US2440278A

US2440278A - Pulse selecting and eliminating system

Info

Publication number: US2440278A
Application number: US487072A
Authority: US
Inventors: Labin Emile; Donald D Grieg
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC; Federal Telephone and Radio Corp
Priority date: 1943-05-15
Filing date: 1943-05-15
Publication date: 1948-04-27
Anticipated expiration: 1965-04-27
Also published as: FR944348A; CH275289A

Description

Patented Apr. 27, 1 948 UNITED STATES PATENT OFFICE 9 Claims.

This invention relates: toradio-impulse systems and-more particularlyto a system-for discriminating between pulses-of different widths.

In" the copending application. of Emi ie Labin, Serial No. 467,509, filedv December 1, 1942 since issuedas Patent #ZAHLIZ Z methods and means-are disclosedfor selectivelyfiltering a wave modulated with pulses. oliilieriingv in Width-soas toohtainfrom thepu-lse modulatedwave pulsesof a given width to the. exclusion of pulses ofgreater and lesser duration than a wanted-pulse.

It is an objectof thislinvention.to'provide an additional method and means for accomplishing the same result.

Another object of'our invention isto provide a pulse selectingoreliminating? system which re..- quires only a few parts, is light inweight and takesnp'aminimumofspace.

In accordance with our-invention; there isprovidedmeansto -first limit clip a pulse modulated wave to a given amplitude. The wave is thenapplied to a damped! controlledth-C. circuit similar to-that covered intour copendingapplication,- entitled Pulse width-measuring system? Serial No. 489.624,- filed March. 26,. 1943. since issusdaas Patent-#ZAILML The L.-C.- circuit is. tuned preferably to a-periodoi oscillationequal.totwice the width ofthe wanted pulse. The wave aiter the clippingoperation, is applied to the tuned L.--C.. circuit to producetherein. a damped. Wave of oscillations foreach-pulses The first undulationof the damnedwave following. thev trailing edge ofthey pulse initiating; the oscillationhas, an amplitude which forthewanted pulse is. larger than the corresponding undulations produced. in response. to pulses. of greater and. lessen duration. This-iolloWs-irom. the fact that. the pulses of. larger'and-smaller duration are. out of. step. with thetuned frequency oft-he. circuit.

To suppress those undulations which normallyv follow the. representative undulatiomwe have dis- Posed. across the tuned. circuit a. vacuum-tube which. when made. conductiveprovides a, low re.- sistance shunt. adapted-to damp outany oscillations occurring. in the circuit. The. grid oi the. tube-is arranged to receive anegative. voltage for the. durationofv each. pulse and the anodeand cathode. of. the: tube are so. connected. across. the circuit. thatwheni the polarity. of. the oscillating. current is in one directionit. blocks conduction Joy the tube. and when in the opposite direction it,un-, blocks the tube. By this]arrangement'thetube operatestosuppress oscillations by. becominaconductive. when. the. voltage across. the circuit. has the rightpolarity and whenthe. voltageofltheap- 2: plied. pulse becomes. zero, The system. according to our. invention will therefore produce a representative undulation. following; the. trailing edge of each. pulse andthereaiter suppress all further oscillations until the next. succeeding pulse of the wave isappliedtothe circuit.

From. the foregoing-it will beclear thata representative pulse or undulation isproduced corresponding to the relation ofeach of the pulses-of theinput wavato the tuned frequency. By properly tuning the-shock-exci-table circuit to a frequency, thewavelength or period of which-is twice the duration-of the-wanted pulse; the-:undulation corresponding to the wanted pulse will be the maximnmundulation obtained. The undulations corresponding to the-pulses of; greater andlesser widths will be 1ess:-than the undulation corresponding to the wanted pulse. By threshold. cliping the:undulations:at'a-proper level,v the maxiundulationsrwhich correspcnd'to thewanted pulses" can be isolated? thereby eliminating the undulations corresponding to the pulses ofgreater andlesserduration.

For: a further? understandingof the invention, reference maybe hadit'o the fol'lowing d'etaileddescription' t'o be read in connection with the accompanying drawings, in'which-z Fig. 1 isa schematic wiring diagram of the pulse eliminating system according to our invention;

and

Fig. 2 15" a'gra-phieal illustration of the steps carriedout by the system'for' pulses of di-fi'erent widths.

Referring; to the drawing, a pulse modulated wavesuch asrepresented" by curve a ofFig. 2 is appliedto'the grid input connection I [lot a known limit; clipping tube l 2' shown in Fig. l. Thislimit clipping operation limits the pulses to substantially the same amplitude as indicatedby the clipping level I'B'. This is'necessaryin cases Where other shaped pulses are imposed on the same carrier frequencyfor jamming purposes or for other channelsof comm-ur'iication. Thus,- the anode output of the. tubev {2 will pass pulse energy of constant amplitude.

Theinput wave ais shown modulated fOlLf'pllY- poses of illustration with awanted pulsezfl of a given widthand threeunwantedpulses.21, 225 and 23'. The widths of the. pulses. 21 and 22" are respectively smaller andlarger than the width of the wanted. pulse 28. The. third pulse 23 is ineluded. to give an example of a pulse havin width equal to an odd multiple of the width of the Wanted. pulse. According to our; invention,

the pulses 2|, 22 and 23 may all be eliminated thereby isolating the wanted pulses 20.

The output pulse energy from the tube I2 is applied through a resistor R to a shock-excitable L.-C. circuit 25. The condenser C of the circuit is preferably adjustable so that the circuit may be tuned to a wavelength the period of which is twice the duration of the wanted pulse. It will be understood, of course, that the inductance coil L may also be made adjustable either in place of an adjustment for the condenser C or together with an adjustable condenser, whichever may be desired.

Connected across the tunable circuit 25 is a vacuum tube 36 the cathode 3| of which is connected to the input side 26 of the circuit 25 while the anode 32 is connected to the opposite side 21 of the circuit. The side 21 is also connected to a source of potential B+ to provide a suitable positive bias for the anode connection M.

The energy output of the anode connection I 4 is applied to a grid 34 of the tube 36 so as to block the conduction between the cathode 3| and the anode 32 while pulse energy is applied to the circuit 25. The undulations outputof the circuit 25 are taken oif through a connection 36 for application to a known threshold clipping amplifier stage 46. The bias on the grid 43 is controlled by adjustment of resistor 44.

The operation of the system of Fig. 1 will be better understood by reference to Fig. 2 in which all the curves are applied to the same time base. Curve a as hereinbefore stated represents the pulse input energy on the grid connection IU of the limit tube I2. While I have included the limiting action of tube l2 for limiting the amplitude of the pulses, it will be understood that the limiting feature may be dispensed with where the input pulses are of substantially the same amplitude and only differ in width characteristics, or where the limiting action takes place in a previous stage.

Curve b represents the anode voltage across the resistor R. Curve represents the oscillations produced at theoutput 36 of the circuit 25 in response to the pulse energy of curve b. Curve d represents the pulse output at 4| after the undulations have been threshold clipped by the tube 46.

When the leading edge of the wanted pulse 20 is applied to the circuit 25, an undulation 52, curve 0, is produced. The circuit 25 will oscillate tending to produce in response to the edge 5| a damped wave according to

undulations

52, 53, 54, etc. When the trailing edge 55 of the pulse 20 is applied to the circuit 25, a further shock excitation occurs in the opposite

direction producing undulations

56, 51, etc. The

undulations

53 and 56 are in timed relation since the circuit is tuned to a period equal to twice the duration of the pulse 2!! and they combine to produce a maximum undulation 65). The succeeding pairs of undulations produced by the leading and trailing edges of the pulse 20 will produce the damped oscillations indicated by the broken line 58. This damped wave, should it be present when the next succeeding ulse 2| is applied to the circuit 25, will addalgebraically to the oscillations produced loythe pulse 2| thus interfering with the width measuring properties of the circuit. The damping tube 36, as will be further described hereinafter, eliminates the trailing oscillations 58, and all other trailing oscillations produced by the successive pulses. l

' The leading and trailing edges of the Pu ses ll,

22 and 23 in turn shock excite the circuit 25 initiating successive damped waves producing for each pulse a corresponding undulation 6|, 62 and 63. 'These undulations 6|, 62 and 63 are, of course, representative undulations produced in response to these pulses for the one tuned frequency of the circuit 25. The oscillations 54 and produced by the edges of pulse 2| have a period corresponding to the period at which the circuit 25 is tuned, but since the leading and trailing edges of the pulse 2| are closer together than one half of the period, the resulting oscillations produced thereby are out of step. The resulting undulation 6|, therefore, is of less amplitude than the undulation 60 produced by the pulse 26.

The same follows for those pulses of greater duration than the wanted pulse 25. The leading and trailing edges of the pulse 22 being further apart than the distance corresponding to a half wavelength at which the circuit 25 is tuned, produce

oscillations

66 and 61 which are out of step thereby producing an undulation 62 of lesser amplitude than the undulation 58.

For pulses such as pulse 23 which is in the order of an odd multiple of the duration of the wanted pulse 26, the leading edge initiates the oscillation 12 which in this case passes through three undulations before the trailing edge 13 is applied to the circuit. While the undulations 14 produced by the trailing edge 13 are of an amplitude similar to the amplitude of the undulation 56, the corresponding undulation 15 of the oscillations produced by leading edge H is now considerably less due to the natural damping of the tuned circuit so that the resulting undulation produced by the sum of the undulations T4 and 15 is less in amplitude than the undulation 66. It follows therefore that while the leading and trailing edges of a pulse which is an odd multiple of the wanted pulse are in timed relation, the damping eifect of the oscillation produced by the leading edge is such that the sum of the combined undulations results in an undulation of less amplitude than the undulation 60.

With the. tube 30 in the circuit, the undulations following the first undulation after the trailing edge of each pulse are suppressed by the damping function of the tube. The grid 34 of the tube is applied with a potential corresponding to the voltage across the resistor R when a pulse such as pulse 20 is applied to the circuit. This potential being negative (curve 12) blocks conduction in the tube 30 so that the Q of the circuit 25 will remain high and the circuit will respond to the leading edge of the pulse. to initiate the oscillation. The connection of the cathode 3| and the anode 32 of the tube 36 across the circuit 25 is such that the polarity of the undulation 60 directly following the trailing edge of pulse 29 is such that the tube is again blocked against conduction. Thus, the tube remains blocked for the duration of the undulations 60, 6|, 62 and 63. When the energy of oscillation changes in polarity from positive to negative, the change immediately produced conduction in the tube 39 thereby shunting the low resistancev of the tube across the circuit 25. This shunting operation so lowers the Q of the circuit as to absorb the energy that would normally produce the next succeeding undulation, thereby suppressing the further tendency of the circuit to produce oscillations. This shunting action results in a substantially zero output 59 (curve 0) following the undulation 65 until the leading edge of the next succeeding pulse 2| is applied to the circuit. This damping operation ofthe tubes!) suppresses theunwanted oscillati-ons produced by the pulses so that: they; will not interfere or adversely afiect the oseillations produced by later occurringpulses;

The clipping operation of the tube 40 which may be adjusted to-clip theoutputat a level 80 thereby eliminating the undulations GI, 62 and 63 resulting H178, final output of .undulation pulses Ella corresponding to the wanted pulses: 20. The interferingor unwanted pulses are eiTecti-v'el-y eliminated. The output pulses Ella; may, of course, be amplified and sharpened or otherwise treated asmay be desired dependingon the use intended for the pulse energy thus obtained;

While we have shown and described the-principles of our invention inconnection with-aspecific embodiment, we recognize that Various changes and modifications maybe made therein without departing from't'he invention. It isour aim, therefore, to cover in thea-ppended claims all such changes and modifications as fall within the scope of the invention.

We claim:

1. A system for selectingslirom av pulse wave a pulse of a given duration to the exclusion of pulses of greater andle'sseridura tion'comprising a resonant circuit, means to apply said. wave for shock excitation of said circuit by the leading and trailing edges of pulses thereof, control means to maintain the circuit oscillatory condition for the duration ofeach pulses-o: that theos'cillations initiated by theedges of each pulse combi'ne to forman undulation iollnwing thetrailing edge of the pulse means to damp-out the oscillations so. that oscillations produced by one pul'se will not affect the oscillations:produced by the next pulse comprising means adapted to form a W resistance shunt connection across the tuned circuit and control means responsive to the pulse of said Wave to block said shunt connection for the duration of each pulse, said circuit being tuned to a period equal to twice the duration of said wanted pulse so that the oscillation set up by the edges of the wanted pulses are timed one half period apart to provide an undulation of maximum amplitude and the undulations produced by the edges of pulses of greater or lesser duration are timed greater and lesser apart than half a period to form undulations of amplitude less than said maximum undulation, and means for threshold clipping said undulations to obtain a pulse output corresponding to the pulses of said given duration.

2. A system for selecting from a pulse wave a pulse of a given duration to the exclusion of pulses of greater and lesser duration comprising a resonant circuit, means to apply said wave for shock excitation of said circuit by the leading and trailing edges of pulses thereof, control means to maintain the circuit in oscillatory condition for the duration of each pulse so that the oscillations initiated by the edges of each pulse combine to form an undulation following the trailing edge of the pulse, means to damp out the oscillations so that oscillations produced by one pulse will not affect the oscillations produced by the next pulse comprising means adapted to form a low resistance shunt connection across the tuned circuit and means responsive to the pulses of said wave to block the shunt connection for the duration of each pulse plus the duration of the undulation following the trailing edge of the pulse, said circuit being tuned to a period equal to twice the duration of said wanted pulse so that the oscillations set up by the edges of the wanted pulse are timed one: halfuperiod apart. to provide an undulationi of: maximum: amplitude and the undulations producedaby the edges of pulses of greater. or lesser. duration are timed greater and lesser apart than: half a period toform undulations. of amplitude'less than said maximum uridulationand: means for. threshold clipping said undulations to obtain: a pulse. output corresponding to the pulses of saidrgiven duration.

3; A system for. selecting from a pulse wave a pulse oil a given duration to the exclusion of pulses of greater and lesser duration comprising a resonant circuit, means to; apply said. wave for shock excitation of said circuit by the leading and trailing edges of pulses thereof, control meanstomaintain: the circuit in oscillatory condition for the duration of each pulse so that the oscillations initiated by' the edges of each pulse combine: to form: an undulation following the trailing edge oi the pulse, means to damp out the oscillations comprising a vacuum tube connected across the tuned circuit and control means to-bias the tube to cut off for the duration of the-pulse, the polarity of the circuit connections across the tube beirig such during the formation of said undulation as to maintain the tube at out off" for the duration of said undulation and the change in polarity of the oscillating energy at the end of Said undulation operating to produce a state of conductionin said tube therebydamping out the oscillation in said circuitso that oscillations produced by one pulse will not affect the oscillations produced by thenext pulse, said circuit being tuned to a period equal to twice the duration of said'fwanted pulse so that the oscillati'ons set up by the edges of the wanted'pulses are timed one half period apart to provide an undulation of maximum amplitude and the undulations produced by the edges of pulses of greater or lesser duration, are timed greater and lesser apart than half a period to form undulations of amplitude less than said maximum undulation and means for threshold clipping said undulations to obtain a pulse output corresponding to the pulses of said given duration.

4. A system for selecting from a pulse modulated wave those pulses of a given duration to the exclusion of pulses of greater and lesser duration, comprising a shock excitable circuit, means to apply the wave to the circuit to produce oscillations therein in response to the leading and trailing edges of the pulses, the oscillations initiated by the edges of a pulse combining normally to form undulations following the trailing edge of each pulse, means to tune said circuit to a wavelength the period of which is twice the duration of said wanted pulse so that the undulations produced by the wanted pulse are of greater amplitude than the corresponding undulations of the pulses of greater and lesser duration, a vacuum tube having anode, cathode and grid electrodes, means connecting the anode and cathode electrodes across said circuit, means to apply each pulse to said grid electrode to block said tube for the duration of said pulse, and the anode and cathode connections being arranged to produce a blocking potential for the tube for the duration of the first undulation following the trailing edge of each pulse, the change in polarity of the oscillating energy at the end of said first undulation operating to unblock said tube for damping of further oscillations so that the oscillations of one pulse will not affect oscillations produced by the next succeeding pulse, and means to threshold clip the undulations to obtain a pulse output corresponding to the pulses of said given width,

5. The system defined in claim 4, in combination with an input limiting tube to limit the pulses ofthe wave to a given amplitude before application of the pulses to the shock excitable circuit.

6. A system for distinguishing by greater amplitude a wanted pulse of a. given duration from pulses of greater duration but of substantially the same amplitude, comprising a resonant circuit, means to apply the pulses for shock excitation of said circuit by the leading and trailing edges of the pulses, control means to maintain the circuit in oscillatory condition for the duration of each pulse so that the oscillations initiated by the edges of each pulse combine to form an undulation following the trailing edge of the pulse, means to damp out the oscillations normally following said undulation, means to render the means for damping out oscillations inoperative for the duration of each applied pulse, said circuit being tuned to a wavelength the period of which is twice the duration of said wanted pulse so that the oscillations set up by the edges of the wanted pulse are timed one half wavelength apart to provide an undulation of maximum amplitude and the oscillations produced by the edges of pulses of greater duration are timed greater distances apart than said one half wavelength to form undulations of amplitude less than said maximum undulation, and means for threshold clipping the peak portions of the maximum undulations.

'7. The system defined in claim 6, wherein the means to damp out the oscillations comprises means adapted to form a low resistance shunt connection across the tuned circuit and the con- 8 trol means includes means responsive to the pulses to block said shunt connection for the duration of each pulse.

8. The system defined in claim 6, wherein the means to damp out the oscillations comprises a vacuum tube connected across the tuned circuit,

and the control means includes means to bias the tube to cut-off for the duration of the pulse, the polarity of the circuit connections across the tube being such during the formation of said undulation as to maintain the tube at cut-off for the duration of said undulation, and the change in polarity of the oscillating energy at the end of said undulation operating to produce a state of conduction in said tube thereby damping out the oscillations in said circuit.

9. The system defined in claim 6, in combination with an input limiting tube to limit the pulses to a given amplitude before application of the pulses to the resonant circuit.

EMILE LABIN. DONALD D. GRIEG.

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

UNITED STATES PATENTS