US2403624A - Apparatus for and method of pulse keying - Google Patents

Description

I. WOLFF APPARATUS FOR AND METHOD OF PULSE KEYING July 9, 1946.

Filed Dec 50, 1937 grllllllll a Lox s n 0 {noun Patented I July 1946 APPARATUS FOR AND KEYING METHOD OF PULSE Irving Wolff, Merchantville, J., assignor to Radio Corporation of America, a corporation of Delaware Application December 30, 1937, Serial N0. 182,418

11 Claims. (c1.25017) My invention relates to an apparatus for and a method of pulse keyingand more specifically to a keying system in which the marking pulses are of extremely short duration.

- I am aware that numerous high speed mechanical keying systems have been devised for forming telegraphic characters. It has also been proposed to use multivibrators for generating a keying pulse, The multivibrator is used to establish currents of saw-tooth wave form. These currents are applied to a limiter which selects the peaks and thereby establishes a short marking impulse. In systems in which small keying powers are required, the multivibrator type keying may sufiice. When larger powers and extremely short marking pulses are required, the problem is not as easily solved. For example, in systems which require marking pulses of the order of a microsecond or..less duration and substantial amounts of power, it becomes increasingly diflicult to shorten thepulses and equally difficult to efficiently amplify the pulses. 1

I propose to apply the initial pulses-to a device which not'only eificiently amplifies the pulses but also shortens the duration of the pulse. The device in certain respects resembles a resistance coupled amplifier in which inductors are substituted for the resistances, and in which only the positive pulses are transmitted. Keying or marking devices of this type are used to start and stop oscillators, amplifiers, or modulators. In practice, myinvention may be applied to obstacle detectors operating on the radio echo principle, radio operated altimeters, television synchronizing impulses and the like. I

One of the objects of my invention is to provide means for generating keying pulses of very short duration and substantial amplitude.

Another object is to provide means for eniciently amplifying pulse currents having a, duration of the order of microseconds.

An additional object is to provide means for amplifying pulse currents of short duration and simultaneously decreasing the pulse duration.

A still further object is to provide means for keying an obstacle detector transmitter by marking pulses of extremely high periodicity.

My invention may be best understood by reference to the accompanying drawing which is a schematic diagram. A multivibrator I,' which generates currents of saw-tooth wave form 3, is connected through a transformer 5 to a vacuum tube amplifier l. Theprimary 9 of th transformer 5 may be shielded from thesecondary ll.

byan electrostatic screen I3. The secondary. II is preferablyof low impedance and, together'with the'input capacity of the amplifier I, may be arranged to resonate at substantially the period of the applied pulse I5. The grid electrode I4 of the .2 amplifier l is. biasedLne'gatively with respect to cathode I6 bya biasing battery l1.

The anode. of the amplifier I is connected through a low impedance inductor I9 to the positive terminal of a B battery 2|. The negative terminal of the battery 2| isconnected to the positive terminal of the biasing battery I'I, cathode I6, and ground. The inductor I9 is coupled through a blocking capacitor 23 to the grid 24 of a second amplifier 25. ,The grid Ziisbiased negatively with respect to. cathode 26 by a grid resistor 21 which is connected to the' negative terminal of the biasing battery 25. The natural period of the inductor 25 and associatedcapacities is preferably of the order of the natural period of the applied pulses 29.

The anode of amplifier 25 is connected through a low. impedance inductor 3| to the positive terminal of the B battery 2!. A potentiometer 33 is shunted. across the inductor 3|. The inductor is coupled through a network 35 and a serially connected source 31 of biasing voltage to key an oscillator 39 or the like. The output of the oscillator is applied to an antenna 4| or otherload circuit.

Having described the circuit, the mode of operation will be set forth; In the condenser char ing circuit of the multivibrator, pulses of current are available. These discrete pulses l5 are applied to the primary 90f the transformer 5. The pulses l5 are suitably phased by the transformer II so that the grid I4 is driven positive with respect to its cathode I6. p 1

r The amplified positive pulses act on the in ductor I9 and, due to its differentiating effect in a mathematical sense, create negative pulses during the rise and positive pulses during the fall of current of pulses I8. Due to the action of the resonant circuit, including inductor l9 and itsassociated capacities in tubes 1 and 25, and the shunt resistor 21 and grid circuit losses in tube 25; a highly damped wave train- 29 is created. It will be observed that the duration of the first negative and first positive portions oi the wave train 29 is substantially equal to the duration of the applied-positive pulse, Thus the original pulse duration is decreased.

The wave train 29 is applied through the blocking capacitor 23 to the input of the second amplifier 25. This amplifier is biased so that its output current is near cut-01f. Because of this bias, the first positive pulse of the wave train '29, and sometimes the following positive pulse, will actuate the amplifier 25. The inwill overcome the bias 3'! which normally prevents the oscillator 39 from functioning and will abruptly key the oscillator. The oscillator 89, thus keyed, will generate oscillatory currents 34 during a portion of the first positive pulse duration. The pulse duration may be adjusted from a fraction of a microsecond to several microseconds. other at the required rate of keying. 4

It should be understood that the transformer 5 may be replaced by an inductor, blocking capacitor and grid resistor. In order to effectively match impedances, the inductors may be used as autotransformers.

I claim as my invention:

1. A pulse generator device including in combination a source of rapidly varying currents, means for transforming said currents into highly damped wave trains, means for amplifying the positive pulses of said wave trains, and means for applying the amplified positive pulses to an output circuit.

2. A pulse keying device for a transmitter including in combination a source of pulses, means for transforming said pulses into highly damped wave trains, means for amplifying the first positive pulse of said wave train, means actuated by said amplified positive pulse for creating a second highly damped wave train, and means for applying the first positive pulse of said second highly damped wave train to key said transmitter.

3. A keying device including in combination a circuit to be keyed, a source of discrete pulses, means for converting said discrete pulses into a a first series of highly damped wave trains, means for amplifying the first positive pulse of said wave trains, means for deriving from said amplified positive pulses a second series of highly for transforming said pulses into series of wavetrains, means for highly damping said Wave trains, said trains including negative phased pulses and positive phased pulses, means for amplifying the first of each of said positive pulses, means responsive to said positive pulses for creating a second series of wave trains, means-for highly damping said second series of Wave trains, said second series of wave trains including negatively phased pulses and positive phased pulses and means for applying the first of each of said last-mentioned positively phased pulses to a keying circuit.

5. The method of establishing and applying keying pulses to a load circuit which comprises, generating discrete discharge currents, converting said discrete discharge currents into discrete pulses, transforming said discrete pulses into wave trains including highly damped negatively and positively phased pulses, amplifying said positively phased pulses, and applying the first of said amplified positive pulses to said load circuit.

6. The method of establishing keying pulses of extremely short duration which comprises generating discrete discharge currents, converting said discrete discharge currents into discrete pulses, transforming said discrete pulses into v highly damped oscillatory currents, amplifying The keying pulses may follow each he first positively phased oscillation, converting said amplified oscillation into a second series of highly damped oscillatory currents, and deriving from said last oscillatory currents a positively phased pulse of extremely short duration.

'7. A pulse keying device including a source of discrete pulses of current of a single phase, means for converting each of said pulses of single phase into currents of positive and negative phases forming highly damped wave trains,

means for selectively amplifying currents of the first positive phase of eacli of said wave trains, and means for creating from said positive phase currents a second current having negative and positive phases of less duration than said first mentioned currents of positive and negative phases.

8. A pulse keying device including a source of discrete pulses of current of a single phase, means for converting each of said pulses of single phase into highly damped waves including currents of positive and negative phases, means for selectively amplifying currents of the first positive phase of each of said waves, and means for creating from said positive phase currents a second current having negative and positive phases of greater amplitude and less duration than said first mentioned currents of positive and negative phases.

9. A pulse keying device including a source of discrete pulses of current of substantially uniform duration, means for converting said discrete pulses of currents into highly damped waves including positively and negatively phased currents, the period of said two phases being 01' substantially the same duration as said discrete pulses, and means for selecting in each of said Waves the first positive phase currents and excluding said negatively phased currents whereby the duration of said selected phases is less than the duration of said discrete pulses.

10. A pulse keying device including a source of discrete pulses of current of substantially uniform duration, means for converting said discrete pulses of currents into highly damped Wave trains including positively and negatively phased currents, the period of said two phases being of substantially the same duration as said discrete pulses, means for selecting the first of the positively phased currents of each of said Wave trains and excluding said negatively phased currents whereby the duration of said selected phases is less than the duration of said discrete pulses, means for amplifying said positively phased currents, and means for establishing currents of positive and negative phases of a duration controlled at least in part by said first mentioned positively phased currents.

11. A pulse amplifier including a source of positive pulse voltages, means for converting said positive pulse voltages into a highly damped wave train having negative and positive voltage peaks,

4 and means for amplfying the first positive peak without amplifying negative peaks of said wave train.

IRVING WOLFF.

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