at a voltage U, rises slightly, then very abruptly increases to the saturation value Is, and then remains at that value. The oscillating current IA starts at the same time as Ip, increases abruptly with it, passes through an extensive maximum, and then progressively decreases down to zero, the fall of current being less steep than the rise.

The property is employed, according to this invention, for the production of synchronised impulses of very high frequency oscillations.

In certain applications, notably in radio detection or so-called radar systems, it is required to 3 Claims (Cl. 250 3(;)

transmit impulses of a'very high frequency sent out during very short periods at regular intervals.

The interval between two pulse emissions is regulated by an alternating synchronisation voltage, the frequency of which is chosen in dependence upon the application in question, The envelope curve for such an emission is required to be of trapezoidal shape, that is to say, that the amplitude of the high frequency oscillations must increase very rapidly from zero up to a certain maximum and then, at the end of the pulse, de-

crease very rapidly back to zero.

Figure 3 shows one arrangement in accordance with the invention.

Referring to Figure 3, a magnetron I has its anode point connected to a source of positive voltage Up through a resistor 2 and an inductance 3, the latter being shunted by a resistor 4 provided for the purpose of damping self-oscillation in the inductance. The source Up also feeds the anode of a tube 5 shown as a triode, the control grid thereof being negatively biassed through a resistance 6.

- This grid receives through a condenser I, synchronised impulses of the shape shown in Figure 4 (wherein T is the synchronisation period), and produced in any convenient known way. In the arrangement actually shown in Figure 3 a multi-electrode tube, the anode of which is fed with positive voltage through a coil '8, is shunted by a damping resistor 8. The control grid of this tube receives the synchronising voltage through a resistor l3 and a transformer I4. The grid is negatively biased bythe action of a resistor l I, in the cathode return path and shunted by a condenser. 12. When an alternating voltage of suiilcient amplitude is applied to the primary of the transformer I4, voltage impulses of the wave shape shown in Figure 4 appear upon plate of the tube ID. This part of the circuit forms per se no part of this invention.

The control grid of the tube 5 is so biased as to cut off the plate current in the absence of signal input so that positive impulses applied to the said grid cause plate current impulses of similar shape, negative input impulses having no effect.

The plate current impulses produce at the terminals of the coil 3 an induced voltage U the phase of which with reference to the current I is represented graphically in Figure 5.

The voltage applied to the anode point of the magnetron through the resistance 2 is composed as shown in Figure 6 of a continuous feed component U0 upon which are superimposed alternasensor tions of snort duration which follow one another at the frequency of the synchronisation voltage.

In actual practice, transitory phenomena and the eifects of self-capacity of the winding somewhat modify the behaviour from that just described, but the foregoing explanation is sufficient for an understanding of the working of the system.

If desired the amplitude of the alternations may be modified by producing reaction in the proper direction between the plate and "control grid circuits of the tube 5.

Now, upon reference to the characteristics of the magnetron, it will be seen from Figure? that if the variable voltage represented by the curve u (shown in Figure 6) is applied to the magnetron, and the D. C. feed voltage is at a value 110 lower than, or equal to, the value u at which the magnetron anode current rises, the magnetron will oscillate intermittently for periods each of which .cor.responds to theapplication of the positive part of a synchronisingim-pulse. The duration of each such stable period of oscillation working may be relatively long as compared with the duration of the periods of starting and stopping. The maximum oscillation will be reached with a voltage in and-maintained so long as the voltage is between ill and 1.12. The envelope of the high frequency impulses 'will therefore be a double trapezium, as shown in. Figure 8, the small base of which is of a width depending on the amplitude of the voltage applied. The plate current envelope curve of the --magnetron will also be of trapezoidal form. The sudden setting up of current throughthe coil 3 tends to give rise to stray oscillations which it is the purpose of the resistance -2 todamp out;

In the absence of oscillations, the plate current and consequently the anode losses are 'zero. The meanpower dissipated is therefore very small as compared with the power applied during an impulse. This is of great advantage because it means that the magnetron is working under-much better conditions than if it were working with continuous power applied.

The major part "of the voltage applied to the ,rnagnetron is suppliedbythe source of continuous current. This is also an advantage, because the variable portion of the voltage-which portion is only contributory-can be obtained more easily than would-be thecase if it had to have an amplitude equal to the total peak voltage.

The arrangement shown is, in efiect, an amplifier of the positive impulses produced by the tube :Ill. It will be obvious-that such amplifica- .tion could be dispensed with and that it ispossible :to apply directly to the magnetron coil 3 impulses of the shape shown inFigure 4 and produced by tube 5, .by excitation of its .grid through a resistance.

a transformer such as M and a resistor such as l3. In such a case of course the synchronising voltage would have to be of greater amplitude than in the case illustrated.

What I claim is:

1. Arrangement for producing trans of oscillations at ultra high frequency comprising, a tube of the magnetron type having an anode, a cathode coaxialtherewith, and a magnetic field parallel to the cathode, .a source of direct current voltage connected between said cathode and said anode, said direct current voltage being lower than the cut-off and means connected to said anode for superimposing onsaid direct current voltage impulses at the frequency of said trains and having positive amplitudes such as to carry said anode voltage into saturated current condition and thereby cause the magnetron to oscillate during said impulses with its proper frequency.

2. Arrangement for producing trains of oscillations at ultra highfrequencywcomprising-a tube of magnetron type having ananode, a cathode .coaxial therewith and a magnetic field parallel with the cathode,;a source of direct current voltage connected between said anode andsaid cathode, said voltage being below that required for current saturation in the-tubaasource of sinusoidal oscillationsof the frequency of said trains ,;means for shapingsaid oscillations into substantially triangular form and for superimposing them upon said directcu-rrentvoltage vso as to-carry the magnetron into the saturated, current conditionduring the positive alternationsiof said impulses and then cause it to oscillatewith its proper frequency.

'3. Arrangement :forintroducing trains of oscillations according 'to claim -2, in which said shaping and superimposing-meansinclude an electronic relay 'fed' fromsaidsinusoidal source and having its imput circuit negatively biassed, and means forcoupling its output circuit to-said anode of the magnetron, saidvcoupling means comprising acommonshuntz'induetance -in parallel with MAURICE REFERENCES CITED The following references are o'f record in the file of this 'patent':

Gerhard vJan. .28, 1941

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