US2456952A - Sensitivity time control - Google Patents

Description

Dec; 21, 194a. .E. c. KLUENDER 2,456,952

SENSITIVITY TIME CONTROL Filed May 3, 1946 CONTROL some: 43

SAW TODTH SOURCE Inventor": Edward C. Kluenderm,

H is Attorney.

Patented Dec. 21, 1948 N TED 4, P TENT OFFICE.

Edward C. Kluender, Schenectady, assignor to General Electric' Company, a corporation of New York Applicationli Iayis, 1946, Serial No. 666,897

'3 claims. (01.. 179-171) My invention relates to varying the sensitivity of an electron discharge device amplifiercwith time and more particularly to controlling the operationof a remote object detecting system in accordance with'thedistan'ce to the remote objects. A a

In one type of remote object detecting system, recurrent pulses of radio frequency energy are transmitted in thedirectionof remote objects desired to be located. Reflected energy pulses, from these objects arepioked'up by an appropriate radio receiving systemand converted to {a unidirectional voltage 'varying in accord with the intensity of the received waves. This voltage, together with time varying-voltages indicating elapsed time after each transmitted pulse, is applied to a cathode ray deviceito pr'oduc'e an indication onthe viewing screen thereof corresponding to the position of each: remote M AY i It is an. object of my invention to provide improved means whereby the sensitivity of the receiving systemof a remote object detecting system is varied in' accordancexwith- ;the time interval-rafter the last transmitted energy pulse so that the unidirectional output voltage ofzt'he receiving system is dependent primarily on. the energy reflecting properties of thecorresponding reflecting object and not on the distance thereto;

his a further object of my invention'toprovide improved means to' control the. gain of a radio receiver in a manner adaptable to use in. a radio type pulse-echo object detectingsystem.

Another object of .my invention is to provide improved means. to control the sensitivity or gain of an electron discharge device'lamplifier after a predetermined event, whichomeans are simple and reliable inbperation, use a'mimmum number of circuit components, and take-maxi;- mum advantage of the inherent characteristicsof the amplifier circuits. t?

The novel features which I believe to be characteristic of my invention are set-forth with particularity in the appended claims. 1 My? invention itself, both as to its organization and method of operation may best be understood by reference to the following description taken in connection with the accompanying'drawings in which Fig. 1 shows a radio type 'pulse-echosystem. incorporating the apparatusof m'yinven- 2 most advantageously applied; In the figure, l represents a pulse generator capable of generating pulses of radio frequency energy when actuated by control voltage from source 4. Source 4 may, for example, produce 0.5 microsecond voltage pulses at a frequency of 1500 pulses per second across resistance =42, these pulses having the wave shape shown at 40. These pulses are applied to directional antenna 3, thereby causing a directional beam of radio frequency energy to be transmitted at the instant voltage is applied from control source 4. It is the purpose of T. R. box 2 automatically to prevent entrance of radio frequency energy to unit 5 when generator I is operating. This may; for example, be accomplished by providinga resonant cavity with a spark gap capable of breaking down when pulses are produced by unit I but to pass energy from antenna 3 to unit-Fat allother times. Radio frequency energy from generator I and radiated by antenna 3 travels from the position of antenna 3 to a region containing remote ob jectsdesired to be located. .These obj'ectsre fleet 'or re-radiate the transmitted energy, there by producing return waves travelling: inthe 'reverse direction and, after the period of time re-' quired to complete the travel, appearing again at antenna 3 from which unit they are applied to unit 5 by T. R. box 2; Units 5, 6, '1, and 30011- stitute a radio receiver, capable of producing a unidirectional voltage varying in accordance with the intensity of the reflectedradio frequency energy appearing at antenna 3. This receiver may, for example, be of the superheterodyne type in which unit- 5 represents the. radio frequency amplifier (if any) the first detector, and a first group of intermediate frequency amplifiers (if any). Two additional stages of intermediate frequency amplification are provided by the circuits shown generally at 5, these circuits providing adjustment of the receiver gain in a manner to be described in detail hereafter; Unit 1 represents further stages of intermediate frequency amplification (if any) and the second detector whereas unit 8 represents the video amplifier portion of the receiver. The unidirectional Voltage produced by video amplifier 3 is applied to the control electrode of cathode ray device '9 to vary the intensity of the ray beam of that device in accordance with the reflected radio waves appearing at antenna 3. T Source In is arranged to produce a saw tooth current wave after each pulse of voltage from control source 4'; This unit might, for example;

include a square wave voltage generator triggered by voltage of source t and wave shaping amplifiers to change this voltage to the form necessary to produce a saw tooth current wave in coil I i. This current is applied to the deflecting coil of cathode ray device 9 to deflect the ray beam from the center position in accordance With es agn tu eof this currenttt us cans ing this beam to execute successive traverses from the 'center of the viewing screen to the periphery thereof, each swing taking place after a transmitted energy pulse. Inasmuch as the intensity of the ray beam varies in accord with the reflected energy from remote objects-and the instant of each variation occurs at atime interval after the transmitted pulse determined by the distance to the corresponding remote object, luminous spots appear on the viewing screen corresponding to the various remote objects de tected, each spot appearing at a distance from the-reenter thereof, determinedbythe di tance between the remote object and-the detectin equipment andhafiug intensity determine by the intensity oi the, radio echo. The axis alon whichthe electron beam is movediby aw tooth current from source, It; is varied by m ans of thevmechanismlshowngenerallyrat t to ome sound with the'direotion of'most intense. radiatiorr from antenna 3. This causes the.-1.umino.us

spots to appear on-thes' viewing screenin add-nectionsfrom the center thereoi'determined by the direction of the corresponding remote; obiccts 'ancliat a: distancedetermined bythe distances the eto, thus producin -on the viewin screen a maul-like indication of the location and radio. re: fl ting: characteristics of remote objects a out the equipment antenna. 3 and deflectin coil H are1 rotated;

Therintensityoi the received radiant ener y antenna 3 varies in accordance with'thedistance to the remote objectas well as theadimensionsrand construction thereof: This resu ts from the-fact that the attenuationor reduction in. intensity of radio waves let-determined by the distance; which the t avel- Hence, objects in: closeproximity tothe detecting-equipment produce, stron er a io echoesand hence greater voltage at" thecontrol electrode of device sz-thanthe same objects if located at some distance therefrom. Consequentiy theluminous indications on the viewing screen .ojf-"devlee 9 corresponding to close objects are relativelysmuch more intense than the indications of similarobjects atssomedistancie away. Furthermore; if remoteobjects are to be displayed withahighxdegreeof brilliance-it is often 'neces.- sary toraise the -'gainof the receiving system to suchahighlevel that extraneous'eehoes due-to slightly reflecting objectsclose at hand" obscure the-image screen; in the area corresponding to the latter objects, thereby preventing: identifioation: of larger objects-located in this area. This condition is shown in Fig; 2' (a) which illus-i trates the appearance. .of-v the viewing screen when the gain of the system-. is adjustedato displayre! remote objects whileIextraneousroflectionsirom aditrsenumher of sli tly refl tin objects close athand bscure. the-portion of theimage screen co r sponding t cl se objects. The condition of: therviewing screen with l minous points indi ea ing: o ly. the actual relative radioreflecties properties of: the remote obj cts s shown Fig. 2 (b). p I

i Itisthe numosaof: heioircnits: shown eneral y atzfi to: alter h'errelativ s-s sensitivity of," the reeelw objects of like radio reflecting properties to produce like values of voltage at the control electrode of device 9. This is accomplished by varying the gain of these two stages of intermediate frequency amplification. The first of these stages utilizes electron discharge device l3 having its cathode connected to ground through bias resistante bland bypass capacitor I5 and its anode connected to unidirectional-voltage sou-roe l6 by resistances l1 and I8. The screen electrode of device [3 is connected to the junction of resistanccs ll and l8 and the radio frequency voltage appearing across this junction bypassed to ground bynondenser l9.- Voltage is applied to the control electrode; of device l3 through coupling condenser 20, coil 2!, and bypass capacitor 22. Coil Z I is tuned byits-distributed capacitance and the interelectrode capacitances of device [3 to resonatefiat the frequency of the intermediate frequency amplifier, thereby causing maximum amplifloetion of si nals of this frequency. which migh f example; be .39. me acycles,.per-second. Electron discharge device 23.. is connected in a manner similarsto. devi e I 3; deriving its cathode bia voltage iromlresistance-z l; and. capacitor 25, its anode voltage from resistances 26 and 2]" and unidirectional voltage source. 2.8, and havin i screen electrode bypassedto-ground by condenser 2-9 Control electrode volta e is, applied to this device by means f: coupling: condenser 31L coil 3!. andhypass-condenser'si, c'oil;3.l being tuned by? i s. distributed capacitance and the inter ele trode capacitancesioi device 23 to resonate atnthe desired-1 intermediate frequency Ample fled. voltage from device-231s applied to unit 1 through coupling capacitor'33: Theigainof the amplifier stagesvshowngenerally-.atfiisdetermined bythe unidirectional bias voltage applied to thecontrolelectrodes of devices l3 and 23 from the network comprising resistances 3A.";S5 and 5i i potentiometer 31; and unidirectiona1 volta e: source 38. TO1-1 rQVide maximum-o con, tlfilt l this iashion; devices and 23, are otthe vsriab'lcmuor remote eutrofitype in which the ampl cation issreducedasithe negative control electrode-bias voltage is increased; -Manual ad justment o f 1'this-, voltage "is provided by-potenti+ OmGter ST'I'; thereby permitting-the operatorof the equipment to controlzthe varying component of beamintensity of cathode ray-device 9 andcause an image ofmaximum usefulness toappear-o'n the image screen thereof.

In additiontothe manual control of the bias voltage at devices 13 and- 23: achieved through if variationof potentiometer 31', automatic control equivalent radioirefl cting properties regardless f? their-distance from th pulswechosystem.

operation: oi:.-t.h.e. circuit of Fig: 1- to on duce the varyingdegree .of sensitivity" of the resistance 35, condenser 32,and the' currentpath through inductance-3l,*-the control electrode; cathode space path o'fdevice 23;"andresistance 24; the latter current path being in'shunt with condensers 39 and 32 immediately begin to charg'ef the charge being in direction" tending to'make point 4| relatively more positive and taking place at a time constant determined "primarily byresistance 35; The'actual positivevoltage at this point, however, is limited by the control electrodecathode space path current of device '23 which begins to flow as soon as condenser sz ce'mmences to charge. Inasmuch asthis current does not charge condenser 32, itproduces no voltage thereacross and correspondingly reduces the positive potential of point 4l-, below thepotentialr that would exist in the absence ofzdevice'23.

Inasmuch as the charge oncondenser 32 cannot change when the voltage of wave 40 disappears, the potential of point 4! remains constant at that time. However, charging of condensers 3-9 and 32 immediately begins, the time constant v of this charge :being determined principally by the value of resistance 35.' Resistor 42 has a low value as compared to the resistor 35. Due to the large capacity of thecapacitor 39 as compared with the capacitor 32, and the relative discharge condition of 32 resulting from its discharge by the device 23, the capacitor 39 quickly charges 32 until it has substantially the same negative potential. After their voltages become equal. they then both discharge through the resistors 36, 31 and 42. This discharge continues until capacitors 39 and 32 each reach a predetermined potential as determined by the value of resistor 31.

The above-described negative voltage at point 4| appears very soon after the pulse of Wave 40 disappears since the time constant of the circuits involved is relatively short. The resultant charge on condensers 32 and 39, however, leaks off through the relatively long time constant circuit including resistance 36 and potentiometer 31. This relatively slow decay of negative voltage slowly increases the gain of amplifier 23 and thus restores the sensitivity of the receiver after the transmitted energy pulse at a rate commensurate with the decreased intensity of echo pulses at antenna 3.

During the time of each transmitted pulse, when the control electrode of device 23 is positive with respect to the cathode, amplifier 6 is inoperative. However, this does not influence performance of the pulse-echo system since breakdown of the spark gap in T. R. box 2 prevents radio energy from antenna 3 from entering the receiver during this period. Similarly, the short period of time after each pulse during which point 4| has a positive voltage does not influence system operation because T. R. box 2 does not permit radio energy to pass from antenna 3 to the receiver for a corresponding time after each a pulse.

The above description has been made with reference to condenser 32 and device 23 only. The current path through resistance 34 and condenser 22, together with the current'path through inductance 2| and the control electro-cathode space path of device 13, also influences this action. In effect these current paths are in parallel with the current paths due to capacitor 32 and device 2a and, whilethey' alter the relative distribution of voltage after the positive pulses of wave-40 and the time constant of gain restoration ofthe receiver, they do notalter the basic operation of In a" particular embodiment of theabove -described circuit which has been found to operate satisfactorily in practice, the following-circuit conditions existed:

i f b microsecond P lses of 50 vol s jat the rate of 1200 pulses per second. I, Capacitor 39-001 microfarad Capacitors I5, 22, 25 and 32-0001 microfarad";

Resistances i4 and 24-120 ohms Resistances 34 and 35-180 ohms Condensers 20 and 300.005 microfarad Resistance 363000 ohms Source 38--210 volts Potentiometer 31210,000 ohms Devices l3 and 23-Type 6AK5 It has heretofore been considered necessaryin .gaincontrol devices of. the type herein described to apply a negative voltage pulse to the control electrodes of the electron discharge devicesdesired to be rendered insensitive. .This has required the use of special equipment to generate these pulses in a satisfactorymanner, suchequipment generally requiring multivibrators, gas

tubes, rectifiers, amplifiers, additional transformers and the like. This not only increases the expense of the equipment but also decreases the reliability and adds to the complexity thereof. I have discovered that a method contrary to that of the prior art produces superior and unanticipated results, probably as a result of the theory outlined herein. Thus by taking advantage of the inherent characteristics of the circuits, I am enabled to produce a negative bias voltage varying in accordance with the desired gain control without the disadvantages of the prior art circuits.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects. In particular, this system is applicable to radio receivers and electron discharge device amplifiers other than the pulse-echo equipment specifically described herein. Furthermore, the principles of this invention may be applied to pulse-echo equipments utilizing waves other than radio waves and displaying the location of remote objects in a manner different from that described herein. I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a radio detecting apparatus of the type wherein radio energy pulses are successively transmitted and the corresponding reflected energy received to determine the location of remote objects, an electron discharge device having a cathode, control electrode, and anode, said device being capable of reducing the sensitivity of said system as said control electrode has increased negative potential relative to said cathode, pulse generating means to produce a voltage wave having positive pulses at the instants of said transmitted pulses, means to impress said positive pulses upon a time constant network comprising first and second capacitors in series, means connecting the control electrode-to-cathode path of said device across said second capacitor, said oncogene P? 38 math i'bcing rendered ,conductive ibyisaid pulse :to my athe woltage Iflletween 5a. :eontrol electrode sand ea iprovide 9a low impedance across :said "second nathodesa'sourcecof positivemoltage;rpu1ses,.means scapacitoriduring each; pulse; saidznetworkmaving zto-impzess said zpulses upon a -;-time .constant metto. low '..time r constant zrela'tive 1to:the {pulse 1period, "work :cnznprising afil'st .and second capacitors, 1 in said first capacitor being charged rapidly by said as .series, .nneans {connecting the "control grid-(t0- apiilseswandzdischargingrrapidlyzintotsaid asecond cathode xpace :path iof said device :across said mapacitor :at Lthe termination of, :each spulse, -second capacitor,;-saidpath beingi-rendered-conithereby :to rreducethe rsensitivitykofisaid :syst'em, fluctiveby-said puiseszto shunnsaidrsecond capacand means for discharging said mapacitors'rat :2, itor-iforithedurationaof.said pulsesg said network i-predetermined rate .to.restore. said sensitivity, ahavingazshonttimeconstant rrelative tozthespulse '2. In combination, an electromdischarge device period,-said first. capacitor:Joeing:chargediforndurahaving cathode, anode, and'controLelectrodes a, ation of 1said-.pu1ses and scharging :s-aid ,second pulse generating source, two icapacitors in series aeap eitvri-rapidlyiupon terminationof each pulse, connection across sa'i'disource, means connecting fi er-8103' tO-I'Bduce-the ampl fic fln of d device, the cathodeecontrol electrode space pathof said 15 andsmeans-foradischarg n a d cfllp s 1704116- device across one ofsaid capacitorsso 'that;sai'd z storxe the amplification \ofisaid device at :a {precontrol electrode "becomes positive :with respect determined-rate. to-said cathode when a positive pulse ;is amilied V ZEDWARD CJKLUENDER. from said source, ,meansiorapplymg anegatme potential to said vcontrol -,1ec-tr0de at 'the'.ter---;20 REFERENCES CITED mination of said pu1se,thus causing said control m ifinowmgirefermces sarerof record zt ilentrode -to have apnegative potential relative to fil of :sai'd ncathode, and means for discharging said mapae'itors to remove :said'negative potential at UNITED STATESPATENTS a rpre'determined rate. 26 Number Name Date 131A sensitivity control circuit :compris'ing, in -2;374,20.4 Hoover April 24, 1945 -conibination, an amp1ifier in'c1uding aneleritron 2375283 Cloud I'May 8, 1945 sfiisohargeideviceihaving 'amplificatiomdetemiined 2,427,523 Delberg -Sept. 16, 31947

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