US2408076A - Pulse transmitter - Google Patents

Description

Sept. 24, 1946. E. LABIN PULSE TRANSMITTER 2 Shets-Sht 1 Filed Aug. 12, 1941 F IG.2.

IN VEN TOR 671/15 143/ A TTORNE Y Sept. 24, 1946. LABlN PULSE TRANSMITTER Filed Aug. 12, 1941 2 S hets-Sheet 2 TME 'l I INT/Enron '/7/LE LAB/N W c O M. n M m F I j F T 0 v 3 I44 B 0 T l mfi 5% Nfifi fi QQQ 5 5 W W 7 m b g m m m TV a p a 3 a Q$Q 55k wmfi wax 53k ATTORNEY.

Patented Sept. 24, 1946' PULSE TRANSMITTER Emile L abin, New York, N. Y., ass ignor to International Standard Electric Corporation, New 4 York, N. Y., a corporation of Delaware Application August 12, 1941, Serial No. 406,499

Claims.

The present invention relates generally to apparatus for producing brief trains of oscillation and particularly to apparatus for producing brief high power trains of high frequency oscillations.

There are many uses for such'a source of brief trains of high frequency oscillations, among them being their use in distance finding apparatus for generating high power impulses. In distance finding apparatus it is necessary and desirable to produce wave trains of large peak power so that;

these wave trains may be directly radiated without amplification, while still giving a large amount of radiated power and hence a large useful operating range for the. apparatus.

It is an object of my invention to provide an eflicient apparatus for delivering brief wave trains of high power'waves.

' It is a further object to provide such an apparatus suitable for delivering high power brief wave trains of ultra-high frequency waves, the.

wave trains being of accurately controlled length and spacing. r

' It is a further object to provide such an apparatus which when powered by a plate supply source of given voltage is capable of delivering wave trains of substantially higher power than could be delivered by conventional .apparatus using a plate supply of said given voltage.

' It has: heretofore. been proposed to produce high power trains of oscillations by applying to the plateof a suitableoscillation generator. tube, brief high power impulses derived from a B supi I be as much as ten times the plate supplyvoltage.

ply of moderate voltage by a controlled amplifier having an inductance in its output circuit. In

. accordance with thissystem the current in an' inductance connected in the plate circuit of the amplifier tube is interrupted by means of control signals of the desired form applied to the grid of this tube and obtained from a separate low power impulse generator. This system operates fairly satisfactorily, but it has;several disadvantages:

(a) During the period of charging current flow in the inductance, a high positive voltage must be applied to the grid of this amplifier tube in order that the plate current may approach the maximum emission current of the tube. g

, (b) Because of the grid current which flows during the charging period, the amplifier or generator which drives the amplifier in (a) ,must supply a considerable amount of power to a low impedance (the effective grid resistance time being from 100 to .500 ohms).

at this (0) During the period of discharge of the inductance, the instantaneousplate voltagefmay .vention; Y

The negative grid voltage consequently must be raised to several times the normal cut-off value to insure that thetube isblocked duringthe discharge or pulsing period.

It is both difiicult and expensive to build an amplifier which will pass a wide band of frequencies (to allow a very fast blocking action), deliver alarge amount. of power into a low resistance and supply a high negative voltage to an infinite resistance.

For medium power installations it is possible to reduce some of the above difiiculties by employing'aflpentode tube as the amplifier tube connected to the inductance. However, for high power applicationspentodes are costly and introduce circuit complications.

It is an object of my invention to provide a source of brief waveftrains of high power and high frequency waves while'avoiding the difliculties above mentioned. J 'According to my invention, I provide as the source of plate supply for a high frequency oscillator an impulse generator comprising an amplifier tube having an inductance coil in its output circuit and means for coupling the inductance coil to the grid circuit of the amplifier tube. In

the preferred embodiment of my invention I employ a triode as an amplifier tube.

.It is a further object of my invention to provide an improved impulse generator capable of producing impulses of high peak power.

It is another object of my invention to provide a self-excited impulse generator capable of producing impulses of high peak power.

It is another object of my invention to employ in said high power impulse generator a triode as an amplifier-generator tube.

It is another object of my invention to provide apparatus for accurately controlling the duration of high frequency pulses.

Myinvention will be more clearly understood by referring to the accompanying drawings wherein:

Fig. 1 illustrates an impulse transmitter for delivering brief wavetrains of high power in accordance .withmy invention; I 1

Fig. 2 is a diagram used in explaining my in- Fig. 3 shows a circuit employed in operation tests; I

Figs. 4a, 4b, 4c and 4d are diagrams used in describing the operation of the impulsegenerator of m n en o I I I Fig.5 illustrates an embodiment of y invention wherein a high frequency oscillator is controlled by both positive and negative impulses from an impulse generator.

Fig. 1 discloses an impulse generator connected as the power supply for an oscillator. The impulse generator comprises a vacuum tube 2 having a plate 3, a control grid i and an electron emissive cathodei5=which may be directly Or indirectly heated. An inductance 6 is connected in series with the energy source 1' in the plate circuit of the tube 2 between the plate 3 and the cathode 5. circuit and the grid circuit is obtained by means of coil 8 which is inductively:coupled-to the-inductance B and which may be considered'as one coil of the transformer 6, 8. The is primarily determined ance timing circuit consisting of condenser 9 and resistance l0. As shown, the condenser and resistance H! are in series with the grid 4, but they may, instead, be connectedin series with the cathode 5. I

-When the inductance 6 is charging, "that is, when current is flowing in tube2,'- the plate end of the inductance is negative with-respect tothe other end of the inductance. When the inductance is discharging (no tube current), the .re- 'verse polarity exists.

-In practice, the load 'resistance for inductance '6 will vary between 10,000 ohms for 10 to microsecond impulses, and 2,000ohms for -l to.2 microsecond impulses. 'Thisload resistanceis of' the same'or'der as the plate resistanceofmanycommonly employed oscillator tubes. In the preferred embodiment of my inventioml employ the impulse generator as the ;plate voltage supply for an oscillator. The impulse generator .may alsoact as'the power supply for any other power electrode-such as the screen grid of the oscillator tube. In Fig. 1, one end of the inductance 'coil 6 of the impulse generator lSCOIlIlECtEdTtO the mid-point of a pair of lecher Wires 36zand 31. These lecher wires 35 and B'Lserve to tune :the plate circuit of the tubes 38 andi139, .and-the lecher wires are connected to the plates or:power electrodes 40 and Moi the tube. The grids :or control electrodes 42-and 43 areconnected to .a 'pair of lecher wires M1 and 45 whichserveto tune the grid circuit =0f't1l6'tubeSl38. and;39. A resistor '46 serves as a'biasing resistor. odesor electron emissive electrodes '48 and '49 are connected to a common return point.

During the charging and steady state .periods of the impulse generator the "oscillator comprising the tubes tive. When the inductance 6 discharges, .the tubes 38 and 39 and their accompanying circuits are energizedandoscillations are;produced. It will thus be seen that high frequency energy is produced for an interval substantially equal to the discharge time of theinductancecoil 6. Actually the oscillator will cease to oscillate'before the inductance coil '6 is completely discharged, and the high frequency pulse'w'ill-be a 'little shorter than that delivered by'the inductance coil 6 to a resistance load.

The oscillator stage is preferably coupled to transmitting system directly, .but it may also be coupled to an amplifier or amplifiers and then to a transmitting system. .As. shown iniFigg-ljthe oscillator is coupled by means of loop 35 tothe transmitting system I. It is to be understood that although'I have shown a push-pull'oscillator as a preferred type other types of'osc-illator's' may "be employed.

Positive feedback betweenthe plate 7 .38 and 39 'is inopera-' inductance with a negative resistance.

Although impulse generators and oscillators are both known, I shall describe the impulse generator employed in accordance with my invention in more detail in order that my invention may be more clearly understood.

The use of inductive coupling between the plate andgrid circuits has the effector" shunting the For the present purposes'the circuit shown inFig. 1 may be considered during the charging period as "equivalent to an inductance in parallel with a .15' pulsing rate by the capacity-resistvnegativeresistance and with the capacities of the components of the circuit. 'A circuit consisting of inductance, capacity and resistance, which'is capable of oscillating at high values of resistance, may become aperiodic if the resistance is;small, even though negative. If Re is the resistance for critical damping, the circuit 'will be aperiodic as long as the shunt or parallel resistance remains between +Rc and -P.c. When the circuit is made aperiodic by damping with a negative resistance (-Rc), the operation is not at all normal. Any small current increase develops into a very rapid and large exponential increase. From the moment at which the current begins to rise, it continues torise to its ab solute limit, always in the same direction and with'increasing speed. Similarly, a decrease in current will also follow an exponential law.

When the inductance 6 is charging and this inductance is connected to the oscillator as a plate supply for the tubes-thereof, the efiect of the oscillator tubes may be neglected since, as pointed out above, the polarity of the potential on the inductance is such that the plates of the tubes are at a negative potential with respect tothe cathodes and the resistance of the tubes may, therefore, be consideredas infinite. When, however, the inductance discharges, its-polarity reverses, and the inductance discharges into the tubes as well as the circuit components of the generator itself. During the discharge, the oscillator tubes act substantiallyas a resistance load.

The discharge 'of the inductance begins .at the instant that the plate current is blocked. The plate current of the tube 2 having :been blocked,.the resistance of tube 2 may be considered as infinite, and consequently, the .zcircuit consists of the inductanc Gin parallel with the inherent resistanceof the oscillator (if substantially resistive) and a-capacity consisting substantially of the capacities of tube 2 and the oscillator, the.distributed'capacity'of coils 6 and 8, condenser l and other capacities to ground. From the theory of parallel inductance, capacity and resistance circuits, it is known that the discharge of the .inductance fi into the oscillator (considered as a 'load) will be made in a minimum time and with a maximumpeak power if the circuit constants are given critical values which satisfy the equation.

Under these conditions, the discharge of the inductance will follow a curve l'ikethat shown in Fig. 2.

For-abetter understanding of the operation of the impulse generator a cycle of operation will be described as follows:

(a) Charge.-As soon as the grid condenser '9 almost completely discharges through the resistance l0, plate current will begin to flow. This current will increase continuously to a value 'near= the'satur-ation current value ior the t'ubezi. Atthefsame'timethe' voltage at the Jplata'alil will decrease dueto the reactance drop across inductance. 6; andthegrid' voltage will increase positivelyudue to the feedbackbetween .the. grid, and plate circuits giving a large grid current flow. The power furnished to the grid circuit is obtained from the plate voltage source.

(b) Discharge.,-The increase in plate current will cease when the plate current approaches the. saturation current of the tube. At this time the grid voltage, which has been held at a high ..Yalue ,due to the inductive coupling between the plateandgridjcircuits, will begin to decrease :causing a decrease in the'plate current. The direction of plate current; variation will then re- Yerse,1and this effect becomes cumulative causinggthe platecurrent to decrease rapidly. The grid voltage will decrease and finally become negative.

be stopped in a Very short time producing a high voltage'at theterminals. of the inductance Theiresultis that the plate current 6.-; If; the coupling between coils 6 and 8 is properly adjusted, a highrnegative voltage apthe inductance there will be no voltage across coil 8, and therefore, dueto the charge on condenser 9, plate current will notflow. The condenser will discharge through resistance l0, and finally plate current will again fiow and the cycle will ,be repeated.

For best operation the tube 2 shouldhave a. high saturation current to allow high values of charging current, shouldv have a highmutual conductance to provide properdamping for cir-' cuit component impedance values-other than the critical values and for negative resistance values and should be well evacuated in order to withstand the high peak voltage which is produced during the discharge of. 00116. It may be seen that with the exponential variations which take place the inducance will stor alarge. amount of energy during its charge, and this energy will be released during a very short period A peak voltage as high as 20,000 volts may be realized across the plate inductance coil with a power supply voltage of only 1000 volts. Accordingly, the circuit components of the impulse generator and associated apparatus must be carefully insulated, and one of the chief points of concern is .7 .the insulation between the plate lead of the tube and other apparatus. It has been found possible with well evacuated low power tubes having thoriated' filaments to use peak currents and peak voltages from 10 to times the normal operating values without damaging the tubes or Y shortening the lives of the tubes. These. values correspond to peak powers from 100 to 400 times -the normal. tube rating.v I 1 .7

.In order to' observe the operationof the im- .-pulse. generator an oscillographic analysis was made. with the circuit shown in- Fig. 3. In this figure 22 is a high vacuum tube having a plate "or anode 23, a grid 24am a cathode 25. Con 'nected to the anode 23is an inductance 26, and the grid 24.; is coupled to. the-inductance, 26 by coil .128 shuntedby resistance 2| Resistance [9 and:

*6 theshighvacuum diode '20 in. series therewith form a .load for the inductance. Resistance 30 in parallel-with condenser 29 serves asa timing circuit to control the impulse frequency. .Source 1 2.1, which maintains a potential of about 350 .lvolts, serves as a power supply for the generator. .1 Meters 3|. and 33 serve to indicate thecurrents insthe respective circuits, and resistances 32 and 34. are'providedas voltage sources for an oscilloraph;

. In the circuit-of Fig. 3 the-following elements were employed:

Tube '22 I 'a, 'type Ell-'3 receiving tube manufactured by N. V. {Philips Gloeilampenfabrieken I of Eindhoven, Holland; Th operating characteristics are:

- Amplification factor 20 Plate resistance ohms 2000 Grid resistance do 100 Plate voltage volts 350v Tube 20 a rectifier of the so-called type which is widely sold in the United States.

Condenser 29 a 1 mfd. condenser Resistance 30 a rheostat variable from 1000 ohms to 200,000 ohms.

Resistances 32 and 344 ohm fixed resistors.- Resistances I'Sand 2| loading resistors. Inductance 26 an inductance of about 15 millihenrys and requiringa critical resistance of W about 8,000 ohms. "Q

With the above apparatus it has been found 'pQSSlbIB to'produce currents of about 1 ampere and; peak voltages as high as 6,000 volts, the peak power being about {i kilowatts. V The development of 4 kilowatts peak power with a small receiving tube and a 350 volt plate supply illustrates the advantage of the present invention. These results for a small tube were duplicated on a much larger scale with larger triodes such' as the Eimac tube T2,000 manufactured by Eitel-McCullough, -In c.,jof San Bruno, California. Tubes of this latter type, using my circuit, can deliver 3 micro- 45' second pulses of 30,000 volts in a 3,000 ohm resistance with a D. 0. power supply of only 6,000 volts; Thiscorresponds toa peak power of. 300

- With the circuit shown in Fig. 3, a transformation ratio of 0.5 and a coupling coefiicient of 0.8, the oscillograms shown in Figs. 4a, 4b, 4c and 4d were obtained. These oscillograms show that at'the time A, the grid condenser, has discharged sufficiently for plate current to flow. The flowin plate current decreases the plate voltage due to the drop across the inductance 26 and-causes the grid voltage to become positive. At this time grid current Will begin to flow. I

' During-the time interval from B to C, the plate current approaches saturation, the plate voltage 1 approaches the voltage of the plate supply, the grid voltage reaches a positive maximum and the grid current remains substantially constant at its original value. When plate current saturation isreached at the point C, the inductance Zfidischarges producing amaximum of voltage, the grid voltage suddenly becomes neg-, ative and "the flow of grid current is stopped. After the discharge of the inductance 26 all of the current" and'voltages except the grid voltage assume their steady state value, the grid voltage reaching its steady state value only after-the discharge of the grid condenser. These oscillograms bear ,out the series of operations set forth in connection withFig. -1.

--'discharge of the inductance -26. ---sistance it in the circuit, the grid voltage will \During :the .oscillographic analysis of itheiimpulselgenerator operation, it was found that the ratio of transformation .and the ccoupling .co- :efficient 'ihave .considera'blelinfluence :on the Yeperation .of .the generator. .It1was.:found:.that for ..*small .values :of "transformation ratio the grid .current is excessive;andsubtracts from the plate current. .For large valueskof transformation ratio the grid excitationisinsumcient. InJorder to obtain a maximum value of peak plate current, .Iiprefer to use transformation :ratios between 0.5 and 0.8.

:The leakage reactance-of-the coupling trans- ,fo'rmer .afiects both'thecleng 'th of the charging ,period and the ratio of ithe, plate voltage to. the grid voltage. 'I have 'found that .thelbestoperating results are not obtained with coupling values near unity. -By -lowering thecoeflicient of coupling slightly-that is,by introducing an appreciable amount of leakage reactance, the moment at which the grid voltage reaches its peak value will be retarded. It is desirable that the grid voltage and the anode voltage increase simultaneously 'for under this condition high peak currents are obtained. The leakage reactance provides a convenient means for regulating the relation between the anode voltage and the grid voltage. I have found that preferable .values for the coefiicient of coupling arebetween approximately 0.6 and 09.

If the transformer has a transformationratio of approximately and if no precautions are taken-the grid'voltage'during the discharge of the-inductance -26 w'ill'be approximately equal to one-half oithe-instantaneous plate voltage. Suchahigh grid voltage=wil1- cause arc-over between-the filament and the grid of the tube and will lower the maximum peak voltage obtainable. -For cut-oi? at the peak plate voltage it is *only necessary that the grid voltage'be equal to-the peak'plate divided-by the amplification factor or the tube. The amplification 4 factor of tubes commonlyemployedin amplifiers is usually considerably more than two. Accordingly, the-grid voltage may be'reduced to-a'value less than one-half'ofthe anode voltage.

'In accordance with'my invention, I provide a resistance 2| connected across the terminal of the-grid coil 28 of the transformer--2B-28 shown in -Fig.'-3. Due tothe effect of the transformer leakage reactance, the resistance 2! across the grid coil will cause the negative grid" impulse to be' li-rnited'tothe desired value-without changing the maximum voltage obtainableacross the plate coil 26.

The 'useof the resistance "2| in the grid cirin the grid circuitmay'be substantially elim- "inated. It has been found that unless a resistance similar to theresistance 2| is-employed, oscillationsmay continue in the grid circuit after'the With the reincrease-smoothly'in the positive direction after the 'dischargecf the inductance, -and'therefore, "the regularity of the'pulsing cycle'will be assured. V

The length of the transmitted high frequency pulse" may be controlledby applying 'a negative impulse'to the grid of the-oscillator. Therefore, -in accordance with a further'feature of my in verition I -'-employ the negative impulse which controls the impulse generator for controlling the high frequency oscillator. Fig. '5'i1lustrates one embodiment of my invention wherein high .frequency oscillator Pis controlled by a negative impulse from the Iimpulse generator. L In .this figure the oscillator and generator are substantially .theisame asithose showniin Fig. 1. Since 5 :the negativegimpulsei produced .at the grid A-and the positive impulse produced by the coil G are produced simultaneously, the Lnegative impulse which is appliedto' the oscillator must bedelayed. The negative impulse may, -.for example; be applied to the grids 42.=and'43zby means of block- .ing condenser :Bfl andthettime delay :circuit consisting of coil 5| :and :condenser "52 connected to cne-end ofresistahcelfi. The time delayin- -troduced 'may :be regulated 'by :adjusting the values rof thezcoil-il and the condenser 52. The

ratio of the coil 5| to the condenser 52 is preferably i substantially equal to the squared 1 value of the resistance lfi. The condenser '53'is a by- :pass condenser. Although I: have shown'the 'timing circuit 9, ill! in series with the cathode, itis tobe understood that I stilllconsider that the inductance 6 and the source'l are connected in serieszbetweenzthe-anode 3 and-the cathode 5.

.While I'have'described particular embodiments 0i myinvention, for 'purposes of illustration, it will be understood that warious modifications thereof maybe made without departingirom the scope of my invention.

What I claim is:

-1. A pulse transmitter comprising an oscillator comprising a vacuum :tubehaving-a power electrode, an electronemissive electrode and a control electrode, an output circuit coupled-to-said power-electrode, an input "circuit coupled to "said contro1'electrode and=meansforieeding energy from' 'said output-to said input circuit, means for supplying operatingipotential to-said power electrodes comprising an impulse generator comprising a vacuum tube having an anode, a control 40 electrodeand an electron emissiveelectrode, an i output circuit coupled to said anode, an input circuit coupled t'o'said grid and means for feeding energy from saidlast+mentioned output circuit to said last-mentioned input circuit, anddirect current #eonnections for coupling said last-mentioned output circuit to the power electrode of said oscillator.

. 2. 'A pulse transmitter comprising an'oscillator comprising a vacuum tube having an :anode, a

'50 control-grid and a'cathode, atunedinput circuit I connected to said control grid, a tuned'output circuit connected to said anode-and means for feeding energy from said outputcircuit to said input .circuit, an impulse generator comprising a vacuum tube-havingan anode, acontrolgrid and a cathode, an inductanceconnected in series with said generator anode and cathode, means for coupling said inductance 'to said generator grid -and tirning means connected between a said gen- 50 erator. grid an'd cathode, and direct current connecting means for .connecting in coupling relation -said oscillator anode to the junctionotsaid inductance andisaid generator anode.

3. A pulse transmitter according to :claim 5 wherein said means for coupling :saicl inductance and said timing means arefrespectively 'acoil inductively coupled to saidi inductance 'anda condenser and resistance.iin-rparallel, ;-said :coupling meansi and said timing emeans being.connected :in series between said generator :cathode rand said generator grid.

4. A: pulse Ltransmittericomprising a'.push-pu1l V oscillator-comprising! a pair ofivacuum tubes .each having an anoole, Ia grid and :a 1 cathode, :.said "anode and 'said .gridlbeing :capacitively xzcoupled.

tuned lecher wires connected between the anodes of said tubes, tuned lecher wires connected between the grids of said tubes, biasing means connected between said grid lecher wires and a common ground point and means for connecting said cathodes together and to said common ground point, an impulse generator comprising a vacuum tube having an anode, a grid and a cathode, an inductance coil connected between said generator anode and said common ground point, a resistance and a condenser in parallel forming a timing circuit, a coil inductively coupled to said inductance, a resistive impedance connected in parallel with said coil, said coil and resistive impedance forming a coupling circuit and said coupling circuit and said timing circuit being connected in series between said generator grid and said generator cathode, a source of energy supply and means for connecting said source between said generator cathode and said common ground point, and means for connecting for direct current coupling the end of said inductance connected to said generator anode to said anode lecher wires.

5. A pulse transmitter comprising an oscillator comprising a vacuum tube having an anode, a control grid and a cathode, a tuned input circuit connected to said control grid, a tuned output circuit connected to said anode and means for feeding energy from said output circuit to said input circuit, an impulse generator comprising a vacuum tube having an anode, a control grid and a cathode, an inductance connected in series with said generator anode, means for coupling said inductance to said generator grid and timing means connected at the cathode terminal of said generator to control the potential of said generator grid, direct current connecting means for connectin said oscillator anode to the junction of said inductance and said generator anode, and a time delay network connected between said oscillator grid and said generator grid.-

6. A pulse transmitter according to claim 4 further comprising a time-delay network connected between said grid lecher wires and said generator grid, said net-work comprising a blocking condenser and a coil connected in series between said generator grid and said grid lecher wires and a further condenser connected between said last-mentioned coil and said common ground point.

7. A pulse transmitter according to claim 4 wherein said oscillator biasing means comprises a resistance and further comprising a time-delay network connected between said grid lecher wires and said generator grid, said network comprising a condenser and a coil connected in series between said generator grid and said grid lecher wires and a further condenser connected between said last-mentioned coil and said common ground point, the ratio of the magnitude of the last men- 10 tioned coil to the magnitude of said further condenser being substantially equal to the squared value of the magnitude of said biasing resistance.

8. A pulse transmittercomprising an oscillator comprising an input circuit, an output circuit, a vacuum tube having a power electrode, means for connecting said circuits to said vacuum tube and means for feeding regenerative energy from said output circuit to said input circuit, an impulse generator comprising a vacuum tube having an anode, a control electrode and a cathode, means for coupling said anode to said control electrode, an inductance, a source of direct current energy, means for connecting said source and said inductance in series and to said anode, said impulse generator producing a series of impulses having a peak voltage greater than the voltage of said direct current source and means for feeding said impulses to said power electrode of said oscillator comprising a conductive connection from said power electrode to the end of said inductance connected to said anode.

9. A pulse transmitter comprising an oscillator comprising a vacuum tube having an anode, a

control grid and a cathode, a tuned input circuit connected between said cathode and said grid, a tuned output circuit connected between said cathode and said anode, and means for feeding regenerative energy from said output circuit to said inputcircuit, an impulse generator comprising a vacuum tube having an anode, a control grid and a'cathode, an inductance, a source of direct current energy, means for connecting said source and said inductance in series between said anode and said cathode, a coupling coil inductively coupled to said inductance, the transformation ratio and the coefiicient of coupling between said inductance and said coil being between 0.5 and 0.8 and 0.6 and 0.9 respectively, a timing circuit comprising a condenser and a resistance connected in parallel, means for connecting said coil and said circuit in series between said grid and said cathode, a further resistance, means for connecting said further resistance in parallel with said coil, means for connecting said oscillator anode to the end of said inductance connected to said generator anode, and means for connecting said oscillator cathode to the other end of said induct ance.

10. A pulse transmitter comprising an oscillator, a vacuum tube in said oscillator having a power electrode, an electron emissive cathode and a control electrode, an impulse generator, means for feeding positive impulses from said generator to said power electrode and means for feeding negative impulses to one of said electrodes, said latter means comprising a time delay circuit to delay said negative impulses with respect to said positive impulses.

EMILE LABlN.

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